Question

有人可以告诉我发生了什么事吗？

当按下Label1时，我试图在Button1中显示一个随机问题。我只想让每个问题出现一次。

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，但是在这段代码中

    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。而且因为你做list.RemoveAt(index)，list一直在缩小，但Qtn.Length保持不变。当randomValue.Next(0, Qtn.Length)降为2或1个元素时，list很有可能产生越界值。

索引超出范围，必须是非负数且小于集合的大小

1 个答案: