android - 滚动时 Gridview 内的 ImageView 重复图像(使用 ImageDownloader)

Question

正如标题所说，我有这个问题。

因为我需要从网络检索图像，所以我实现了一个解决方案，解释为 here

我将发布 Adapter 和 ImageDownloader 代码(我已自由修改下载器以使功能更适合我的程序)。

适配器方法:

@Override
public View getView(int position, View view, ViewGroup parent) {

    ViewHolder holder;

    if (view == null) {
        view = inflater.inflate(R.layout.grid_adapter_camera_layout, parent, false);

        holder = new ViewHolder();
        holder.progress = (ProgressBar) view.findViewById(R.id.progressBar);
        holder.image = (ImageView) view.findViewById(R.id.camera_image);
        holder.text = (TextView) view.findViewById(R.id.camera_name);
        holder.text.setEllipsize(TextUtils.TruncateAt.END);
        holder.text.setLines(2);
        view.setTag(holder);
    } else {
        holder = (ViewHolder) view.getTag();
    }

    imgDownloader.download(values.get(position).getUrl(), holder.image, holder.progress);
}

这里是 ImageDownloader(我只发布了最合适的代码部分，如果您需要更多，请不要犹豫，索取它)。

public void download(String url, ImageView imageView, ProgressBar progress) {

    Bitmap bitmap = getBitmapFromCache(url);
    if (bitmap != null) {
        cancelPotentialDownload(url, imageView);
        imageView.setImageBitmap(bitmap);
    } else if(cancelPotentialDownload(url, imageView)){
        BitmapDownloaderTask task = new BitmapDownloaderTask(imageView, progress);
        imageView.setTag(new WeakReference<BitmapDownloaderTask>(task));
        task.execute(url);
    }
}

private boolean cancelPotentialDownload(String url, ImageView imageView) {
    BitmapDownloaderTask bitmapDownloaderTask = getBitmapDownloaderTask(imageView);

    if (bitmapDownloaderTask != null) {
        String bitmapUrl = bitmapDownloaderTask.url;
        if ((bitmapUrl == null) || (!bitmapUrl.equals(url))) {
            bitmapDownloaderTask.cancel(true);
        } else {
            // The same URL is already being downloaded.
            return false;
        }
    }
    return true;
}

@SuppressWarnings("unchecked")
private BitmapDownloaderTask getBitmapDownloaderTask(ImageView imageView) {
    if (imageView != null && imageView.getTag() != null) {
        return ((WeakReference<BitmapDownloaderTask>) imageView.getTag()).get();
    }
    return null;
}

public class BitmapDownloaderTask extends AsyncTask<String, Void, Bitmap> {
    String url;
    WeakReference<ImageView> viewReference;
    WeakReference<ProgressBar> progressReference;

    public BitmapDownloaderTask(ImageView view, ProgressBar progress) {
        view.setTag(false);
        viewReference = new WeakReference<ImageView>(view);
        progressReference = new WeakReference<ProgressBar>(progress);
    }

    @Override
    protected Bitmap doInBackground(String... params) {
        url=params[0];
        Log.e("DOWNLOAD URL", url);
        return downloadBitmap(params[0]);
    }

    @Override
    protected void onPostExecute(Bitmap result) {
        if (isCancelled())
            result = null;

        addBitmapToCache(url, result);

        if (viewReference != null) {
            ImageView imgView = viewReference.get();
            BitmapDownloaderTask bitmapDownloaderTask = getBitmapDownloaderTask(imgView);

            if (this == bitmapDownloaderTask) {
                if (result != null)
                    imgView.setImageBitmap(result);
                else
                    imgView.setImageResource(R.drawable.no_signal);
            }
        }

        if (progressReference != null) {
            ProgressBar prog = progressReference.get();
            if (prog != null)
                prog.setVisibility(View.GONE);
        }

    }

}

Answer 1

我建议你使用一个库来下载图像，picasso做得很好。另一件事看看this来自 dev-bytes 的视频。它是关于动画的，但下载图像的技巧应该是一样的。这两个步骤应该有效，我已经这样做了几次并且效果很好。