Shaped drawable with selectableItemBackground as background

Here's a simpler solution now in 2020 (API >= 21 because we're using the ?attr syntax) :

<ripple
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:color="?colorControlHighlight">
    <!-- 🡡 the ripple's color (1) -->

    <!-- 🡣 no `id` so our <shape> will be drawn and not just used as mask -->
    <item>
        <shape>
            <corners android:radius="9dp" />
            <solid android:color="@color/white" />
        </shape>
    </item>

</ripple>

(1) If you don't override colorControlHighlight in your theme, the ripple's color will be Android's default. If you do override it but still want to use Android's default use ?android:colorControlHighlight instead

Having round_corners.xml:

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
       android:shape="rectangle">
    <solid android:color="@android:color/transparent"/>
    <corners android:radius="15dp" />
    <stroke
        android:width="1px"
        android:color="#000000" />
</shape>

And my_ripple.xml:

<?xml version="1.0" encoding="utf-8"?>
<ripple xmlns:android="http://schemas.android.com/apk/res/android"
        android:color="?android:attr/colorControlHighlight">
    <item android:id="@android:id/mask">
        <shape android:shape="rectangle">
            <solid android:color="#000000" />
            <corners android:radius="15dp" />
        </shape>
    </item>
    <item android:drawable="@drawable/round_corners" />
</ripple>

And button:

<Button
    android:background="@drawable/my_ripple"
    ... />

Will result in this:

See this article.

I have a simpler version of the first answer:

<ripple
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:color="?colorControlHighlight"> <!-- default ripple color -->

    <item>
        <!-- the background shape when it's not being clicked -->
        <shape android:shape="rectangle">
            <solid android:color="@color/colorPrimary" />
            <corners android:radius="32dp" />
        </shape>
    </item>
</ripple>

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Just apply it as background but remember to REMOVE THE SHADOW if it applys to Button:

style="?borderlessButtonStyle"

Good luck!

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