android退出應用：彈出對話框退出應用

（1）定義棧，寫一個Exitactivity 類，利用單例模式管理Activity，在每個在
Activity 的onCreate()方法中調用Exitactivity.getInstance().addActivity(this)方法,在退
出時調用Exitactivity.getInstance().exit()方法，就可以完全退出應用程序了。這個主要建立了一個對話框退出activity

（2）Exitactivity類：

package com.liuzuyi.exit;

import java.util.LinkedList;
import java.util.List;

import android.app.Activity;
import android.app.Application;

public class Exitactivity extends Application {
	
	
	private List activityList=new LinkedList();

	 private static Exitactivity instance;
	
	 private Exitactivity()
	 {
	  }
	 //單例模式中獲取唯一的ExitApplication 實例
	 public static Exitactivity getInstance()
	 {
	  if(null == instance)
	   {
	     instance = new Exitactivity();
	   }
      return instance;
	
	 }
	 //添加Activity 到容器中
	 public void addActivity(Activity activity)
	 {
	 activityList.add(activity);
	 }
	 //遍歷所有Activity 並finish
	
	 public void exit()
	 {
	
	 for(Activity activity:activityList)
	  {
	    activity.finish();
	  }
	
	   System.exit(0);
	
	 }
	}

MainActivity:

package com.liuzuyi.exit;

import android.app.Activity;
import android.app.AlertDialog;
import android.app.AlertDialog.Builder;
import android.content.DialogInterface;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.Toast;

public class MainActivity extends Activity {
	private Button next;
	private Button exit;
	 int i = 0;
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		
		next=(Button)findViewById(R.id.button2);
		exit=(Button)findViewById(R.id.button1);
	
		next.setOnClickListener(l);
		
		exit.setOnClickListener(ll);
		 Exitactivity.getInstance().addActivity(this);
	  } 
	OnClickListener l = new OnClickListener() {
		
		public void onClick(View v) {
			 Intent intent=new Intent(MainActivity.this,TwoActivity.class);
			 startActivity(intent);		
		}
	};
	OnClickListener ll = new OnClickListener() {
		
		@Override
		public void onClick(View v) {
			 builddialog();	
		}
	}; 
	public void builddialog()
	{
		AlertDialog.Builder  ad = new Builder(MainActivity.this) ;
		ad.setTitle("退出應用");
		ad.setMessage("是否退出應用？");	
		ad.setPositiveButton("確認", new DialogInterface.OnClickListener() {
			  public void onClick(DialogInterface dialog, int which) {
				Exitactivity.getInstance().exit();	
			  } }
		);
			  ad.setNegativeButton("取消", new DialogInterface.OnClickListener() {
			   public void onClick(DialogInterface dialog, int which) {
		     	dialog.dismiss();
			   }			 
			 });
		ad.create().show();		
	}
 
	}