概述：

基于上一篇博客《Android退出程序（上）——单例模式》的学习，我们知道了如何利用单例和循环遍历的方式来退出我们的应用程序。这篇博客则要从另一个角度来解决问题——广播。即是，接收到一个关闭Activity的广播时，就去关闭当前Activity。

类图展示及说明：

从上面的类图中可以看到这里做了一个处理，而这个处理是学习面向对象的Coder要必须掌握的。这里就是对Activity进行了一个扩展——BaseActivity。如果我们要对每个Activity进行添加内部ExitappReceiver类的话，这样势必增加了代码量，且后期不好维护。所以这里就是把ExitappReceiver封装到了一个基础类中，然后让其他需要实现关闭activity的Activity来继承它就好了。

代码示例：

这里只贴出两个比较关键的代码：

1.接收事件

public class BaseActivity extends Activity {

    public static final String TAG = BaseActivity.class.getName();
    
    public static final String BROAD_CAST_MESSAGE = TAG + ".BROAD_CAST_MESSAGE";
    
    private ExitappReceiver mReceiver = null;
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        
        registerReceiver();
    }
    
    private void registerReceiver() {
        IntentFilter filter = new IntentFilter();  
        try {  
            if (mReceiver != null) {  
                unregisterReceiver(mReceiver);  
            }  
        } catch (Exception e) {  
            e.printStackTrace();  
        }  
          
        mReceiver = new ExitappReceiver();  
        filter.addAction(BROAD_CAST_MESSAGE);  
        registerReceiver(mReceiver, filter);
    }
    
    @Override
    protected void onDestroy() {
        if (mReceiver != null) {
            unregisterReceiver(mReceiver);
        }
        super.onDestroy();
    }
    
    class ExitappReceiver extends BroadcastReceiver {

        @Override
        public void onReceive(Context context, Intent intent) {
            if (intent.getAction().equals(BROAD_CAST_MESSAGE)) {
                finish();
            }
        }
    }
}

2.触发事件：

public class TwoActivity extends BaseActivity {

    private int getLayoutResID() {
        return R.layout.activity_two;
    }
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        
        setContentView(getLayoutResID());
        
        Button nextButton = (Button) findViewById(R.id.activity_two_button);
        nextButton.setOnClickListener(new OnClickListener() {
            
            @Override
            public void onClick(View v) {
                sendBroadcast();
            }
        });
    }
    
    private void sendBroadcast() {
        Intent intent = new Intent();
        intent.setAction(BaseActivity.BROAD_CAST_MESSAGE);
        sendBroadcast(intent);
    }
}