安卓Gallery配合ImageSwitcher不显示图片

Gallary装的是缩略图(thumb)，ImageSwitcher装的是大图。

不显示图片的一个可能原因是gallery没设置代理器，另一个原因是没使用相对布局。

GalleryActivity.java:

 public class GalleryActivity extends Activity implements OnItemSelectedListener, ViewFactory {
     /** Called when the activity is first created. */
     private ImageSwitcher is;
     private Gallery gallery;
     @Override
     public void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         requestWindowFeature(Window.FEATURE_NO_TITLE);
         setContentView(R.layout.main);

         is = (ImageSwitcher)findViewById(R.id.imageSwitcher1);
         is.setFactory(this);
         gallery = (Gallery)findViewById(R.id.gallery1);
         gallery.setAdapter(new ImageAdapter(this));
         gallery.setOnItemSelectedListener(this);
     }

     @Override
     public void onItemSelected(AdapterView<?> arg0, View arg1, int arg2,
             long arg3) {
         // TODO Auto-generated method stub
         is.setImageResource(mImageIds[arg2]);

     }

     @Override
     public View makeView() {
         // TODO Auto-generated method stub
         ImageView iv = new ImageView(this);
         iv.setBackgroundColor(0xFF000000);
         iv.setScaleType(ImageView.ScaleType.FIT_CENTER);
         iv.setLayoutParams(new ImageSwitcher.LayoutParams(LayoutParams.FILL_PARENT, LayoutParams.FILL_PARENT));

         return iv;
     }
     @Override
     public void onNothingSelected(AdapterView<?> arg0) {
         // TODO Auto-generated method stub

     }
     class ImageAdapter extends BaseAdapter {
         private Context ctx;
         public ImageAdapter(Context ctx) {
             this.ctx = ctx;
         }
         @Override
         public int getCount() {
             // TODO Auto-generated method stub
             return mThumbIds.length-1;
         }

         @Override
         public Object getItem(int position) {
             // TODO Auto-generated method stub
             return mThumbIds[position];
         }

         @Override
         public long getItemId(int position) {
             // TODO Auto-generated method stub
             return position;
         }

         @Override
         public View getView(int position, View convertView, ViewGroup parent) {
             // TODO Auto-generated method stub
             ImageView iv = new ImageView(ctx);
             iv.setBackgroundColor(0x000000);
             iv.setImageResource(mThumbIds[position]);
             iv.setLayoutParams(new Gallery.LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT));
             iv.setBackgroundResource(R.drawable.picture_frame);
             return iv;
         }

     }
     private int[] mThumbIds = {
             R.drawable.sample_thumb_0,
             R.drawable.sample_thumb_1,
             R.drawable.sample_thumb_2,
             R.drawable.sample_thumb_3,
             R.drawable.sample_thumb_4,
             R.drawable.sample_thumb_5,
             R.drawable.sample_thumb_6,
             R.drawable.sample_thumb_7,
     };
     private int[] mImageIds = {
             R.drawable.sample_0,
             R.drawable.sample_1,
             R.drawable.sample_2,
             R.drawable.sample_3,
             R.drawable.sample_4,
             R.drawable.sample_5,
             R.drawable.sample_6
     };

 }

main.xml(layout):

 <?xml version="1.0" encoding="utf-8"?>
 <RelativeLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent">

        <ImageSwitcher
        android:id="@+id/imageSwitcher1"
               android:layout_width="fill_parent"
               android:layout_height="fill_parent"
               android:layout_alignParentTop="true"
               android:layout_alignParentLeft="true" />

        <Gallery android:id="@+id/gallery1"
        android:background="#55000000"
               android:layout_width="fill_parent"
               android:layout_height="60dp"
               android:layout_alignParentBottom="true"
               android:layout_alignParentLeft="true"
               android:gravity="center_vertical"
               android:spacing="16dp" />
 </RelativeLayout>