Android - Grabbing an image from a URL and displaying it in an ImageView with an AsyncTask

Question

I'm trying to get the app to show an image from a URL, im fairly certain the issue is with the AsyncTask but I've returned to this code several times over the past week and I still cant see where I'm going wrong.

The Internet permission is set and I am getting no LogCat

ImageView eventImage2;
eventImage2 = (ImageView) findViewById(R.id.eventImage2);

new imageupdate().execute();

public class imageupdate extends AsyncTask<Bitmap, Void, Bitmap> {

    @Override
    protected Bitmap doInBackground(Bitmap... url) {


        URL url1;

        try {


            url1 = new URL("http://masterzangetsu.eu/Apps/NowIGetYou/banner.png");
            HttpURLConnection connection  = (HttpURLConnection) url1.openConnection();

            InputStream is = connection.getInputStream();
            Bitmap img = BitmapFactory.decodeStream(is);


        } catch (MalformedURLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }


        return img;

    }

    protected void onPreExecute(String result) {


    }

    protected void onPostExecute(Bitmap result) {
        super.onPostExecute(result);

        eventImage2.setImageBitmap(result);

    }

}

As far as I can tell the img variable defined with the

img = BitmapFactory.decodeStream(is);

isnt being linked to the variable being returned

return img;

Both variables result and img are coming back as null

You set result to null then use img = result...this will mean that img is null. Did you mean to switch around img and result? — codeMagic
– codeMagic, Commented Apr 9, 2013 at 12:58

codeMagic · Accepted Answer · 2013-04-09 13:32:15Z

Change this

  Bitmap result = null;

        InputStream is = connection.getInputStream();
        Bitmap img = BitmapFactory.decodeStream(is); 


        img = result;

to

  Bitmap img = null;

        InputStream is = connection.getInputStream();
        Bitmap img = BitmapFactory.decodeStream(is); 


        result = img;

and return result in doInBackground(). You have them switched around so 'img' will be null no matter what happens.

Also, you can't use Toast in doInBackground() as this method isn't run on the UI thread. You will need to make that a Log or put your Toast in onPostExecute() or onProgressUpdate(). These are the things I see. If you are still having problems then you need to be a little more clear on what specifically. You will need to debug and use breakpoints to see what isn't being returned that should be and pinpoint a little more what the problem is

AsyncTask - any UI updates must be done in one of the other methods of AsyncTask other than doInBackground() or you can pass a value back to the Activity to update the UI there.

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