Create a new file inside res/drawable folder and save it as triangle.xml
<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android" >
<item>
<rotate android:fromDegrees="45"
android:toDegrees="45"
android:pivotX="-40%"
android:pivotY="87%" >
<shape android:shape="rectangle" >
<stroke android:color="#000000"
android:width="10dp"/>
<solid android:color="#000000" />
</shape>
</rotate>
</item>
</layer-list>
