注销BroadcastReceiver

Question

在我的应用程序中，我有一个将BroadcastReceiver注册到onStart()方法的服务：

public void onStart() {
    if(something....) {
        IntentFilter filter = new IntentFilter(Intent.ACTION_SCREEN_ON);
        filter.addAction(Intent.ACTION_SCREEN_OFF);
        screenReceiver = new ScreenReceiver();
        registerReceiver(screenReceiver, filter);
    } else {
        if(screenReceiver != null) {
            unregisterReceiver(screenReceiver);
        }
    }
}

而且它工作正常。但我会在else中注销此BroadcastReceiver，并收到以下错误：

01-25 09:30:03.730: ERROR/AndroidRuntime(11748): FATAL EXCEPTION: main
01-25 09:30:03.730: ERROR/AndroidRuntime(11748): java.lang.RuntimeException: Unable to start service com.myservice.Service@460ce7d8 with Intent { cmp=com.myservice/.Service (has extras) }: java.lang.IllegalArgumentException: Receiver not registered: com.myreceiver.ScreenReceiver@46079370
01-25 09:30:03.730: ERROR/AndroidRuntime(11748):     at android.app.ActivityThread.handleServiceArgs(ActivityThread.java:3063)
01-25 09:30:03.730: ERROR/AndroidRuntime(11748):     at android.app.ActivityThread.access$3600(ActivityThread.java:125)
01-25 09:30:03.730: ERROR/AndroidRuntime(11748):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2096)
01-25 09:30:03.730: ERROR/AndroidRuntime(11748):     at android.os.Handler.dispatchMessage(Handler.java:99)
01-25 09:30:03.730: ERROR/AndroidRuntime(11748):     at android.os.Looper.loop(Looper.java:123)
01-25 09:30:03.730: ERROR/AndroidRuntime(11748):     at android.app.ActivityThread.main(ActivityThread.java:4627)
01-25 09:30:03.730: ERROR/AndroidRuntime(11748):     at java.lang.reflect.Method.invokeNative(Native Method)
01-25 09:30:03.730: ERROR/AndroidRuntime(11748):     at java.lang.reflect.Method.invoke(Method.java:521)
01-25 09:30:03.730: ERROR/AndroidRuntime(11748):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
01-25 09:30:03.730: ERROR/AndroidRuntime(11748):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
01-25 09:30:03.730: ERROR/AndroidRuntime(11748):     at dalvik.system.NativeStart.main(Native Method)
01-25 09:30:03.730: ERROR/AndroidRuntime(11748): Caused by: java.lang.IllegalArgumentException: Receiver not registered: com.myreceiver.ScreenReceiver@46079370
01-25 09:30:03.730: ERROR/AndroidRuntime(11748):     at android.app.ActivityThread$PackageInfo.forgetReceiverDispatcher(ActivityThread.java:793)
01-25 09:30:03.730: ERROR/AndroidRuntime(11748):     at android.app.ContextImpl.unregisterReceiver(ContextImpl.java:814)
01-25 09:30:03.730: ERROR/AndroidRuntime(11748):     at android.content.ContextWrapper.unregisterReceiver(ContextWrapper.java:331)
01-25 09:30:03.730: ERROR/AndroidRuntime(11748):     at com.myservice.Service.onStart(Service.java:291)
01-25 09:30:03.730: ERROR/AndroidRuntime(11748):     at android.app.Service.onStartCommand(Service.java:420)
01-25 09:30:03.730: ERROR/AndroidRuntime(11748):     at android.app.ActivityThread.handleServiceArgs(ActivityThread.java:3053)
01-25 09:30:03.730: ERROR/AndroidRuntime(11748):     ... 10 more

你能帮帮我吗?

Answer 1

修改代码，如下所示

public void onStart() {
    if(something....) {
        IntentFilter filter = new IntentFilter(Intent.ACTION_SCREEN_ON);
        filter.addAction(Intent.ACTION_SCREEN_OFF);
        screenReceiver = new ScreenReceiver();
        registerReceiver(screenReceiver, filter);
    } else {
        if(screenReceiver != null) {
            unregisterReceiver(screenReceiver);
            screenReceiver = null;
        }
    }
}

调用unregisterReceiver()不会将screenReceiver设置为null，并且当控件到达该块时，您的接收方可能并不总是注册的情况。例如，考虑按顺序进行以下操作，

1. if(something...)为true，因此这次实例化了接收器，registered.
2. if(something...)为false，因此unregistered.
3. if(something...)为false，此处，在步骤1中实例化了screenReceiver，因此其不为空，但在步骤2中取消注册，因此出现异常"Receiver not screenReceiver : screenReceiver“

将screenReceiver设置为null后，依次考虑上述3个步骤。它将正确执行。