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POLoading asynchronous images in a GridView (Android)
 

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    <p>I have a <code>GridView</code> with pictures/text, loaded from different servers (I only know the URL). I tried to modify my code, based on <a href="http://www.ryac.ca/blog/2011/08/multi-threading-images-from-the-web-into-an-adapter/">the tutorial of ryac</a>.</p> <p>In my Activity file, I set the <code>GAdapter</code> to my <code>GridView</code> like this:</p> <pre><code>GridView mGridMain = (GridView)findViewById(R.id.gvMain); mGridMain.setAdapter(new GAdapter(this, listAppInfo)); </code></pre> <p>I have modified my own adapter and try to adapt it:</p> <pre><code>public class GAdapter extends BaseAdapter { private Context mContext; private List&lt;SiteStaff&gt; mListAppInfo; private HashMap&lt;Integer, ImageView&gt; views; /** * @param context * @param list */ public GAdapter(Context context, List&lt;SiteStaff&gt; list) { mContext = context; mListAppInfo = list; } @Override public int getCount() { return mListAppInfo.size(); } @Override public Object getItem(int position) { return mListAppInfo.get(position); } @Override public long getItemId(int position) { return position; } @Override public View getView(int position, View convertView, ViewGroup parent) { SiteStaff entry = mListAppInfo.get(position); if(convertView == null) { LayoutInflater inflater = LayoutInflater.from(mContext); convertView = inflater.inflate(R.layout.list_g, null); } ImageView v; // get the ImageView for this position in the GridView.. v = (ImageView)convertView.findViewById(R.id.ivIcon); //set default image v.setImageResource(android.R.drawable.ic_menu_gallery); TextView tvName = (TextView)convertView.findViewById(R.id.tvName); tvName.setText(entry.getName()); Bundle b = new Bundle (); b.putString("file", "http://www.test.com/mypict.jpg"); b.putInt("pos", position); // this executes a new thread, passing along the file // to load and the position via the Bundle.. new LoadImage().execute(b); // puts this new ImageView and position in the HashMap. views.put(position, v); // return the view to the GridView.. // at this point, the ImageView is only displaying the // default icon.. return v; } // this is the class that handles the loading of images from the cloud // inside another thread, separate from the main UI thread.. private class LoadImage extends AsyncTask&lt;Bundle, Void, Bundle&gt; { @Override protected Bundle doInBackground(Bundle... b) { // get the file that was passed from the bundle.. String file = b[0].getString("file"); URL UrlImage; Bitmap bm=null; try { UrlImage = new URL (file); HttpURLConnection connection; connection = (HttpURLConnection) UrlImage.openConnection(); bm= BitmapFactory.decodeStream(connection.getInputStream()); } catch (MalformedURLException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } // now that we have the bitmap (bm), we'll // create another bundle to pass to 'onPostExecute'. // this is the method that is called at the end of // our task. like a callback function.. // this time, we're not passing the filename to this // method, but the actual bitmap, not forgetting to // pass the same position along.. Bundle bundle = new Bundle(); bundle.putParcelable("bm", bm); bundle.putInt("pos", b[0].getInt("pos")); bundle.putString("file", file); // this is only used for testing.. return bundle; } @Override protected void onPostExecute(Bundle result) { super.onPostExecute(result); // just a test to make sure that the position and // file name are matching before and after the // image has loaded.. Log.d("test", "*after: " + result.getInt("pos") + " | " + result.getString("file")); // here's where the photo gets put into the // appropriate ImageView. we're retrieving the // ImageView from the HashMap according to // the position.. ImageView view = views.get(result.getInt("pos")); // then we set the bitmap into that view. and that's it. view.setImageBitmap((Bitmap) result.getParcelable("bm")); } } } </code></pre> <p>But the below error is displayed:</p> <pre><code>11-16 06:16:08.285: E/AndroidRuntime(517): FATAL EXCEPTION: main 11-16 06:16:08.285: E/AndroidRuntime(517): java.lang.NullPointerException 11-16 06:16:08.285: E/AndroidRuntime(517): at common.adapter.GAdapter.getView(GAdapter.java:139) 11-16 06:16:08.285: E/AndroidRuntime(517): at android.widget.AbsListView.obtainView(AbsListView.java:1315) 11-16 06:16:08.285: E/AndroidRuntime(517): at android.widget.GridView.onMeasure(GridView.java:932) 11-16 06:16:08.285: E/AndroidRuntime(517): at android.view.View.measure(View.java:8171) 11-16 06:16:08.285: E/AndroidRuntime(517): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3132) 11-16 06:16:08.285: E/AndroidRuntime(517): at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1012) 11-16 06:16:08.285: E/AndroidRuntime(517): at android.widget.LinearLayout.measureVertical(LinearLayout.java:381) 11-16 06:16:08.285: E/AndroidRuntime(517): at android.widget.LinearLayout.onMeasure(LinearLayout.java:304) 11-16 06:16:08.285: E/AndroidRuntime(517): at android.view.View.measure(View.java:8171) 11-16 06:16:08.285: E/AndroidRuntime(517): at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:3132) 11-16 06:16:08.285: E/AndroidRuntime(517): at android.widget.FrameLayout.onMeasure(FrameLayout.java:245) 11-16 06:16:08.285: E/AndroidRuntime(517): at android.view.View.measure(View.java:8171) </code></pre> <p>Until now, I never used Threads in Android. I would be grateful if someone can help me.</p>
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