Android仅下载horizo​​ntalScrollView中可见的图像

Question

我有一个Horizo​​ntalScrollView,它包含一个LinearLayout来保存我的所有视图.我添加了大约20个RelativeLayout,它包含一个ImageView和TextView到LinearLayout.我想只在ImageView在屏幕上时加载图像(当我滚动到ImageView时).

我尝试在缩略图上使用此帖子getHitRect(),但缩略图的Rect(边界)始终为0,0-0,0,导致我的方法返回false.我究竟做错了什么？

thumbnailLayout是Horizo​​ntalScrollView里面的LinearLayout
thumbnailScroll是我的Horizo​​ntalScrollView

runOnUiThread(new Runnable() {

    @Override
    public void run() {
           Log.e(TAG, "running");
           for (int i = 0; i < thumbnailLayout.getChildCount(); i++) {
                RelativeLayout view = (RelativeLayout) thumbnailLayout.getChildAt(i);
                ImageView thumbnail = (ImageView) view.findViewById(R.id.thumbnail);
                if (thumbnailIsOnScreen(thumbnail)) {
                    Log.e(TAG, items.get(i).getTitle() + " has downloaded");
                    app.setImage(items.get(i).getThumbnailSmall(), thumbnail);
                }
           }


       }
   });

private boolean thumbnailIsOnScreen(ImageView thumbnail) {
        Rect bounds = new Rect();
        thumbnail.getHitRect(bounds);

        Rect scrollBounds = new Rect(thumbnailScroll.getScrollX(), thumbnailScroll.getScrollY(),
                thumbnailScroll.getScrollX() + thumbnailScroll.getWidth(), thumbnailScroll.getScrollY()
                        + thumbnailScroll.getHeight());
        return Rect.intersects(scrollBounds, bounds);
    }

编辑我使用TreeObserver并发现我的方法来检查是否在屏幕上显示缩略图是错误的.它仍然抓取所有图像,并不断循环(因为我正在使用onPreDrawListener？)

thumbnailLayout.getViewTreeObserver().addOnPreDrawListener(new OnPreDrawListener() {

            @Override
            public boolean onPreDraw() {
                Log.e(TAG, "running");

                for (int i = 0; i < thumbnailLayout.getChildCount(); i++) {
                    RelativeLayout view = (RelativeLayout) thumbnailLayout.getChildAt(i);
                    ImageView thumbnail = (ImageView) view.findViewById(R.id.thumbnail);
                    if (thumbnailIsOnScreen(thumbnail)) {
                        Log.e(TAG, items.get(i).getTitle() + " has downloaded");
                        app.setImage(items.get(i).getThumbnailSmall(), thumbnail);
                    }
                }
                return true;
            }
        });

Answer 1

你需要一个ListView，但android中没有原生的Horizo​​ntallListView。您可以尝试DevSmart 的 Horizo​​ntallListView。它的工作方式类似于本机列表视图，如果需要，可以使用适配器和自定义视图。