DraweeHolder 中的 Fresco 淡入淡出

Question

我在自定义视图中使用 DraweeHolder 来显示图像。当我想使用新资源更新图像时，我创建一个新的 DraweeController，然后将 setController 设置为 DraweeHolder。

我要实现的是新旧图像之间的淡入淡出效果。对于 fade in/out，我递归地将 Alpha 设置为 drawable。

void handleTransition(DraweeHolder draweeHolder, long startingTime) {
    Drawable drawable = draweeHolder.getTopLevelDrawable().mutate();
    int duration = 2000;
    long currTime = System.currentTimeMillis();
    int diff = (int) (currTime - startingTime);
    int toAlpha = Math.max(0, 255 - (255 * diff / duration));
    drawable.setAlpha(toAlpha);
    invalidate();
}


@Override
protected void onDraw(Canvas canvas) {
    Log.d(TAG, "onDraw()");
    super.onDraw(canvas);
    synchronized (this) {
        handleTransition(draweeHolder, mCurrentTransStartTime);
    }
}

看起来工作正常，除了 onDraw 会被调用太多次。但是，我不知道我们如何在这个 DraweeHolder 中同时出现两个图像（淡入淡出）。即使为 DraweeHolder 设置 high/low 分辨率图像也没有提供淡入淡出的选项。

Answer 1

你走在正确的轨道上。您将必须编写自定义视图（例如，通过扩展 ImageView）。请记住，为了让 Drawee 正常工作，您需要连接一些东西，请阅读 here 如何做到这一点。

您将需要两个 DraweeHolders。使用多个支架时，最好将它们放在 MultiDraweeHolder:

中

  private void init() {
    mMultiDraweeHolder = new MultiDraweeHolder<GenericDraweeHierarchy>();
    // holders for the two images to cross-fade between
    Drawable drawables[] = new Drawable[2];
    for (int i = 0; i < drawables.length; i++) {
      GenericDraweeHierarchy hierarchy = createDraweeHierarchy();
      mMultiDraweeHolder.add(DraweeHolder.create(hierarchy, getContext()));
      drawables[i] = hierarchy.getTopLevelDrawable();
    }
    mFadeDrawable = new FadeDrawable(drawables);
    // no need to override onDraw, ImageView superclass will correctly draw our fade drawable if we set it like this:
    super.setImageDrawable(mFadeDrawable);
    mCurrentIndex = 0;
  }

  void loadNextImage(DraweeController controller) {
    mCurrentIndex = (mCurrentIndex + 1) % 2;
    mMultiDraweeHolder.get(mCurrentIndex).setController(controller);
    mFadeDrawable.fadeToLayer(mCurrentIndex);
  }

  GenericDraweeHierarchy createDraweeHierarchy() {
    // create a new drawee hierarchy here,
    // as each image needs to have its own instance
  }

DraweeHolder 中的 Fresco 淡入淡出

Fresco crossfading within a DraweeHolder

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