《第一行代码》 随手笔记——第五章 广播机制

5.2.1动态注册监听网络变化public class MainActivity extends Activity {private IntentFilter intentFilter;private NetworkChangeReceiver networkChangeReceiver;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);intentFilter = new IntentFilter();intentFilter.addAction("android.net.conn.CONNECTIVITY_CHANGE");networkChangeReceiver = new NetworkChangeReceiver();registerReceiver(networkChangeReceiver, intentFilter);}@Overrideprotected void onDestroy() {super.onDestroy();unregisterReceiver(networkChangeReceiver);//动态注册的广播接收器一定都要取消注册}class NetworkChangeReceiver extends BroadcastReceiver {@Overridepublic void onReceive(Context context, Intent intent) {<p><strong><span style="white-space:pre"> </span>ConnectivityManager connectionManager = (ConnectivityManager)</strong></p><p>                    <strong>getSystemService(Context.CONNECTIVITY_SERVICE);</strong></p><p><strong>            NetworkInfo networkInfo =connectionManager.getActiveNetworkInfo();</strong></p><p><strong>            if (networkInfo !=null && networkInfo.isAvailable()) {</strong></p><p><strong>                Toast.makeText(context,"network is available",</strong></p><p><strong>                        Toast.LENGTH_SHORT).show();</strong></p><p><strong>            } else {</strong></p><p><strong>                Toast.makeText(context,"network is unavailable",</strong></p><p><strong>                        Toast.LENGTH_SHORT).show();</strong></p><p><strong>            }</strong></p>}}}AndroidManifest.xml 配置权限<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>5.2.2 静态注册广播实现开机启动新建一个BootCompleteReceiver继承自BroadcastReceiver，代码如下所示：

public class BootCompleteReceiver extends BroadcastReceiver {

@Override
public void onReceive(Context context, Intent intent) {
Toast.makeText(context, "Boot Complete", Toast.LENGTH_LONG).show();
}

}

配置Androidmanifest文件

<manifest xmlns:android="http://schemas.android.com/apk/res/android"package="com.example.broadcasttest"android:versionCode="1"android:versionName="1.0" >……<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" /><uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED" /><applicationandroid:allowBackup="true"android:icon="@drawable/ic_launcher"android:label="@string/app_name"android:theme="@style/AppTheme" >……<receiver android:name=".BootCompleteReceiver" ><intent-filter><action android:name="android.intent.action.BOOT_COMPLETED" /></intent-filter></receiver></application></manifest>

5.3 发送有序广播button.setOnClickListener(new OnClickListener() {@Overridepublic void onClick(View v) {Intent intent = new Intent("com.example.broadcasttest. MY_BROADCAST");<strong>sendOrderedBroadcast(intent, null);</strong>}});

<manifest xmlns:android="http://schemas.android.com/apk/res/android"package="com.example.broadcasttest"android:versionCode="1"android:versionName="1.0" >……<applicationandroid:allowBackup="true"android:icon="@drawable/ic_launcher"android:label="@string/app_name"android:theme="@style/AppTheme" >……<receiver android:name=".MyBroadcastReceiver"><strong><intent-filter android:priority="100" ></strong><action android:name="com.example.broadcasttest.MY_BROADCAST"/></intent-filter></receiver></application></manifest>

android:priority属性给广播接收器设置了优先级public class MyBroadcastReceiver extends BroadcastReceiver {@Overridepublic void onReceive(Context context, Intent intent) {Toast.makeText(context, "received in MyBroadcastReceive", Toast.LENGTH_SHORT).show();abortBroadcast();}}如果在onReceive()方法中调用了abortBroadcast()方法，就表示将这条广播截断。5.4 本地广播public class MainActivity extends Activity {private IntentFilter intentFilter;<strong> private LocalReceiver localReceiver;private LocalBroadcastManager localBroadcastManager;</strong>@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);<strong>localBroadcastManager = LocalBroadcastManager.getInstance(this); // 获取实例</strong>Button button = (Button) findViewById(R.id.button);button.setOnClickListener(new OnClickListener() {@Overridepublic void onClick(View v) {Intent intent = new Intent("com.example.broadcasttest. LOCAL_BROADCAST");<strong>localBroadcastManager.sendBroadcast(intent); // 发送本地广播</strong>}});intentFilter = new IntentFilter();intentFilter.addAction("com.example.broadcasttest.LOCAL_BROADCAST");localReceiver = new LocalReceiver();<strong>localBroadcastManager.registerReceiver(localReceiver, intentFilter); // 注册本地广播监听器</strong>}@Overrideprotected void onDestroy() {super.onDestroy();<strong>localBroadcastManager.unregisterReceiver(localReceiver);//注销广播</strong>}class LocalReceiver extends BroadcastReceiver {@Overridepublic void onReceive(Context context, Intent intent) {Toast.makeText(context, "received local broadcast", Toast.LENGTH_SHORT).show();}}}本地广播是无法通过静态注册的方式来接收的使用本地广播的几点优势1.        可以明确地知道正在发送的广播不会离开我们的程序，因此不需要担心机密数据泄漏的问题。2.        其他的程序无法将广播发送到我们程序的内部，因此不需要担心会有安全漏洞的隐患。3.        发送本地广播比起发送系统全局广播将会更加高效。5.5 广播的最佳实践——实现强制下线先创建一个ActivityCollector类用于管理所有的活动，代码如下所示：

public class ActivityCollector {public static List<Activity> activities = new ArrayList<Activity>();public static void addActivity(Activity activity) {activities.add(activity);}public static void removeActivity(Activity activity) {activities.remove(activity);}public static void finishAll() {for (Activity activity : activities) {if (!activity.isFinishing()) {activity.finish();}}}}

创建BaseActivity类作为所有活动的父类public class BaseActivity extends Activity {@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);ActivityCollector.addActivity(this);}@Overrideprotected void onDestroy() {super.onDestroy();ActivityCollector.removeActivity(this);}}广播接收器public class ForceOfflineReceiver extends BroadcastReceiver {@Overridepublic void onReceive(final Context context, Intent intent) {AlertDialog.Builder dialogBuilder = new AlertDialog.Builder(context);dialogBuilder.setTitle("Warning");dialogBuilder.setMessage("You are forced to be offline. Please try to login again.");dialogBuilder.setCancelable(false);dialogBuilder.setPositiveButton("OK",new DialogInterface.OnClickListener() {@Overridepublic void onClick(DialogInterface dialog, int which) {ActivityCollector.finishAll(); // 销毁所有活动Intent intent = new Intent(context, LoginActivity.class);intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);context.startActivity(intent); // 重新启动LoginActivity}});AlertDialog alertDialog = dialogBuilder.create();// 需要设置AlertDialog的类型，保证在广播接收器中可以正常弹出alertDialog.getWindow().setType(WindowManager.LayoutParams.TYPE_SYSTEM_ALERT);alertDialog.show();}}首先肯定是使用AlertDialog.Builder来构建一个对话框，注意这里一定要调用setCancelable()方法将对话框设为不可取消，否则用户按一下Back键就可以关闭对话框继续使用程序了。然后使用setPositiveButton()方法来给对话框注册确定按钮，当用户点击了确定按钮时，就调用ActivityCollector的finishAll()方法来销毁掉所有活动，并重新启动LoginActivity这个活动。另外，由于我们是在广播接收器里启动活动的，因此一定要给Intent加入FLAG_ACTIVITY_NEW_TASK这个标志。最后，还需要把对话框的类型设为TYPE_SYSTEM_ALERT，不然它将无法在广播接收器里弹出。由于我们在ForceOfflineReceiver里弹出了一个系统级别的对话框，因此必须要声明android.permission.SYSTEM_ALERT_WINDOW权限<uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW" />