Android四大组件之广播接收器 Broadcast Receiver

对《第一行代码——android》的读书笔记

广播的类型：

       1.标准广播：一种完全异步的广播，在广播发出后，所有的广播接收器几乎都会在同一时刻接收到这条广播消息，因此他们之间没有任何前后顺序可言。这种广播效率高，但 

         是同时也意味着他是无法被截断的。

       2.有序广播：一种同步执行的广播，同一时刻只有一个广播接收器能够收到这条广播。优先级高的会先收到这条广播，并且前面的广播接收器可以截断这条广播。

接收系统广播：

       Android系统内置了许多系统级别的广播，比如电量的广播，位置信息变更的广播。接受这些广播就需要广播接收器。

       注册广播的形式一般有两种：动态在代码中注册或者在AndroidManifest.xml中注册。

广播接收器创建：

      新建一个类继承BroadcastReceiver，并重写父类的onReceive()方法。当有广播到来，onReceive()方法就会得到执行，具体的逻辑就在这个方法中处理。

      我们的广播接收器想要监听什么广播，就相应的添加action

      动态注册监听网络变化

调用registerReceiver（）进行注册 

intentFilter=new IntentFilter();
intentFilter.addAction("android.net.conn.CONNECTIVITY_CHANGE");
net=new NetworkChangeReceiver();
registerReceiver(net, intentFilter);

class NetworkChangeReceiver extends BroadcastReceiver{@Overridepublic void onReceive(Context context, Intent intent) {// TODO Auto-generated method stubConnectivityManager connectionManager=(ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);NetworkInfo networkinfo=connectionManager.getActiveNetworkInfo();if(networkinfo!=null&&networkinfo.isAvailable()){Toast.makeText(context, "有网络", Toast.LENGTH_LONG).show();}else{Toast.makeText(context, "mei有网络", Toast.LENGTH_LONG).show();}}

通过getSystemService得到ConnectivityManager的实例，这是一个系统服务类，专门用来管理网络连接。然后调用getActiveNetworkInfo得到networkinof实例，接着调用isAvailable就可以判断当前是否有网络

动态注册的广播接收器一定要取消注册才行

protected void onDestroy(){
super.onDestroy();
unregisterReceiver(net);
}

  静态注册实现了开机启动

     动态注册的滚广播接收器可以*的控制注册与注销，但有一个缺点，即必须在程序启动后才能接受到广播，所以需要静态注册。

   

public class BootCompleteReceiver extends BroadcastReceiver {

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

}

  <receiver android:name=".BootCompleteReceiver" >            <intent-filter>                <action android:name="android.intent.action.BOOT_COMPLETED" />            </intent-filter>        </receiver>

所有静态注册的广播都在receiver中进行注册，通过android:name=".BootCompleteReceiver" 指定具体注册哪一个广播接收器，然后在《intent-filter>标签里加入想要接受的广播就行了。由于Android系统启动后会发出android.intent.action.BOOT_COMPLETED的广播，因此在这添加了相应的action

发送自定义广播

    发送标准广播

        Intent inten t=new intent("antion");

        sendBroadcast(intent);

    发送有序广播

        intent intent =new intent("action");

        sendOrderedBroadcast(intent,null);

   截断广播  abortBroadcast();

使用本地广播

使用这种机制的广播只能在应用程序的内部进行传递，并且广播接收器只能接受来自本应用程序发出的广播。

public class MainActivity extends Activity {

private IntentFilter intentFilter;

private LocalReceiver localReceiver;

private LocalBroadcastManager localBroadcastManager;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
localBroadcastManager = LocalBroadcastManager.getInstance(this);
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");
localBroadcastManager.sendBroadcast(intent);
}
});
intentFilter = new IntentFilter();
intentFilter.addAction("com.example.broadcasttest.LOCAL_BROADCAST");
localReceiver = new LocalReceiver();
localBroadcastManager.registerReceiver(localReceiver, intentFilter);
}

@Override
protected void onDestroy() {
super.onDestroy();
localBroadcastManager.unregisterReceiver(localReceiver);
}

class LocalReceiver extends BroadcastReceiver {

@Override
public void onReceive(Context context, Intent intent) {
Toast.makeText(context, "received local broadcast",
Toast.LENGTH_SHORT).show();
}

}

}

这是添加了LocalBroadcastManager对发送，注册 销毁进行了管理

需要注意的是：本地广播无法通过静态注册的方法来接受。    

广播的最佳实践----实现强制下线功能

创建ActivityCollector类用于管理所有的活动

public class ActivityCollector {

private 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);
}

}

登录页面

public class LoginActivity extends BaseActivity {

private SharedPreferences pref;

private SharedPreferences.Editor editor;

private EditText accountEdit;

private EditText passwordEdit;

private Button login;

private CheckBox rememberPass;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.login);
pref = PreferenceManager.getDefaultSharedPreferences(this);
accountEdit = (EditText) findViewById(R.id.account);
passwordEdit = (EditText) findViewById(R.id.password);
rememberPass = (CheckBox) findViewById(R.id.remember_pass);
login = (Button) findViewById(R.id.login);
boolean isRemember = pref.getBoolean("remember_password", false);
if (isRemember) {
String account = pref.getString("account", "");
String password = pref.getString("password", "");
accountEdit.setText(account);
passwordEdit.setText(password);
rememberPass.setChecked(true);
}
login.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
String account = accountEdit.getText().toString();
String password = passwordEdit.getText().toString();
if (account.equals("admin") && password.equals("123456")) {
editor = pref.edit();
if (rememberPass.isChecked()) {
editor.putBoolean("remember_password", true);
editor.putString("account", account);
editor.putString("password", password);
} else {
editor.clear();
}
editor.commit();
Intent intent = new Intent(LoginActivity.this, MainActivity.class);
startActivity(intent);
finish();
} else {
Toast.makeText(LoginActivity.this,
"account or password is invalid",
Toast.LENGTH_SHORT).show();
}
}
});
}

}

发送广播

public class MainActivity extends BaseActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button forceOffline = (Button) findViewById(R.id.force_offline);
forceOffline.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
Intent intent = new Intent(
"com.example.broadcastbestpractice.FORCE_OFFLINE");
sendBroadcast(intent);
}
});
}

}

广播接收器类

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);//对话框设置为不可取消
dialogBuilder.setPositiveButton("OK",
new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
ActivityCollector.finishAll();
Intent intent = new Intent(context, LoginActivity.class);intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);//在广播接收其中必须加入加入一个标志
context.startActivity(intent);
}
});
AlertDialog alertDialog = dialogBuilder.create();
alertDialog.getWindow().setType(
WindowManager.LayoutParams.TYPE_SYSTEM_ALERT);//设置类型 保证在接受器中可以弹出
alertDialog.show();
}

}

进行权限设置和注册

弹出一个系统级别的对话框，必须声明 <uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW" />

并制定接受

<receiver android:name=".ForceOfflineReceiver" >
            <intent-filter>
                <action android:name="com.example.broadcastbestpractice.FORCE_OFFLINE" />
            </intent-filter>
        </receiver>