Question

I am using listview to display data, inside listview i am using image in every listeitem.

I am following this tutorial http://developer.android.com/guide/samples/ApiDemos/src/com/example/android/apis/view/List4.html

new Handler().post(new Runnable(){

                @Override 
                public void run() {
                    //Need to subclass to use Asynctask
                    class DownloadImage extends AsyncTask<Void, Void, Void>{
                        @Override
                        protected Void doInBackground(Void... params) {
                                Drawable dImage = Util.getImageFromURL(imageURL); 
                                    getImageIcon().setImageDrawable(dImage);
                            return null;
                        }

                    }
                    new DownloadImage().execute();
                }

            });

this looks good for lazzy loading image, but there is one problem it won t display any image until user touch screen or try to scroll results or any interaction by the user to handset device keys.

If i try to scroll results it dispaly all list item images.... what may go wrong ???

Answer 1

It s hard to say without more context. In particular, where is this code being called from, and what does getImageIcon() do??

One problem I see is that you re setting the image icon in a background thread rather than in the UI thread. This could be the reason why it doesn t seem to change until a ui event triggers a refresh. Try changing DownloadImage to something like the following:

class DownloadImage extends AsyncTask<Void, Void, Drawable>{
        @Override
        protected Drawable doInBackground(Void... params) {
            return Util.getImageFromURL(imageURL); 
        }

        @Override
        protected void onPostExecute( Drawable d ) {
            getImageIcon().setImageDrawable(d);
        }

}
new DownloadImage().execute();

If I m right, that should fix the problem.

If that does work, great, although I think your code could use a little cleanup. Provided that this is all taking place in the UI thread (which is probably true given that you re instantiating a new Handler in this thread), you shouldn t need to use a Handler at all, nor should you need to create a new Runnable. Just strip those out and create a new DownloadImage instance directly and call execute().

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