带有排球图像请求（取消请求）的回收者视图

Question

So i am using recycler view to show images in a grid and downloading images from url as bitmaps using volley library.

public void onBindViewHolder(final TrendingAdapter.ViewHolder viewHolder, int i) {
    ImageRequest request = new ImageRequest(url, new Response.Listener<Bitmap>() {
        @Override
        public void onResponse(Bitmap bitmap) {
            if (bitmap != null) {
                viewHolder.getmImageView().setImageBitmap(bitmap);
            }
        }
    }, 0, 0, null,
            new Response.ErrorListener() {
                @Override
                public void onErrorResponse(VolleyError volleyError) {
                }
            });
    AppController.getInstance().addToRequestQueue(request);
}

The problem is when i scroll and skip one or more views before the image is downloaded and that view is recycled the image donwnload reqest is not canceled on those intermediate view resulting in a flash of that/those image(s) before the actual image is loaded in that view.

So i thought of canceling those intermediate image requests using tags but cannot figure out how as it results in canceling of request in other parallel views as well!

Also when i use volley NetworkImageView (that handels such image canceling by itself) gives perfect results. But i need to get bitmap of every image to pick colors from it so i cannot use NetworkImageView.

Q) How do i cancel all pending volley image requsts (except the one it should be loading and without effecting other parallel views) on a specific imageview inflated using recyclerview?

Answer 1

You should use the ImageLoader class instead of directly adding a request to the RequestQueue . That way, the get() method, which is used to get images, will return an object of type ImageContainer .

Save this ImageContainer in the ViewHolder , and when a view gets recycled, simply call the cancelRequest() method on the recycled image to cancel the request if it hasn't been performed yet.

Take a look at the NetworkImageView 's code. It works in a similar way.

Answer 2

I solved the problem ! yaaeeye :D @Itai 's answer pointed me in the correct direction. I took a close look at NetworkImageView code and modified it according to my need. So i made a CustumNetworkImageView

public class CustomNetworkImageView extends ImageView {

    // Added code block start

    public interface ResponseObserver {
        public void onError();

        public void onSuccess();
    }

    private ResponseObserver mResponseObserver;

    public void setmResponseObserver(ResponseObserver observer) {
        mResponseObserver = observer;
    }

    private Bitmap bmp = null;

    // Added code block end

    private String mUrl;

    private int mDefaultImageId;

    private int mErrorImageId;

    private ImageLoader mImageLoader;

    public CustomNetworkImageView(Context context) {
        this(context, null);
    }

    public CustomNetworkImageView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public CustomNetworkImageView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }

    public void setImageUrl(String url, ImageLoader imageLoader) {
        mUrl = url;
        mImageLoader = imageLoader;
        loadImageIfNecessary();
    }

    public void setDefaultImageResId(int defaultImage) {
        mDefaultImageId = defaultImage;
    }

    public void setErrorImageResId(int errorImage) {
        mErrorImageId = errorImage;

        // Added code block start

        if (mResponseObserver != null) {
            mResponseObserver.onError();
        }

        // Added code block end

    }

    // Added code block start

    public Bitmap getBitmap() {
        return bmp;
    }

    // Added code block end

    private void loadImageIfNecessary() {
        int width = getWidth();
        int height = getHeight();

        if (width == 0 && height == 0) {
            return;
        }

        if (TextUtils.isEmpty(mUrl)) {
            ImageContainer oldContainer = (ImageContainer) getTag();
            if (oldContainer != null) {
                oldContainer.cancelRequest();
                setImageBitmap(null);
            }
            return;
        }

        ImageContainer oldContainer = (ImageContainer) getTag();

        if (oldContainer != null && oldContainer.getRequestUrl() != null) {
            if (oldContainer.getRequestUrl().equals(mUrl)) {

                return;
            } else {

                oldContainer.cancelRequest();
                setImageBitmap(null);
            }
        }

        ImageContainer newContainer = mImageLoader.get(mUrl,
                ImageLoader.getImageListener(this, mDefaultImageId, mErrorImageId));

        setTag(newContainer);

        final Bitmap bitmap = newContainer.getBitmap();
        if (bitmap != null) {

            setImageBitmap(bitmap);

           // Added code block start

            bmp = bitmap;
            if (mResponseObserver != null) {
                mResponseObserver.onSuccess();
            }

           // Added code block end
        }
    }

    @Override
    protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
        super.onLayout(changed, left, top, right, bottom);
        loadImageIfNecessary();
    }

    @Override
    protected void onDetachedFromWindow() {
        ImageContainer oldContainer = (ImageContainer) getTag();
        if (oldContainer != null) {

            oldContainer.cancelRequest();
            setImageBitmap(null);

            setTag(null);
        }
        super.onDetachedFromWindow();
    }

    @Override
    protected void drawableStateChanged() {
        super.drawableStateChanged();
        invalidate();
    }
}

Using CustomNetworkImageView :

    viewHolder.getmImageView().setImageUrl(wallThumb.get(i), AppController.getInstance().getImageLoader());

    viewHolder.getmImageView().setmResponseObserver(new CustomNetworkImageView.ResponseObserver() {

            @Override
            public void onError() {
            }

            @Override
            public void onSuccess() {
                // Image is loaded in ImageView.. Do Something..
                Bitmap bitmap = viewHolder.getmImageView().getBitmap();
            }
        });

SetmResponseObserver listens for if bitmap is loaded in ImageView and onSuccess is called if task is completed.. I also made a fuction that returns the bitmap on the image view and can be used as

Bitmap bmp = viewHolde.getmImageView.getBitmap();

I am new to android so please feel free to comment and correct me if i have done anything wrong. Yaaaeeyeee happy dayyy

Answer 3

public class RecyclerViewPagerNetworkImageView extends NetworkImageView {
public RecyclerViewPagerNetworkImageView(Context context) {
    super(context);
}

public RecyclerViewPagerNetworkImageView(Context context, AttributeSet attrs) {
    super(context, attrs);
}

public RecyclerViewPagerNetworkImageView(Context context, AttributeSet attrs, int defStyle) {
    super(context, attrs, defStyle);
}

@Override
protected void onDetachedFromWindow() {
    // delete
    /*if (mImageContainer != null) {
        // If the view was bound to an image request, cancel it and clear
        // out the image from the view.
        mImageContainer.cancelRequest();
        setImageBitmap(null);
        // also clear out the container so we can reload the image if necessary.
        mImageContainer = null;
    }
    super.onDetachedFromWindow();*/
}

}

Answer 4

I faced the same problem. I couldn't use NetworkImageView and image loader because I wanted to have a custom image request.

So I found another way to cancel in flight request. I simply passed the image request in ViewHolder object from onBindViewHolder callback. In ViewHolder created a method setRequest(Request request) .

In this method check if the request is not null then call request.cancel() first otherwise just set the request into the holder.

public class ViewHolder extends RecyclerView.ViewHolder {

    public Request request;

    public ViewHolder(View view) {
        super(view);
    }

    public void setRequest(Request request) {
       if (this.request != null) {
            this.request.cancel();
       }
       this.request = request;
    }
}

@Override
public void onBindViewHolder(ViewHolder holder, int position) {

        ImageRequest imageRequest = new ImageRequest(.......);
        holder.setRequest(request);

        mRequestQueue.add(request);
}