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;@Overrideprotected 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);}@Overrideprotected void onDestroy() {if (mReceiver != null) {unregisterReceiver(mReceiver);}super.onDestroy();}class ExitappReceiver extends BroadcastReceiver {@Overridepublic 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;}@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(getLayoutResID());Button nextButton = (Button) findViewById(R.id.activity_two_button);nextButton.setOnClickListener(new OnClickListener() {@Overridepublic void onClick(View v) {sendBroadcast();}});}private void sendBroadcast() {Intent intent = new Intent();intent.setAction(BaseActivity.BROAD_CAST_MESSAGE);sendBroadcast(intent);}}
一个人身边的位置只有这么多，
