主题：android底部菜单应用

在android中实现菜单功能有多种方法。

Options Menu：用户按下menu Button时显示的菜单。

Context Menu：用户长时间按下屏幕，所显示出来的菜单也称为上下文菜单。

Submenu：子菜单。

但是有时候这些内置的菜单并不能满足我们功能，这就需要自己自定义一种菜单。接下来我说的这种就是通过TabHost与RadioGroup结合完成的菜单。这也是很常用的一种底部菜单做法。先上图：

首先看布局文件：

Xml代码

<?xml version="1.0" encoding="UTF-8"?>
<TabHost android:id="@android:id/tabhost" android:layout_width="fill_parent" android:layout_height="fill_parent"
xmlns:android="http://schemas.android.com/apk/res/android">
<LinearLayout
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
<FrameLayout
android:id="@android:id/tabcontent"
android:layout_width="fill_parent"
android:layout_height="0.0dip"
android:layout_weight="1.0" />
<TabWidget
android:id="@android:id/tabs"
android:visibility="gone"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_weight="0.0" />
<RadioGroup
android:gravity="center_vertical"
android:layout_gravity="bottom"
android:orientation="horizontal"
android:id="@+id/main_radio"
android:background="@drawable/maintab_toolbar_bg"
android:layout_width="fill_parent"
android:layout_height="wrap_content">
<RadioButton
android:id="@+id/radio_button0"
android:tag="radio_button0"
android:layout_marginTop="2.0dip"
android:text="@string/alarm"
android:drawableTop="@drawable/icon_1"
style="@style/main_tab_bottom" />
<RadioButton
android:id="@+id/radio_button1"
android:tag="radio_button1"
android:layout_marginTop="2.0dip"
android:text="@string/message"
android:drawableTop="@drawable/icon_2"
style="@style/main_tab_bottom" />
<RadioButton
android:id="@+id/radio_button2"
android:tag="radio_button2"
android:layout_marginTop="2.0dip"
android:text="@string/photo"
android:drawableTop="@drawable/icon_3"
style="@style/main_tab_bottom" />
<RadioButton
android:id="@+id/radio_button3"
android:tag="radio_button3"
android:layout_marginTop="2.0dip"
android:text="@string/music"
android:drawableTop="@drawable/icon_4"
style="@style/main_tab_bottom" />
<RadioButton
android:id="@+id/radio_button4"
android:tag="radio_button4"
android:layout_marginTop="2.0dip"
android:text="@string/setting"
android:drawableTop="@drawable/icon_5"
style="@style/main_tab_bottom" />
RadioGroup>
LinearLayout>
TabHost>

<?xml version="1.0" encoding="UTF-8"?>

需要注意的是，如果用TabHost这个控件，其中有几个ID是必须这么写的，android:id="@android:id/tabhost ；android:id="@android:id/tabcontent" ；android:id="@android:id/tabs" ；之所以要这么写是因为在TabHost这个类中。需要实例化上述这个ID的控件。看源码：

在TabActivity中有么个方法：

Java代码

@Override
public void onContentChanged() {
super.onContentChanged();
mTabHost = (TabHost) findViewById(com.android.internal.R.id.tabhost);
if (mTabHost == null) {
throw new RuntimeException(
"Your content must have a TabHost whose id attribute is " +
"'android.R.id.tabhost'");
}
mTabHost.setup(getLocalActivityManager());
}
private void ensureTabHost() {
if (mTabHost == null) {
this.setContentView(com.android.internal.R.layout.tab_content);
}
}

 @Override    public void onContentChanged() {        super.onContentChanged();        mTabHost = (TabHost) findViewById(com.android.internal.R.id.tabhost);        if (mTabHost == null) {            throw new RuntimeException(                    "Your content must have a TabHost whose id attribute is " +                    "'android.R.id.tabhost'");        }        mTabHost.setup(getLocalActivityManager());    }    private void ensureTabHost() {        if (mTabHost == null) {            this.setContentView(com.android.internal.R.layout.tab_content);        }    }

当内容发生改变时它会调用这个方法，来更新列表或者其他视图，而这个方法中需要实例化TabHost，所以必须通过ID为tabhost实例化。

再看看TabHost这个类中，

Java代码

public void setup() {
mTabWidget = (TabWidget) findViewById(com.android.internal.R.id.tabs);
if (mTabWidget == null) {
throw new RuntimeException(
"Your TabHost must have a TabWidget whose id attribute is 'android.R.id.tabs'");
}
// KeyListener to attach to all tabs. Detects non-navigation keys
// and relays them to the tab content.
mTabKeyListener = new OnKeyListener() {
public boolean onKey(View v, int keyCode, KeyEvent event) {
switch (keyCode) {
case KeyEvent.KEYCODE_DPAD_CENTER:
case KeyEvent.KEYCODE_DPAD_LEFT:
case KeyEvent.KEYCODE_DPAD_RIGHT:
case KeyEvent.KEYCODE_DPAD_UP:
case KeyEvent.KEYCODE_DPAD_DOWN:
case KeyEvent.KEYCODE_ENTER:
return false;
}
mTabContent.requestFocus(View.FOCUS_FORWARD);
return mTabContent.dispatchKeyEvent(event);
}
};
mTabWidget.setTabSelectionListener(new TabWidget.OnTabSelectionChanged() {
public void onTabSelectionChanged(int tabIndex, boolean clicked) {
setCurrentTab(tabIndex);
if (clicked) {
mTabContent.requestFocus(View.FOCUS_FORWARD);
}
}
});
mTabContent = (FrameLayout) findViewById(com.android.internal.R.id.tabcontent);
if (mTabContent == null) {
throw new RuntimeException(
"Your TabHost must have a FrameLayout whose id attribute is "
+ "'android.R.id.tabcontent'");
}
}

  public void setup() {        mTabWidget = (TabWidget) findViewById(com.android.internal.R.id.tabs);        if (mTabWidget == null) {            throw new RuntimeException(                    "Your TabHost must have a TabWidget whose id attribute is 'android.R.id.tabs'");        }        // KeyListener to attach to all tabs. Detects non-navigation keys        // and relays them to the tab content.        mTabKeyListener = new OnKeyListener() {            public boolean onKey(View v, int keyCode, KeyEvent event) {                switch (keyCode) {                    case KeyEvent.KEYCODE_DPAD_CENTER:                    case KeyEvent.KEYCODE_DPAD_LEFT:                    case KeyEvent.KEYCODE_DPAD_RIGHT:                    case KeyEvent.KEYCODE_DPAD_UP:                    case KeyEvent.KEYCODE_DPAD_DOWN:                    case KeyEvent.KEYCODE_ENTER:                        return false;                }                mTabContent.requestFocus(View.FOCUS_FORWARD);                return mTabContent.dispatchKeyEvent(event);            }        };        mTabWidget.setTabSelectionListener(new TabWidget.OnTabSelectionChanged() {            public void onTabSelectionChanged(int tabIndex, boolean clicked) {                setCurrentTab(tabIndex);                if (clicked) {                    mTabContent.requestFocus(View.FOCUS_FORWARD);                }            }        });        mTabContent = (FrameLayout) findViewById(com.android.internal.R.id.tabcontent);        if (mTabContent == null) {            throw new RuntimeException(                    "Your TabHost must have a FrameLayout whose id attribute is "                            + "'android.R.id.tabcontent'");        }    }

这个方法，是在增加选项卡之前由系统调用。在这个方法中需要通过tabs 这个ID实例化一个TabWidget，通过tabcontent这个ID实例化一个FrameLayout，用来放置选项卡内容。所以这两个ID也是固定的。

在上述布局文件中隐藏了系统默认的Widget，取而代之的是带有图片的Button。

看一下主要代码：

Java代码

package com.iteye.androidtoast;
import android.app.TabActivity;
import android.content.Intent;
import android.os.Bundle;
import android.widget.RadioGroup;
import android.widget.RadioGroup.OnCheckedChangeListener;
import android.widget.TabHost;
public class MainActivity extends TabActivity implements OnCheckedChangeListener{
/** Called when the activity is first created. */
private TabHost mHost;
private RadioGroup radioderGroup;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.maintabs);
//实例化TabHost
mHost=this.getTabHost();
//添加选项卡
mHost.addTab(mHost.newTabSpec("ONE").setIndicator("ONE")
.setContent(new Intent(this,OneActivity.class)));
mHost.addTab(mHost.newTabSpec("TWO").setIndicator("TWO")
.setContent(new Intent(this,TwoActivity.class)));
mHost.addTab(mHost.newTabSpec("THREE").setIndicator("THREE")
.setContent(new Intent(this,ThreeActivity.class)));
mHost.addTab(mHost.newTabSpec("FOUR").setIndicator("FOUR")
.setContent(new Intent(this,FourActivity.class)));
mHost.addTab(mHost.newTabSpec("FIVE").setIndicator("FIVE")
.setContent(new Intent(this,FiveActivity.class)));
radioderGroup = (RadioGroup) findViewById(R.id.main_radio);
radioderGroup.setOnCheckedChangeListener(this);
}
@Override
public void onCheckedChanged(RadioGroup group, int checkedId) {
switch(checkedId){
case R.id.radio_button0:
mHost.setCurrentTabByTag("ONE");
break;
case R.id.radio_button1:
mHost.setCurrentTabByTag("TWO");
break;
case R.id.radio_button2:
mHost.setCurrentTabByTag("THREE");
break;
case R.id.radio_button3:
mHost.setCurrentTabByTag("FOUR");
break;
case R.id.radio_button4:
mHost.setCurrentTabByTag("FIVE");
break;
}
}
}

package com.iteye.androidtoast;import android.app.TabActivity;import android.content.Intent;import android.os.Bundle;import android.widget.RadioGroup;import android.widget.RadioGroup.OnCheckedChangeListener;import android.widget.TabHost;public class MainActivity extends TabActivity implements OnCheckedChangeListener{    /** Called when the activity is first created. */private TabHost mHost;private RadioGroup radioderGroup;    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.maintabs);        //实例化TabHost        mHost=this.getTabHost();                //添加选项卡        mHost.addTab(mHost.newTabSpec("ONE").setIndicator("ONE")        .setContent(new Intent(this,OneActivity.class)));        mHost.addTab(mHost.newTabSpec("TWO").setIndicator("TWO")        .setContent(new Intent(this,TwoActivity.class)));        mHost.addTab(mHost.newTabSpec("THREE").setIndicator("THREE")        .setContent(new Intent(this,ThreeActivity.class)));        mHost.addTab(mHost.newTabSpec("FOUR").setIndicator("FOUR")        .setContent(new Intent(this,FourActivity.class)));        mHost.addTab(mHost.newTabSpec("FIVE").setIndicator("FIVE")        .setContent(new Intent(this,FiveActivity.class)));                radioderGroup = (RadioGroup) findViewById(R.id.main_radio);radioderGroup.setOnCheckedChangeListener(this);    }@Overridepublic void onCheckedChanged(RadioGroup group, int checkedId) {switch(checkedId){case R.id.radio_button0:mHost.setCurrentTabByTag("ONE");break;case R.id.radio_button1:mHost.setCurrentTabByTag("TWO");break;case R.id.radio_button2:mHost.setCurrentTabByTag("THREE");break;case R.id.radio_button3:mHost.setCurrentTabByTag("FOUR");break;case R.id.radio_button4:mHost.setCurrentTabByTag("FIVE");break;}}}

这个应该没有什么好难理解的。OK该睡了。有什么问题留言！

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