Question

我必须为大学编写一个WPF应用程序，该应用程序从csv文件中读取。当我想将CSV行的部分输出到数组中时，我得到一个空引用异常。您可以在评论中找到错误发生的行。这是代码。

Imports System.Windows.Forms
Imports System.IO
Imports System.Globalization

Class MainWindow
Private foldername As String
Private arrGemeenten As String()
Private arrOppervlakte As Double()
Private arrInwoners As Integer()
Private arrDeelgemeenten As Integer()


Private Sub cboProvincie_SelectionChanged(ByVal sender As System.Object, ByVal e As System.Windows.Controls.SelectionChangedEventArgs) Handles cboProvincie.SelectionChanged
    CSVInlezen()
End Sub

Private Sub MainWindow_Loaded(ByVal sender As Object, ByVal e As System.Windows.RoutedEventArgs) Handles Me.Loaded


    FileBrowserAanmaken()
    comboBoxVullen()

End Sub



Private Sub comboBoxVullen()
    For Each file As String In IO.Directory.GetFiles(foldername)

        If file.EndsWith(".csv") Then
            Dim filenaam As String = System.IO.Path.GetFileNameWithoutExtension(file)
            cboProvincie.Items.Add(filenaam)
        End If

    Next
End Sub

Private Sub FileBrowserAanmaken()
    'folderbrowserdialog aanmaken
    Dim fbd As New FolderBrowserDialog

    fbd.SelectedPath = AppDomain.CurrentDomain.BaseDirectory


    ' Show the FolderBrowserDialog. 

    Dim result As DialogResult = fbd.ShowDialog()

    If (result = Forms.DialogResult.OK) Then
        foldername = fbd.SelectedPath
    End If
End Sub



Private Sub CSVInlezen()
    Dim filepath As String = foldername & "\" & cboProvincie.SelectedValue & ".csv"
    If File.Exists(filepath) Then
        fileInlezenHulpMethode(filepath)
    End If
End Sub

Private Sub fileInlezenHulpMethode(ByVal path As String)
    'declarations
    Dim sr As New StreamReader(path)
    Dim iTeller As Integer = 0
    Dim arrLijn As String()
    Dim culture As New System.Globalization.CultureInfo("nl-BE")

    'eerste lijn meteen uitlezen, dit zijn kolomkoppen en hebben we niet nodig
    'read out first line, these are titles and we don't need them
    sr.ReadLine()

    Do While sr.Peek <> -1
        Dim lijn As String = sr.ReadLine()
        arrLijn = lijn.Split(";")
        arrGemeenten(iTeller) = Convert.ToString(arrLijn(0)) 'HERE I GET THE ERROR!
        arrOppervlakte(iTeller) = Double.Parse(arrLijn(2), NumberStyles.AllowDecimalPoint, culture.NumberFormat)
        arrInwoners(iTeller) = Integer.Parse(arrLijn(3), NumberStyles.Integer Or NumberStyles.AllowThousands, culture.NumberFormat)
        arrDeelgemeenten(iTeller) = Convert.ToString(arrLijn(4))
    Loop
End Sub

End Class

Answer 1

您尚未创建数组，您只为其创建了引用。要创建数组，您需要指定大小，例如：

Private arrGemeenten As String(100)

但是，要指定大小，您需要在创建阵列时知道大小。（好吧，实际上你把所有数据放在第一个项目中，所以只有大小1才能防止它崩溃，但我不是那个你想要的东西。）你可能想要改用列表：

Private gemeenten As New List(Of String)()

然后使用Add方法将项目添加到列表中：

gemeenten.Add(Convert.ToString(arrLijn(0)))

另外，请考虑将数据放在自定义对象的单个列表中，而不是使用几个松散耦合的数据列表。

空参考例外 - 从CSV读取

1 个答案: