前言：前段时间突然想起来看下并行广播和串行广播，并行广播项目中经常用到，或者说是无意识地用到，因为默认就是并行的，串行广播工作三年来都没接触过，自己写个demo玩一下。
参考链接：
1.Android四大组件——BroadcastReceiver普通广播、有序广播、拦截广播、本地广播、Sticky广播、系统广播
2.Android源码解析四大组件系列（六）---广播的处理过程
demo: jiatai 的 demo for ordered broadcast
调试手机：小米Mix2(突然想到调试什么的用nexus会好一点，毕竟国产机会对framework进行优化，也可能和Android源码对不上)虚拟机一直会莫名其妙重启=-=，调试结果也和mix2不大一样。
1. 串行广播的简单demo
1.1 新建broadcastReceiver
package com.example.demo_33_broadcast_parallel;
import android.app.job.JobScheduler;
import android.app.job.JobService;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.os.Handler;
import android.util.Log;
public class BroadcastReceiverList {
public static String TAG = "BroadcastReceiverList";
public static class HighLevelBroadcastReceiver extends BroadcastReceiver{
/**
* This method is called when the BroadcastReceiver is receiving an Intent
* broadcast. During this time you can use the other methods on
* BroadcastReceiver to view/modify the current result values. This method
* is always called within the main thread of its process, unless you
* explicitly asked for it to be scheduled on a different thread using
* {@link Context#registerReceiver(BroadcastReceiver, * IntentFilter, String, Handler)}. When it runs on the main
* thread you should
* never perform long-running operations in it (there is a timeout of
* 10 seconds that the system allows before considering the receiver to
* be blocked and a candidate to be killed). You cannot launch a popup dialog
* in your implementation of onReceive().
* <p>
* <p><b>If this BroadcastReceiver was launched through a <receiver> tag,
* then the object is no longer alive after returning from this
* function.</b> This means you should not perform any operations that
* return a result to you asynchronously. If you need to perform any follow up
* background work, schedule a {@link JobService} with
* {@link JobScheduler}.
* <p>
* If you wish to interact with a service that is already running and previously
* bound using {@link Context#bindService(Intent, ServiceConnection, int) bindService()},
* you can use {@link #peekService}.
* <p>
* <p>The Intent filters used in {@link Context#registerReceiver}
* and in application manifests are <em>not</em> guaranteed to be exclusive. They
* are hints to the operating system about how to find suitable recipients. It is
* possible for senders to force delivery to specific recipients, bypassing filter
* resolution. For this reason, {@link #onReceive(Context, Intent) onReceive()}
* implementations should respond only to known actions, ignoring any unexpected
* Intents that they may receive.
*
* @param context The Context in which the receiver is running.
* @param intent The Intent being received.
*/
@Override
public void onReceive(Context context, Intent intent) {
Log.d(TAG, "high level receiver");
setResult(0, "high", null);
}
}
public static class MidLevelBroadcastReceiver extends BroadcastReceiver{
@Override
public void onReceive(Context context, Intent intent) {
Log.d(TAG, "middle level receiver-->getResultCode: " + getResultCode() + " getResultData: " + getResultData());
setResult(1, "middle", null);
//abortBroadcast();
}
}
public static class LowLevelBroadcastReceiver extends BroadcastReceiver{
@Override
public void onReceive(Context context, Intent intent) {
Log.d(TAG, "low level receiver-->getResultCode: " + getResultCode() + " getResultData: " + getResultData());
setResult(2, "low", null);
}
}
}
其中onReceive的文档注释很有内涵，讲了以下几点：
1. onReceive一般是运行在主线程中的
2. onReceive不支持耗时操作，需要控制在10s执行完成
3.onReceive中不支持弹框操作
1.2 注册BroadcastReceiver
我就简单的在manifest里注册了一下，activity里用registerReceiver也行。
<receiver android:name=".BroadcastReceiverList$HighLevelBroadcastReceiver">
<intent-filter android:priority="3000">
<action android:name="com.jiatai.broadcast.ordered" />
</intent-filter>
</receiver>
<receiver android:name=".BroadcastReceiverList$MidLevelBroadcastReceiver">
<intent-filter android:priority="2000">
<action android:name="com.jiatai.broadcast.ordered" />
</intent-filter>
</receiver>
<receiver android:name=".BroadcastReceiverList$LowLevelBroadcastReceiver">
<intent-filter android:priority="1000">
<action android:name="com.jiatai.broadcast.ordered" />
</intent-filter>
</receiver>
1.3 发送有序广播
package com.example.demo_33_broadcast_parallel;
import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
public class BroadcastTestActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_broadcast_test);
Intent intent = new Intent("com.jiatai.broadcast.ordered");
sendOrderedBroadcast(intent, null);
}
}
1.4 调试
1.5 试下有序广播拦截
1.6 用虚拟机调试
用虚拟机调试的时候如果没有指定包名，广播会被framework拦截下来不会传递到应用侧，结合广播在Android 8.0里的修改，如果是隐式广播，并且是静态注册的话，会大概率收不到广播。对应解决方法是对广播的intent设置对应的包名将其改为显示广播。（我试了下如果设置对应类名则会继续收不到广播，这是否意味着类名会限制只在对应类里接收么=-=）
参考：点击打开链接
“限制在AndroidManifest.xml中注册接收隐式广播，如ACTION_PACKAGE_REPLACED ，但也有些例外如ACTION_BOOT_COMPLETED，ACTION_LOCALE_CHANGED（所有例外参考文末连接）。（注意此部分限制都是只针对targetSdkVersion为android O，或者编译的SDK为android O及以上的的，低于的则不受影响）”
对应框架代码：
else if (((r.intent.getFlags()&Intent.FLAG_RECEIVER_EXCLUDE_BACKGROUND) != 0)
|| (r.intent.getComponent() == null
&& r.intent.getPackage() == null
&& ((r.intent.getFlags()
& Intent.FLAG_RECEIVER_INCLUDE_BACKGROUND) == 0)
&& !isSignaturePerm(r.requiredPermissions))) {
mService.addBackgroundCheckViolationLocked(r.intent.getAction(),
component.getPackageName());
Slog.w(TAG, "Background execution not allowed: receiving "
+ r.intent + " to "
+ component.flattenToShortString());
skip = true;
}可以看出如果没有指定Component和Package则会将skip设为true, 至于源码中的flag是hide类型的，第三方中调用不到。
/**
* If set, the broadcast will never go to manifest receivers in background (cached
* or not running) apps, regardless of whether that would be done by default. By
* default they will receive broadcasts if the broadcast has specified an
* explicit component or package name.
* @hide
*/
public static final int FLAG_RECEIVER_EXCLUDE_BACKGROUND = 0x00800000;
2. 总结
有序广播适用于广播依次处理并且需要得到上一次处理结果的情况，大部分情况下并行广播够用了，另外有序广播又被拦截的风险。