（八）Android广播接收器BroadcastReceiver
一、使用Broadcast Reciver
1.右击java文件夹，new->other->Broadcast Receiver后会在AndroidManifest.xml文件中生成一个receiver项
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.shiyanshi.learnbroadcast" >
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name=".MainActivity"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<receiver
android:name=".MyReceiver"
android:enabled="true"
android:exported="true" >
</receiver>
</application>
</manifest>
2.同时生成了一个MyReceiver 的类，该类中onReceive用于响应sendBroadcast函数发送的消息
package com.example.shiyanshi.learnbroadcast;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
public class MyReceiver extends BroadcastReceiver {
public MyReceiver() {
}
@Override
public void onReceive(Context context, Intent intent) {
// TODO: This method is called when the BroadcastReceiver is receiving
// an Intent broadcast.
// throw new UnsupportedOperationException("Not yet implemented");
System.out.println("Recv Data:"+intent.getStringExtra("data"));
}
}
3.调用sendBroadcast函数进行发送消息，该函数需要一个Intent
package com.example.shiyanshi.learnbroadcast;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
public class MainActivity extends Activity implements View.OnClickListener {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
findViewById(R.id.btnSendMsg).setOnClickListener(this);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
@Override
public void onClick(View view) {
switch (view.getId()){
case R.id.btnSendMsg:
Intent intent =new Intent(this,MyReceiver.class);
intent.putExtra("data","henry");
sendBroadcast(intent);
break;
}
}
}
二、动态注册和注销
1.删去AndroidManifest.xml文件中的receiver时，需要动态注册和注销，才能发送和接收消息
<receiver
android:name=".MyReceiver"
android:enabled="true"
android:exported="true" >
</receiver>
2.MainActivity更改如下：发送消息消息时，Intent要使用隐式Intent（MyReceiver.ACTION为定义的一个常量字符串
public static final String ACTION="com.example.shiyanshi.learnbroadcast.intent.action.MyReceiver";//前半部分时包名，后半部分时intent的格式，MyReceiver是上述中用于
响应sendBroadcast的类），注册时使用registerReceiver函数，注销时使用unregisterReceiver函数
函数原型为：
public Intent registerReceiver(BroadcastReceiver receiver, IntentFilter filter)
public void unregisterReceiver(BroadcastReceiver receiver)
receiver是我们新建Broadcast时声称的用于响应sendBroadcast的MyReceiver类，filter是过滤器，需想起传递隐式Intent类似的参数。
public class MainActivity extends Activity implements View.OnClickListener {
private MyReceiver receiver=null;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
findViewById(R.id.btnSendMsg).setOnClickListener(this);
findViewById(R.id.btnRegister).setOnClickListener(this);
findViewById(R.id.btnUnregister).setOnClickListener(this);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
@Override
public void onClick(View view) {
switch (view.getId()){
case R.id.btnSendMsg:
// Intent intent =new Intent(this,MyReceiver.class);
//动态注册和注销时要使用隐式Intent，而不能使用显示Intent了
Intent intent=new Intent(MyReceiver.ACTION);
intent.putExtra("data","henry");
sendBroadcast(intent);
break;
case R.id.btnRegister:
if (receiver==null){
receiver=new MyReceiver();
registerReceiver(receiver,new IntentFilter(MyReceiver.ACTION));
}
break;
case R.id.btnUnregister:
if(receiver!=null){
unregisterReceiver(receiver);
receiver=null;
}
break;
}
}
}
三、Broadcast的优先级
当发送数据时，采用隐式Intent的形式（如上），两个receiver中的action name相同时，二者可以同时接收到数据。
默认情况下最后写的那个receiver所对应的优先级高，此外可以显示的在receiver下的Intent-filter中指明优先级priority，其数值越大，优先级越高，越先响应数据
<receiver
android:name=".MyReceiver1"
android:enabled="true"
android:exported="true" >
<intent-filter android:priority="2">
<action android:name="com.example.shiyanshi.learnbroadcast.intent.action.MyReceiver"/>
</intent-filter>
</receiver>
<receiver android:name=".MyReceiver"
android:enabled="true"
android:exported="true">
<intent-filter android:priority="1">
<action android:name="com.example.shiyanshi.learnbroadcast.intent.action.MyReceiver"/>
</intent-filter>
</receiver>
</application>
此外，当优先级高的那个onReceive执行后，可以在其中调用abortBroadcast来终止数据的传递，优先级别低的onReceive便不会执行了.
注意：若想使用abortBroadcast函数，发送时需使用sendOrderedBroadcast而非sendBroadcast，否则会弹出错误java.lang.RuntimeException: BroadcastReceiver trying to return result during a non-ordered broadcast。
Intent intent=new Intent(MyReceiver.ACTION);
intent.putExtra("data","henry");
// sendBroadcast(intent);
sendOrderedBroadcast(intent,null);
其中sendOrderedBroadcast的第二个参数用来指明权限，可以为空
