Caricamento di immagini asincrone in una GridView (Android)

Question

Ho un GridView con immagini/testo, caricato da diversi server (conosco solo l'URL). Ho provato a modificare il mio codice, in base a the tutorial of ryac.

Nel mio file di attività, ho impostato il GAdapter alla mia GridView in questo modo:

GridView mGridMain = (GridView)findViewById(R.id.gvMain); 
mGridMain.setAdapter(new GAdapter(this, listAppInfo)); 

ho modificato la mia scheda e cercare di adattarlo:

public class GAdapter extends BaseAdapter { 

private Context mContext; 
private List<SiteStaff> mListAppInfo; 
private HashMap<Integer, ImageView> views; 

/** 
    * @param context 
    * @param list 
    */ 
public GAdapter(Context context, List<SiteStaff> 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<Bundle, Void, Bundle> { 

    @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")); 
    } 

} 

} 

Ma l'errore di seguito è visualizzato:

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) 

Fino ad ora, non ho mai utilizzato Thread in Android. Sarei grato se qualcuno potesse aiutarmi.

Answer 1

ho fonte in GetView() alla fine si stanno facendo

views.put(position, v); 

Ma views mai inizializzato. È per questo che si stanno ottenendo java.lang.NullPointerException

Per evitare questo piacere inizializzato mappa oggetto hash nel vostro in GAdapter Constructor

public GAdapter(Context context, List<SiteStaff> list) { 
    mContext = context; 
    mListAppInfo = list; 
    views = new HashMap<Integer, ImageView>(); 

} 

Se si controlla l'esempio che si sta riferendo nella tua domanda troverete

public ImageAdapter (Context c, String f, ArrayList<HashMap<String, Object>> p) { 
     ... 
     views = new HashMap<Integer, ImageView>(); 
    }