当我尝试向asp.net细节视图添加插入值时，出现“对象引用未设置为对象实例”的错误。

Question

如何修复“对象引用未设置为对象实例”的错误。它指的是哪个对象？

代码：

Private Sub dvSMasterCurrentYear_DataBound(sender As Object, e As EventArgs) Handles dvSMasterCurrentYear.DataBound
    Dim dv As DetailsView = New DetailsView
    If DetailsViewMode.Insert Then
        DirectCast(dv.FindControl("PlantYear"), TextBox).Text = GetYear()
    End If
End Sub

GetYear返回当前年份，它显示在DetailsView文本框“PlantYear”中。我尝试使用以上代码插入该值。

感谢您的帮助。

- jim davis

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你必须允许FindControl返回null/Nothing。如果它这样做，那么代码将抛出NRE异常。 - Ňɏssa Pøngjǣrdenlarp

Answer 1

很可能FindControl并没有真正找到控件。最好进行检查，确保它已经找到了你想要找的内容：

Private Sub dvSMasterCurrentYear_DataBound(sender As Object, e As EventArgs) Handles dvSMasterCurrentYear.DataBound
    Dim dv As DetailsView = New DetailsView
    If DetailsViewMode.Insert Then
        Dim ctl = dv.FindControl("PlantYear")
        If ctl IsNot Nothing Then
            DirectCast(dv.FindControl("PlantYear"), TextBox).Text = GetYear()
        Else
            Throw New Exception("Control was not found")
        End If        
    End If
End Sub

- Matt Wilko

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这解决了空对象引用的问题。但我仍无法将值保存到记录中。以下是我用于获取年份的函数：Public Function GetYear() Dim thisDate As Date = Now Dim thisYear As String 'thisDate = #2/12/1969# thisYear = Year(thisDate) Return thisYear End Function - jim davis