Android四大组件之————广播

1. 定义

广播，是一个全局的监听器，属于Android四大组件之一.
Android 广播分为两个角色：广播发送者、广播接收者

2.广播接收器注册

注册的方式分为两种：静态注册、动态注册

静态注册:在AndroidManifest.xml里通过<receive>标签声明
动态注册:在代码中调用Context.registerReceiver()方法

3.广播接收代码案例(监听网络状态,动态注册)

①自定义一个类继承BroadcastReceiver

public class MyReceiver extends BroadcastReceiver {

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

        //获取网络管理器类
        ConnectivityManager connectivityManager = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
        //网络信息
        NetworkInfo networkInfo = connectivityManager.getActiveNetworkInfo();

        if (networkInfo != null && networkInfo.isAvailable()) {
            Toast.makeText(context, "有网！", Toast.LENGTH_SHORT).show();
        } else {
            Toast.makeText(context, "没网！", Toast.LENGTH_SHORT).show();
        }
    }
}

②动态注册广播

public class MainActivity extends AppCompatActivity {

    private MyReceiver receiver;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        //注册广播
        receiver = new MyReceiver();
        IntentFilter intentFilter = new IntentFilter();
        intentFilter.addAction("android.net.conn.CONNECTIVITY_CHANGE");//接收网络变化

        registerReceiver(receiver,intentFilter);
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        unregisterReceiver(receiver);//注销广播
    }
}

③AndroidManifest.xml

  <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />

4.广播接收(开启状态,静态注册)

①静态注册

public class MyReceiver2 extends BroadcastReceiver {
    //广播接收器：接收系统开机广播
    @Override
    public void onReceive(Context context, Intent intent) {
        Toast.makeText(context, "开机完成！", Toast.LENGTH_SHORT).show();
    }
}

②AndroidManifest.xml,创建广播时选择New——Other——Broadcast Receiver会自动生成下面的标签

        <receiver
            android:name=".reciver.MyReceiver2"
            android:enabled="true"
            android:exported="true">
            <intent-filter>
                <action android:name="android.intent.action.BOOT_COMPLETED" />
            </intent-filter>
        </receiver>

5.广播发送

广播的类型主要分为5类：
普通广播（Normal Broadcast）
系统广播（System Broadcast）
有序广播（Ordered Broadcast）
粘性广播（Sticky Broadcast）
App应用内广播（Local Broadcast

下面只介绍了普通广播（标准广播）和有序广播

1.创建3个MyReceiver

public class MyReceiver01 extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {
        Toast.makeText(context, "MyReceiver01", Toast.LENGTH_SHORT).show();
    }
}

public class MyReceiver02 extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {
        Toast.makeText(context, "MyReceiver02", Toast.LENGTH_SHORT).show();
        abortBroadcast();//拦截广播
    }
}

public class MyReceiver03 extends BroadcastReceiver {

    @Override
    public void onReceive(Context context, Intent intent) {
        Toast.makeText(context, "MyReceiver03", Toast.LENGTH_SHORT).show();
    }
}

2.布局文件activity_main.xml

<Button
    android:text="标准"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:id="@+id/btn_send"/>
<Button
    android:text="无序"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"/>

3.MainActivity.java中

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

    private Button btn_send;
    private Button btn_sendOrder;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main2);
        initView();
    }

    private void initView() {
        btn_send = (Button) findViewById(R.id.btn_send);
        btn_sendOrder = (Button) findViewById(R.id.btn_sendOrder);

        btn_send.setOnClickListener(this);
        btn_sendOrder.setOnClickListener(this);
    }

    @Override
    public void onClick(View v) {
        switch (v.getId()) {
            case R.id.btn_send:
                Intent intent = new Intent("com.ABC");
                sendBroadcast(intent);//发送标准广播
                break;
            case R.id.btn_sendOrder:
                Intent intent2 = new Intent("com.ABC");
                sendOrderedBroadcast(intent2, null);//发送有序广播
                break;
        }
    }
}

3.清单文件，AndroidManifest.xml

        <receiver
            android:name=".reciver2.MyReceiver01"
            android:enabled="true"
            android:exported="true">
            <intent-filter android:priority="80">
                <action android:name="com.ABC" />
            </intent-filter>
        </receiver>

        <receiver
            android:name=".reciver2.MyReceiver02"
            android:enabled="true"
            android:exported="true">
            <intent-filter android:priority="90">
                <action android:name="com.ABC" />
            </intent-filter>
        </receiver>

        <receiver
            android:name=".reciver2.MyReceiver03"
            android:enabled="true"
            android:exported="true">
            <intent-filter android:priority="100">//priority是设置优先级，值越大越靠前
                <action android:name="com.ABC" />
            </intent-filter>
        </receiver>