3.12. Android broadcast receiver (Broadcast Receivers)

Broadcast receivers are used to respond to broadcast messages from other applications or systems. These messages are sometimes called events or intentions. For example, an application can initialize a broadcast to let other applications know that some data has been downloaded to the device and can be used by them. In this way, the broadcast receiver can define the appropriate actions to intercept these communications.

There are two important steps to make the broadcast intention of the system work with the broadcast receiver.

Create a broadcast receiver
Register a broadcast receiver

As an additional step, to achieve custom intentions, you must create and broadcast them.

3.12.1. Create a broadcast receiver ¶

The broadcast receiver needs to be implemented as BroadcastReceiver Class and overrides the onReceive() Method to receive a Intent A message whose object is a parameter.

public class MyReceiver extends BroadcastReceiver {
   @Override
   public void onReceive(Context context, Intent intent) {
      Toast.makeText(context, "Intent Detected.", Toast.LENGTH_LONG).show();
   }
}

3.12.2. Register a broadcast receiver ¶

The application passes through the AndroidManifest.xml Register a broadcast receiver in to listen for established broadcast intentions. Suppose we are going to register MyReceiver to listen for what the system generates ACTION_BOOT_COMPLETED Events. This event is issued when the startup process of the Android system is complete.

<application
   android:icon="@drawable/ic_launcher"
   android:label="@string/app_name"
   android:theme="@style/AppTheme" >
   <receiver android:name="MyReceiver">

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

   </receiver>
</application>

Now, whenever the Android device is activated, it will be broadcast by the receiver MyReceiver Intercepted, and in the onReceive() The logic implemented in the.

There are many system-generated events that are defined as classes Intent The static constant value in the. The following table lists important system events.

Event constant	Description
android.intent.action.BATTERY_CHANGED	A persistent broadcast that contains battery charging status, level and other information.
android.intent.action.BATTERY_LOW	Identifies the low power condition of the device.
android.intent.action.BATTERY_OKAY	Indicates that the battery is ready now after the battery is low.
android.intent.action.BOOT_COMPLETED	Broadcast once after the system has finished booting.
android.intent.action.BUG_REPORT	Displays the activity for reporting bug.
android.intent.action.CALL	Someone who performs the call data assignment.
android.intent.action.CALL_BUTTON	The user clicks the “call” button to open the dialer or other appropriate dialing interface.
android.intent.action.DATE_CHANGED	The date has changed.
android.intent.action.REBOOT	The device restarts.

3.12.3. Broadcast custom intent ¶

If you want to generate and send custom intentions in your application, you need to pass the sendBroadcast() To create and send these intentions. If you use the sendStickyBroadcast(Intent) Method, the intention is sticky, which means that the intention you send is maintained after the broadcast is completed.

public void broadcastIntent(View view)
{
   Intent intent = new Intent();
   intent.setAction("com.runoob.CUSTOM_INTENT");
   sendBroadcast(intent);
}

com.runoob.CUSTOM_INTENT The intention can be registered like the intention generated by our registration system before.

<application
   android:icon="@drawable/ic_launcher"
   android:label="@string/app_name"
   android:theme="@style/AppTheme" >
   <receiver android:name="MyReceiver">

      <intent-filter>
         <action android:name="com.runoob.CUSTOM_INTENT">
         </action>
      </intent-filter>

   </receiver>
</application>

3.12.4. Example ¶

This example explains how to create a broadcast receiver to intercept custom intentions. Once you are familiar with custom intentions, you can program for the application to intercept the intentions generated by the system. Let’s follow the steps below to modify the Android application we created in the Hello World instance section.

Steps	Description
1	Use Android Studio to create the Android application and name it broadcastreceiver, and put it under the com.runoob.broadcastreceiver package in the Hello World instance chapter.
2	Modify the main active file MainActivity.java to add the broadcastIntent () method.
3	在com.runoob.broadcastreceiver包下创建名为MyReceiver.java的新的Java文件来定义广播接收器。
4	应用程序可以处理一个或多个自定义或者系统的意图，没有任何限制。每个你想拦截的意图都需要使用<receiver…/>标签在AndroidManifest.xml中注册。
5	修改res/layout/activity_main.xml文件中的默认内容来包含一个广播意图的按钮。
6	There is no need to modify the string file, Android Studio will pay attention to the string.xml file.
7	Start the Android emulator to run the application and verify the results of the application’s changes.

The following is the contents of the modified main active file src/com.runoob.broadcastreceiver/MainActivity.java. This file contains each basic lifecycle method. We added the broadcastIntent () method to broadcast custom events.

package com.runoob.broadcastreceiver;

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.content.Intent;
import android.view.View;

public class MainActivity extends Activity {

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

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    // 广播自定义意图
    public void broadcastIntent(View view){
        Intent intent = new Intent();
        intent.setAction("cn.programmer.CUSTOM_INTENT");
        sendBroadcast(intent);
    }
}

下面是src/com.runoob.broadcastreceiver/MyReceiver.java的内容：

package com.runoob.broadcastreceiver;

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.widget.Toast;

public class MyReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        Toast.makeText(context, "检测到意图。", Toast.LENGTH_LONG).show();
    }
}

Next, modify AndroidManifest.xml Files. Here by adding <receiver.../> Tags to contain our broadcast receivers:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.runoob.broadcastreceiver"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="22" />

    <application
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >

        <activity
            android:name=".MainActivity"
            android:label="@string/title_activity_main" >

            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER"/>
            </intent-filter>

        </activity>

        <receiver android:name="MyReceiver">

            <intent-filter>
                <action android:name="cn.programmer.CUSTOM_INTENT">
                </action>
            </intent-filter>

        </receiver>

    </application>

</manifest>

The following is res/layout/activity_main.xml The contents of the file that contains buttons to broadcast custom intentions.

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
    android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">

    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="广播实例"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:textSize="30dp" />

    <TextView
        android:id="@+id/textView2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="www.runoob.com"
        android:textColor="#ff87ff09"
        android:textSize="30dp"
        android:layout_above="@+id/imageButton"
        android:layout_centerHorizontal="true"
        android:layout_marginBottom="40dp" />

    <ImageButton
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/imageButton"
        android:src="@drawable/ic_launcher"
        android:layout_centerVertical="true"
        android:layout_centerHorizontal="true" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/button2"
        android:text="广播意图"
        android:onClick="broadcastIntent"
        android:layout_below="@+id/imageButton"
        android:layout_centerHorizontal="true" />

</RelativeLayout>

The following is res/values/strings.xml The contents of the file define two new constants.

<?xml version="1.0" encoding="utf-8"?>
<resources>

    <string name="app_name">Android Broadcast Receiver</string>
    <string name="action_settings">Settings</string>
    <string name="menu_settings">Settings</string>
    <string name="title_activity_main">Main Activity</string>

</resources>

Let’s run the Hello World we just modified! Applications. I assume that you have created AVD when you installed the environment. Open the active file in your project and click the icon in the toolbar to run the application in Android Studio. Android Studio installs the application on AVD and starts it. If all goes well, it will be displayed on the simulator window as follows:

Now click the “broadcast intention” button to broadcast our custom intention. This will broadcast our custom intent “cn.programmer.CUSTOM_INTENT” in our registered broadcast receiver MyReceiver Intercept and execute the logic we implemented in the. The bottom of the simulator will appear toast . As follows:

You can try to implement other broadcast receivers to intercept the intentions generated by the system, such as system startup, date change, and low power.