How to get a Bitmap from a drawable defined in a xml?

How can I get the bitmap from a xml shape drawable. What am I doing wrong?

shadow.xml

<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle" >

    <gradient
        android:angle="270.0"
        android:endColor="@android:color/transparent"
        android:startColor="#33000000"
        android:type="linear" />

    <size android:height="7.0dip" />

</shape>

My method to retrieve the bitmap from drawable:

private Bitmap getBitmap(int id) {
    return BitmapFactory.decodeResource(getContext().getResources(), id);
}

getBitmap() is returning null when the id passed in is the shadow.xml drawable id.

This is a fully working solution:

private Bitmap getBitmap(int drawableRes) {
    Drawable drawable = getResources().getDrawable(drawableRes);
    Canvas canvas = new Canvas();
    Bitmap bitmap = Bitmap.createBitmap(drawable.getIntrinsicWidth(), drawable.getIntrinsicHeight(), Bitmap.Config.ARGB_8888);
    canvas.setBitmap(bitmap);
    drawable.setBounds(0, 0, drawable.getIntrinsicWidth(), drawable.getIntrinsicHeight());
    drawable.draw(canvas);

    return bitmap;
}

And here is an example:

Bitmap drawableBitmap = getBitmap(R.drawable.circle_shape);

circle_shape.xml

<?xml version="1.0" encoding="utf-8"?>
<shape
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="oval">
    <size
        android:width="15dp"
        android:height="15dp" />
    <solid
        android:color="#94f5b6" />
    <stroke
        android:width="2dp"
        android:color="#487b5a"/>
</shape>

a ShapeDrawable doesn't have a bitmap associated with it - its sole purpose is to be drawn on a canvas. Until its draw method is called, it has no image. If you can get a canvas element at the place where you need to draw the shadow, you can draw it as a shapeDrawable, otherwise you might need a separate, empty view in your layout with the shadow as a background.

You should add size attribute to your shape drawable for preventing "java.lang.IllegalArgumentException: width and height must be > 0".

<shape xmlns:android="http://schemas.android.com/apk/res/android"
       android:shape="oval">
       <solid android:color="@color/colorAccent" />
       <stroke
           android:width="1.3dp"
           android:color="@color/white" />

       <size android:height="24dp" android:width="24dp"/>
</shape>