Web image loaded by thread in android

问题

I have an extended BaseAdapter in a ListActivity:

private static class RequestAdapter extends BaseAdapter {

and some handlers and runnables defined in it

// Need handler for callbacks to the UI thread
    final Handler mHandler = new Handler();

    // Create runnable for posting
    final Runnable mUpdateResults = new Runnable() {
        public void run() {
            loadAvatar();
        }
    };

    protected static void loadAvatar() {
        // TODO Auto-generated method stub
        //ava.setImageBitmap(getImageBitmap("URL"+pic));
        buddyIcon.setImageBitmap(avatar);
    }

In the getView function of the Adapter, I'm getting the view like this:

if (convertView == null) {
            convertView = mInflater.inflate(R.layout.messageitem, null);

            // Creates a ViewHolder and store references to the two children views
            // we want to bind data to.
            holder = new ViewHolder();
            holder.username = (TextView) convertView.findViewById(R.id.username);
            holder.date = (TextView) convertView.findViewById(R.id.dateValue);
            holder.time = (TextView) convertView.findViewById(R.id.timeValue);
            holder.notType = (TextView) convertView.findViewById(R.id.notType);
            holder.newMsg = (ImageView) convertView.findViewById(R.id.newMsg);
            holder.realUsername = (TextView) convertView.findViewById(R.id.realUsername);
            holder.replied = (ImageView) convertView.findViewById(R.id.replied);
            holder.msgID = (TextView) convertView.findViewById(R.id.msgID_fr);
            holder.avatar = (ImageView) convertView.findViewById(R.id.buddyIcon);
            holder.msgPreview = (TextView) convertView.findViewById(R.id.msgPreview);


            convertView.setTag(holder);
        } else {
            // Get the ViewHolder back to get fast access to the TextView
            // and the ImageView.
            holder = (ViewHolder) convertView.getTag();
        }

and the image is getting loaded this way:

Thread sepThread = new Thread() {
                    public void run() {
                        String ava;
                        ava = request[8].replace(".", "_micro.");
                        Log.e("ava thread",ava+", username: "+request[0]);
                        avatar = getImageBitmap(URL+ava);
                        buddyIcon = holder.avatar;
                        mHandler.post(mUpdateResults);
                        //holder.avatar.setImageBitmap(getImageBitmap(URL+ava));
                    }
                };
                sepThread.start();

Now, the problem I'm having is that if there are more items that need to display the same picture, not all of those pictures get displayed. When you scroll up and down the list maybe you end up filling all of them.

When I tried the commented out line (holder.avatar.setImageBitmap...) the app sometimes force closes with "only the thread that created the view can request...". But only sometimes.

Any idea how I can fix this? Either option.

回答1:

When getView is called you've got a avatar ImageView. You should pass this instance to sepThread, and sepThread should pass this instance to mUpdateResults. This way the bitmap will be displayed exactly to ImageView it was downloaded for. Otherwise bitmap is displayed to some budddyIcon instance that is incorrect. Your thread was downloading image for some time and when it's ready budddyIcon references another ImageView because another getView has already been called.

Should look something like that:

public View getView(...){
  //skip
  (new SepThread(holder.avatar)).start();
}

public class SepThread extends Thread() {
    ImageView imageView;
    public SepThread(ImageVIew iv){
      imageView=iv;
    }
    public void run() {
        //skip
        Bitmap avatar = getImageBitmap(URL+ava);
        mHandler.post(new UpdateResults(imageView, avatar));
    }
};

class UpdateResults extends Runnable() {
  ImageView imageView;
  Bitmap bitmap;
  public UpdateResults(ImageView iv, Bitmap b){
    imageView=iv;
    bitmap=b;
  }
  public void run() {
      loadAvatar(imageView, bitmap);
  }
};

protected static void loadAvatar(ImageView iv, Bitmap b) {
    iv.setImageBitmap(b);
}

And of course you should be aware of recycled convertViews as disretrospect says above.

I made a complete example of LazyList and posted the source, may also be helpful Lazy load of images in ListView.

回答2:

So you shouldn't try and add the image to the view in another thread. My advice would be to use an AsyncTask something like this:

class GetImageTask extends AsyncTask<String, int[], Bitmap> {

    @Override
    protected Bitmap doInBackground(String... params) {
      Bitmap bitmap = null;

      // Get your image bitmap here

      return bitmap;
    }

    @Override
    protected void onPostExecute(Bitmap bitmapResult) {
      super.onPostExecute(bitmapResult);
      // Add your image to your view
      holder.avatar.setImageBitmap(bitmapResult);
    }
}

You call an AsyncTask like:

new GetImageTask().execute(param1, param2, etc);

For more info on an AsyncTask have a look at: http://developer.android.com/reference/android/os/AsyncTask.html

回答3:

there's this awesome library guys for downloading/caching Images from the web https://github.com/koush/UrlImageViewHelper

just put the imageview and url and you're done =)

来源：https://stackoverflow.com/questions/2957287/web-image-loaded-by-thread-in-android