Android广播机制

Android广播机制 Android 广播机制 1.广播机制简介

Android中的广播主要分为标准广播和有序广播.
标准广播（Normal broadcasts）是一种完全异步执行的广播，在广播发出之后，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，因此它们之间没有任何先后顺序可 言。这种广播的效率会比较高，但同时也意味着它是无法被截断的。
有序广播（Orderedbroadcasts）则是一种同步执行的广播，在广播发出之后，同一时刻 只会有一个广播接收器能够收到这条广播消息，当这个广播接收器中的逻辑执行完毕后，广 播才会继续传递。所以此时的广播接收器是有先后顺序的，优先级高的广播接收器就可以先 收到广播消息，并且前面的广播接收器还可以截断正在传递的广播，这样后面的广播接收器 就无法收到广播消息了。

2.接收系统广播

广播接收器可以自由地对自己感兴趣的广播进行注册,这样当有相应的广播发出时,广播接收器就能够接收到该广播,并在内部处理相应的逻辑…注册广播的方式有动态和静态注册.

1.动态注册监听事件变化

public class MainActivity extends AppCompatActivity {
    private IntentFilter intentFilter;
    private NetworkChangeReceiver networkChangeReceiver;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        intentFilter=new IntentFilter();
        //广播监听器所要监听的广播,添加相应的action
        intentFilter.addAction("android.net.conn.CONNECTIVITY_CHANGE");
        //进行注册
        networkChangeReceiver=new NetworkChangeReceiver();
        registerReceiver(networkChangeReceiver,intentFilter);
    }
    @Override
    protected void onDestroy() {
        super.onDestroy();
        //取消注册
        unregisterReceiver(networkChangeReceiver);
    }
    //每当网络状态发生变化时,onReceive()方法就会得到执行
    class NetworkChangeReceiver extends BroadcastReceiver{
        @Override
        public void onReceive(Context context, Intent intent) {
            Toast.makeText(context,"network changes",Toast.LENGTH_SHORT).show();
        }
    }
}

进一步优化

public class MainActivity extends AppCompatActivity {
    private IntentFilter intentFilter;
 class NetworkChangeReceiver extends BroadcastReceiver{
        @Override
        public void onReceive(Context context, Intent intent) {
        //getSystemService()方法得到了ConnectivityManager的实例,这是一个系统服务类,专门用于管理网络连接的.
            ConnectivityManager connectivityManager=(ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
            NetworkInfo networkInfo= connectivityManager.getActiveNetworkInfo();
            //isAvailable()判断是否有网络
            if(networkInfo!=null&& networkInfo.isAvailable()){
                Toast.makeText(context,"network changes",Toast.LENGTH_SHORT).show();
            }else{
                Toast.makeText(context,"network is unavailable",Toast.LENGTH_SHORT).show();
            }
        }
    }
}

AndroidManifest文件,设置访问系统网络状态的权限.

2.静态注册实现开机启动

New->Other->Broadcast Receiver自动创建广播接收器.

public class BootCompleteReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        // TODO: This method is called when the BroadcastReceiver is receiving
        // an Intent broadcast.
        Toast.makeText(context,"Boot Complete",Toast.LENGTH_LONG).show();
    }
}

AndroidManifest.xml

            
                
            
        
        ......
 

3.发送自定义广播 1.发送标准广播

//收到自定义广播就会d出提示
public class MyBroadcastReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        Toast.makeText(context, "received in MyBroadcastReceiver", Toast.LENGTH_SHORT).show();
    }
}

AndroidManifast.xml

在activity_main.xml中

public class MainActivity extends AppCompatActivity {
    private IntentFilter intentFilter;
     class NetworkChangeReceiver extends BroadcastReceiver{
        @Override
        public void onReceive(Context context, Intent intent) {
            ConnectivityManager connectivityManager=(ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
            NetworkInfo networkInfo= connectivityManager.getActiveNetworkInfo();
            if(networkInfo!=null&& networkInfo.isAvailable()){
                Toast.makeText(context,"network changes",Toast.LENGTH_SHORT).show();
            }else{
                Toast.makeText(context,"network is unavailable",Toast.LENGTH_SHORT).show();
            }
        }
    }
 @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button button=(Button) findViewById(R.id.button);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent=new Intent("com.example.broadcasttest.MY_BROADCAST");
                sendBroadcast(intent);
            }
        });
    }
}

2.发送有序广播

新建一项目,新建AnotherBroadcastReceiver

public class AnotherBroadcastReceiver extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {

            Toast.makeText(context, "received in AnotherBroadcastReceiver", Toast.LENGTH_SHORT).show();
    }
}

在AndroidManifest.xml中修改

将原项目修改

public class MainActivity extends AppCompatActivity {
    private IntentFilter intentFilter;
     class NetworkChangeReceiver extends BroadcastReceiver{
        @Override
        public void onReceive(Context context, Intent intent) {
            ConnectivityManager connectivityManager=(ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
            NetworkInfo networkInfo= connectivityManager.getActiveNetworkInfo();
            if(networkInfo!=null&& networkInfo.isAvailable()){
                Toast.makeText(context,"network changes",Toast.LENGTH_SHORT).show();
            }else{
                Toast.makeText(context,"network is unavailable",Toast.LENGTH_SHORT).show();
            }
        }
    }
 @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Button button=(Button) findViewById(R.id.button);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent=new Intent("com.example.broadcasttest.MY_BROADCAST");
                //修改此处
               sendOrderedBroadcast(intent,null);
            }
        });
    }
}

定义先后顺序
AndroidManifest.xml中

public class MyBroadcastReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        Toast.makeText(context, "received in MyBroadcastReceiver", Toast.LENGTH_SHORT).show();
        abortBroadcast();
    }
}

4.使用本地广播

Android引入了一套本地广播机制,这个机制发出的广播只能够在应用程序内部进行传递,并且广播的接收器也只能接受来自本应用程序发出的广播.

public class MainActivity extends AppCompatActivity {
    private IntentFilter intentFilter;
    private LocalReceiver localReceiver;
    private LocalBroadcastManager localBroadcastManager;

    class NetworkChangeReceiver extends BroadcastReceiver{
        @Override
        public void onReceive(Context context, Intent intent) {
            ConnectivityManager connectivityManager=(ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
            NetworkInfo networkInfo= connectivityManager.getActiveNetworkInfo();
            if(networkInfo!=null&& networkInfo.isAvailable()){
                Toast.makeText(context,"network changes",Toast.LENGTH_SHORT).show();
            }else{
                Toast.makeText(context,"network is unavailable",Toast.LENGTH_SHORT).show();
            }
        }
    }

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        //获取实例
        localBroadcastManager=LocalBroadcastManager.getInstance(this);
        Button button=(Button) findViewById(R.id.button);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent=new Intent("com.example.broadcasttest.LOCAL_BROADCAST");
                localBroadcastManager.sendBroadcast(intent);//发送本地广播
           }
        });
        intentFilter=new IntentFilter();
        intentFilter.addAction("com.example.broadcasttest.LOCAL_BROADCAST");
        localReceiver=new LocalReceiver();
        localBroadcastManager.registerReceiver(localReceiver,intentFilter);//注册本地广播监听其
    }

    @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();
        }
    }
}

本地广播的优势
1.可以明确的知道正在发送的广播不会离开我们的程序,因此不必担心机密数据泄露.
2.其他的程序无法将广播发送到我们的程序的内部,因此不需要担心会有安全漏洞的隐患.
3.发送本地广播比发送系统全局广播将会更加高效.