android-calculatorpp/android-app-core/res/drawable/gray_button.xml

<?xml version="1.0" encoding="utf-8"?>

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

	<item a:state_pressed="true" a:drawable="@drawable/metro_button_pressed"/>

	<item a:drawable="@drawable/gray_button_shape"/>

</selector>