Android上的GridView适配器（错误）

调用适配器时出现错误：

在我的主班我有：

    public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.discotecas_layout);

    // Hashmap for ListView
    discotecaslist = new ArrayList<HashMap<String, String>>();
    gridView = (GridView) findViewById(R.id.gridview);
            // Loading products in Background Thread
    new LoadAllProducts().execute();

在后台，我在后执行此操作：

  protected void onPostExecute(String file_url) {
    // dismiss the dialog after getting all products
      pDialog.dismiss();
      gridView.setAdapter(new Gridadapter(activity.this, imagenes));
      // updating UI from Background Thread
   }

我的适配器是这样的：

public class Gridadapter extends BaseAdapter {

    private Context mContext;
    private Bitmap[] imagenes;

    public Gridadapter(Context c, Bitmap[] imagenes) {
        this.mContext = c;
        this.imagenes = imagenes;
    }

    public int getCount() {
        return imagenes.length;
    }

    public Object getItem(int position) {
        return null;
    }

    public long getItemId(int position) {
        return 0;
    }

    public View getView(int position, View convertView, ViewGroup parent) {
        ImageView imageView;
        if (convertView == null) {
            imageView = new ImageView(mContext);
            imageView.setLayoutParams(new GridView.LayoutParams(200, 150));
            imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
            imageView.setPadding(0, 0, 0, 0);
        } else {
            imageView = (ImageView) convertView;
        }
        imageView.setImageBitmap(imagenes[position]);
        return imageView;
    }

}

我做错了什么？我认为它与适配器有关，但我不知道是什么

错误是：

01-14 18:32:20.149: E/AndroidRuntime(16322): FATAL EXCEPTION: AsyncTask #1
01-14 18:32:20.149: E/AndroidRuntime(16322): java.lang.RuntimeException: An error occured while executing doInBackground()
01-14 18:32:20.149: E/AndroidRuntime(16322):    at android.os.AsyncTask$3.done(AsyncTask.java:299)
01-14 18:32:20.149: E/AndroidRuntime(16322):    at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:352)
01-14 18:32:20.149: E/AndroidRuntime(16322):    at java.util.concurrent.FutureTask.setException(FutureTask.java:219)
01-14 18:32:20.149: E/AndroidRuntime(16322):    at java.util.concurrent.FutureTask.run(FutureTask.java:239)
01-14 18:32:20.149: E/AndroidRuntime(16322):    at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
01-14 18:32:20.149: E/AndroidRuntime(16322):    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
01-14 18:32:20.149: E/AndroidRuntime(16322):    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
01-14 18:32:20.149: E/AndroidRuntime(16322):    at java.lang.Thread.run(Thread.java:864)
01-14 18:32:20.149: E/AndroidRuntime(16322): Caused by: java.lang.NullPointerException
01-14 18:32:20.149: E/AndroidRuntime(16322):    at com.example.apparty.TabDiscotecas$LoadAllProducts.doInBackground(TabDiscotecas.java:192)
01-14 18:32:20.149: E/AndroidRuntime(16322):    at com.example.apparty.TabDiscotecas$LoadAllProducts.doInBackground(TabDiscotecas.java:1)
01-14 18:32:20.149: E/AndroidRuntime(16322):    at android.os.AsyncTask$2.call(AsyncTask.java:287)
01-14 18:32:20.149: E/AndroidRuntime(16322):    at java.util.concurrent.FutureTask.run(FutureTask.java:234)
01-14 18:32:20.149: E/AndroidRuntime(16322):    ... 4 more
01-14 18:32:20.399: D/qdmemalloc(16322): ion: Unmap buf  base:0x6cd53000 size:1216512
01-14 18:32:20.399: D/qdmemalloc(16322): ion: Unmap buf  base:0x6cadc000 size:4096
01-14 18:32:20.399: D/qdmemalloc(16322): ion: Unmap buf  base:0x6d98e000 size:1216512
01-14 18:32:20.399: D/qdmemalloc(16322): ion: Unmap buf  base:0x6cbfd000 size:4096
01-14 18:32:20.399: D/qdmemalloc(16322): ion: Unmap buf  base:0x6e2af000 size:1216512
01-14 18:32:20.399: D/qdmemalloc(16322): ion: Unmap buf  base:0x6cbff000 size:4096
01-14 18:32:20.409: D/qdmemalloc(16322): ion: Unmap buf  base:0x6d052000 size:8355840
01-14 18:32:20.409: D/qdmemalloc(16322): ion: Unmap buf  base:0x6cb3e000 size:4096
01-14 18:32:20.409: D/qdmemalloc(16322): ion: Unmap buf  base:0x6dab7000 size:8355840
01-14 18:32:20.409: D/qdmemalloc(16322): ion: Unmap buf  base:0x6cbfe000 size:4096
01-14 18:32:20.409: D/qdmemalloc(16322): ion: Unmap buf  base:0x6e3d8000 size:8355840
01-14 18:32:20.409: D/qdmemalloc(16322): ion: Unmap buf  base:0x6cc26000 size:4096
01-14 18:32:20.439: E/WindowManager(16322): Activity com.example.apparty.MainActivity    has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView{41b0c038 V.E..... R......D 0,0-1026,288} that was originally added here
01-14 18:32:20.439: E/WindowManager(16322): android.view.WindowLeaked: Activity com.example.apparty.MainActivity has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView{41b0c038 V.E..... R......D 0,0-1026,288} that was originally added here
01-14 18:32:20.439: E/WindowManager(16322):     at android.view.ViewRootImpl.<init>(ViewRootImpl.java:394)
01-14 18:32:20.439: E/WindowManager(16322):     at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:239)
01-14 18:32:20.439: E/WindowManager(16322):     at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:94)
01-14 18:32:20.439: E/WindowManager(16322):     at android.app.Dialog.show(Dialog.java:286)
01-14 18:32:20.439: E/WindowManager(16322):     at com.example.apparty.TabDiscotecas$LoadAllProducts.onPreExecute(TabDiscotecas.java:142)
01-14 18:32:20.439: E/WindowManager(16322):     at android.os.AsyncTask.executeOnExecutor(AsyncTask.java:586)
01-14 18:32:20.439: E/WindowManager(16322):     at android.os.AsyncTask.execute(AsyncTask.java:534)
01-14 18:32:20.439: E/WindowManager(16322):     at com.example.apparty.TabDiscotecas.onCreate(TabDiscotecas.java:81)
01-14 18:32:20.439: E/WindowManager(16322):     at android.app.Activity.performCreate(Activity.java:5195)
01-14 18:32:20.439: E/WindowManager(16322):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1111)
01-14 18:32:20.439: E/WindowManager(16322):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2473)
01-14 18:32:20.439: E/WindowManager(16322):     at android.app.ActivityThread.startActivityNow(ActivityThread.java:2298)
01-14 18:32:20.439: E/WindowManager(16322):     at android.app.LocalActivityManager.moveToState(LocalActivityManager.java:135)
01-14 18:32:20.439: E/WindowManager(16322):     at android.app.LocalActivityManager.startActivity(LocalActivityManager.java:347)
01-14 18:32:20.439: E/WindowManager(16322):     at android.widget.TabHost$IntentContentStrategy.getContentView(TabHost.java:759)
01-14 18:32:20.439: E/WindowManager(16322):     at android.widget.TabHost.setCurrentTab(TabHost.java:413)
01-14 18:32:20.439: E/WindowManager(16322):     at android.widget.TabHost.addTab(TabHost.java:240)
01-14 18:32:20.439: E/WindowManager(16322):     at com.example.apparty.MainActivity.onCreate(MainActivity.java:88)
01-14 18:32:20.439: E/WindowManager(16322):     at android.app.Activity.performCreate(Activity.java:5195)
01-14 18:32:20.439: E/WindowManager(16322):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1111)
01-14 18:32:20.439: E/WindowManager(16322):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2473)
01-14 18:32:20.439: E/WindowManager(16322):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2574)
01-14 18:32:20.439: E/WindowManager(16322):     at android.app.ActivityThread.access$600(ActivityThread.java:162)
01-14 18:32:20.439: E/WindowManager(16322):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1413)
01-14 18:32:20.439: E/WindowManager(16322):     at android.os.Handler.dispatchMessage(Handler.java:99)
01-14 18:32:20.439: E/WindowManager(16322):     at android.os.Looper.loop(Looper.java:158)
01-14 18:32:20.439: E/WindowManager(16322):     at android.app.ActivityThread.main(ActivityThread.java:5789)
01-14 18:32:20.439: E/WindowManager(16322):     at java.lang.reflect.Method.invokeNative(Native Method)
01-14 18:32:20.439: E/WindowManager(16322):     at java.lang.reflect.Method.invoke(Method.java:525)
01-14 18:32:20.439: E/WindowManager(16322):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1027)
01-14 18:32:20.439: E/WindowManager(16322):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:843)
01-14 18:32:20.439: E/WindowManager(16322):     at dalvik.system.NativeStart.main(Native Method)