SnippetArticleViewHolder.java 文件源码

private void fadeThumbnailIn(SnippetArticle snippet, Bitmap thumbnail) {
    mImageCallback = null;
    if (thumbnail == null) return; // Nothing to do, we keep the placeholder.

    // We need to crop and scale the downloaded bitmap, as the ImageView we set it on won't be
    // able to do so when using a TransitionDrawable (as opposed to the straight bitmap).
    // That's a limitation of TransitionDrawable, which doesn't handle layers of varying sizes.
    Resources res = mThumbnailView.getResources();
    int targetSize = res.getDimensionPixelSize(R.dimen.snippets_thumbnail_size);
    Bitmap scaledThumbnail = ThumbnailUtils.extractThumbnail(
            thumbnail, targetSize, targetSize, ThumbnailUtils.OPTIONS_RECYCLE_INPUT);

    // Store the bitmap to skip the download task next time we display this snippet.
    snippet.setThumbnailBitmap(scaledThumbnail);

    // Cross-fade between the placeholder and the thumbnail.
    Drawable[] layers = {mThumbnailView.getDrawable(),
            new BitmapDrawable(mThumbnailView.getResources(), scaledThumbnail)};
    TransitionDrawable transitionDrawable = new TransitionDrawable(layers);
    mThumbnailView.setImageDrawable(transitionDrawable);
    transitionDrawable.startTransition(FADE_IN_ANIMATION_TIME_MS);
}