PopupWindow是一个弹出式窗口，它可以展示任意View。他会浮在当前窗口的上方展示。

下面看代码：
代码如下：

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
    }
}

菜单的布局文件：

代码如下：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

              android:layout_width="fill_parent"

              android:layout_height="fill_parent"

              android:orientation="horizontal"

        >

    <ImageView

        android:id="@+id/icon_1"

        android:background="@drawable/icon_1"

        android:layout_width="40dp"

        android:layout_height="40dp"/>

    <ImageView

        android:id="@+id/icon_2"

        android:background="@drawable/icon_2"

        android:layout_width="40dp"

        android:layout_height="40dp"/>

    <ImageView

        android:id="@+id/icon_3"

        android:background="@drawable/icon3"

        android:layout_width="40dp"

        android:layout_height="40dp"/>

    <ImageView

        android:id="@+id/icon_4"

        android:background="@drawable/icon4"

        android:layout_width="40dp"

        android:layout_height="40dp"/>
</LinearLayout>