当应用程序处于后台时启动后台服务

Question

当我们收到通知时，如何使用后台服务启动警报？当我的应用程序处于活动状态时，后台服务就很容易启动，但是当应用程序处于后台时，后台服务就无法运行。

Answer 1

1.为什么会发生这种情况？

FCM (Firebase Cloud messages )中有两种类型的消息：

显示消息：这些消息只有在应用程序处于前台时才触发onMessageReceived()回调

foreground/background/killed数据消息:即使应用程序在中，数据消息也会触发onMessageReceived()回调

override fun onMessageReceived(remoteMessage: RemoteMessage) {
    // ...

    // TODO(developer): Handle FCM messages here.
    // Not getting messages here? See why this may be:
    Log.d(TAG, "From: ${remoteMessage.from}")

    // Check if message contains a data payload.
    if (remoteMessage.data.isNotEmpty()) {
        Log.d(TAG, "Message data payload: ${remoteMessage.data}")

        if (/* Check if data needs to be processed by long running job */ true) {
            // For long-running tasks (10 seconds or more) use WorkManager.
            scheduleJob()
        } else {
            // Handle message within 10 seconds
            handleNow()
        }
    }

    // Check if message contains a notification payload.
    remoteMessage.notification?.let {
        Log.d(TAG, "Message Notification Body: ${it.body}")
    }

    // Also if you intend on generating your own notifications as a result of a received FCM
    // message, here is where that should be initiated. See sendNotification method below.
}