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Broadcast Receiver是四大组件之一,是一种广泛运用在应用程序之间传输信息的机制,通过发送Intent来传送我们的数据。
按发送顺序
按发送范围
按Broadcast Receiver的实现
广播的使用包括以下几个步骤:
「以上1~3步骤需要开发者完成,4~5步骤由Android系统完成。」
「样例:」
public class SCCReceiver extends BroadcastReceiver {
@Override
public void onReceive(Context context, Intent intent) {
Log.e(getClass().getName(),"SCCReceiver,传递内容:"+intent.getStringExtra("scc"));
}
}
<receiver
android:name=".SCCReceiver"
android:enabled="true"
android:exported="true"/>
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center_horizontal"
android:orientation="vertical">
<Button
android:id="@+id/btn_send"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="发送静态广播" />
</LinearLayout>
public class MainActivity extends AppCompatActivity implements View.OnClickListener {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
findViewById(R.id.btn_send).setOnClickListener(this);
}
@Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.btn_send:
Log.e(getClass().getName(),"点击R.id.btn_send");
Intent intent = new Intent(this, SCCReceiver.class);
intent.putExtra("scc", "真的帅");
sendBroadcast(intent);
break;
}
}
}
public class SCCReceiver2 extends BroadcastReceiver {
public static final String ACTION = "com.scc.broadcastreceiver.SCCReceiver";
@Override
public void onReceive(Context context, Intent intent) {
Log.e(getClass().getName(),"SCCReceiver2,传递内容:"+intent.getStringExtra("scc"));
}
}
在代码中通过registerReceiver(BroadcastReceiver receiver, IntentFilter filter)来动态注册广播,该方法包含两个参数,receiver即我们自己定义的SCCReceiver2,IntentFilter即需要过滤的条件。
private SCCReceiver2 sccReceiver2;
@Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.btn_reg:
Log.e(getClass().getName(),"点击R.id.btn_reg");
if (sccReceiver2 == null) {//防止重复注册
sccReceiver2 = new SCCReceiver2();
registerReceiver(sccReceiver2, new IntentFilter(SCCReceiver2.ACTION));
}
break;
}
}
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center_horizontal"
android:orientation="vertical">
<Button
android:id="@+id/btn_reg"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="注册动态广播" />
<Button
android:id="@+id/btn_unreg"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="注销动态广播" />
<Button
android:id="@+id/btn_send_action"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="发送动态广播" />
</LinearLayout>
private SCCReceiver2 sccReceiver2;
@Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.btn_reg:
Log.e(getClass().getName(),"点击R.id.btn_reg");
if (sccReceiver2 == null) {//防止重复注册
sccReceiver2 = new SCCReceiver2();
registerReceiver(sccReceiver2, new IntentFilter(SCCReceiver2.ACTION));
}
break;
case R.id.btn_unreg:
Log.e(getClass().getName(),"点击R.id.btn_unreg");
if (sccReceiver2 != null) {//防止重复注销
unregisterReceiver(sccReceiver2);
sccReceiver2 = null;
}
break;
case R.id.btn_send_action:
Log.e(getClass().getName(),"点击R.id.btn_send_action");
Intent intentAction = new Intent(SCCReceiver2.ACTION);
intentAction.putExtra("scc", "动态,真的帅");
sendBroadcast(intentAction);
break;
}
}
使用unregisterReceiver(BroadcastReceiver receiver)来注销注册,动态注册的广播在应用停止运行后无法接收广播,比如在MainActivity中注册,则应当在MainActivity销毁前,使用unregisterReceiver(BroadcastReceiver receiver)来注销注册
对于动态广播注意:
无序广播直接通过Context.sendBroadcast()来发送。上面的4.1静态广播和4.2动态广播实现都是无序广播。无序广播被发送后,BroadCastReceiver之间是无顺序,完全异步的,各个Receiver之间无关联。无序广播无法通过abortBroadcast终止,也无法使用setResult和getResult来传递处理结果。
有序广播需要通过Context.sendOrderedBroadcast()来发送。有序广播发送后会按照优先级顺序被不同的广播接收器接收,优先级可以通过intent-filter的android:priority属性来设置,定义范围为-1000~1000,数值越大,优先级越高(如果优先级相同,动态注册的广播优先)。
先接收的广播接收者可以对广播进行截断abortBroadcast,即后接收的广播接收者不再接收到此广播;
先接收的广播接收者可以对广播进行修改,那么后接收的广播接收者将接收到被修改后的广播。
4.4.1不设置android:priority点击发送有序广播运行效果:
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.scc.broadcastreceiver">
<application
android:allowBackup="true"
android:icon="@mipmap/ic_launcher"
android:label="@string/app_name"
android:roundIcon="@mipmap/ic_launcher_round"
android:supportsRtl="true"
android:theme="@style/Theme.BroadcastReceiverDemo">
<activity
android:name=".MainActivity"
android:label="@string/app_name"
android:theme="@style/Theme.BroadcastReceiverDemo.NoActionBar">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<receiver
android:name=".SCCReceiver"
android:enabled="true"
android:exported="true"/>
<receiver
android:name=".SCCReceiver3">
<intent-filter>
<action android:name="com.scc.broadcastreceiver.SCCReceiver"/>
</intent-filter>
</receiver>
<receiver
android:name=".SCCReceiver4">
<intent-filter>
<action android:name="com.scc.broadcastreceiver.SCCReceiver"/>
</intent-filter>
</receiver>
<receiver
android:name=".SCCReceiver5">
<intent-filter>
<action android:name="com.scc.broadcastreceiver.SCCReceiver"/>
</intent-filter>
</receiver>
</application>
</manifest>
case R.id.btn_send_ordered:
Log.e(getClass().getName(),"点击R.id.btn_send_ordered");
Intent intentActionOrdered = new Intent(SCCReceiver2.ACTION);
intentActionOrdered.putExtra("scc", "有序,真的牛");
sendOrderedBroadcast(intentActionOrdered,null);
break;
运行效果:
SCCReceiver3>SCCReceiver4>SCCReceiver5
<receiver
android:name=".SCCReceiver3">
<intent-filter android:priority="-100">
<action android:name="com.scc.broadcastreceiver.SCCReceiver"/>
</intent-filter>
</receiver>
<receiver
android:name=".SCCReceiver4">
<intent-filter android:priority="0">
<action android:name="com.scc.broadcastreceiver.SCCReceiver"/>
</intent-filter>
</receiver>
<receiver
android:name=".SCCReceiver5">
<intent-filter android:priority="100">
<action android:name="com.scc.broadcastreceiver.SCCReceiver"/>
</intent-filter>
</receiver>
运行效果:
SCCReceiver5(100)>SCCReceiver4(0)>SCCReceiver3(-100)
public class SCCReceiver5 extends BroadcastReceiver {
@Override
public void onReceive(Context context, Intent intent) {
Log.e(getClass().getName(),"SCCReceiver5,传递内容:"+intent.getStringExtra("scc"));
Bundle bundle = getResultExtras(true);
bundle.putString("scc","改了数据");
setResultExtras(bundle);
}
}
public class SCCReceiver4 extends BroadcastReceiver {
@Override
public void onReceive(Context context, Intent intent) {
Bundle bundle = getResultExtras(true);
String name = bundle.getString("scc");
Log.e(getClass().getName(),"SCCReceiver4,传递内容:"+name);
abortBroadcast();
Log.e(getClass().getName(),"SCCReceiver4,拦截");
}
}
运行效果:
SCCReceiver5(100)修改数据>SCCReceiver4(0)拦截>没有SCCReceiver3(-100)
在Android中,广播的出现是为了组件间的通信。其实在Android中,进程间通信有Binder,而同进程的通信方式就更多了,之所以使用广播,发送者与接受者都不需要知道对方的存在,这样带来的好处便是,系统的各个组件可以松耦合地组织在一起,这样系统就具有高度的可扩展性,容易与其它系统进行集成。
Android中的广播使用了**「观察者模式」**:基于消息发布/订阅模式的事件驱动模型。
「广播模型中包含三个角色:」
实现步骤:
整个广播发送与接收过程中,发送者与接收者是异步的,发送者不需要知道是否有接受者,也不需要知道接受者何时收到广播。
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