索引超出范围，必须为非负数且小于集合的大小

Question

谁能告诉我这是怎么回事？

当按下Button1 时，我试图在Label1 中出现一个随机问题。我只希望每个问题出现一次。

Dim Qtn(4) As String
Private Sub LoadQs()
    Qtn(0) = "What is 1 + 10?"
    Qtn(1) = "What is 1 + 11?"
    Qtn(2) = "What is 1 + 12?"
    Qtn(3) = "What is 1 + 13?"
    Qtn(4) = "What is 1 + 14?"
End Sub
Private Sub RndQtn()
    Dim list As New ArrayList
    For i As Integer = 0 To 4
        'Add the numbers to the collection.
        list.Add(i)
    Next i
    Dim randomValue As New Random
    Dim index As Integer
    Dim item As Object
    'Display the items in random order.
    While list.Count > 0
        'Choose a random index.
        index = randomValue.Next(0, Qtn.Length)
        'Get the item at that index.
        item = list(index)
        'Remove the item so that it cannot be chosen again.
        list.RemoveAt(index)
        'Display the item.
        Label1.Text = Qtn(item)
    End While
End Sub

Answer 1

我不懂VB，但在这段代码中

    index = randomValue.Next(0, Qtn.Length)
    'Get the item at that index.
    item = list(index)
    'Remove the item so that it cannot be chosen again.
    list.RemoveAt(index)

您正在根据Qtn 的长度生成索引，但使用它来索引list，这是一个不同的变量。因为你做了list.RemoveAt(index)，list 不断缩小，但Qtn.Length 保持不变。当list 减少到 2 或 1 个元素时，randomValue.Next(0, Qtn.Length) 很有可能会产生越界值。