DrawableCrossFadeTransition.java 文件源码

/**
 * Animates from the previous drawable to the current drawable in one of two ways.
 *
 * <ol> <li>Using the default animation provided in the constructor if the previous drawable is
 * null</li> <li>Using the cross fade animation with the duration provided in the constructor if
 * the previous drawable is non null</li> </ol>
 *
 * @param current {@inheritDoc}
 * @param adapter {@inheritDoc}
 * @return {@inheritDoc}
 */
@Override
public boolean transition(Drawable current, ViewAdapter adapter) {
  Drawable previous = adapter.getCurrentDrawable();
  if (previous != null) {
    TransitionDrawable transitionDrawable =
        new TransitionDrawable(new Drawable[] { previous, current });
    transitionDrawable.setCrossFadeEnabled(isCrossFadeEnabled);
    transitionDrawable.startTransition(duration);
    adapter.setDrawable(transitionDrawable);
    return true;
  } else {
    defaultAnimation.transition(current, adapter);
    return false;
  }
}