How to draw a circle inside a circle using Android xml shapes?

Question

I'm trying to make a thumb for a seekbar for my app, and I want to have an inner circle surrounded by a different, larger (semi-transparent) outer circle. I'm trying to use layer-list, but I'm having issues. Below is my code...

<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android" >
<item>
    <shape
        android:shape="oval" >
        <solid android:color="#00f" />

        <size
            android:height="15dp"
            android:width="15dp" />
    </shape>
</item>

<item>
    <shape
        android:shape="oval" >
        <solid android:color="#f00" />

        <size
            android:height="10dp"
            android:width="10dp" />
    </shape>
</item>

</layer-list>

I would expect to see a small red circle on top of a larger blue circle, but all I'm seeing is the small red circle. Does anyone have any ideas?

Answer 1

The only way I've gotten this to work is to define a transparent stroke for the inner (i.e., top) circle that's the difference between the size of the larger and smaller circle.

For example, this:

<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
<!-- Larger blue circle in back -->
<item>
    <shape android:shape="oval">
        <solid android:color="#00f"/>
        <size
                android:width="15dp"
                android:height="15dp"/>
    </shape>
</item>
<!-- Smaller red circle in front -->
<item>
    <shape android:shape="oval">
        <!-- transparent stroke = larger_circle_size - smaller_circle_size -->
        <stroke android:color="@android:color/transparent"
                android:width="5dp"/>
        <solid android:color="#f00"/>
        <size
                android:width="10dp"
                android:height="10dp"/>
    </shape>
</item>
</layer-list>

...looks like this: