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{

		@Override
		public void onReceive(Context context, Intent intent) {
			// TODO Auto-generated method stub
			ConnectivityManager 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自由的控制注册与注销，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>