Android 包装到引用对象中，以便在闭包中捕获时进行修改

所以我对Kotlin在android上有点陌生，对什么是“”非常困惑。我也看了很多视频，但什么都没看

我在第5行完成了对mutualList的初始化，但是之后我无法在块中为它设置值

谁能帮帮我吗

private fun returnArray(url: String) : MutableList<String> {

    Log.d("Alele", "returnArray(url)")

    var arrayList = mutableListOf<String>()

    val jsonObjectRequest = JsonObjectRequest(
            Request.Method.GET,
            url,
            null,
            Response.Listener { response ->
                try {

                    Log.d("Alele", "Try block")
                    var jsonObject = response.getJSONObject("response").getJSONArray("docs").getJSONObject(0)

                    Log.d("Alele", jsonObject.toString())

                    var id = jsonObject.getString("id")
                    Log.d("Alele", id.toString())

                    var journal = jsonObject.getString("journal")
                    Log.d("Alele", journal)

                    arrayList[0] = id
                    arrayList[1] = journal

                } catch (e: JSONException) {
                    Log.d("Alele", "catch block")
                    e.printStackTrace()
                }
            },
            Response.ErrorListener {
                it.printStackTrace()
                Log.d("Alele", it.printStackTrace().toString())
            })
    Log.d("Alele", " $arrayList[0]")
    Log.d("Alele", " $arrayList[1]")

    // add the queue to the request
    requestQueue.add(jsonObjectRequest)
    return arrayList
}

正在导致应用程序崩溃，每当我将光标放在这些行上寻找任何提示时，我都会被包装到引用对象中，当在闭包中捕获时将被修改，这对我来说是非常混乱的

2020-02-21 10:22:48.560 31603-31603/com.hylton.volleyproject D/Alele: returnArray(url)

2020-02-21 10:22:48.563 31603-31603/com.hylton.volleyproject D/Alele:  [][0]

2020-02-21 10:22:48.563 31603-31603/com.hylton.volleyproject D/Alele:  [][1]

2020-02-21 10:22:51.108 31603-31603/com.hylton.volleyproject D/Alele: Try block

2020-02-21 10:22:51.110 31603-31603/com.hylton.volleyproject D/Alele: {"id":"10.1371\/journal.pone.0084896","journal":"PLoS ONE","eissn":"1932-6203","publication_date":"2014-01-17T00:00:00Z","article_type":"Research Article","author_display":["Marcel A. L. M. van Assen","Robbie C. M. van Aert","Michèle B. Nuijten","Jelte M. Wicherts"],"abstract":["Background: De Winter and Happee [1] examined whether science based on selective publishing of significant results may be effective in accurate estimation of population effects, and whether this is even more effective than a science in which all results are published (i.e., a science without publication bias). Based on their simulation study they concluded that “selective publishing yields a more accurate meta-analytic estimation of the true effect than publishing everything, (and that) publishing nonreplicable results while placing null results in the file drawer can be beneficial for the scientific collective” (p.4). Methods and Findings: Using their scenario with a small to medium population effect size, we show that publishing everything is more effective for the scientific collective than selective publishing of significant results. Additionally, we examined a scenario with a null effect, which provides a more dramatic illustration of the superiority of publishing everything over selective publishing. Conclusion: Publishing everything is more effective than only reporting significant outcomes. "],"title_display":"Why Publishing Everything Is More Effective than Selective Publishing of Statistically Significant Results","score":9.342657}

2020-02-21 10:22:51.110 31603-31603/com.hylton.volleyproject D/Alele: 10.1371/journal.pone.0084896

2020-02-21 10:22:51.110 31603-31603/com.hylton.volleyproject D/Alele: PLoS ONE

这是坠机报告打印出来的

E/AndroidRuntime: FATAL EXCEPTION: main

    Process: com.hylton.volleyproject, PID: 569

    java.lang.IndexOutOfBoundsException: Index: 0, Size: 0

        at java.util.ArrayList.set(ArrayList.java:453)

        at com.hylton.volleyproject.MainActivity$returnArray$jsonObjectRequest$1.onResponse(MainActivity.kt:71)

        at com.hylton.volleyproject.MainActivity$returnArray$jsonObjectRequest$1.onResponse(MainActivity.kt:26)

        at com.android.volley.toolbox.JsonRequest.deliverResponse(JsonRequest.java:90)

        at com.android.volley.ExecutorDelivery$ResponseDeliveryRunnable.run(ExecutorDelivery.java:102)

        at android.os.Handler.handleCallback(Handler.java:883)

        at android.os.Handler.dispatchMessage(Handler.java:100)

        at android.os.Looper.loop(Looper.java:214)

        at android.app.ActivityThread.main(ActivityThread.java:7356)

        at java.lang.reflect.Method.invoke(Native Method)

        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)

        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)

I/Process: Sending signal. PID: 569 SIG: 9

Application terminated.

---

我认为警告是关于您可以修改id和journal的事实，因为它们被声明为var。请尝试将它们声明为val（值而不是变量）。关于坠机，控制台说了些什么吗？堆栈跟踪还是错误消息？此外，使用arrayList.add（id）而不是使用索引，这是正确的方法。@Andrea Nisticò这就是堆栈跟踪错误显示的

E/AndroidRuntime:FATAL EXCEPTION:main Process:com.hylton.volleyproject，PID:569 java.lang.IndexOutOfBoundsException:Index:0，Size:0 at java.util.arrayList.set（ArrayList.java:453）在com.hylton.volleyproject.MainActivity$returnArray$jsonObjectRequest$1.onResponse（MainActivity.kt:71）在com.hylton.volleyproject.MainActivity$returnArray$jsonObjectRequest$1.onResponse（MainActivity.kt:26）

尝试使用ArrayList.add（id）和ArrayList.add（journal）代替直接访问。

E/AndroidRuntime: FATAL EXCEPTION: main

    Process: com.hylton.volleyproject, PID: 569

    java.lang.IndexOutOfBoundsException: Index: 0, Size: 0

        at java.util.ArrayList.set(ArrayList.java:453)

        at com.hylton.volleyproject.MainActivity$returnArray$jsonObjectRequest$1.onResponse(MainActivity.kt:71)

        at com.hylton.volleyproject.MainActivity$returnArray$jsonObjectRequest$1.onResponse(MainActivity.kt:26)

        at com.android.volley.toolbox.JsonRequest.deliverResponse(JsonRequest.java:90)

        at com.android.volley.ExecutorDelivery$ResponseDeliveryRunnable.run(ExecutorDelivery.java:102)

        at android.os.Handler.handleCallback(Handler.java:883)

        at android.os.Handler.dispatchMessage(Handler.java:100)

        at android.os.Looper.loop(Looper.java:214)

        at android.app.ActivityThread.main(ActivityThread.java:7356)

        at java.lang.reflect.Method.invoke(Native Method)

        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)

        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)

I/Process: Sending signal. PID: 569 SIG: 9

Application terminated.