尝试实施 beginBackgroundTaskWithExpirationHandler 和 UILocalNotification

Trying to implement beginBackgroundTaskWithExpirationHandler and UILocalNotification

当我的应用程序进入后台时,我的 AppDelegate 中有以下代码:

var backgroundUpdateTask: UIBackgroundTaskIdentifier!

func beginBackgroundUpdateTask() {
    self.backgroundUpdateTask = UIApplication.sharedApplication().beginBackgroundTaskWithExpirationHandler({
        self.endBackgroundUpdateTask()
    })
}

func endBackgroundUpdateTask() {
    UIApplication.sharedApplication().endBackgroundTask(self.backgroundUpdateTask)
    self.backgroundUpdateTask = UIBackgroundTaskInvalid
}

func doBackgroundTask() {
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), {
        self.beginBackgroundUpdateTask()

        // Do something with the result.
        var timer = NSTimer.scheduledTimerWithTimeInterval(5, target: self, selector: "displayAlert", userInfo: nil, repeats: false)
        NSRunLoop.currentRunLoop().addTimer(timer, forMode: NSDefaultRunLoopMode)
        NSRunLoop.currentRunLoop().run()

        // End the background task.
        self.endBackgroundUpdateTask()
    })
}

func displayAlert() {
    let note = UILocalNotification()
    note.alertBody = "As a test I'm hoping this will run in the background every X number of seconds..."
    note.soundName = UILocalNotificationDefaultSoundName
    UIApplication.sharedApplication().scheduleLocalNotification(note)
}

func applicationDidEnterBackground(application: UIApplication) {
    self.doBackgroundTask()
}

我希望它在 NSTimer.scheduledTimerWithTimeInterval() 中指定的每 X 秒执行一次 UILocalNotification() 但是它只执行一次。

我仍在努力了解后台任务的工作原理。有什么我想念的吗?

在代码示例中,您创建的计时器只会触发一次,因为您在初始化程序中将 "repeats" 值设置为 false。