Android: Drawable does not show correctly

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http://stackoverflow.com – In my app i have an expandable list view that i want to set groupIndicator for it, i add an image for it but image have an elongation, i don't have any idea. How can i fix it? these are my code and the picture of expandable list view: <ExpandableListView android:layout_weight="1" android:layout_width="fill_parent" android:layout_height="0dp" android:id="@+id/expandableListView" android:groupIndicator="@drawable/group_indicator"/> group_indicator.xml : <?xml version="1.0" encoding="utf-8"?> <selector xmlns:android (HowTos)