使用CursorLoader和LoaderManager从Android应用程序中检索图像

Question

目前我正在使用getContentResolver().query()/ managedQuery()来获取光标以从图库应用程序中检索图像.因为我正在使用的API部分弃用,所以我想将CursorLoader与LoaderManager一起使用.

/**
 * Creates a cursor to access the content defined by the image uri for API
 * version 11 and newer.
 * 
 * @return The created cursor.
 */
@TargetApi(Build.VERSION_CODES.HONEYCOMB)
private Cursor createCursorHoneycomb() {
    String[] projection = {
            MediaStore.Images.Media.DATA
    };
    Cursor cursor = getContentResolver().query(imageUri, projection, null, null, null);

    return cursor;
}

/**
 * Creates a cursor to access the content defined by the image uri from API
 * version 8 to 10.
 * 
 * @return The created cursor.
 */
@SuppressWarnings("deprecation")
@TargetApi(Build.VERSION_CODES.FROYO)
private Cursor createCursorFroyo() {
    String[] projection = {
            MediaStore.Images.Media.DATA
    };
    Cursor cursor = managedQuery(imageUri, projection, null, null, null);

    return cursor;
}

由于我没有ListView,我不使用任何适配器.我只是为ImageView设置了一个图像位图.

/**
 * Sets the image bitmap for the image view.
 */
private void setupImageView() {
    String imagePath = getImagePathFromUri(imageUri);
    Bitmap bitmap = BitmapFactory.decodeFile(imagePath);
    ImageView imageView = (ImageView) findViewById(R.id.image_view);

    imageView.setImageBitmap(bitmap);
}

/**
 * Returns an image path created from the supplied image uri.
 * 
 * @param imageUri The supplied image uri.
 * @return Returns the created image path.
 */
@SuppressWarnings("deprecation")
private String getImagePathFromUri(Uri imageUri) {
    Cursor cursor = null;
    String imagePath = null;

    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
        cursor = createCursorHoneycomb();
    } else {
        cursor = createCursorFroyo();
    }

    // if image is loaded from gallery
    if (cursor != null) {
        startManagingCursor(cursor);

        int columnIndex = cursor.getColumnIndexOrThrow(MediaStore.Images.Media.DATA);

        cursor.moveToFirst();
        imagePath = cursor.getString(columnIndex);
    }
    // if image is loaded from file manager
    else {
        imagePath = imageUri.getPath();
    }

    return imagePath;
}

是否可以使用CursorLoader和LoaderManager从图库应用程序或文件管理器加载图像？我找不到任何解决方案.

Answer 1

通过在需要时调用getSupportLoaderManager来启动加载程序管理器.

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    if (requestCode == REQUEST_CODE) {
        if (resultCode == Activity.RESULT_OK) {
            imageUri = data.getData();
            getSupportLoaderManager().initLoader(0, null, this);
        } else if (resultCode == Activity.RESULT_CANCELED) {
            Toast.makeText(this, "Action canceled.", Toast.LENGTH_LONG).show();
        } else {
            Toast.makeText(this, "Action failed!", Toast.LENGTH_LONG).show();
        }
    }
}

然后创建一个用于检索图像路径的游标加载器.

@Override
public Loader<Cursor> onCreateLoader(int id, Bundle args) {
    String[] projection = {
            MediaStore.Images.Media.DATA
    };
    CursorLoader cursorLoader = new CursorLoader(this, imageUri, projection, null, null, null);

    return cursorLoader;
}

当光标加载器完成时,它使用检索到的数据来更新UI.

@Override
public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
    if (data != null) {
        int columnIndex = data.getColumnIndexOrThrow(MediaStore.Images.Media.DATA);

        data.moveToFirst();
        imagePath = data.getString(columnIndex);
    } else {
        imagePath = imageUri.getPath();
    }

    setupImageView();
}

这很容易做到.但我必须了解如何使用onCreateLoader()和onLoadFinished().