如何从SD卡（android-gallery）获取所有图像？

Question

在我的应用程序中，我需要为用户实现一个选项，以便从SD卡或手机内存中选择图像。我使用自定义封面流来动画图像。我编写了一个代码，使用光标从SD卡中检索图像。但我只得到了一些图像，而不是全部。这些图像在我的封面流程中多次显示。每张图片都显示两次。

如果SD卡上没有图像，则应用程序崩溃。

这是我的代码，请有人帮忙

public class CoverFlowActivityMain extends Activity {

    private Cursor cursor;
    private int columnIndex;
    private File file;

    @Override
    public void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);

         CoverFlow coverFlow;
         coverFlow = new CoverFlow(this);

         file = new File("/sdcard/");
         // I am using this file to check iamges on sd-card,
         // but this does not search files in subdirectories.
         File[] allFiles = file.listFiles();
         for(int i=0; i<allFiles.length; i++) {
             Log.v("File: "+i, ""+allFiles[i].getName().toString());
         }


         // Set up an array of the Thumbnail Image ID column we want
         String[] projection = {MediaStore.Images.Thumbnails._ID};
         // Create the cursor pointing to the SDCard
         cursor = managedQuery( MediaStore.Images.Thumbnails.EXTERNAL_CONTENT_URI,
                                    projection, // Which columns to return
                                    null,       // Return all rows
                                    null,
                                    MediaStore.Images.Thumbnails.IMAGE_ID);
         // Get the column index of the Thumbnails Image ID
         columnIndex = cursor.getColumnIndexOrThrow(MediaStore.Images.Thumbnails._ID);

         coverFlow.setAdapter(new ImageAdapter(this));

         ImageAdapter coverImageAdapter =  new ImageAdapter(this);

          coverFlow.setAdapter(coverImageAdapter);

         coverFlow.setSpacing(-5);
         coverFlow.setSelection(0, true);
         coverFlow.setAnimationDuration(1500);

         setContentView(coverFlow);
    }

 public class ImageAdapter extends BaseAdapter {
     int mGalleryItemBackground;
     private Context mContext;

     public ImageAdapter(Context c) {
         mContext = c;
     }

     public int getCount() {
         return cursor.getCount();
     }

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

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

     public View getView(int position, View convertView, ViewGroup parent) {

        //-- Use this code if you want to load from sdcard --\\

         ImageView picturesView;
         if (convertView == null) {
             picturesView = new ImageView(mContext);
             // Move cursor to current position
             cursor.moveToPosition(position);
             // Get the current value for the requested column
             int imageID = cursor.getInt(columnIndex);
             // Set the content of the image based on the provided URI
             picturesView.setImageURI(Uri.withAppendedPath(
                     MediaStore.Images.Thumbnails.EXTERNAL_CONTENT_URI, "" + imageID));

             picturesView.setLayoutParams(new CoverFlow.LayoutParams(380, 450));
             picturesView.setScaleType(ImageView.ScaleType.CENTER_INSIDE);
           //Make sure we set anti-aliasing otherwise we get jaggies
         BitmapDrawable drawable = (BitmapDrawable) picturesView.getDrawable();
         drawable.setAntiAlias(true);
         }
            else {
                picturesView = (ImageView)convertView;
            }
         return picturesView;
     }
 }
}