How can I write a Drawable resource to a File?

Question

I need to export some Drawable resources to a file.

For example, I have a function that returns to me a Drawable object. I want to write it out to a file in /sdcard/drawable/newfile.png. How can i do it?

Answer 1

Although the best answer here have a nice approach. It's link only. Here's how you can do the steps:

Convert Drawable to Bitmap

You can do that in at least two different ways, depending on where you're getting the Drawable from.

1. Drawable is on res/drawable folders.

Say you want to use a Drawable that is on your drawable folders. You can use the BitmapFactory#decodeResource approach. Example below.

Bitmap bm = BitmapFactory.decodeResource(mContext.getResources(), R.drawable.your_drawable);

2. You have a PictureDrawable object.

If you're getting a PictureDrawable from somewhere else "at runtime", you can use the Bitmap#createBitmap approach to create your Bitmap. Like the example below.

public Bitmap drawableToBitmap(PictureDrawable pd) {
    Bitmap bm = Bitmap.createBitmap(pd.getIntrinsicWidth(), pd.getIntrinsicHeight(), Bitmap.Config.ARGB_8888);
    Canvas canvas = new Canvas(bm);
    canvas.drawPicture(pd.getPicture());
    return bm;
}

Save the Bitmap to disk

Once you have your Bitmap object, you can save it to the permanent storage. You'll just have to choose the file format (JPEG, PNG or WEBP).

/**
 * @param dir you can get from many places like Environment.getExternalStorageDirectory() or mContext.getFilesDir() depending on where you want to save the image.
 * @param fileName The file name.
 * @param bm The Bitmap you want to save.
 * @param format Bitmap.CompressFormat can be PNG,JPEG or WEBP.
 * @param quality quality goes from 1 to 100. (Percentage).
 * @return true if the Bitmap was saved successfully, false otherwise.
 */
boolean saveBitmapToFile(File dir, String fileName, Bitmap bm, 
    Bitmap.CompressFormat format, int quality) {
    
    File imageFile = new File(dir,fileName);

    FileOutputStream fos = null;
    try {
        fos = new FileOutputStream(imageFile);

        bm.compress(format,quality,fos);

        fos.close();

        return true;
    }
    catch (IOException e) {
        Log.e("app",e.getMessage());
        if (fos != null) {
            try {
                fos.close();
            } catch (IOException e1) {
                e1.printStackTrace();
            }
        }
    }
    return false;
}

And to get the target directory, try something like:

File dir = new File(Environment.getExternalStorageDirectory() + File.separator + "drawable");

boolean doSave = true;
if (!dir.exists()) {
    doSave = dir.mkdirs();
}

if (doSave) {
    saveBitmapToFile(dir,"theNameYouWant.png",bm,Bitmap.CompressFormat.PNG,100);
}
else {
    Log.e("app","Couldn't create target directory.");
}

Obs: Remember to do this kind of work on a background Thread if you're dealing with large images, or many images, because it can take some time to finish and might block your UI, making your app unresponsive.