《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;
@Override
protected 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);
}
@Override
protected 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 {
@Override
public 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" />
<application
android: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() {
@Override
public 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" >
……
<application
android: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 {
@Override
public 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>
@Override
protected 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() {
@Override
public 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>
}
@Override
protected void onDestroy() {
super.onDestroy();
<strong>localBroadcastManager.unregisterReceiver(localReceiver);//注销广播</strong>
}
class LocalReceiver extends BroadcastReceiver {
@Override
public 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 {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
ActivityCollector.addActivity(this);
}
@Override
protected void onDestroy() {
super.onDestroy();
ActivityCollector.removeActivity(this);
}
}
广播接收器
public class ForceOfflineReceiver extends BroadcastReceiver {
@Override
public 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() {
@Override
public 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" />