Android PopupMenu弹出菜单的实现

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"   xmlns:tools="http://schemas.android.com/tools"   android:layout_width="match_parent"   android:layout_height="match_parent"   android:paddingBottom="@dimen/activity_vertical_margin"   android:paddingLeft="@dimen/activity_horizontal_margin"   android:paddingRight="@dimen/activity_horizontal_margin"   android:paddingTop="@dimen/activity_vertical_margin"   tools:context=".MainActivity" >    <Button     android:id="@+id/button1"     android:layout_width="wrap_content"     android:layout_height="wrap_content"     android:layout_alignParentLeft="true"     android:layout_alignParentTop="true"     android:layout_marginLeft="96dp"     android:layout_marginTop="111dp"     android:onClick="showPopup"     android:text="弹出菜单" />  </RelativeLayout>