How can I return bitmap from AsyncTask?

Question

I'm tring to receive a bitmap image from web and show it on list view's item which contain image view.
But this seems got a trouble in setting image to Bitmap Object "bmImage".
How can i copy received bitmap and return it?

public class DownloadListImageTask extends AsyncTask<String, Integer, Bitmap> {
    Bitmap bmImage;
    public DownloadListImageTask(Bitmap bmImage){
        this.bmImage = bmImage;
    }
    protected Bitmap doInBackground(String... urls){
        String url = urls[0];
        Bitmap bitmap = null;
        try{
            InputStream in = new URL(url).openStream();
            bitmap = BitmapFactory.decodeStream(in);
        }catch(Exception e){
            e.printStackTrace();
        }
        return bitmap;
    }
    protected void onPostExecute(Bitmap result){
        bmImage = result.copy(result.getConfig(), true);
    }
}

following is a useage

Bitmap bitmap;
new DownloadListImageTask(bitmap).execute(url);
adapter.addItem(bitmap);

please have a look into this question http://stackoverflow.com/questions/12575068/how-to-get-the-result-of-onpostexecute-to-main-activity-because-asynctask-is-a — Inder R Singh, Apr 14 '17 at 20:05
You should copy in the background thread, not in the post execution. — Submersed, Apr 14 '17 at 20:07

Josh Laird · Accepted Answer · 2017-04-14T20:07:42.977

You create the Bitmap bmImage in your AsyncTask but then you do not return it to the Activity that called the AsyncTask.

One thing you can do is to create a listener in the AsyncTask:

public interface OnBitmapDownloadedListener
{
    void setBitmap(Bitmap bmImage);
}

Implement that in the Activity

public class MyActivity extends AppCompatActivity implements DownloadListImageTask.OnBitmapDownloadListener

Pass that it into the AsyncTask constructor like so:

new DownloadListImageTask(bitmap, this).execute(url)

Then in postExecute() you can call

bmImage = result.copy(result.getConfig(), true);
listener.setBitmap(bmImage)
// Do stuff with the bitmap in setBitmap()

http://stackoverflow.com/questions/12575068/how-to-get-the-result-of-onpostexecute-to-main-activity-because-asynctask-is-a would give all answers what he needs i believe. — Inder R Singh, Apr 14 '17 at 20:07

How can I return bitmap from AsyncTask?

1 Answers1