android - 如何知道异步任务何时在android studio中完全完成？

Question

已解决： 我遇到了并发修改问题，我认为这是由于在任务完成之前调用了我的过滤器，最终对我有用的是在 onPostExecute 中添加对外部方法的调用，该方法将值复制到 copyonwritearraylist。

所以我有一个 AsyncTask 从网站解析 json 并在完成后初始化一个列表。

    inner class GetSchoolAsync : AsyncTask<String, String, String>() {
    lateinit var list: MutableList<Info>
    override fun onPreExecute() {
        // Before doInBackground
    }

    override fun doInBackground(vararg urls: String?): String {
        var urlConnection: HttpURLConnection? = null

        try {
            val url = URL(urls[0])

            urlConnection = url.openConnection() as HttpURLConnection
            urlConnection.connectTimeout = CONNECTON_TIMEOUT_MILLISECONDS
            urlConnection.readTimeout = CONNECTON_TIMEOUT_MILLISECONDS

            val inString = urlConnection.inputStream.bufferedReader().readText()

            publishProgress(inString)
        } catch (ex: Exception) {
            println("HttpURLConnection exception" + ex)
        } finally {
            if (urlConnection != null) {
                urlConnection.disconnect()
            }
        }

        return " "
    }

    override fun onProgressUpdate(vararg values: String?) {
        try {
            var list = mutableListOf<Info>()
            var data = Gson().fromJson(values[0], Read::class.java)

            for(item in data.schools){
                list.add(item)
               // println(item)
            }
            this.list = list



        } catch (ex: Exception) {
            println("JSON parsing exception" + ex.printStackTrace())
        }
    }

    override fun onPostExecute(result: String?) {
        // Done
        schoolList = this.list

    }
}

它与另一个渲染地图的异步函数一起在 mainactivity OnCreate 中执行。学校列表是主要活动中的私有lateinit var。

    override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_maps)
    // Obtain the SupportMapFragment and get notified when the map is ready to be used.
    val mapFragment = supportFragmentManager
            .findFragmentById(R.id.map) as SupportMapFragment
    GetSchoolAsync().execute("https://code.org/schools.json")
    mapFragment.getMapAsync(this)
}

我需要知道 json 部分何时完成并初始化列表，以便我可以向地图添加标记。每当我尝试在调试器中检查异步任务的状态时，它总是显示它处于挂起状态或正在运行。我什么时候可以确定它完成了？

标签： androidkotlinandroid-asynctask

Answer 1

您应该更好地为您的案例使用接口

 interface ReturnListener {
            fun result(result:String)
        }



  inner class GetSchoolAsync : AsyncTask<Object, String, String>() {
    lateinit var list: MutableList<Info>
    override fun onPreExecute() {
        // Before doInBackground
    }

    override fun doInBackground(vararg urls: Object?): String {
        var urlConnection: HttpURLConnection? = null
        var listener: ReturnListener? = null

        try {
            val url = URL(urls[0] as String)
            listener = urls[1] as ReturnListener

            urlConnection = url.openConnection() as HttpURLConnection
            urlConnection.connectTimeout = CONNECTON_TIMEOUT_MILLISECONDS
            urlConnection.readTimeout = CONNECTON_TIMEOUT_MILLISECONDS

            val inString = urlConnection.inputStream.bufferedReader().readText()

            publishProgress(inString)
        } catch (ex: Exception) {
            println("HttpURLConnection exception" + ex)
        } finally {
            if (urlConnection != null) {
                urlConnection.disconnect()
            }
        }

        return " "
    }

    override fun onProgressUpdate(vararg values: String?) {
        try {
            var list = mutableListOf<Info>()
            var data = Gson().fromJson(values[0], Read::class.java)

            for(item in data.schools){
                list.add(item)
               // println(item)
            }
            this.list = list



        } catch (ex: Exception) {
            println("JSON parsing exception" + ex.printStackTrace())
        }
    }

    override fun onPostExecute(result: String?) {
        // Done
        schoolList = this.list
     if (listener!=null)
       listener.result(result)

    }

在 OnCreate 下：

      override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_maps)
        // Obtain the SupportMapFragment and get notified when the map is ready to be used.
        val mapFragment = supportFragmentManager
                .findFragmentById(R.id.map) as SupportMapFragment
        GetSchoolAsync().execute("https://code.org/schools.json", object: ReturnListener{
 override fun result(result:String) {

                 //ToDo: .......

             }
       })
        mapFragment.getMapAsync(this)
    }