content: /*
   * Copyright (C) 2010 The Android Open Source Project
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package com.stone.customview.view;
  
  import android.content.Context;
  import android.graphics.Canvas;
  import android.util.AttributeSet;
  import android.view.View;
  import android.widget.ListAdapter;
  import android.widget.ListView;
  
  /**
   * A ListView that maintains a header pinned at the top of the list. The
   * pinned header can be pushed up and dissolved as needed.
   */
  public class PinnedHeaderListView extends ListView {
  
      /**
       * Adapter interface.  The list adapter must implement this interface.
       */
      public interface PinnedHeaderAdapter {
  
          /**
           * Pinned header state: don't show the header.
           */
          public static final int PINNED_HEADER_GONE = 0;
  
          /**
           * Pinned header state: show the header at the top of the list.
           */
          public static final int PINNED_HEADER_VISIBLE = 1;
  
          /**
           * Pinned header state: show the header. If the header extends beyond
           * the bottom of the first shown element, push it up and clip.
           */
          public static final int PINNED_HEADER_PUSHED_UP = 2;
  
          /**
           * Computes the desired state of the pinned header for the given
           * position of the first visible list item. Allowed return values are
           * {@link #PINNED_HEADER_GONE}, {@link #PINNED_HEADER_VISIBLE} or
           * {@link #PINNED_HEADER_PUSHED_UP}.
           */
          int getPinnedHeaderState(int position);
  
          /**
           * Configures the pinned header view to match the first visible list item.
           *
           * @param header pinned header view.
           * @param position position of the first visible list item.
           * @param alpha fading of the header view, between 0 and 255.
           */
          void configurePinnedHeader(View header, int position, int alpha);
      }
  
      private static final int MAX_ALPHA = 255;
  
      private PinnedHeaderAdapter mAdapter;
      private View mHeaderView;
      private boolean mHeaderViewVisible;
  
      private int mHeaderViewWidth;
  
      private int mHeaderViewHeight;
  
      public PinnedHeaderListView(Context context) {
          super(context);
      }
  
      public PinnedHeaderListView(Context context, AttributeSet attrs) {
          super(context, attrs);
      }
  
      public PinnedHeaderListView(Context context, AttributeSet attrs, int defStyle) {
          super(context, attrs, defStyle);
      }
  
      public void setPinnedHeaderView(View view) {
          mHeaderView = view;
  
          // Disable vertical fading when the pinned header is present
          // TODO change ListView to allow separate measures for top and bottom fading edge;
          // in this particular case we would like to disable the top, but not the bottom edge.
          if (mHeaderView != null) {
              setFadingEdgeLength(0);
          }
          requestLayout();
      }
  
      @Override
      public void setAdapter(ListAdapter adapter) {
          super.setAdapter(adapter);
          mAdapter = (PinnedHeaderAdapter)adapter;
      }
  
      @Override
      protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
          super.onMeasure(widthMeasureSpec, heightMeasureSpec);
          if (mHeaderView != null) {
              measureChild(mHeaderView, widthMeasureSpec, heightMeasureSpec);
              mHeaderViewWidth = mHeaderView.getMeasuredWidth();
              mHeaderViewHeight = mHeaderView.getMeasuredHeight();
          }
      }
  
      @Override
      protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
          super.onLayout(changed, left, top, right, bottom);
          if (mHeaderView != null) {
              mHeaderView.layout(0, 0, mHeaderViewWidth, mHeaderViewHeight);
              configureHeaderView(getFirstVisiblePosition());
          }
      }
  
      public void configureHeaderView(int position) {
          if (mHeaderView == null) {
              return;
          }
  
          int state = mAdapter.getPinnedHeaderState(position);
          switch (state) {
              case PinnedHeaderAdapter.PINNED_HEADER_GONE: {
                  mHeaderViewVisible = false;
                  break;
              }
  
              case PinnedHeaderAdapter.PINNED_HEADER_VISIBLE: {
                  mAdapter.configurePinnedHeader(mHeaderView, position, MAX_ALPHA);
                  if (mHeaderView.getTop() != 0) {
                      mHeaderView.layout(0, 0, mHeaderViewWidth, mHeaderViewHeight);
                  }
                  mHeaderViewVisible = true;
                  break;
              }
  
              case PinnedHeaderAdapter.PINNED_HEADER_PUSHED_UP: {
                  View firstView = getChildAt(0);
                  int bottom = firstView.getBottom();
                  int itemHeight = firstView.getHeight();
                  int headerHeight = mHeaderView.getHeight();
                  int y;
                  int alpha;
                  if (bottom < headerHeight) {
                      y = (bottom - headerHeight);
                      alpha = MAX_ALPHA * (headerHeight + y) / headerHeight;
                  } else {
                      y = 0;
                      alpha = MAX_ALPHA;
                  }
                  mAdapter.configurePinnedHeader(mHeaderView, position, alpha);
                  if (mHeaderView.getTop() != y) {
                      mHeaderView.layout(0, y, mHeaderViewWidth, mHeaderViewHeight + y);
                  }
                  mHeaderViewVisible = true;
                  break;
              }
          }
      }
  
      @Override
      protected void dispatchDraw(Canvas canvas) {
          super.dispatchDraw(canvas);
          if (mHeaderViewVisible) {
              drawChild(canvas, mHeaderView, getDrawingTime());
          }
      }
  }
  