content: package ca.allanwang.kau.swipe;
  
  import android.content.Context;
  import androidx.core.view.ViewCompat;
  import android.util.Log;
  import android.view.MotionEvent;
  import android.view.VelocityTracker;
  import android.view.View;
  import android.view.ViewConfiguration;
  import android.view.ViewGroup;
  import android.view.animation.Interpolator;
  import android.widget.OverScroller;
  
  import java.util.Arrays;
  
  import static ca.allanwang.kau.swipe.SwipeBackHelperKt.SWIPE_EDGE_BOTTOM;
  import static ca.allanwang.kau.swipe.SwipeBackHelperKt.SWIPE_EDGE_LEFT;
  import static ca.allanwang.kau.swipe.SwipeBackHelperKt.SWIPE_EDGE_RIGHT;
  import static ca.allanwang.kau.swipe.SwipeBackHelperKt.SWIPE_EDGE_TOP;
  
  /**
   * Created by Allan Wang on 2017-07-05.
   * <p>
   * ViewDragHelper is a utility class for writing custom ViewGroups. It offers a number
   * of useful operations and state tracking for allowing a user to drag and reposition
   * views within their parent ViewGroup.
   * <p>
   * This is an extension of {@link androidx.customview.widget.ViewDragHelper}
   * Along with additional methods defined in {@link ViewDragHelperExtras}
   */
  class ViewDragHelper implements ViewDragHelperExtras {
      private static final String TAG = "ViewDragHelper";
  
      /**
       * A null/invalid pointer ID.
       */
      public static final int INVALID_POINTER = -1;
  
      /**
       * A view is not currently being dragged or animating as a result of a fling/snap.
       */
      public static final int STATE_IDLE = 0;
  
      /**
       * A view is currently being dragged. The position is currently changing as a result
       * of user input or simulated user input.
       */
      public static final int STATE_DRAGGING = 1;
  
      /**
       * A view is currently settling into place as a result of a fling or
       * predefined non-interactive motion.
       */
      public static final int STATE_SETTLING = 2;
  
      /**
       * Edge flag indicating that the left edge should be affected.
       */
      public static final int EDGE_LEFT = 1 << 0;
  
      /**
       * Edge flag indicating that the right edge should be affected.
       */
      public static final int EDGE_RIGHT = 1 << 1;
  
      /**
       * Edge flag indicating that the top edge should be affected.
       */
      public static final int EDGE_TOP = 1 << 2;
  
      /**
       * Edge flag indicating that the bottom edge should be affected.
       */
      public static final int EDGE_BOTTOM = 1 << 3;
  
      /**
       * Edge flag set indicating all edges should be affected.
       */
      public static final int EDGE_ALL = EDGE_LEFT | EDGE_TOP | EDGE_RIGHT | EDGE_BOTTOM;
  
      /**
       * Indicates that a check should occur along the horizontal axis
       */
      public static final int DIRECTION_HORIZONTAL = 1 << 0;
  
      /**
       * Indicates that a check should occur along the vertical axis
       */
      public static final int DIRECTION_VERTICAL = 1 << 1;
  
      /**
       * Indicates that a check should occur along all axes
       */
      public static final int DIRECTION_ALL = DIRECTION_HORIZONTAL | DIRECTION_VERTICAL;
  
      private static final int EDGE_SIZE = 20; // dp
  
      private static final int BASE_SETTLE_DURATION = 256; // ms
      private static final int MAX_SETTLE_DURATION = 600; // ms
  
      // Current drag state; idle, dragging or settling
      private int mDragState;
  
      // Distance to travel before a drag may begin
      private int mTouchSlop;
  
      public int edgeFlag = SWIPE_EDGE_LEFT;
  
      // Last known position/pointer tracking
      private int mActivePointerId = INVALID_POINTER;
      private float[] mInitialMotionX;
      private float[] mInitialMotionY;
      private float[] mLastMotionX;
      private float[] mLastMotionY;
      private int[] mInitialEdgesTouched;
      private int[] mEdgeDragsInProgress;
      private int[] mEdgeDragsLocked;
      private int mPointersDown;
  
      private VelocityTracker mVelocityTracker;
      private float mMaxVelocity;
      private float mMinVelocity;
  
      private int mEdgeSize;
      private int mTrackingEdges;
  
      private OverScroller mScroller;
  
      private final Callback mCallback;
  
      private View mCapturedView;
      private boolean mReleaseInProgress;
  
      private final ViewGroup mParentView;
  
      /**
       * A Callback is used as a communication channel with the ViewDragHelper back to the
       * parent view using it. <code>on*</code>methods are invoked on siginficant events and several
       * accessor methods are expected to provide the ViewDragHelper with more information
       * about the state of the parent view upon request. The callback also makes decisions
       * governing the range and draggability of child views.
       */
      public abstract static class Callback {
          /**
           * Called when the drag state changes. See the <code>STATE_*</code> constants
           * for more information.
           *
           * @param state The new drag state
           * @see #STATE_IDLE
           * @see #STATE_DRAGGING
           * @see #STATE_SETTLING
           */
          public void onViewDragStateChanged(int state) {
          }
  
          /**
           * Called when the captured view's position changes as the result of a drag or settle.
           *
           * @param changedView View whose position changed
           * @param left        New X coordinate of the left edge of the view
           * @param top         New Y coordinate of the top edge of the view
           * @param dx          Change in X position from the last call
           * @param dy          Change in Y position from the last call
           */
          public void onViewPositionChanged(View changedView, int left, int top, int dx, int dy) {
          }
  
          /**
           * Called when a child view is captured for dragging or settling. The ID of the pointer
           * currently dragging the captured view is supplied. If activePointerId is
           * identified as {@link #INVALID_POINTER} the capture is programmatic instead of
           * pointer-initiated.
           *
           * @param capturedChild   Child view that was captured
           * @param activePointerId Pointer id tracking the child capture
           */
          public void onViewCaptured(View capturedChild, int activePointerId) {
          }
  
          /**
           * Called when the child view is no longer being actively dragged.
           * The fling velocity is also supplied, if relevant. The velocity values may
           * be clamped to system minimums or maximums.
           * <p>
           * <p>Calling code may decide to fling or otherwise release the view to let it
           * settle into place. It should do so using {@link #settleCapturedViewAt(int, int)}
           * or {@link #flingCapturedView(int, int, int, int)}. If the Callback invokes
           * one of these methods, the ViewDragHelper will enter {@link #STATE_SETTLING}
           * and the view capture will not fully end until it comes to a complete stop.
           * If neither of these methods is invoked before <code>onViewReleased</code> returns,
           * the view will stop in place and the ViewDragHelper will return to
           * {@link #STATE_IDLE}.</p>
           *
           * @param releasedChild The captured child view now being released
           * @param xvel          X velocity of the pointer as it left the screen in pixels per second.
           * @param yvel          Y velocity of the pointer as it left the screen in pixels per second.
           */
          public void onViewReleased(View releasedChild, float xvel, float yvel) {
          }
  
          /**
           * Called when one of the subscribed edges in the parent view has been touched
           * by the user while no child view is currently captured.
           *
           * @param edgeFlags A combination of edge flags describing the edge(s) currently touched
           * @param pointerId ID of the pointer touching the described edge(s)
           * @see #EDGE_LEFT
           * @see #EDGE_TOP
           * @see #EDGE_RIGHT
           * @see #EDGE_BOTTOM
           */
          public void onEdgeTouched(int edgeFlags, int pointerId) {
          }
  
          /**
           * Called when the given edge may become locked. This can happen if an edge drag
           * was preliminarily rejected before beginning, but after {@link #onEdgeTouched(int, int)}
           * was called. This method should return true to lock this edge or false to leave it
           * unlocked. The default behavior is to leave edges unlocked.
           *
           * @param edgeFlags A combination of edge flags describing the edge(s) locked
           * @return true to lock the edge, false to leave it unlocked
           */
          public boolean onEdgeLock(int edgeFlags) {
              return false;
          }
  
          /**
           * Called when the user has started a deliberate drag away from one
           * of the subscribed edges in the parent view while no child view is currently captured.
           *
           * @param edgeFlags A combination of edge flags describing the edge(s) dragged
           * @param pointerId ID of the pointer touching the described edge(s)
           * @see #EDGE_LEFT
           * @see #EDGE_TOP
           * @see #EDGE_RIGHT
           * @see #EDGE_BOTTOM
           */
          public void onEdgeDragStarted(int edgeFlags, int pointerId) {
          }
  
          /**
           * Called to determine the Z-order of child views.
           *
           * @param index the ordered position to query for
           * @return index of the view that should be ordered at position <code>index</code>
           */
          public int getOrderedChildIndex(int index) {
              return index;
          }
  
          /**
           * Return the magnitude of a draggable child view's horizontal range of motion in pixels.
           * This method should return 0 for views that cannot move horizontally.
           *
           * @param child Child view to check
           * @return range of horizontal motion in pixels
           */
          public int getViewHorizontalDragRange(View child) {
              return 0;
          }
  
          /**
           * Return the magnitude of a draggable child view's vertical range of motion in pixels.
           * This method should return 0 for views that cannot move vertically.
           *
           * @param child Child view to check
           * @return range of vertical motion in pixels
           */
          public int getViewVerticalDragRange(View child) {
              return 0;
          }
  
          /**
           * Called when the user's input indicates that they want to capture the given child view
           * with the pointer indicated by pointerId. The callback should return true if the user
           * is permitted to drag the given view with the indicated pointer.
           * <p>
           * <p>ViewDragHelper may call this method multiple times for the same view even if
           * the view is already captured; this indicates that a new pointer is trying to take
           * control of the view.</p>
           * <p>
           * <p>If this method returns true, a call to {@link #onViewCaptured(android.view.View, int)}
           * will follow if the capture is successful.</p>
           *
           * @param child     Child the user is attempting to capture
           * @param pointerId ID of the pointer attempting the capture
           * @return true if capture should be allowed, false otherwise
           */
          public abstract boolean tryCaptureView(View child, int pointerId);
  
          /**
           * Restrict the motion of the dragged child view along the horizontal axis.
           * The default implementation does not allow horizontal motion; the extending
           * class must override this method and provide the desired clamping.
           *
           * @param child Child view being dragged
           * @param left  Attempted motion along the X axis
           * @param dx    Proposed change in position for left
           * @return The new clamped position for left
           */
          public int clampViewPositionHorizontal(View child, int left, int dx) {
              return 0;
          }
  
          /**
           * Restrict the motion of the dragged child view along the vertical axis.
           * The default implementation does not allow vertical motion; the extending
           * class must override this method and provide the desired clamping.
           *
           * @param child Child view being dragged
           * @param top   Attempted motion along the Y axis
           * @param dy    Proposed change in position for top
           * @return The new clamped position for top
           */
          public int clampViewPositionVertical(View child, int top, int dy) {
              return 0;
          }
      }
  
      /**
       * Interpolator defining the animation curve for mScroller
       */
      private static final Interpolator sInterpolator = new Interpolator() {
          @Override
          public float getInterpolation(float t) {
              t -= 1.0f;
              return t * t * t * t * t + 1.0f;
          }
      };
  
      private final Runnable mSetIdleRunnable = new Runnable() {
          @Override
          public void run() {
              setDragState(STATE_IDLE);
          }
      };
  
      /**
       * Factory method to create a new ViewDragHelper.
       *
       * @param forParent Parent view to monitor
       * @param cb        Callback to provide information and receive events
       * @return a new ViewDragHelper instance
       */
      public static ViewDragHelper create(ViewGroup forParent, Callback cb) {
          return new ViewDragHelper(forParent.getContext(), forParent, cb);
      }
  
      /**
       * Factory method to create a new ViewDragHelper.
       *
       * @param forParent   Parent view to monitor
       * @param sensitivity Multiplier for how sensitive the helper should be about detecting
       *                    the start of a drag. Larger values are more sensitive. 1.0f is normal.
       * @param cb          Callback to provide information and receive events
       * @return a new ViewDragHelper instance
       */
      public static ViewDragHelper create(ViewGroup forParent, float sensitivity, Callback cb) {
          final ViewDragHelper helper = create(forParent, cb);
          helper.mTouchSlop = (int) (helper.mTouchSlop * (1 / sensitivity));
          return helper;
      }
  
      /**
       * Apps should use ViewDragHelper.create() to get a new instance.
       * This will allow VDH to use internal compatibility implementations for different
       * platform versions.
       *
       * @param context   Context to initialize config-dependent params from
       * @param forParent Parent view to monitor
       */
      private ViewDragHelper(Context context, ViewGroup forParent, Callback cb) {
          if (forParent == null) {
              throw new IllegalArgumentException("Parent view may not be null");
          }
          if (cb == null) {
              throw new IllegalArgumentException("Callback may not be null");
          }
  
          mParentView = forParent;
          mCallback = cb;
  
          final ViewConfiguration vc = ViewConfiguration.get(context);
          final float density = context.getResources().getDisplayMetrics().density;
          mEdgeSize = (int) (EDGE_SIZE * density + 0.5f);
  
          mTouchSlop = vc.getScaledTouchSlop();
          mMaxVelocity = vc.getScaledMaximumFlingVelocity();
          mMinVelocity = vc.getScaledMinimumFlingVelocity();
          mScroller = new OverScroller(context, sInterpolator);
      }
  
      /**
       * Sets the sensitivity of the dragger.
       *
       * @param context     The application context.
       * @param sensitivity value between 0 and 1, the final value for touchSlop =
       *                    ViewConfiguration.getScaledTouchSlop * (1 / s);
       *                    1 is the default
       */
      @Override
      public void setSensitivity(Context context, float sensitivity) {
          float s = Math.max(0f, Math.min(1.0f, sensitivity));
          ViewConfiguration viewConfiguration = ViewConfiguration.get(context);
          mTouchSlop = (int) (viewConfiguration.getScaledTouchSlop() * (1 / s));
      }
  
      @Override
      public float getSensitivity() {
          return mTouchSlop;
      }
  
  
      /**
       * Set the minimum velocity that will be detected as having a magnitude greater than zero
       * in pixels per second. Callback methods accepting a velocity will be clamped appropriately.
       *
       * @param minVel Minimum velocity to detect
       */
      public void setMinVelocity(float minVel) {
          mMinVelocity = minVel;
      }
  
      /**
       * Return the currently configured minimum velocity. Any flings with a magnitude less
       * than this value in pixels per second. Callback methods accepting a velocity will receive
       * zero as a velocity value if the real detected velocity was below this threshold.
       *
       * @return the minimum velocity that will be detected
       */
      public float getMinVelocity() {
          return mMinVelocity;
      }
  
      @Override
      public void setMaxVelocity(float maxVel) {
          mMaxVelocity = maxVel;
      }
  
      @Override
      public float getMaxVelocity() {
          return mMaxVelocity;
      }
  
      /**
       * Retrieve the current drag state of this helper. This will return one of
       * {@link #STATE_IDLE}, {@link #STATE_DRAGGING} or {@link #STATE_SETTLING}.
       *
       * @return The current drag state
       */
      public int getViewDragState() {
          return mDragState;
      }
  
      /**
       * Enable edge tracking for the selected edges of the parent view.
       * The callback's {@link Callback#onEdgeTouched(int, int)} and
       * {@link Callback#onEdgeDragStarted(int, int)} methods will only be invoked
       * for edges for which edge tracking has been enabled.
       *
       * @param edgeFlags Combination of edge flags describing the edges to watch
       * @see #EDGE_LEFT
       * @see #EDGE_TOP
       * @see #EDGE_RIGHT
       * @see #EDGE_BOTTOM
       */
      public void setEdgeTrackingEnabled(int edgeFlags) {
          mTrackingEdges = edgeFlags;
      }
  
      /**
       * Return the size of an edge. This is the range in pixels along the edges of this view
       * that will actively detect edge touches or drags if edge tracking is enabled.
       *
       * @return The size of an edge in pixels
       * @see #setEdgeTrackingEnabled(int)
       */
      public int getEdgeSize() {
          return mEdgeSize;
      }
  
      @Override
      public void setEdgeSize(int size) {
          mEdgeSize = size;
      }
  
      /**
       * Capture a specific child view for dragging within the parent. The callback will be notified
       * but {@link Callback#tryCaptureView(android.view.View, int)} will not be asked permission to
       * capture this view.
       *
       * @param childView       Child view to capture
       * @param activePointerId ID of the pointer that is dragging the captured child view
       */
      public void captureChildView(View childView, int activePointerId) {
          if (childView.getParent() != mParentView) {
              throw new IllegalArgumentException("captureChildView: parameter must be a descendant "
                      + "of the ViewDragHelper's tracked parent view (" + mParentView + ")");
          }
  
          mCapturedView = childView;
          mActivePointerId = activePointerId;
          mCallback.onViewCaptured(childView, activePointerId);
      }
  
      /**
       * @return The currently captured view, or null if no view has been captured.
       */
      public View getCapturedView() {
          return mCapturedView;
      }
  
      /**
       * @return The ID of the pointer currently dragging the captured view,
       * or {@link #INVALID_POINTER}.
       */
      public int getActivePointerId() {
          return mActivePointerId;
      }
  
      /**
       * @return The minimum distance in pixels that the user must travel to initiate a drag
       */
      public int getTouchSlop() {
          return mTouchSlop;
      }
  
      /**
       * The result of a call to this method is equivalent to
       * {@link #processTouchEvent(android.view.MotionEvent)} receiving an ACTION_CANCEL event.
       */
      public void cancel() {
          mActivePointerId = INVALID_POINTER;
          clearMotionHistory();
  
          if (mVelocityTracker != null) {
              mVelocityTracker.recycle();
              mVelocityTracker = null;
          }
      }
  
      /**
       * {@link #cancel()}, but also abort all motion in progress and snap to the end of any
       * animation.
       */
      public void abort() {
          cancel();
          if (mDragState == STATE_SETTLING) {
              final int oldX = mScroller.getCurrX();
              final int oldY = mScroller.getCurrY();
              mScroller.abortAnimation();
              final int newX = mScroller.getCurrX();
              final int newY = mScroller.getCurrY();
              mCallback.onViewPositionChanged(mCapturedView, newX, newY, newX - oldX, newY - oldY);
          }
          setDragState(STATE_IDLE);
      }
  
      /**
       * Animate the view <code>child</code> to the given (left, top) position.
       * If this method returns true, the caller should invoke {@link #continueSettling(boolean)}
       * on each subsequent frame to continue the motion until it returns false. If this method
       * returns false there is no further work to do to complete the movement.
       * <p>
       * <p>This operation does not count as a capture event, though {@link #getCapturedView()}
       * will still report the sliding view while the slide is in progress.</p>
       *
       * @param child     Child view to capture and animate
       * @param finalLeft Final left position of child
       * @param finalTop  Final top position of child
       * @return true if animation should continue through {@link #continueSettling(boolean)} calls
       */
      public boolean smoothSlideViewTo(View child, int finalLeft, int finalTop) {
          mCapturedView = child;
          mActivePointerId = INVALID_POINTER;
  
          return forceSettleCapturedViewAt(finalLeft, finalTop, 0, 0);
      }
  
      /**
       * Settle the captured view at the given (left, top) position.
       * The appropriate velocity from prior motion will be taken into account.
       * If this method returns true, the caller should invoke {@link #continueSettling(boolean)}
       * on each subsequent frame to continue the motion until it returns false. If this method
       * returns false there is no further work to do to complete the movement.
       *
       * @param finalLeft Settled left edge position for the captured view
       * @param finalTop  Settled top edge position for the captured view
       * @return true if animation should continue through {@link #continueSettling(boolean)} calls
       */
      public boolean settleCapturedViewAt(int finalLeft, int finalTop) {
          if (!mReleaseInProgress) {
              throw new IllegalStateException("Cannot settleCapturedViewAt outside of a call to "
                      + "Callback#onViewReleased");
          }
  
          return forceSettleCapturedViewAt(finalLeft, finalTop,
                  (int) mVelocityTracker.getXVelocity(mActivePointerId),
                  (int) mVelocityTracker.getYVelocity(mActivePointerId));
      }
  
      /**
       * Settle the captured view at the given (left, top) position.
       *
       * @param finalLeft Target left position for the captured view
       * @param finalTop  Target top position for the captured view
       * @param xvel      Horizontal velocity
       * @param yvel      Vertical velocity
       * @return true if animation should continue through {@link #continueSettling(boolean)} calls
       */
      private boolean forceSettleCapturedViewAt(int finalLeft, int finalTop, int xvel, int yvel) {
          final int startLeft = mCapturedView.getLeft();
          final int startTop = mCapturedView.getTop();
          final int dx = finalLeft - startLeft;
          final int dy = finalTop - startTop;
  
          if (dx == 0 && dy == 0) {
              // Nothing to do. Send callbacks, be done.
              mScroller.abortAnimation();
              setDragState(STATE_IDLE);
              return false;
          }
  
          final int duration = computeSettleDuration(mCapturedView, dx, dy, xvel, yvel);
          mScroller.startScroll(startLeft, startTop, dx, dy, duration);
  
          setDragState(STATE_SETTLING);
          return true;
      }
  
      private int computeSettleDuration(View child, int dx, int dy, int xvel, int yvel) {
          xvel = clampMag(xvel, (int) mMinVelocity, (int) mMaxVelocity);
          yvel = clampMag(yvel, (int) mMinVelocity, (int) mMaxVelocity);
          final int absDx = Math.abs(dx);
          final int absDy = Math.abs(dy);
          final int absXVel = Math.abs(xvel);
          final int absYVel = Math.abs(yvel);
          final int addedVel = absXVel + absYVel;
          final int addedDistance = absDx + absDy;
  
          final float xweight = xvel != 0 ? (float) absXVel / addedVel :
                  (float) absDx / addedDistance;
          final float yweight = yvel != 0 ? (float) absYVel / addedVel :
                  (float) absDy / addedDistance;
  
          int xduration = computeAxisDuration(dx, xvel, mCallback.getViewHorizontalDragRange(child));
          int yduration = computeAxisDuration(dy, yvel, mCallback.getViewVerticalDragRange(child));
  
          return (int) (xduration * xweight + yduration * yweight);
      }
  
      private int computeAxisDuration(int delta, int velocity, int motionRange) {
          if (delta == 0) {
              return 0;
          }
  
          final int width = mParentView.getWidth();
          final int halfWidth = width / 2;
          final float distanceRatio = Math.min(1f, (float) Math.abs(delta) / width);
          final float distance = halfWidth + halfWidth
                  * distanceInfluenceForSnapDuration(distanceRatio);
  
          int duration;
          velocity = Math.abs(velocity);
          if (velocity > 0) {
              duration = 4 * Math.round(1000 * Math.abs(distance / velocity));
          } else {
              final float range = (float) Math.abs(delta) / motionRange;
              duration = (int) ((range + 1) * BASE_SETTLE_DURATION);
          }
          return Math.min(duration, MAX_SETTLE_DURATION);
      }
  
      /**
       * Clamp the magnitude of value for absMin and absMax.
       * If the value is below the minimum, it will be clamped to zero.
       * If the value is above the maximum, it will be clamped to the maximum.
       *
       * @param value  Value to clamp
       * @param absMin Absolute value of the minimum significant value to return
       * @param absMax Absolute value of the maximum value to return
       * @return The clamped value with the same sign as <code>value</code>
       */
      private int clampMag(int value, int absMin, int absMax) {
          final int absValue = Math.abs(value);
          if (absValue < absMin) return 0;
          if (absValue > absMax) return value > 0 ? absMax : -absMax;
          return value;
      }
  
      /**
       * Clamp the magnitude of value for absMin and absMax.
       * If the value is below the minimum, it will be clamped to zero.
       * If the value is above the maximum, it will be clamped to the maximum.
       *
       * @param value  Value to clamp
       * @param absMin Absolute value of the minimum significant value to return
       * @param absMax Absolute value of the maximum value to return
       * @return The clamped value with the same sign as <code>value</code>
       */
      private float clampMag(float value, float absMin, float absMax) {
          final float absValue = Math.abs(value);
          if (absValue < absMin) return 0;
          if (absValue > absMax) return value > 0 ? absMax : -absMax;
          return value;
      }
  
      private float distanceInfluenceForSnapDuration(float f) {
          f -= 0.5f; // center the values about 0.
          f *= 0.3f * (float) Math.PI / 2.0f;
          return (float) Math.sin(f);
      }
  
      /**
       * Settle the captured view based on standard free-moving fling behavior.
       * The caller should invoke {@link #continueSettling(boolean)} on each subsequent frame
       * to continue the motion until it returns false.
       *
       * @param minLeft Minimum X position for the view's left edge
       * @param minTop  Minimum Y position for the view's top edge
       * @param maxLeft Maximum X position for the view's left edge
       * @param maxTop  Maximum Y position for the view's top edge
       */
      public void flingCapturedView(int minLeft, int minTop, int maxLeft, int maxTop) {
          if (!mReleaseInProgress) {
              throw new IllegalStateException("Cannot flingCapturedView outside of a call to "
                      + "Callback#onViewReleased");
          }
  
          mScroller.fling(mCapturedView.getLeft(), mCapturedView.getTop(),
                  (int) mVelocityTracker.getXVelocity(mActivePointerId),
                  (int) mVelocityTracker.getYVelocity(mActivePointerId),
                  minLeft, maxLeft, minTop, maxTop);
  
          setDragState(STATE_SETTLING);
      }
  
      /**
       * Move the captured settling view by the appropriate amount for the current time.
       * If <code>continueSettling</code> returns true, the caller should call it again
       * on the next frame to continue.
       *
       * @param deferCallbacks true if state callbacks should be deferred via posted message.
       *                       Set this to true if you are calling this method from
       *                       {@link android.view.View#computeScroll()} or similar methods
       *                       invoked as part of layout or drawing.
       * @return true if settle is still in progress
       */
      public boolean continueSettling(boolean deferCallbacks) {
          if (mDragState == STATE_SETTLING) {
              boolean keepGoing = mScroller.computeScrollOffset();
              final int x = mScroller.getCurrX();
              final int y = mScroller.getCurrY();
              final int dx = x - mCapturedView.getLeft();
              final int dy = y - mCapturedView.getTop();
  
              if (dx != 0) {
                  ViewCompat.offsetLeftAndRight(mCapturedView, dx);
              }
              if (dy != 0) {
                  ViewCompat.offsetTopAndBottom(mCapturedView, dy);
              }
  
              if (dx != 0 || dy != 0) {
                  mCallback.onViewPositionChanged(mCapturedView, x, y, dx, dy);
              }
  
              if (keepGoing && x == mScroller.getFinalX() && y == mScroller.getFinalY()) {
                  // Close enough. The interpolator/scroller might think we're still moving
                  // but the user sure doesn't.
                  mScroller.abortAnimation();
                  keepGoing = false;
              }
  
              if (!keepGoing) {
                  if (deferCallbacks) {
                      mParentView.post(mSetIdleRunnable);
                  } else {
                      setDragState(STATE_IDLE);
                  }
              }
          }
  
          return mDragState == STATE_SETTLING;
      }
  
      /**
       * Like all callback events this must happen on the UI thread, but release
       * involves some extra semantics. During a release (mReleaseInProgress)
       * is the only time it is valid to call {@link #settleCapturedViewAt(int, int)}
       * or {@link #flingCapturedView(int, int, int, int)}.
       */
      private void dispatchViewReleased(float xvel, float yvel) {
          mReleaseInProgress = true;
          mCallback.onViewReleased(mCapturedView, xvel, yvel);
          mReleaseInProgress = false;
  
          if (mDragState == STATE_DRAGGING) {
              // onViewReleased didn't call a method that would have changed this. Go idle.
              setDragState(STATE_IDLE);
          }
      }
  
      private void clearMotionHistory() {
          if (mInitialMotionX == null) {
              return;
          }
          Arrays.fill(mInitialMotionX, 0);
          Arrays.fill(mInitialMotionY, 0);
          Arrays.fill(mLastMotionX, 0);
          Arrays.fill(mLastMotionY, 0);
          Arrays.fill(mInitialEdgesTouched, 0);
          Arrays.fill(mEdgeDragsInProgress, 0);
          Arrays.fill(mEdgeDragsLocked, 0);
          mPointersDown = 0;
      }
  
      private void clearMotionHistory(int pointerId) {
          if (mInitialMotionX == null || !isPointerDown(pointerId)) {
              return;
          }
          mInitialMotionX[pointerId] = 0;
          mInitialMotionY[pointerId] = 0;
          mLastMotionX[pointerId] = 0;
          mLastMotionY[pointerId] = 0;
          mInitialEdgesTouched[pointerId] = 0;
          mEdgeDragsInProgress[pointerId] = 0;
          mEdgeDragsLocked[pointerId] = 0;
          mPointersDown &= ~(1 << pointerId);
      }
  
      private void ensureMotionHistorySizeForId(int pointerId) {
          if (mInitialMotionX == null || mInitialMotionX.length <= pointerId) {
              float[] imx = new float[pointerId + 1];
              float[] imy = new float[pointerId + 1];
              float[] lmx = new float[pointerId + 1];
              float[] lmy = new float[pointerId + 1];
              int[] iit = new int[pointerId + 1];
              int[] edip = new int[pointerId + 1];
              int[] edl = new int[pointerId + 1];
  
              if (mInitialMotionX != null) {
                  System.arraycopy(mInitialMotionX, 0, imx, 0, mInitialMotionX.length);
                  System.arraycopy(mInitialMotionY, 0, imy, 0, mInitialMotionY.length);
                  System.arraycopy(mLastMotionX, 0, lmx, 0, mLastMotionX.length);
                  System.arraycopy(mLastMotionY, 0, lmy, 0, mLastMotionY.length);
                  System.arraycopy(mInitialEdgesTouched, 0, iit, 0, mInitialEdgesTouched.length);
                  System.arraycopy(mEdgeDragsInProgress, 0, edip, 0, mEdgeDragsInProgress.length);
                  System.arraycopy(mEdgeDragsLocked, 0, edl, 0, mEdgeDragsLocked.length);
              }
  
              mInitialMotionX = imx;
              mInitialMotionY = imy;
              mLastMotionX = lmx;
              mLastMotionY = lmy;
              mInitialEdgesTouched = iit;
              mEdgeDragsInProgress = edip;
              mEdgeDragsLocked = edl;
          }
      }
  
      private void saveInitialMotion(float x, float y, int pointerId) {
          ensureMotionHistorySizeForId(pointerId);
          mInitialMotionX[pointerId] = mLastMotionX[pointerId] = x;
          mInitialMotionY[pointerId] = mLastMotionY[pointerId] = y;
          mInitialEdgesTouched[pointerId] = getEdgesTouched((int) x, (int) y);
          mPointersDown |= 1 << pointerId;
      }
  
      private void saveLastMotion(MotionEvent ev) {
          final int pointerCount = ev.getPointerCount();
          for (int i = 0; i < pointerCount; i++) {
              final int pointerId = ev.getPointerId(i);
              // If pointer is invalid then skip saving on ACTION_MOVE.
              if (!isValidPointerForActionMove(pointerId)) {
                  continue;
              }
              final float x = ev.getX(i);
              final float y = ev.getY(i);
              mLastMotionX[pointerId] = x;
              mLastMotionY[pointerId] = y;
          }
      }
  
      /**
       * Check if the given pointer ID represents a pointer that is currently down (to the best
       * of the ViewDragHelper's knowledge).
       * <p>
       * <p>The state used to report this information is populated by the methods
       * {@link #shouldInterceptTouchEvent(android.view.MotionEvent)} or
       * {@link #processTouchEvent(android.view.MotionEvent)}. If one of these methods has not
       * been called for all relevant MotionEvents to track, the information reported
       * by this method may be stale or incorrect.</p>
       *
       * @param pointerId pointer ID to check; corresponds to IDs provided by MotionEvent
       * @return true if the pointer with the given ID is still down
       */
      public boolean isPointerDown(int pointerId) {
          return (mPointersDown & 1 << pointerId) != 0;
      }
  
      void setDragState(int state) {
          mParentView.removeCallbacks(mSetIdleRunnable);
          if (mDragState != state) {
              mDragState = state;
              mCallback.onViewDragStateChanged(state);
              if (mDragState == STATE_IDLE) {
                  mCapturedView = null;
              }
          }
      }
  
      /**
       * Attempt to capture the view with the given pointer ID. The callback will be involved.
       * This will put us into the "dragging" state. If we've already captured this view with
       * this pointer this method will immediately return true without consulting the callback.
       *
       * @param toCapture View to capture
       * @param pointerId Pointer to capture with
       * @return true if capture was successful
       */
      boolean tryCaptureViewForDrag(View toCapture, int pointerId) {
          if (toCapture == mCapturedView && mActivePointerId == pointerId) {
              // Already done!
              return true;
          }
          if (toCapture != null && mCallback.tryCaptureView(toCapture, pointerId)) {
              mActivePointerId = pointerId;
              captureChildView(toCapture, pointerId);
              return true;
          }
          return false;
      }
  
      /**
       * Tests scrollability within child views of v given a delta of dx.
       *
       * @param v      View to test for horizontal scrollability
       * @param checkV Whether the view v passed should itself be checked for scrollability (true),
       *               or just its children (false).
       * @param dx     Delta scrolled in pixels along the X axis
       * @param dy     Delta scrolled in pixels along the Y axis
       * @param x      X coordinate of the active touch point
       * @param y      Y coordinate of the active touch point
       * @return true if child views of v can be scrolled by delta of dx.
       */
      protected boolean canScroll(View v, boolean checkV, int dx, int dy, int x, int y) {
          if (v instanceof ViewGroup) {
              final ViewGroup group = (ViewGroup) v;
              final int scrollX = v.getScrollX();
              final int scrollY = v.getScrollY();
              final int count = group.getChildCount();
              // Count backwards - let topmost views consume scroll distance first.
              for (int i = count - 1; i >= 0; i--) {
                  // TODO: Add versioned support here for transformed views.
                  // This will not work for transformed views in Honeycomb+
                  final View child = group.getChildAt(i);
                  if (x + scrollX >= child.getLeft() && x + scrollX < child.getRight()
                          && y + scrollY >= child.getTop() && y + scrollY < child.getBottom()
                          && canScroll(child, true, dx, dy, x + scrollX - child.getLeft(),
                          y + scrollY - child.getTop())) {
                      return true;
                  }
              }
          }
  
          return checkV && (v.canScrollHorizontally(-dx) || v.canScrollVertically(-dy));
      }
  
      /**
       * Check if this event as provided to the parent view's onInterceptTouchEvent should
       * cause the parent to intercept the touch event stream.
       *
       * @param ev MotionEvent provided to onInterceptTouchEvent
       * @return true if the parent view should return true from onInterceptTouchEvent
       */
      public boolean shouldInterceptTouchEvent(MotionEvent ev) {
          final int action = ev.getActionMasked();
          final int actionIndex = ev.getActionIndex();
  
          if (action == MotionEvent.ACTION_DOWN) {
              // Reset things for a new event stream, just in case we didn't get
              // the whole previous stream.
              cancel();
          }
  
          switch (action) {
              case MotionEvent.ACTION_DOWN: {
                  final float x = ev.getX();
                  final float y = ev.getY();
                  final int pointerId = ev.getPointerId(0);
                  saveInitialMotion(x, y, pointerId);
  
                  final View toCapture = findTopChildUnder((int) x, (int) y);
  
                  // Catch a settling view if possible.
                  tryCaptureViewForDrag(toCapture, pointerId);
  
                  if (mDragState == STATE_SETTLING) {
                      setDragState(STATE_DRAGGING);
                  } else if (mDragState == STATE_IDLE) {
                      final int edgesTouched = mInitialEdgesTouched[pointerId];
                      if ((edgesTouched & mTrackingEdges) != 0) {
                          mCallback.onEdgeTouched(edgesTouched & mTrackingEdges, pointerId);
                      }
                      setDragState(STATE_JUDGING);
                  }
                  break;
              }
  
              case MotionEvent.ACTION_POINTER_DOWN: {
                  final int pointerId = ev.getPointerId(actionIndex);
                  final float x = ev.getX(actionIndex);
                  final float y = ev.getY(actionIndex);
                  saveInitialMotion(x, y, pointerId);
                  break;
              }
  
              case MotionEvent.ACTION_MOVE: {
                  if (mDragState != STATE_JUDGING) break;
                  if (mVelocityTracker == null)
                      mVelocityTracker = VelocityTracker.obtain();
                  if (mDragState == STATE_DRAGGING)
                      mVelocityTracker.addMovement(ev);
                  final int i = ev.findPointerIndex(mActivePointerId);
  
                  final float x = ev.getX(i);
                  final float y = ev.getY(i);
                  final float dx = x - mInitialMotionX[mActivePointerId];
                  final float dy = y - mInitialMotionY[mActivePointerId];
  
                  reportNewEdgeDrags(dx, dy, mActivePointerId);
  
                  final View toCapture = findTopChildUnder((int) x, (int) y);
                  int slop = checkTouchSlop(toCapture, dx, dy);
  
                  if (slop == -1) cancel();
                  else if (slop > 0 && tryCaptureViewForDrag(toCapture, mActivePointerId)) {
                      break;
                  }
                  saveLastMotion(ev);
  
                  break;
              }
  
              case MotionEvent.ACTION_POINTER_UP: {
                  final int pointerId = ev.getPointerId(actionIndex);
                  clearMotionHistory(pointerId);
                  break;
              }
  
              case MotionEvent.ACTION_UP: {
                  releaseViewForPointerUp();
                  cancel();
                  break;
              }
  
              case MotionEvent.ACTION_CANCEL: {
                  dispatchViewReleased(0, 0);
                  cancel();
                  break;
              }
          }
  
          return mDragState == STATE_DRAGGING;
      }
  
      /**
       * Process a touch event received by the parent view. This method will dispatch callback events
       * as needed before returning. The parent view's onTouchEvent implementation should call this.
       *
       * @param ev The touch event received by the parent view
       */
      public void processTouchEvent(MotionEvent ev) {
          final int action = ev.getActionMasked();
          final int actionIndex = ev.getActionIndex();
  
          if (action == MotionEvent.ACTION_DOWN) {
              // Reset things for a new event stream, just in case we didn't get
              // the whole previous stream.
              cancel();
          }
  
          switch (action) {
              case MotionEvent.ACTION_DOWN: {
                  final float x = ev.getX();
                  final float y = ev.getY();
                  final int pointerId = ev.getPointerId(0);
                  saveInitialMotion(x, y, pointerId);
                  final View toCapture = findTopChildUnder((int) x, (int) y);
  
  
                  // Since the parent is already directly processing this touch event,
                  // there is no reason to delay for a slop before dragging.
                  // Start immediately if possible.
                  tryCaptureViewForDrag(toCapture, pointerId);
  
                  if (mDragState == STATE_SETTLING) {
                      setDragState(STATE_DRAGGING);
                  } else if (mDragState == STATE_IDLE) {
                      final int edgesTouched = mInitialEdgesTouched[pointerId];
                      if ((edgesTouched & mTrackingEdges) != 0) {
                          mCallback.onEdgeTouched(edgesTouched & mTrackingEdges, pointerId);
                      }
                      setDragState(STATE_JUDGING);
                  }
                  break;
              }
  
              case MotionEvent.ACTION_POINTER_DOWN: {
                  final int pointerId = ev.getPointerId(actionIndex);
                  final float x = ev.getX(actionIndex);
                  final float y = ev.getY(actionIndex);
  
                  saveInitialMotion(x, y, pointerId);
                  break;
              }
  
              case MotionEvent.ACTION_MOVE: {
                  if (mDragState == STATE_JUDGING) {
  
                      final int i = ev.findPointerIndex(mActivePointerId);
                      final float x = ev.getX(i);
                      final float y = ev.getY(i);
                      final float dx = x - mInitialMotionX[mActivePointerId];
                      final float dy = y - mInitialMotionY[mActivePointerId];
  
                      reportNewEdgeDrags(dx, dy, mActivePointerId);
                      if (mDragState == STATE_DRAGGING) {
                          // Callback might have started an edge drag.
                          break;
                      }
  
                      final View toCapture = findTopChildUnder((int) x, (int) y);
                      int slop = checkTouchSlop(toCapture, dx, dy);
                      if (slop == -1) cancel();
                      else if (slop > 0 && tryCaptureViewForDrag(toCapture, mActivePointerId)) {
                          break;
                      }
                      saveLastMotion(ev);
                  }
  
  
                  if (mDragState == STATE_DRAGGING) {
                      if (mVelocityTracker == null) {
                          mVelocityTracker = VelocityTracker.obtain();
                      }
                      if (mDragState == STATE_DRAGGING)
                          mVelocityTracker.addMovement(ev);
  
                      final int index = ev.findPointerIndex(mActivePointerId);
                      if (index == -1) break;
  
                      final float x = ev.getX(index);
                      final float y = ev.getY(index);
                      final int idx = (int) (x - mLastMotionX[mActivePointerId]);
                      final int idy = (int) (y - mLastMotionY[mActivePointerId]);
                      dragTo(mCapturedView.getLeft() + idx, mCapturedView.getTop() + idy, idx, idy);
                      saveLastMotion(ev);
                  }
                  break;
              }
  
              case MotionEvent.ACTION_POINTER_UP: {
                  final int pointerId = ev.getPointerId(actionIndex);
                  clearMotionHistory(pointerId);
                  break;
              }
  
              case MotionEvent.ACTION_UP: {
                  releaseViewForPointerUp();
                  cancel();
                  break;
              }
  
              case MotionEvent.ACTION_CANCEL: {
                  dispatchViewReleased(0, 0);
                  cancel();
                  break;
              }
          }
      }
  
      private void reportNewEdgeDrags(float dx, float dy, int pointerId) {
          int dragsStarted = 0;
          if (checkNewEdgeDrag(dx, dy, pointerId, EDGE_LEFT)) {
              dragsStarted |= EDGE_LEFT;
          }
          if (checkNewEdgeDrag(dy, dx, pointerId, EDGE_TOP)) {
              dragsStarted |= EDGE_TOP;
          }
          if (checkNewEdgeDrag(dx, dy, pointerId, EDGE_RIGHT)) {
              dragsStarted |= EDGE_RIGHT;
          }
          if (checkNewEdgeDrag(dy, dx, pointerId, EDGE_BOTTOM)) {
              dragsStarted |= EDGE_BOTTOM;
          }
  
          if (dragsStarted != 0) {
              mEdgeDragsInProgress[pointerId] |= dragsStarted;
              mCallback.onEdgeDragStarted(dragsStarted, pointerId);
          }
      }
  
      private boolean checkNewEdgeDrag(float delta, float odelta, int pointerId, int edge) {
          final float absDelta = Math.abs(delta);
          final float absODelta = Math.abs(odelta);
  
          if ((mInitialEdgesTouched[pointerId] & edge) != edge || (mTrackingEdges & edge) == 0
                  || (mEdgeDragsLocked[pointerId] & edge) == edge
                  || (mEdgeDragsInProgress[pointerId] & edge) == edge
                  || (absDelta <= mTouchSlop && absODelta <= mTouchSlop)) {
              return false;
          }
          if (absDelta < absODelta * 0.5f && mCallback.onEdgeLock(edge)) {
              mEdgeDragsLocked[pointerId] |= edge;
              return false;
          }
          return (mEdgeDragsInProgress[pointerId] & edge) == 0 && absDelta > mTouchSlop;
      }
  
      /**
       * Check if we've crossed a reasonable touch slop for the given child view.
       * If the child cannot be dragged along the horizontal or vertical axis, motion
       * along that axis will not count toward the slop check.
       *
       * @param child Child to check
       * @param dx    Motion since initial position along X axis
       * @param dy    Motion since initial position along Y axis
       * @return 1 if the touch slop has been crossed on our desired axis
       * -       0 if the touch slop has not been crossed
       * -       -1 if the touch slop has been crossed on the other axis
       * -       2 if the touch slop has been crossed on both
       */
      private int checkTouchSlop(View child, float dx, float dy) {
          if (child == null) {
              return 0;
          }
          switch (edgeFlag) {
              case SWIPE_EDGE_LEFT:
                  if (dx <= mTouchSlop && Math.abs(dy) <= mTouchSlop) {
                      return 0;
                  } else if (dx > mTouchSlop && Math.abs(dy) <= mTouchSlop) {
                      mDragState = STATE_DRAGGING;
                      return 1;
                  } else if (dx <= mTouchSlop && Math.abs(dy) > mTouchSlop) {
                      mDragState = STATE_IDLE;
                      cancel();
                      return -1;
                  }
                  break;
              case SWIPE_EDGE_RIGHT:
                  if (dx >= -mTouchSlop && Math.abs(dy) <= mTouchSlop) {
                      return 0;
                  } else if (dx < -mTouchSlop && Math.abs(dy) <= mTouchSlop) {
                      mDragState = STATE_DRAGGING;
                      return 1;
                  } else if (dx >= mTouchSlop && Math.abs(dy) > mTouchSlop) {
                      mDragState = STATE_IDLE;
                      cancel();
                      return -1;
                  }
                  break;
              case SWIPE_EDGE_TOP:
                  if (dy <= mTouchSlop && Math.abs(dx) <= mTouchSlop) {
                      return 0;
                  } else if (dy > mTouchSlop && Math.abs(dx) <= mTouchSlop) {
                      mDragState = STATE_DRAGGING;
                      return 1;
                  } else if (dy <= mTouchSlop && Math.abs(dx) > mTouchSlop) {
                      mDragState = STATE_IDLE;
                      cancel();
                      return -1;
                  }
                  break;
              case SWIPE_EDGE_BOTTOM:
                  if (dy >= -mTouchSlop && Math.abs(dx) <= mTouchSlop) {
                      return 0;
                  } else if (dy < -mTouchSlop && Math.abs(dx) <= mTouchSlop) {
                      mDragState = STATE_DRAGGING;
                      return 1;
                  } else if (dy >= mTouchSlop && Math.abs(dx) > mTouchSlop) {
                      mDragState = STATE_IDLE;
                      cancel();
                      return -1;
                  }
                  break;
          }
          return 2;
      }
      //TODO
  
      /**
       * Check if any of the edges specified were initially touched in the currently active gesture.
       * If there is no currently active gesture this method will return false.
       *
       * @param edges Edges to check for an initial edge touch. See {@link #EDGE_LEFT},
       *              {@link #EDGE_TOP}, {@link #EDGE_RIGHT}, {@link #EDGE_BOTTOM} and
       *              {@link #EDGE_ALL}
       * @return true if any of the edges specified were initially touched in the current gesture
       */
      public boolean isEdgeTouched(int edges) {
          final int count = mInitialEdgesTouched.length;
          for (int i = 0; i < count; i++) {
              if (isEdgeTouched(edges, i)) {
                  return true;
              }
          }
          return false;
      }
  
      /**
       * Check if any of the edges specified were initially touched by the pointer with
       * the specified ID. If there is no currently active gesture or if there is no pointer with
       * the given ID currently down this method will return false.
       *
       * @param edges Edges to check for an initial edge touch. See {@link #EDGE_LEFT},
       *              {@link #EDGE_TOP}, {@link #EDGE_RIGHT}, {@link #EDGE_BOTTOM} and
       *              {@link #EDGE_ALL}
       * @return true if any of the edges specified were initially touched in the current gesture
       */
      public boolean isEdgeTouched(int edges, int pointerId) {
          return isPointerDown(pointerId) && (mInitialEdgesTouched[pointerId] & edges) != 0;
      }
  
      private void releaseViewForPointerUp() {
          mVelocityTracker.computeCurrentVelocity(1000, mMaxVelocity);
          final float xvel = clampMag(
                  mVelocityTracker.getXVelocity(mActivePointerId),
                  mMinVelocity, mMaxVelocity);
          final float yvel = clampMag(
                  mVelocityTracker.getYVelocity(mActivePointerId),
                  mMinVelocity, mMaxVelocity);
          if (getViewDragState() == STATE_DRAGGING)
              dispatchViewReleased(xvel, yvel);
      }
  
      private void dragTo(int left, int top, int dx, int dy) {
          int clampedX = left;
          int clampedY = top;
          final int oldLeft = mCapturedView.getLeft();
          final int oldTop = mCapturedView.getTop();
          if (dx != 0) {
              clampedX = mCallback.clampViewPositionHorizontal(mCapturedView, left, dx);
              ViewCompat.offsetLeftAndRight(mCapturedView, clampedX - oldLeft);
          }
          if (dy != 0) {
              clampedY = mCallback.clampViewPositionVertical(mCapturedView, top, dy);
              ViewCompat.offsetTopAndBottom(mCapturedView, clampedY - oldTop);
          }
  
          if (dx != 0 || dy != 0) {
              final int clampedDx = clampedX - oldLeft;
              final int clampedDy = clampedY - oldTop;
              mCallback.onViewPositionChanged(mCapturedView, clampedX, clampedY,
                      clampedDx, clampedDy);
          }
      }
  
      /**
       * Determine if the currently captured view is under the given point in the
       * parent view's coordinate system. If there is no captured view this method
       * will return false.
       *
       * @param x X position to test in the parent's coordinate system
       * @param y Y position to test in the parent's coordinate system
       * @return true if the captured view is under the given point, false otherwise
       */
      public boolean isCapturedViewUnder(int x, int y) {
          return isViewUnder(mCapturedView, x, y);
      }
  
      /**
       * Determine if the supplied view is under the given point in the
       * parent view's coordinate system.
       *
       * @param view Child view of the parent to hit test
       * @param x    X position to test in the parent's coordinate system
       * @param y    Y position to test in the parent's coordinate system
       * @return true if the supplied view is under the given point, false otherwise
       */
      public boolean isViewUnder(View view, int x, int y) {
          return view != null;
      }
  
      /**
       * Find the topmost child under the given point within the parent view's coordinate system.
       * The child order is determined using {@link Callback#getOrderedChildIndex(int)}.
       *
       * @param x X position to test in the parent's coordinate system
       * @param y Y position to test in the parent's coordinate system
       * @return The topmost child view under (x, y) or null if none found.
       */
      public View findTopChildUnder(int x, int y) {
          return mParentView.getChildAt(0);
      }
  
      private int getEdgesTouched(int x, int y) {
          int result = 0;
  
          if (x < mParentView.getLeft() + mEdgeSize) result |= EDGE_LEFT;
          if (y < mParentView.getTop() + mEdgeSize) result |= EDGE_TOP;
          if (x > mParentView.getRight() - mEdgeSize) result |= EDGE_RIGHT;
          if (y > mParentView.getBottom() - mEdgeSize) result |= EDGE_BOTTOM;
  
          return result;
      }
  
      private boolean isValidPointerForActionMove(int pointerId) {
          if (!isPointerDown(pointerId)) {
              Log.e(TAG, "Ignoring pointerId=" + pointerId + " because ACTION_DOWN was not received "
                      + "for this pointer before ACTION_MOVE. It likely happened because "
                      + " ViewDragHelper did not receive all the events in the event stream.");
              return false;
          }
          return true;
      }
  }
  