广播机制简介
标准广播(Normal broadcasts)
完全异步执行的广播,广播发出后所有的广播接收器几乎在统一时刻收到这条广播信息,无法被截断。
有序广播(Ordered broadcasts)
同步执行的广播,广播发出后,同一时刻只会有一个广播接收器能收到这条广播消息,当广播接收器中的逻辑执行完毕后,广播才会继续传递。
接收系统广播
Android内置很多系统级别的广播,我们可以在应用程序中监听这些广播。这就需要广播接收器,下面将介绍其用法:
广播接受器可以对自己感兴趣的广播进行注册,这样当有相应广播发出时,接收器就能够收到。
注册广播的方式一般有两种,在代码中注册和在AndroidManifest.xml中注册,前者被称为动态注册,后者被称为静态注册
动态注册监听网络变化
public class MainActivity extends AppCompatActivity {
private IntentFilter intentFiler;
private NetworkChangeReceiver networkchangeReceiver;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
intentFiler = new IntentFilter();
intentFiler.addAction("android.net.conn.CONNECTIVITY_CHANGE");
networkchangeReceiver = new NetworkChangeReceiver();
registerReceiver(networkchangeReceiver,intentFiler);
}
@Override
protected void onDestroy() {
super.onDestroy();
unregisterReceiver(networkchangeReceiver);
}
class NetworkChangeReceiver extends BroadcastReceiver{
@Override
public void onReceive(Context context, Intent intent) {
Toast.makeText(context,"network changes",Toast.LENGTH_SHORT).show();
}
}
}
定义类NetworkChangeReceiver继承自BroadcastReceiver,重写onReceive()方法得到信息
在onCreat()方法中创建IntentFiler的实例。添加监听的广播
创建NetworkChangeReceiver的实例
调用registerReceiver()方法注册,将NetworkChangeReceive和InterFilter的实例传进去。
此时,NetworkChangeReceive就可以收到指定值的广播。
重写onDestroy()方法,加入
unregisterReceiver(networkchangeReceiver);
取消注册
优化代码
重写NetworkChangeReceiver类
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 is available",Toast.LENGTH_SHORT).show();
}else{
Toast.makeText(context,"network is not available",Toast.LENGTH_SHORT).show();
}
}
}
- 通过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。
- 调用ConnectivityManager的getActiveNetworkInfo()方法得到NetworkInfo实例
- 接着调用NetworkInfo的isAvailable()方法,判断是否有网络
在AndroidManifest,xml文件中加入权限:
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE"/>
静态注册实现开机启动
创建广播接收器
Exported:是否允许广播接收器接受程序以外信息
Enabled:是否启用这个广播接收器
修改BootCompleteReceiver中的代码
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_SHORT).show();
}
}
添加权限
<uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED"/>
修改AndroidManifest.xml
<receiver
android:name=".BootCompleteReceiver"
android:enabled="true"
android:exported="true">
<intent-filter>
<action android:name="android.intent.action.BOOT_COMPLETED"/>
</intent-filter>
</receiver>
发送自定义广播
新建广播接收器
在AndroidManifest.xml中
<receiver
android:name=".MyBroadcastReceiver"
android:enabled="true"
android:exported="true">
<intent-filter>
<action android:name="com.example.broadcasttest.MY_BROADCAST"/>
</intent-filter>
</receiver>
自定义广播名
- 发出对应的广播”com.example.broadcasttest.MY_BROADCAST”时接收器可以收到该广播
对于无法接收静态广播的情况(Android 8.0后):
加入
intent.setComponent(new ComponentName(getPackageName(), "包名"));
发送有序广播
- 将sendBroadcast()方法改为sendOrderBroadcast()方法,接收intent和null
- 设置优先级
<receiver
android:name=".MyBroadcastReceiver"
android:enabled="true"
android:exported="true">
<intent-filter android:priority="100">
<action android:name="com.example.broadcasttest01.MY_BROADCAST"/>
</intent-filter>
</receiver>
- 截断代码,在OnReceive()方法中添加abortBroadcast()方法。
使用本地广播
public class MainActivity extends AppCompatActivity {
private IntentFilter intentFilter;
private LocalReceiver localReceiver;
private LocalBroadcastManager localBroadcastManager;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button button = findViewById(R.id.button);
localBroadcastManager = LocalBroadcastManager.getInstance(this);
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Intent intent = new Intent("com.example.LOCAL_BROADCAST");
localBroadcastManager.sendBroadcast(intent);
}
});
intentFilter = new IntentFilter();
intentFilter.addAction("com.example.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 in local broadcast",Toast.LENGTH_SHORT).show();
}
}
}
主要使用一个LocalBroadcastManager来对广播进行管理
新建类LocalReceiver继承自BroadcastReceiver()
通过LocalBroadcastManager.getInstance(this)方法得到实例
调用LocalBroadcastManager的registerReceiver()方法注册广播接收器
调用localBroadcastManager.sendBroadcast()方法发送广播