來自Firebase實時資料庫的資料被檢索，但從函式回傳時未設定？

我正在嘗試從 Firebase 獲取資料并將其作為陣列回傳。到目前為止，這是有效的，但是資料仍然是我設定的默認資料。

這是代碼（我添加了一些注釋以闡明它在哪里起作用以及 id 在何處不起作用）：

fun getRandomQuestion() : ArrayList<ArrayList<String>>{
    val random = Random(1234567)
    val randQuestionId = random.nextInt(0, 27)

    var dataRequestResult : String = "empty"

    var requestSide1 : String = "empty"
    var requestSide2 : String = "empty"
    var requestCount1 : String = "empty"
    var requestCount2 : String = "empty"

    //Get a random question from the DB
    Firebase.database.reference.child(Constants.wyrDBQuestionLocation)
        .child(randQuestionId.toString())
        .get()
        .addOnFailureListener { task ->
            Log.i("Get WYR Question Status", "Failed: "   task.message.toString())
            requestSide1 = "empty"
            requestSide2 = "empty"
            requestCount1 = "empty"
            requestCount2 = "empty"
        }.addOnSuccessListener {
            Log.i("Get WYR Question Status", "Success")

            //Logging this data returns the correct information from firebase, no issue here
            Log.i("Request Data Result", it.value.toString())

            dataRequestResult = it.value.toString()
        }

    requestSide1 = dataRequestResult.substringAfter("side1Question=").substringBefore("}")
    requestSide2 = dataRequestResult.substringAfter("side2Question=").substringBefore(",")
    requestCount1 = dataRequestResult.substringAfter("sideCount1=").substringBefore(",")
    requestCount2 = dataRequestResult.substringAfter("sideCount2=").substringBefore(",")

    //Return the value
    return arrayListOf(arrayListOf(requestSide1, requestCount1), arrayListOf(requestSide2, requestCount2))
}

我嘗試獲取回傳值的活動：

    val myQuestion = databaseController.getRandomQuestion()

    //This is where the issue lies
    //When I get the returned data from the function above, it gives me all of the defaults I had set in the function (which is "empty")
    //It logs:`[["empty", "empty"],["empty", "empty"]]`
    Log.i("My Question", myQuestion.toString())

成功監聽器中的資料是正確的，但回傳值仍然是默認值。這是日志的影像：

“請求日志結果”，不要介意結果，我正在制作一個 WYR 應用程式。

我注意到聽眾的請求是最后一個，而不是第一個

我認為這與資料甚至還沒有完全收集有關，因為在我制作的另一個應用程式中，我所要做的就是給它一個延遲并設定它，但在這種情況下，我不知道該怎么做.

任何幫助將不勝感激！:)

uj5u.com熱心網友回復：

請求資料庫資料時使用的偵聽器將在getRandomQuestion函式回傳之后觸發ArrayList。您可以使用Kotlin 協程來處理回呼并暫停協程直到回呼被觸發，例如：

suspend fun getRandomQuestion() = suspendCoroutine<String> { continuation ->
    Firebase.database.reference.child(Constants.wyrDBQuestionLocation)
    .child(randQuestionId.toString())
    .get()
    .addOnFailureListener { task ->
        continuation.resume("empty")
    }.addOnSuccessListener {
        continuation.resume(it.value.toString())
    }
}

// somewhere in your code (e.g. in ViewModel, Activity or Fragment):

someCoroutineScope.launch {
    val question: String = getRandomQuestion();
    // ... use question to update UI
}

在Activity或者Fragment您可以使用lifecycleScope, ViewModelin- viewModelScope。

suspendCoroutinebuilder 函式用于等待回呼。suspendCoroutine掛起它執行的協程，直到我們決定通過呼叫適當的方法繼續 - Continuation.resume...。

uj5u.com熱心網友回復：

這是我的解決方案

方法一

fun getRandomQuestion() : ArrayList<ArrayList<String>>{
    val random = Random(1234567)
    val randQuestionId = random.nextInt(0, 27)

    var dataRequestResult : String = "empty"

    var requestSide1 : String = "empty"
    var requestSide2 : String = "empty"
    var requestCount1 : String = "empty"
    var requestCount2 : String = "empty"

    //Get a random question from the DB
    Firebase.database.reference.child(Constants.wyrDBQuestionLocation)
        .child(randQuestionId.toString())
        .get()
        .addOnFailureListener { task ->
            Log.i("Get WYR Question Status", "Failed: "   task.message.toString())
            requestSide1 = "empty"
            requestSide2 = "empty"
            requestCount1 = "empty"
            requestCount2 = "empty"
        }.addOnSuccessListener {
            Log.i("Get WYR Question Status", "Success")

            //Logging this data returns the correct information from firebase, no issue here
            Log.i("Request Data Result", it.value.toString())

            dataRequestResult = it.value.toString()
    requestSide1 = dataRequestResult.substringAfter("side1Question=").substringBefore("}")
    requestSide2 = dataRequestResult.substringAfter("side2Question=").substringBefore(",")
    requestCount1 = dataRequestResult.substringAfter("sideCount1=").substringBefore(",")
    requestCount2 = dataRequestResult.substringAfter("sideCount2=").substringBefore(",")

        }

    
    //Return the value
    return arrayListOf(arrayListOf(requestSide1, requestCount1), arrayListOf(requestSide2, requestCount2))
}

方法二

fun getRandomQuestion() : ArrayList<ArrayList<String>>{
    val random = Random(1234567)
    val randQuestionId = random.nextInt(0, 27)

    var dataRequestResult : String = "empty"

    var requestSide1 : String = "empty"
    var requestSide2 : String = "empty"
    var requestCount1 : String = "empty"
    var requestCount2 : String = "empty"

    //Get a random question from the DB
    Firebase.database.reference.child(Constants.wyrDBQuestionLocation)
        .child(randQuestionId.toString())
        .get()
        .addOnFailureListener { task ->
            Log.i("Get WYR Question Status", "Failed: "   task.message.toString())
            requestSide1 = "empty"
            requestSide2 = "empty"
            requestCount1 = "empty"
            requestCount2 = "empty"
        }.addOnSuccessListener {
            Log.i("Get WYR Question Status", "Success")

            //Logging this data returns the correct information from firebase, no issue here
            Log.i("Request Data Result", it.value.toString())

            dataRequestResult = it.value.toString()
    requestSide1 = dataRequestResult.substringAfter("side1Question=").substringBefore("}")
    requestSide2 = dataRequestResult.substringAfter("side2Question=").substringBefore(",")
    requestCount1 = dataRequestResult.substringAfter("sideCount1=").substringBefore(",")
    requestCount2 = dataRequestResult.substringAfter("sideCount2=").substringBefore(",")
//Return the value
    return arrayListOf(arrayListOf(requestSide1, requestCount1), arrayListOf(requestSide2, requestCount2))
        }

return null    
    
}

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