使具有物理按键的手机能够显示Action Bar overflow

public class XxxActivity{

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		...
	    
	    getOverflowMenu();
    }

	//force to show overflow menu in actionbar for android 4.4 below
	private void getOverflowMenu() {
	     try {
	        ViewConfiguration config = ViewConfiguration.get(this);
	        Field menuKeyField = ViewConfiguration.class.getDeclaredField("sHasPermanentMenuKey");
	        if(menuKeyField != null) {
	            menuKeyField.setAccessible(true);
	            menuKeyField.setBoolean(config, false);
	        }
	    } catch (Exception e) {
	        e.printStackTrace();
	    }
	}
}