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

android:id="@+id/menu_news"

android:title="@string/news"/>

android:title="@string/color" >

android:checked="true"

android:title="@string/red"/>

android:title="@string/bule"/>

android:title="@string/greed"/>

android:title="@string/font" >

android:title="@string/big"/>

android:title="@string/small"/>

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;

}

}