VB在列表框中显示多维数组中的元素

Question

由于某些奇怪的原因，当我使用循环显示数组元素时出现错误。我似乎无法理解我在做什么或做得不对。这是到目前为止的代码。这不是上课，我是在自学。

Option Strict On
Option Explicit On
Option Infer Off

Public Class Form1

Private strExams(49, 2) As String
Dim count As Integer = 0

Private Sub btnAdd_Click(sender As Object, e As EventArgs) Handles btnAdd.Click

    Dim strStudent As String = txtStudent.Text
    Dim strTest As String = txtTest.Text
    Dim strScore As String = txtScore.Text

    If count <= 49 Then
        strExams(count, 0) = strStudent
        strExams(count, 1) = strTest
        strExams(count, 2) = strScore
        count += 1
    End If

    txtStudent.Text = String.Empty
    txtTest.Text = String.Empty
    txtScore.Text = String.Empty

    txtStudent.Focus()

End Sub

Private Sub btnDisplay_Click(sender As Object, e As EventArgs) Handles btnDisplay.Click

    Dim intHighRow As Integer = strExams.GetUpperBound(0)
    Dim intHighCol As Integer = strExams.GetUpperBound(1)
    Dim intR As Integer
    Dim intC As Integer
    Do While intC <= intHighCol
        intR = 0
        Do While intR <= intHighRow
            lstMessage.Items.Add(strExams(intR, intC))
            intR += 1
        Loop
        intC += 1
    Loop

End Sub

这是我点击显示按钮时遇到的错误。

System.Windows.Forms.dll 中出现“System.ArgumentNullException”类型的未处理异常

附加信息：值不能为空。

Answer 1

试试这个。这对我来说更有意义。您收到 null 错误的原因是您没有填写数组中的所有内容，并且您的列表框无法列出 null 项目。因此，一种解决方法是仅枚举已经有值的项目，因此，只需循环直到 count 的最后一个值。

Private Sub btnDisplay_Click(sender As Object, e As EventArgs) Handles btnDisplay.Click
    Dim intR As Integer

    lstMessage.Items.Clear()
    Do While intR < count
        lstMessage.Items.Add(strExams(intR, 0) & " - " & strExams(intR, 1) & " - " & strExams(intR, 2))
        intR += 1
    Loop
End Sub