public class MyActivity extends Activity{
    private PopupWindow menu;
    private LayoutInflater inflater;
    private View layout;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.main);

        //实例化PopupWindow创建菜单

        initMenu();

    }
    //判断按键 菜单的显示与隐藏
    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        if(!menu.isShowing()&&keyCode == KeyEvent.KEYCODE_MENU){
           show();
        }else{
            menu.dismiss();
        }
        if(keyCode == KeyEvent.KEYCODE_BACK&&menu.isShowing()){
            menu.dismiss();
        }
        return true;

    }
    //实例化PopupWindow创建菜单
    private void initMenu(){
            //获取LayoutInflater实例
            inflater  = (LayoutInflater) this.getSystemService(LAYOUT_INFLATER_SERVICE);
            //获取弹出菜单的布局
            layout = inflater.inflate(R.layout.menu,null);
            //设置popupWindow的布局
            menu = new PopupWindow(layout, WindowManager.LayoutParams.WRAP_CONTENT,WindowManager.LayoutParams.WRAP_CONTENT);
    }
    //显示菜单
    private void show(){
           //设置位置
            menu.showAtLocation(this.findViewById(R.id.main), Gravity.BOTTOM|Gravity.CENTER_HORIZONTAL,0,0); //设置在屏幕中的显示位置
    }
}