How to right align widget in horizontal linear layout Android?

Try to add empty View inside horizontal LinearLayout before element that you want to see right, e.g.:

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content" >

    <View
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:layout_weight="1" />                

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

</LinearLayout>