Android L’s Ripple Effect – Touch Feedback for Buttons – Using XML

UPDATE Material Components:

With the Material Components Library it is very easy to apply a ripple.
Just use the MaterialButton and the app:rippleColor attribute:

<com.google.android.material.button.MaterialButton
    app:rippleColor="@color/my_selector"
    ../>

With a selector like this:

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

  <item android:alpha="..." android:color="?attr/colorOnPrimary" android:state_pressed="true"/>
  <item android:alpha="..." android:color="?attr/colorOnPrimary" android:state_focused="true" android:state_hovered="true"/>
  <item android:alpha="..." android:color="?attr/colorOnPrimary" android:state_focused="true"/>
  <item android:alpha="..." android:color="?attr/colorOnPrimary" android:state_hovered="true"/>
  <item android:alpha="..." android:color="?attr/colorOnPrimary"/>

</selector>

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Old answer
You can do something like this:

<Button
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:background="@drawable/ripple"
      
    />

Where the ripple.xml is:

<ripple xmlns:android="http://schemas.android.com/apk/res/android" 
                      android:color="?android:colorControlHighlight">
        <item android:id="@android:id/mask">
            <shape android:shape="oval">
                <solid android:color="?android:colorAccent" />
            </shape>
        </item>
 </ripple>