managedQuery (Media.EXTERNAL_CONTENT_URI, Projektion, null, null, null); Gibt null zurück, wenn auf dem Gerät ausgeführt wird

Question

Dieser Cursor gibt null zurück, wenn ich versuche, es auf dem Gerät auszuführen. Es funktioniert gut auf Emulator.

Kann jemand bitte darauf hinweisen, wenn ich etwas vermisse oder falsch mache.

Answer 1

gleiche für diesen Code arbeiten

public class LoadImagesFromSDCardActivity extends Activity implements 
OnItemClickListener { 

/** 
* Grid view holding the images. 
**/ 

private GridView sdcardImages; 
/** 
* Image adapter for the grid view. 
**/ 
private ImageAdapter imageAdapter; 
/** 
* Display used for getting the width of the screen. 
**/ 
private Display display; 
ImageView imgView; 

/** 
* Creates the content view, sets up the grid, the adapter, and the click listener. 
* 
* @see android.app.Activity#onCreate(android.os.Bundle) 
**/ 
@Override 
public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState);   
    // Request progress bar 
    requestWindowFeature(Window.FEATURE_INDETERMINATE_PROGRESS); 
    setContentView(R.layout.main); 

    display = ((WindowManager) getSystemService(Context.WINDOW_SERVICE)).getDefaultDisplay(); 
    imgView=(ImageView)findViewById(R.id.imgView); 
    setupViews(); 
    setProgressBarIndeterminateVisibility(true); 
    loadImages(); 
} 

/** 
* Free up bitmap related resources. 
**/ 
protected void onDestroy() { 
    super.onDestroy(); 
    final GridView grid = sdcardImages; 
    final int count = grid.getChildCount(); 
    ImageView v = null; 
    for (int i = 0; i < count; i++) { 
     v = (ImageView) grid.getChildAt(i); 
     ((BitmapDrawable) v.getDrawable()).setCallback(null); 
    } 
} 
/** 
* Setup the grid view. 
**/ 
private void setupViews() { 
    sdcardImages = (GridView) findViewById(R.id.sdcard); 
    sdcardImages.setNumColumns(display.getWidth()/95); 
    sdcardImages.setClipToPadding(false); 
    sdcardImages.setOnItemClickListener(LoadImagesFromSDCardActivity.this); 
    imageAdapter = new ImageAdapter(getApplicationContext()); 
    sdcardImages.setAdapter(imageAdapter); 
} 
/** 
* Load images. 
*/ 
private void loadImages() { 
    final Object data = getLastNonConfigurationInstance(); 
    if (data == null) { 
     new LoadImagesFromSDCard().execute(); 
    } else { 
     final LoadedImage[] photos = (LoadedImage[]) data; 
     if (photos.length == 0) { 
      new LoadImagesFromSDCard().execute(); 
     } 
     for (LoadedImage photo : photos) { 
      addImage(photo); 
     } 
    } 
} 
/** 
* Add image(s) to the grid view adapter. 
* 
* @param value Array of LoadedImages references 
*/ 
private void addImage(LoadedImage... value) { 
    for (LoadedImage image : value) { 
     imageAdapter.addPhoto(image); 
     imageAdapter.notifyDataSetChanged(); 
    } 
} 

/** 
* Save bitmap images into a list and return that list. 
* 
* @see android.app.Activity#onRetainNonConfigurationInstance() 
*/ 
@Override 
public Object onRetainNonConfigurationInstance() { 
    final GridView grid = sdcardImages; 
    final int count = grid.getChildCount(); 
    final LoadedImage[] list = new LoadedImage[count]; 

    for (int i = 0; i < count; i++) { 
     final ImageView v = (ImageView) grid.getChildAt(i); 
     list[i] = new LoadedImage(((BitmapDrawable) v.getDrawable()).getBitmap()); 
    } 

    return list; 
} 
/** 
* Async task for loading the images from the SD card. 
* 
* @author Mihai Fonoage 
* 
*/ 
class LoadImagesFromSDCard extends AsyncTask<Object, LoadedImage, Object> { 

    /** 
    * Load images from SD Card in the background, and display each image on the screen. 
    * 
    * @see android.os.AsyncTask#doInBackground(Params[]) 
    */ 
    @Override 
    protected Object doInBackground(Object... params) { 
     //setProgressBarIndeterminateVisibility(true); 
     Bitmap bitmap = null; 
     Bitmap newBitmap = null; 
     Uri uri = null;    

     // 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 cursor = managedQuery(MediaStore.Images.Thumbnails.EXTERNAL_CONTENT_URI, 
       projection, // Which columns to return 
       null,  // Return all rows 
       null,  
       null); 
     int columnIndex = cursor.getColumnIndexOrThrow(MediaStore.Images.Thumbnails._ID); 
     int size = cursor.getCount(); 
     // If size is 0, there are no images on the SD Card. 
     if (size == 0) { 
      //No Images available, post some message to the user 
     } 
     int imageID = 0; 
     for (int i = 0; i < size; i++) { 
      cursor.moveToPosition(i); 
      imageID = cursor.getInt(columnIndex); 
      uri = Uri.withAppendedPath(MediaStore.Images.Thumbnails.EXTERNAL_CONTENT_URI, "" + imageID); 
      try { 
       bitmap = BitmapFactory.decodeStream(getContentResolver().openInputStream(uri)); 
       if (bitmap != null) { 
        newBitmap = Bitmap.createScaledBitmap(bitmap, 70, 70, true); 
        bitmap.recycle(); 
        if (newBitmap != null) { 
         publishProgress(new LoadedImage(newBitmap)); 
        } 
       } 
      } catch (IOException e) { 
       //Error fetching image, try to recover 
      } 
     } 
     cursor.close(); 
     return null; 
    } 
    /** 
    * Add a new LoadedImage in the images grid. 
    * 
    * @param value The image. 
    */ 
    @Override 
    public void onProgressUpdate(LoadedImage... value) { 
     addImage(value); 
    } 
    /** 
    * Set the visibility of the progress bar to false. 
    * 
    * @see android.os.AsyncTask#onPostExecute(java.lang.Object) 
    */ 
    @Override 
    protected void onPostExecute(Object result) { 
     setProgressBarIndeterminateVisibility(false); 
    } 
} 

/** 
* Adapter for our image files. 
* 
* @author Mihai Fonoage 
* 
*/ 
class ImageAdapter extends BaseAdapter { 

    private Context mContext; 
    private ArrayList<LoadedImage> photos = new ArrayList<LoadedImage>(); 

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

    public void addPhoto(LoadedImage photo) { 
     photos.add(photo); 
    } 

    public int getCount() { 
     return photos.size(); 
    } 

    public Object getItem(int position) { 
     return photos.get(position); 
    } 

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

    public View getView(int position, View convertView, ViewGroup parent) { 
     final ImageView imageView; 
     if (convertView == null) { 
      imageView = new ImageView(mContext); 
     } else { 
      imageView = (ImageView) convertView; 
     } 
     imageView.setScaleType(ImageView.ScaleType.FIT_CENTER); 
     imageView.setPadding(8, 8, 8, 8); 
     imageView.setImageBitmap(photos.get(position).getBitmap()); 
     return imageView; 
    } 
} 

/** 
* A LoadedImage contains the Bitmap loaded for the image. 
*/ 
private static class LoadedImage { 
    Bitmap mBitmap; 

    LoadedImage(Bitmap bitmap) { 
     mBitmap = bitmap; 
    } 

    public Bitmap getBitmap() { 
     return mBitmap; 
    } 
} 
/** 
* When an image is clicked, load that image as a puzzle. 
*/ 
public void onItemClick(AdapterView<?> parent, View v, int position, long id) {   
    int columnIndex = 0; 
    String[] projection = {MediaStore.Images.Media.DATA}; 
    Cursor cursor = managedQuery(MediaStore.Images.Thumbnails.EXTERNAL_CONTENT_URI, 
      projection, 
      null, 
      null, 
      null); 
    if (cursor != null) { 
     columnIndex = cursor.getColumnIndexOrThrow(MediaStore.Images.Media.DATA); 
     cursor.moveToPosition(position); 
     String imagePath = cursor.getString(columnIndex); 

     FileInputStream is = null; 
     BufferedInputStream bis = null; 
     try { 
      is = new FileInputStream(new File(imagePath)); 
      bis = new BufferedInputStream(is); 
      Bitmap bitmap = BitmapFactory.decodeStream(bis); 
      Bitmap useThisBitmap = Bitmap.createScaledBitmap(bitmap, 200, 200, true); 
      Log.i("called","called"); 
      imgView.setImageBitmap(useThisBitmap); 
      bitmap.recycle(); 
      //Display bitmap (useThisBitmap) 
     } 
     catch (Exception e) { 
      //Try to recover 
     } 
     finally { 
      try { 
       if (bis != null) { 
        bis.close(); 
       } 
       if (is != null) { 
        is.close(); 
       } 
       cursor.close(); 
       projection = null; 
      } catch (Exception e) { 
      } 
     } 
    } 
    } 

} 

Und

main.xml

<GridView 
    android:id="@+id/sdcard" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:verticalSpacing="10dp" 
    android:horizontalSpacing="10dp" 
    android:stretchMode="columnWidth" 
    android:gravity="center" /> 
    <ImageView 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:id="@+id/imgView" 
    ></ImageView> 
</LinearLayout> 

Answer 2

http://www.androidsnippets.com/list-all-music-files