Android - Image Operations Using BitmapFactory

Introduction 

Though it may seem easy to set an image as a wallpaper, there are various small issues that need to be addressed to correctly set a wallpaper. Through a simple app - Walltoday which allows a user to set a wallpaper for each day which changes automatically every morning, this tip shows a number of points which will help in setting the wallpaper.

Background

The app can be downloaded via Google play store using the following links:

• market://details?id=com.app.walltoday

or:

• https://play.google.com/store/apps/details?id=com.app.walltoday

Using the Code

1. Activity

Start activity to select an image from Image Gallery:

Intent intent = new Intent(Intent.ACTION_PICK,
android.provider.MediaStore.Images.Media.INTERNAL_CONTENT_URI);                        
startActivityForResult(intent, RESULT_LOAD_IMAGE);

Set the selected image from gallery:

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    try {
    if (requestCode == RESULT_LOAD_IMAGE && 
            resultCode == RESULT_OK && null != data) 
            {
        Uri selectedImage = data.getData();
        String[] filePathColumn = { MediaStore.Images.Media.DATA };
        Cursor cursor = getContentResolver().query(
                              selectedImage,filePathColumn, null, null, null);
            cursor.moveToFirst();
        int columnIndex = cursor.getColumnIndex(filePathColumn[0]);
        String picturePath = cursor.getString(columnIndex);
        cursor.close();
        ImageButton imgButton = (ImageButton) findViewById(ButtonIdToSet);
                
        File file = new File(picturePath);
        if(file.exists())
        {                    
            Bitmap bmp = decodeFile(file,
            imgButton.getWidth(),imgButton.getHeight());
                    
            imgButton.setImageBitmap(bmp);    
        }
        }
    } catch (Exception e) {            
        e.printStackTrace();
    }
}

2. Working with Bitmaps in Android

Resize (scale) bitmap for given Height and Width:

public static Bitmap decodeFile(File file, int reqWidth, int reqHeight){
    // First decode with inJustDecodeBounds=true to check dimensions
    final BitmapFactory.Options options = new BitmapFactory.Options();
    options.inJustDecodeBounds = true;
    BitmapFactory.decodeFile(file.getPath(), options);

    // Calculate inSampleSize
    options.inSampleSize = calculateInSampleSize(options, reqWidth, reqHeight);

    // Decode bitmap with inSampleSize set
    options.inJustDecodeBounds = false;
    return BitmapFactory.decodeFile(file.getPath(), options);     
}
    
private static int calculateInSampleSize(
    BitmapFactory.Options options, int reqWidth, int reqHeight) {
    // Raw height and width of image
    final int height = options.outHeight;
    final int width = options.outWidth;
    int inSampleSize = 1;

    if (height > reqHeight || width > reqWidth) {

        // Calculate ratios of height and width to requested height and width
        final int heightRatio = Math.round((float) height / (float) reqHeight);
        final int widthRatio = Math.round((float) width / (float) reqWidth);

        // Choose the smallest ratio as inSampleSize value, this will guarantee
        // a final image with both dimensions larger than or equal to the
        // requested height and width.
        inSampleSize = heightRatio < widthRatio ? heightRatio : widthRatio;
    }

    return inSampleSize;
}    

3. Get height and width of display before setting the bitmap:

DisplayMetrics metrics = appContext.getResources().getDisplayMetrics();
int height = metrics.heightPixels; 
int width = metrics.widthPixels;

4. Set the bitmap:

Bitmap bmp = decodeFile(file,width,height);
myWallpaperManager.suggestDesiredDimensions(width, height);
myWallpaperManager.setBitmap(bmp);