在VB.net中处理未知大小的数组

Question

我正在做一个分配，其中从文件读取记录，将记录存储在结构数组中，然后输出到列表框。 根据分配指令，结构数组的大小指定为250个元素。

为了跟踪已处理的记录数，我创建了名为totalElements的变量。 它计算已处理的记录数，因此，对于写入列表框的For循环，我拥有较高的记录数。 这是最好的方法吗？

在测试中，我发现如果我处理的记录少于250条，并且结构数组的元素为空，那么如果我使用这些循环之一，则在将记录写入列表框时会遇到运行时错误。

     For i As Integer = 0 To 249          
     ...write listbox       
     Next 

要么

     Dim highestSub As Integer = mem.Length - 1 
     For i As Integer = 0 To highestSub 
     ...write listbox 
      Next 

这是我完整的代码。 它有效，我只是觉得必须有一种更好的方法来做到这一点。 先谢谢您的帮助！

-Brent

    Public Class MainForm

Structure Members
    Public id As String
    Public lastName As String
    Public firstName As String
    Public middleInitial As String
    Public grade As String
    Public classPeriod As String
End Structure

'declare an array of Members
Private mem(250) As Members

Dim totalElements As Integer = 0



Private Sub MainForm_Load(sender As Object, e As EventArgs) Handles MyBase.Load

    LoadStudentFile()

    WriteStudentFile()

End Sub

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    Me.Close()
End Sub


Private Sub LoadStudentFile()

    Dim inFile As IO.StreamReader
    inFile = IO.File.OpenText("StudentList.txt")
    Dim tempArray(5) As String
    Dim subscript As Integer = 0


    Do Until inFile.Peek = -1

        tempArray = inFile.ReadLine.Split(","c)

        mem(subscript).id = tempArray(0)


        mem(subscript).lastName = tempArray(1)

        mem(subscript).firstName = tempArray(2)

        mem(subscript).middleInitial = tempArray(3)

        mem(subscript).grade = tempArray(4)

        mem(subscript).classPeriod = tempArray(5)

        subscript = subscript + 1

        totalElements = totalElements + 1

    Loop

    inFile.Close()

End Sub


Private Sub WriteStudentFile()


    For i As Integer = 0 To totalElements - 1
        StudentsList.Items.Add(mem(i).id.PadLeft(10, "0") & " " & mem(i).lastName & ", " & mem(i).firstName & " " & mem(i).middleInitial)
    Next
End Sub

Answer 1

在将记录写入列表框之前，请检查是否有空记录。 假设所有记录都将有一个ID。

Private Sub WriteStudentFile()
    For i As Integer = 0 To mem.Length -1
        If Not IsNothing(mem(i).id) then
            StudentsList.Items.Add(mem(i).id.PadLeft(10, "0") & " " & mem(i).lastName & ", " & mem(i).firstName & " " & mem(i).middleInitial)
        End If
    Next
End Sub

尽管如果您可以选择是否使用数组，我可以改用通用List(Of Members) 。 这样，您可以仅添加有效数据，而无需分配过多的空间。