Question

每当用户触摸屏幕时，我都试图使用AsyncTask从数据库中提取数据。每次用户触摸应用程序上的屏幕时，都会创建一个新任务。我想要的是使旧任务停止并销毁，并在用户每次触摸屏幕时都将该任务替换为新任务，而无论该任务是否已完成其工作。

这是在应用程序上下文中完成的，至少是在存储库所在的位置。我已经做了几个控制结构，使其取消了先前的AsyncTask，但似乎没有一个起作用。

var getBoundedMomentsTask : BoundsRequestTask = BoundsRequestTask()

//Starts an asynchronous task
//Called by ViewModel
//A list of moments is returned to the live data object
fun queryMapMoments(bounds : LatLngBounds, zoom : Float ) {

    //If the request is already running, end it
    if (getBoundedMomentsTask.status == AsyncTask.Status.RUNNING) {
        getBoundedMomentsTask.cancel(true)
    }

    //The while loop just hung up the system.
    //while (getBoundedMomentsTask.status == AsyncTask.Status.RUNNING) {
    //    getBoundedMomentsTask.cancel(true)
    //}

    //Begin the new task
    getBoundedMomentsTask.execute(BoundsTaskParams(bounds, zoom))

}


inner class BoundsRequestTask : AsyncTask<BoundsTaskParams, Void, List<Moment>>() {

    override fun doInBackground(vararg params: BoundsTaskParams?): List<Moment> {

        val bounds: LatLngBounds? = params[0]?.bounds
        val zoom: Float? = params[0]?.zoom

        if (!isCancelled) {

            Log.d("doInBackground", "Getting map channel")
            val channel = checkMapChannels(bounds, zoom)

            if (!isCancelled) {

                Log.d("doInBackground", "Asking for moments from database")
                channel.fetchDatabaseMoments()
            } else {
                return mutableListOf()
            }

            if (!channel.networkRequested) {

                if (!isCancelled) {

                    Log.d("doInBackground", "Asking for moments from network")
                    channel.fetchMomentsOnNetwork()
                } else {
                    return mutableListOf()
                }
            }

            //Save the channel and return the moments

            Log.d("doInBackground", "Saving the returned channel")
            channels.add(channel)
            return channel.regionMoments

        } else {
            return mutableListOf()
        }

    }

    override fun onPostExecute(list : List<Moment>) {
        mappedMoments.value = list

    }
}

我得到的错误是Cannot execute task: the task has already been executed (a task can be executed only once)，与getBoundedMomentsTask.execute(BoundsTaskParams(bounds, zoom))

Answer 1

您必须创建一个新的AsyncTask实例。一个实例只能执行一次。

如何取消旧的AsyncTask换一个新的

1 个答案: