如何在广播接收器中设置警报

Question

在我的应用程序中，用户可以选择让他的事件重复，并且该重复事件的每次重复都会有一个通知（警报）提醒用户他的事件即将开始。

因此，当第一个警报被调用时，它会打开 BroadcastReceiver，创建通知并应为下一次重复设置警报：

    @Override
public void onReceive(Context context, Intent intent) {
    // When onReceive gets called the event notification is triggered
    DatabaseHelper myDatabaseHelper = new DatabaseHelper(context);

        // Create notification
        int id = intent.getIntExtra("id", 0);
        String name = intent.getStringExtra("name");
        long notificationTime = intent.getLongExtra("notificationTime", 0);
        String recurrenceType = intent.getStringExtra("recurrenceType");
        String message = intent.getStringExtra("message");

        if (recurrenceType.equals("Every week")) {
            // repeatInterval = unix timestamp so * 1000 to get in Millis for notificationTime
            long repeatInterval = 604800 * 1000;
            notificationTime += repeatInterval;
            myDatabaseHelper.updateNotificationTime(notificationTime);
            setAlarm(context, intent, id, name, notificationTime, recurrenceType, message);
        } else {
            myDatabaseHelper.updateNotificationTime(0);
        }

        createNotification(context, message, name, id);
    }
}

现在这适用于事件的第一个警报。通知已创建。现在，当第二个警报被调用时，意图是空的，所以在第一个警报之后，所有其他意图都是空的并且创建了一个空通知，然后应用程序崩溃并出现 NullPointerException。注意：我让我的应用程序和我的设备保持打开状态。 setAlarm(...) 方法位于 BroadcastReceiver 类中。

我如何设置闹钟：

    public void setAlarm(Context context, Intent intent, int id, String name, long notificationTime, String recurrenceType, String message){
    AlarmManager alarmManager = (AlarmManager) context.getSystemService(Context.ALARM_SERVICE);
    Intent intentAlarm = new Intent(context, AlarmReceiver.class);
    intent.putExtra("id", id);
    intent.putExtra("name", name);
    intent.putExtra("notificationTime", notificationTime);
    intent.putExtra("recurrenceType", recurrenceType);
    intent.putExtra("message", message);
    // A PendingIntent specifies an action to take in the future [context, request code, intent, flag]
    PendingIntent pendingIntent = PendingIntent.getBroadcast(context, id, intentAlarm, PendingIntent.FLAG_UPDATE_CURRENT);
    // RTC_WAKEUP will wake up the device when it goes off
    alarmManager.set(AlarmManager.RTC_WAKEUP, notificationTime, pendingIntent);
}

堆栈跟踪：

08-25 12:12:35.917 19323-19323/com.madgusto.when2game E/AndroidRuntime: FATAL EXCEPTION: main
                                                                    Process: com.madgusto.when2game, PID: 19323
                                                                    java.lang.RuntimeException: Unable to start receiver com.madgusto.when2game.alarm.AlarmReceiver: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.equals(java.lang.Object)' on a null object reference
                                                                        at android.app.ActivityThread.handleReceiver(ActivityThread.java:3018)
                                                                        at android.app.ActivityThread.-wrap18(ActivityThread.java)
                                                                        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1544)
                                                                        at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                        at android.os.Looper.loop(Looper.java:154)
                                                                        at android.app.ActivityThread.main(ActivityThread.java:6077)
                                                                        at java.lang.reflect.Method.invoke(Native Method)
                                                                        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866)
                                                                        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756)
                                                                     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.equals(java.lang.Object)' on a null object reference
                                                                        at com.madgusto.when2game.alarm.AlarmReceiver.onReceive(AlarmReceiver.java:48)
                                                                        at android.app.ActivityThread.handleReceiver(ActivityThread.java:3011)
                                                                        at android.app.ActivityThread.-wrap18(ActivityThread.java) 
                                                                        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1544) 
                                                                        at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                        at android.os.Looper.loop(Looper.java:154) 
                                                                        at android.app.ActivityThread.main(ActivityThread.java:6077) 
                                                                        at java.lang.reflect.Method.invoke(Native Method) 
                                                                        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866) 
                                                                        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:756) 

所以空指针位于：

if (recurrenceType.equals("Every week")) {

现在我该如何以正确的方式在广播接收器中设置警报？谢谢！

Answer 1

很清楚发生了什么。看这段代码：

Intent intentAlarm = new Intent(context, AlarmReceiver.class);
intent.putExtra("id", id);
intent.putExtra("name", name);
intent.putExtra("notificationTime", notificationTime);
intent.putExtra("recurrenceType", recurrenceType);
intent.putExtra("message", message);
PendingIntent pendingIntent = PendingIntent.getBroadcast(context, id, intentAlarm, PendingIntent.FLAG_UPDATE_CURRENT);

您在变量intentAlarm 中创建了一个Intent，但您使用变量intent 将所有“附加”放入Intent。然后将intentAlarm 作为参数传递给PendingIntent.getBroadcast()。当然intentAlarm 里面没有任何“额外”。

尝试将所有“附加”放在intentAlarm 中。