content: /*
   * Copyright (C) 2016 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.android.internal.view;
  
  import android.view.View;
  import android.view.ViewTreeObserver;
  
  /**
   * An OnPreDrawListener that will remove itself after one OnPreDraw call. Typical
   * usage is:
   * <pre><code>
   *     OneShotPreDrawListener.add(view, () -> { view.doSomething(); })
   * </code></pre>
   * <p>
   * The listener will also remove itself from the ViewTreeObserver when the view
   * is detached from the view hierarchy. In that case, the Runnable will never be
   * executed.
   */
  public class OneShotPreDrawListener implements ViewTreeObserver.OnPreDrawListener,
          View.OnAttachStateChangeListener {
      private final View mView;
      private ViewTreeObserver mViewTreeObserver;
      private final Runnable mRunnable;
      private final boolean mReturnValue;
  
      private OneShotPreDrawListener(View view, boolean returnValue, Runnable runnable) {
          mView = view;
          mViewTreeObserver = view.getViewTreeObserver();
          mRunnable = runnable;
          mReturnValue = returnValue;
      }
  
      /**
       * Creates a OneShotPreDrawListener and adds it to view's ViewTreeObserver. The
       * return value from the OnPreDrawListener is {@code true}.
       *
       * @param view The view whose ViewTreeObserver the OnPreDrawListener should listen.
       * @param runnable The Runnable to execute in the OnPreDraw (once)
       * @return The added OneShotPreDrawListener. It can be removed prior to
       * the onPreDraw by calling {@link #removeListener()}.
       */
      public static OneShotPreDrawListener add(View view, Runnable runnable) {
          return add(view, true, runnable);
      }
  
      /**
       * Creates a OneShotPreDrawListener and adds it to view's ViewTreeObserver.
       *
       * @param view The view whose ViewTreeObserver the OnPreDrawListener should listen.
       * @param returnValue The value to be returned from the OnPreDrawListener.
       * @param runnable The Runnable to execute in the OnPreDraw (once)
       * @return The added OneShotPreDrawListener. It can be removed prior to
       * the onPreDraw by calling {@link #removeListener()}.
       */
      public static OneShotPreDrawListener add(View view, boolean returnValue, Runnable runnable) {
          OneShotPreDrawListener listener = new OneShotPreDrawListener(view, returnValue, runnable);
          view.getViewTreeObserver().addOnPreDrawListener(listener);
          view.addOnAttachStateChangeListener(listener);
          return listener;
      }
  
      @Override
      public boolean onPreDraw() {
          removeListener();
          mRunnable.run();
          return mReturnValue;
      }
  
      /**
       * Removes the listener from the ViewTreeObserver. This is useful to call if the
       * callback should be removed prior to {@link #onPreDraw()}.
       */
      public void removeListener() {
          if (mViewTreeObserver.isAlive()) {
              mViewTreeObserver.removeOnPreDrawListener(this);
          } else {
              mView.getViewTreeObserver().removeOnPreDrawListener(this);
          }
          mView.removeOnAttachStateChangeListener(this);
      }
  
      @Override
      public void onViewAttachedToWindow(View v) {
          mViewTreeObserver = v.getViewTreeObserver();
      }
  
      @Override
      public void onViewDetachedFromWindow(View v) {
          removeListener();
      }
  }
  