Android 怎么退出整个应用程序

在开发andorid程序的时候，难免会牵扯到退出整个应用程序的情况，怎么完全退出呢？请参阅下面的关键代码：

[java]
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import java.util.LinkedList;

import java.util.List;

import android.app.Activity;

import android.app.AlertDialog;

import android.app.Application;

import android.content.DialogInterface;

import android.content.Intent;

public class SysApplication
extends Application {
private List<Activity> mList =
new LinkedList<Activity>();
private static SysApplication instance;

private SysApplication() {

}

public synchronized
static SysApplication getInstance() {

if (null == instance) {

instance = new SysApplication();

}
return instance;
}

// add Activity
public void addActivity(Activity activity) {

mList.add(activity);
}

public void exit() {

try {
for (Activity activity : mList) {

if (activity !=
null)
activity.finish();
}
} catch (Exception e) {

e.printStackTrace();
} finally {
System.exit(0);

}
}

@Override

public void onLowMemory() {

super.onLowMemory();

System.gc();
}

}

[java]
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public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

SysApplication.getInstance().addActivity(this);

}

public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
SysApplication.getInstance().addActivity(this);
}

在需要退出程序的时候，调用：

[java]
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SysApplication.getInstance().exit();

SysApplication.getInstance().exit();

简而言之，通过单例模式把每个Activity 的引用添加到一个全局链表中，每次退出程序调用System.exit(0)