Android按键之Menu详解

Android手机一般都有三个键，返回键、Home键、菜单键；

Android系统的菜单支持主要通过4个接口来实现。

从上图可以看出Menu是一个父类接口，它下面有两个子类一个是ContextMenu：它表示是一个上下文菜单，SubMenu表示一个子菜单。它们都可以包含一个或多个的MenuItem菜单项

Menu接口定义了两个方法来添加菜单项和添加子菜单。一个通过add()方法添加菜单项，addSubMenu()方法来添加子菜单。而SubMenu与ContextMenu继承了Munu接口的方法之外，还提供了一些的方法。比如设置菜单的标题、图标等;

开发菜单和子菜单有两种方式；一是在Activity重写的方法onCreateOptionsMenu(Menu menu)方法中调用menu对象添加，然后在重写Activity的onOptionsItemSelected来响应选择的菜单项。二是通过资源文件来定义菜单项，然后在onCreateOptionsMenu方法中加载这个xml资源。onCreateOptionsMenu方法在单击Menu键时触发。

而开发上下文菜单与上类似：分为三个步骤：一是重写onCreateContextMenu(ContextMenu menu,View source,ContextMenu.MenuInfo info)方法，然后调用registerForContextMenu(View viwe)方法为控件注册上下文菜单，最后重写onContextItemSelected(Menuitem item)来响应选择的菜单项

实例如下：

1、代码中添加： 

package com.android.xiong.memu;

import android.os.Bundle;
import android.app.Activity;
import android.app.AlertDialog;
import android.app.AlertDialog.Builder;
import android.view.ContextMenu;
import android.view.ContextMenu.ContextMenuInfo;
import android.view.Menu;
import android.view.MenuItem;
import android.view.SubMenu;
import android.view.View;
import android.widget.Button;

public class MainActivity extends Activity {

    // 定义菜单项的ItemId
    private final int NEWS = 00;
    private final int COLOR = 01;
    private final int FONT = 02;
    private final int RED = 001;
    private final int BULE = 002;
    private final int GREED = 003;

    private final int BIG = 004;
    private final int SMALL = 005;

    Builder bu;

    Button show;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        bu = new AlertDialog.Builder(this);
        show = (Button) findViewById(R.id.context);
        // 为Button注册上下文菜单
        registerForContextMenu(show);

    }

    // 用户单击Menu键时触发
    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // 添加新建菜单项
        menu.add(0, NEWS, 0, "新建");
        // 添加颜色子菜单
        SubMenu color = menu.addSubMenu(0, COLOR, 0, "颜色");
        color.setHeaderTitle("选择颜色");
        color.add(0, RED, 0, "红色");
        color.add(0, BULE, 0, "蓝色");
        color.add(0, GREED, 0, "绿色");
        // 添加字体的菜单
        SubMenu font = menu.addSubMenu(0, FONT, 0, "字体");
        font.setHeaderTitle("选择字体");
        font.add(0, BIG, 0, "大字体");
        font.add(0, SMALL, 0, "小字体");
        return super.onCreateOptionsMenu(menu);
    }

    // 当用户单击菜单项触发
    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
        case RED:
            bu.setMessage("红色").setPositiveButton("确定", null).show();
            break;
        case BULE:
            bu.setMessage("蓝色").setPositiveButton("确定", null).show();
            break;
        case GREED:
            bu.setMessage("绿色").setPositiveButton("确定", null).show();
            break;
        case BIG:
            bu.setMessage("大号").setPositiveButton("确定", null).show();
            break;
        case SMALL:
            bu.setMessage("小号").setPositiveButton("确定", null).show();
            break;
        case NEWS:
            bu.setMessage("新建").setPositiveButton("确定", null).show();
            break;
        }
        return true;
    }

    // 长按组件响应的上下文菜单
    @Override
    public void onCreateContextMenu(ContextMenu menu, View v,
            ContextMenuInfo menuInfo) {
        menu.add(0, RED, 0, "红色");
        menu.add(0, BULE, 0, "蓝色");
        menu.add(0, GREED, 0, "绿色");
    }

    // 点击上下文菜单项触发
    @Override
    public boolean onContextItemSelected(MenuItem item) {
        switch (item.getItemId()) {
        case RED:
            bu.setMessage("红色").setPositiveButton("确定", null).show();
            break;
        case BULE:
            bu.setMessage("蓝色").setPositiveButton("确定", null).show();
            break;
        case GREED:
            bu.setMessage("绿色").setPositiveButton("确定", null).show();
            break;

        }
        return true;
    }

}

2、XML资源定义菜单 

<menu xmlns:android="http://schemas.android.com/apk/res/android" >
    <!-- 添加菜单项 -->
    <item
        android:id="@+id/menu_news"
        android:title="@string/news"/>
    <!-- 添加子菜单 -->
    <item
        android:title="@string/color" >
        <menu>
            <!-- 单项选择 -->
            <group  android:checkableBehavior="single">
                <!-- 选中红色 -->
                <item android:id="@+id/color_red"
                    android:checked="true"
                    android:title="@string/red"/>
                <item android:id="@+id/color_bule"
                    android:title="@string/bule"/>
                <item android:id="@+id/color_greed"
                    android:title="@string/greed"/>

            </group>
        </menu>
        </item>
    <item
        android:title="@string/font" >
        <menu>
            <!-- 多项选择 -->
            <group  android:checkableBehavior="all">
                <item android:id="@+id/font_big"
                    android:title="@string/big"/>
                <item android:id="@+id/font_Small"
                    android:title="@string/small"/>

            </group>
        </menu>
        </item>

</menu>

 

package com.android.xiong.menu2;

import android.os.Bundle;
import android.app.Activity;
import android.app.AlertDialog;
import android.app.AlertDialog.Builder;
import android.view.ContextMenu;
import android.view.ContextMenu.ContextMenuInfo;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;

public class MainActivity extends Activity {

    Button show;
    Builder bu;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        bu = new AlertDialog.Builder(this);
        show=(Button)findViewById(R.id.bt_show);
        registerForContextMenu(show);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.main, menu);
        return super.onCreateOptionsMenu(menu);
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
        case R.id.color_red:
            bu.setMessage("红色").setPositiveButton("确定", null).show();
            break;
        case R.id.color_bule:
            bu.setMessage("蓝色").setPositiveButton("确定", null).show();
            break;
        case R.id.color_greed:
            bu.setMessage("绿色").setPositiveButton("确定", null).show();
            break;
        case R.id.font_big:
            bu.setMessage("大号").setPositiveButton("确定", null).show();
            break;
        case R.id.font_Small:
            bu.setMessage("小号").setPositiveButton("确定", null).show();
            break;
        case R.id.menu_news:
            bu.setMessage("新建").setPositiveButton("确定", null).show();
            break;
        }
        return true;
    }

    @Override
    public void onCreateContextMenu(ContextMenu menu, View v,
            ContextMenuInfo menuInfo) {
        getMenuInflater().inflate(R.menu.main, menu);
    }

    @Override
    public boolean onContextItemSelected(MenuItem item) {
        switch (item.getItemId()) {
        case R.id.color_red:
            bu.setMessage("红色").setPositiveButton("确定", null).show();
            break;
        case R.id.color_bule:
            bu.setMessage("蓝色").setPositiveButton("确定", null).show();
            break;
        case R.id.color_greed:
            bu.setMessage("绿色").setPositiveButton("确定", null).show();
            break;
        case R.id.font_big:
            bu.setMessage("大号").setPositiveButton("确定", null).show();
            break;
        case R.id.font_Small:
            bu.setMessage("小号").setPositiveButton("确定", null).show();
            break;
        case R.id.menu_news:
            bu.setMessage("新建").setPositiveButton("确定", null).show();
            break;
        }
        return true;
    }


}