Question

当我在visual basic中调试我的项目时，收到一条错误消息：

类型'System.InvalidOperationException'的未处理异常   发生在Name Database.exe
中
其他信息：创建表单时出错。看到   Exception.InnerException以获取详细信息。错误是：对象引用   没有设置为对象的实例。

这是我的代码：

Public Class Form1
Dim member As String = TextBoxName.Text
Private Sub ButtonAdd_Click(sender As Object, e As EventArgs) Handles ButtonAdd.Click
    ListBoxName.Items.Add(member & " " & TextBoxDate.Text)
    TextBoxDate.Text = ""
    TextBoxName.Text = ""
End Sub

Private Sub ButtonRemove_Click(sender As Object, e As EventArgs) Handles ButtonRemove.Click
    ListBoxName.Items.Remove(ListBoxName.SelectedItem)
End Sub

Private Sub ButtonCheck_Click(sender As Object, e As EventArgs) Handles ButtonCheck.Click
    If ListBoxName.Items.Contains(member & " " & Date.Today.ToString) Then
        MsgBox(ListBoxName.Items.Contains(Date.Today.ToString) & "membership needs to be renewed")
    End If
End Sub
End Class

Answer 1

 Dim member As String = TextBoxName.Text

这不起作用，TextBoxName变量在执行此赋值时尚未初始化。您必须使用构造函数，如下所示：

 Dim member As String

 Public Sub New()
    InitializeComponent()
    member = TextBoxName.Text
End Sub

设置TextBoxName控件引用的是InitializeComponent（）。请注意，它仍然不太可能工作，用户尚未设置Text属性。所以成员将包含一个空字符串。除非你给设计师一个价值。这表明这更可能是正确的：

 Dim member As String = String.Empty

VB调试错误

1 个答案: