Android后台进程每分钟从网页加载数据

Question

我正在开发一个Android应用程序，有一个不断重复的后台进程。

从设备启动的那一刻起，它应该每分钟加载一个网页上的数据。它使用XmlPullParser和一个简单的URL InputStream。它只有10KB，所以没有那么密集。我相信这种任务叫做延期。一旦用户打开应用程序，流程加载的信息必须可以访问活动。后台进程也需要设置，以便在数据显示某些结果时发出通知。

在Android中似乎有多种方法来实现这一点，例如。然而，JobScheduler、WorkManager或AlarmManager，到目前为止我所尝试的一切似乎要么在活动关闭后停止，要么根本不运行。时间，每分钟，似乎也是一个问题，因为重复的工作和工人的最小间隔是15。这一分钟不一定要精确。我认为，与其让一个重复的进程加载数据，不如让一个长时间运行的进程在加载数据之间Hibernate1m。

Answer 1

使用workmanager很容易，这是在Android中安排重复后台工作的最受欢迎的方式，请参见导言。

正如你所说，重复工作请求的最小间隔被限制在15分钟内，打破这一间隔的唯一方法是重复安排一次性工作。

1.设置员工类：

class ToastShower(context: Context, params: WorkerParameters) : CoroutineWorker(context, params) {
    override suspend fun doWork(): Result {
        withContext(Dispatchers.Main) {      //ui related work must run in Main thread!!
            Toast.makeText(applicationContext, "Hey, I'm Sam! This message will appear every 5 seconds.", Toast.LENGTH_SHORT).show()
        }

        return Result.success()
    }
}

class WorkManagerApplication : Application() {
    private val backgroundScope = CoroutineScope(Dispatchers.Default)       //standard background thread
    private val applicationContext = this

    override fun onCreate() {                           //called when the app launches (same as Activity)
        super.onCreate()

        initWork()
    }

    private fun initWork() {
        backgroundScope.launch {                                //all rnu in background thread
            setupToastShowingWork(0)                            //no delay at first time

            observeToastShowingWork()                       //observe work state changes, see below
        }
    }

    private fun setupToastShowingWork(delayInSeconds: Long) {               //must run in background thread
        val constraints = Constraints.Builder()
            .setRequiredNetworkType(NetworkType.UNMETERED)          //when using WiFi
            .build()

        val oneTimeRequest = OneTimeWorkRequestBuilder<ToastShower>()       //【for breaking 15 minutes limit we have to use one time request】
            .setInitialDelay(delayInSeconds, TimeUnit.SECONDS)          //customizable delay (interval) time
            .setConstraints(constraints)
            .build()

        WorkManager.getInstance(applicationContext).enqueueUniqueWork(      //【must be unique!!】
            ToastShower::class.java.simpleName,                 //work name, use class name for convenient
            ExistingWorkPolicy.KEEP,                        //if new work comes in with same name, discard the new one
            oneTimeRequest
        )
    }

    private suspend fun observeToastShowingWork() {
        withContext(Dispatchers.Main) { //must run in Main thread for using observeForever 
            WorkManager.getInstance(applicationContext).getWorkInfosForUniqueWorkLiveData(ToastShower::class.java.simpleName).observeForever {
                if (it[0].state == WorkInfo.State.SUCCEEDED) {          //when the work is done
                    backgroundScope.launch {                        //prevent from running in Main thread
                        setupToastShowingWork(5)                        //every 5 seconds
                    }
                }
            }
        }
    }
}

<manifest 
    xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.workmanagertest">

    <application
        android:name=".WorkManagerApplication"                  //【here, must!!!】
    
        ...

    </application>

</manifest>