VB.NET未处理Array - NullReferenceException问题

Question

我基本上试图创建一个数组导出选中的项目到word文档。但是我得到了一个错误，说

"对象引用未设置为对象的实例。"

和

"引用的'SelectedMutualFunds'的值为'Nothing'

下面是我的代码:

Public Class ExportFunds
      Public SelectedMutualFunds() As String
 Private Sub ExportFundOkButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ExportFundOkButton.Click
           Dim i As Integer
    Dim array_Counter As Integer
    array_Counter = 0
    For i = 0 To ExportFundCheckedListBox.Items.Count() - 1
        If ExportFundCheckedListBox.GetItemCheckState(i) = CheckState.Checked Then
            SelectedMutualFunds(array_Counter) = ExportFundCheckedListBox.Items(i).ToString
            array_Counter += 1
        End If
    Next
    Me.Close()
End Sub

有人能帮我解决这个问题吗?

Answer 1

您需要为您的字符串数组提供长度

 Public SelectedMutualFunds() As String

到ExportFundOkButton_Click中的以下内容，最好是在for循环之前。

 Redim SelectedMutualFunds(ExportFundCheckedListBox.Items.Count() - 1)

Answer 2

您可以将其简化为一行代码，同时修复NullReference异常:

 Private Sub ExportFundOkButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ExportFundOkButton.Click
     SelectedMutualFunds = ExportFundCheckedListBox.Items.Where(Function(i) i.CheckState = CheckState.Checked).Select(Function(i) i.ToString()).ToArray()
     Me.Close()
End Sub

或者，稍长但更容易阅读:

Private Sub ExportFundOkButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ExportFundOkButton.Click
     SelectedMutualFunds = ExportFundCheckedListBox.Items.
                Where(Function(i) i.CheckState = CheckState.Checked).
                Select(Function(i) i.ToString()).
                ToArray()
     Me.Close()
End Sub