android学习——退出整个应用程序

将下面SysApplication这个类复制到工程里面，然后在每个Acitivity的oncreate方法里面通过SysApplication.getInstance().addActivity(this); 添加当前Acitivity到ancivitylist里面去，最后在想退出的时候调用SysApplication.getInstance().exit();可直接关闭所有的Acitivity并退出应用程序。

package com.example.Emotional.util;

import java.util.LinkedList;
import java.util.List;
import android.app.Activity;
import android.app.Application; 

/**
 *
* 类名称：SysApplication
* 类描述：   退出整个应用程序的类
* 创建时间：2014-4-25 下午1:58:00
* 修改备注：
* @version
*
 */

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);
        }
    }
    public void onLowMemory() {
        super.onLowMemory();
        System.gc();
    }
}

在硬退出按钮点击时

//点击硬退出按钮
    public void clickQuitDialog() { 

            AlertDialog.Builder builder = new Builder(FirstActivity.this);
            builder.setMessage("确定要退出吗?");

//          builder.setTitle("提示");
            builder.setPositiveButton("确认",new android.content.DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        dialog.dismiss();
//                        FirstActivity.this.finish();
//                        System.exit(0);
                        SysApplication.getInstance().exit();
                    }
                });
            builder.setNegativeButton("取消",new android.content.DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        dialog.dismiss();
                    }
                });
            builder.create().show();
        } 

        @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) { 

            //event.getRepeatCount() == 0 防止重复点击
            if (keyCode == KeyEvent.KEYCODE_BACK && event.getRepeatCount() == 0) {
                clickQuitDialog();
                return false;
            }
            return false;
        }