android - 在Kotlin Android中将数据添加到Recyclerview

我正在使用Volley来读取JSON API。一切都为此目的而努力。当我查看从API获得的到达时间时，会有不同的期望。

JSON输出

10-24 08:34:17.831 4671-4671/org.sherman.tony.nexttrain I/System.out: ARRIVAL TIME = 1508849280
10-24 08:34:17.831 4671-4671/org.sherman.tony.nexttrain I/System.out: ARRIVAL TIME = 1508850180
10-24 08:34:17.831 4671-4671/org.sherman.tony.nexttrain I/System.out: ARRIVAL TIME = 1508850600
10-24 08:34:17.831 4671-4671/org.sherman.tony.nexttrain I/System.out: ARRIVAL TIME = 1508848920
10-24 08:34:17.832 4671-4671/org.sherman.tony.nexttrain I/System.out: ARRIVAL TIME = 1508851500
10-24 08:34:17.832 4671-4671/org.sherman.tony.nexttrain I/System.out: ARRIVAL TIME = 1508851980
10-24 08:34:17.832 4671-4671/org.sherman.tony.nexttrain I/System.out: ARRIVAL TIME = 1508849340
10-24 08:34:17.832 4671-4671/org.sherman.tony.nexttrain I/System.out: ARRIVAL TIME = 1508850000
10-24 08:34:17.832 4671-4671/org.sherman.tony.nexttrain I/System.out: ARRIVAL TIME = 1508849760
10-24 08:34:17.832 4671-4671/org.sherman.tony.nexttrain I/System.out: ARRIVAL TIME = 1508849340
10-24 08:34:17.832 4671-4671/org.sherman.tony.nexttrain I/System.out: ARRIVAL TIME = 1508848680
10-24 08:34:17.832 4671-4671/org.sherman.tony.nexttrain I/System.out: ARRIVAL TIME = 1508850000
10-24 08:34:17.832 4671-4671/org.sherman.tony.nexttrain I/System.out: ARRIVAL TIME = 1508851980

我的代码向ArrayList中添加了正确数量的元素，但是当我查看回收器中的数据时，捕获到的最后一个元素多次出现:

10-24 08:34:17.929 4671-4671/org.sherman.tony.nexttrain I/System.out: ARRIVAL TIME ===> 1508851980
10-24 08:34:17.932 4671-4671/org.sherman.tony.nexttrain I/System.out: ARRIVAL TIME ===> 1508851980
10-24 08:34:17.935 4671-4671/org.sherman.tony.nexttrain I/System.out: ARRIVAL TIME ===> 1508851980
10-24 08:34:17.940 4671-4671/org.sherman.tony.nexttrain I/System.out: ARRIVAL TIME ===> 1508851980
10-24 08:34:17.942 4671-4671/org.sherman.tony.nexttrain I/System.out: ARRIVAL TIME ===> 1508851980
10-24 08:34:17.945 4671-4671/org.sherman.tony.nexttrain I/System.out: ARRIVAL TIME ===> 1508851980
10-24 08:34:17.950 4671-4671/org.sherman.tony.nexttrain I/System.out: ARRIVAL TIME ===> 1508851980
10-24 08:34:17.954 4671-4671/org.sherman.tony.nexttrain I/System.out: ARRIVAL TIME ===> 1508851980
10-24 08:34:17.970 4671-4671/org.sherman.tony.nexttrain I/System.out: ARRIVAL TIME ===> 1508851980

这是我的 Activity 代码的核心:

// Get a list of train schedules
//
listOfTrains = ArrayList<TrainStatus>()

volleyRequest = Volley.newRequestQueue(this)
readTrains(url,station)
}

fun readTrains(url:String, station: String) {

var listOfTrains = ArrayList<TrainStatus>()
var trainStatus = TrainStatus()

println("URL ===> $url")
val jsonObjectRequest = JsonObjectRequest(Request.Method.GET,url,
        Response.Listener {
            response: JSONObject ->
            try {
                val responseMode = response.getJSONArray("mode")
                val responseModeRouteObj = responseMode.getJSONObject(0)
                val responseModeRouteObjRoute = responseModeRouteObj.getJSONArray("route")
                for (i in 0..responseModeRouteObjRoute.length() - 1){
                    val responseModeRouteObjRouteRouteObj = responseModeRouteObjRoute.getJSONObject(i)
                    val responseModeRouteObjRouteRouteObjDirection = responseModeRouteObjRouteRouteObj.getJSONArray("direction")
                    for (j in 0.. responseModeRouteObjRouteRouteObjDirection.length() - 1){
                        val responseModeRouteObjRouteRouteObjDirectionDirectionObj = responseModeRouteObjRouteRouteObjDirection.getJSONObject(j)
                        val direction = responseModeRouteObjRouteRouteObjDirectionDirectionObj.getString("direction_id")
                        trainStatus.direction_id = direction.toInt()
                        val tripArray = responseModeRouteObjRouteRouteObjDirectionDirectionObj.getJSONArray("trip")
                        for (k in 0..tripArray.length() - 1){
                            var tripArrayObj = tripArray.getJSONObject(k)
                            var schArrival = tripArrayObj.getString("sch_arr_dt")
                            trainStatus.sch_arr_time = schArrival.toLong()
                            trainStatus.station = station

                            println("ARRIVAL TIME = ${trainStatus.sch_arr_time}") // DEBUGGING print statement

                            listOfTrains!!.add(trainStatus)
                        }
                    }
                }
                trainAdapter = TrainListAdapter(listOfTrains, this)
                layoutManager = LinearLayoutManager(this)
                // Set up recycler Adapter
                recyclerViewID.layoutManager = layoutManager
                recyclerViewID.adapter = trainAdapter
                trainAdapter!!.notifyDataSetChanged()

            } catch (e: JSONException){e.printStackTrace()}
        },
        Response.ErrorListener {
            error: VolleyError? ->
            try{
            error!!.printStackTrace()
        }catch(e:JSONException) {
                e.printStackTrace()
            }
        })
//val list:ArrayList<TrainList>? = null

volleyRequest!!.add(jsonObjectRequest)
println("SIZE OF ARRAY ===> ${listOfTrains.size}")
return
//return list
}

这是我的适配器代码:

package org.sherman.tony.nexttrain.adapters

import android.content.Context
import android.support.v7.widget.RecyclerView
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.TextView
import org.sherman.tony.nexttrain.models.TrainStatus
import org.sherman.tony.nexttrain.R
import java.text.DateFormat
import java.text.SimpleDateFormat
import java.util.*


class TrainListAdapter(var listOfTrains: ArrayList<TrainStatus>,
                       val context: Context): RecyclerView.Adapter<TrainListAdapter.ViewHolder>() {

    override fun onCreateViewHolder(parent: ViewGroup?, position: Int): ViewHolder {
        val view = LayoutInflater.from(context)
                .inflate(R.layout.station_lst_item, parent, false)
        return ViewHolder(view)
    }

    override fun getItemCount(): Int {
        return listOfTrains.size
    }

    override fun onBindViewHolder(holder: ViewHolder?, position: Int) {
        holder!!.bindView(listOfTrains[position])
    }

    inner class ViewHolder(itemView: View): RecyclerView.ViewHolder(itemView) {

        var station = itemView.findViewById<TextView>(R.id.stationListTextViewID)
        var arrivalTime = itemView.findViewById<TextView>(R.id.timeScheduleID)

        fun bindView(train: TrainStatus){
            var humanTime = readableTime(train.sch_arr_time!!)
            println("ARRIVAL TIME ===> ${train.sch_arr_time}")
            station.text = train.station.toString()
            //arrivalTime.text = humanTime
            arrivalTime.text = train.sch_arr_time.toString()
        }
        fun readableTime(milliSeconds: Long): String {
            var date = Date(milliSeconds)
            val dateFormat: DateFormat = SimpleDateFormat("H:mm")
            return dateFormat.format(date)
        }

    }
}

如何获取适配器以添加实际返回的值，而不是最后一个元素的多个副本。

谢谢。

最佳答案

认为我发现了问题。
您正在创建TrainStatus的列表，并从远程API获取该列表。
对于每个 call ，您都要进行迭代并添加给定的结果。问题出在变量trainStatus的声明中。

您在函数readTrains之外执行var trainStatus = TrainStatus()，然后在每次迭代中更改该变量的值并将其添加到列表中。

您可以这样做，但不会为要添加的每个TrainStatus创建一个新实例，因此每次将同一对象的同一实例添加到列表中时，只需更改其中的值即可。这样，列表中的每个元素都指向同一个对象TrainStatus，该对象保存从您的请求中接收到的最后一个元素的值。

要解决该问题，只需在每次启动新迭代时都创建一个新实例。

因此，将代码更改为:

for (i in 0..responseModeRouteObjRoute.length() - 1){
                val responseModeRouteObjRouteRouteObj = responseModeRouteObjRoute.getJSONObject(i)
                val responseModeRouteObjRouteRouteObjDirection = responseModeRouteObjRouteRouteObj.getJSONArray("direction")
                for (j in 0.. responseModeRouteObjRouteRouteObjDirection.length() - 1){
                    val responseModeRouteObjRouteRouteObjDirectionDirectionObj = responseModeRouteObjRouteRouteObjDirection.getJSONObject(j)
                    val direction = responseModeRouteObjRouteRouteObjDirectionDirectionObj.getString("direction_id")
                    val tripArray = responseModeRouteObjRouteRouteObjDirectionDirectionObj.getJSONArray("trip")
                    for (k in 0..tripArray.length() - 1){
                        trainStatus.direction_id = TrainStatus()
                        trainStatus.direction_id = direction.toInt()
                        var tripArrayObj = tripArray.getJSONObject(k)
                        var schArrival = tripArrayObj.getString("sch_arr_dt")
                        trainStatus.sch_arr_time = schArrival.toLong()
                        trainStatus.station = station

                        println("ARRIVAL TIME = ${trainStatus.sch_arr_time}") // DEBUGGING print statement

                        listOfTrains!!.add(trainStatus)
                    }
                }
            }

我还建议您不要为每次调用创建适配器的新实例，而应直接将trainstatus列表保留在适配器中