当我尝试将值添加到 asp.net 详细信息视图中时，我得到一个“对象引用未设置为对象的实例”

Question

如何修复“对象引用未设置为对象的实例”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

Get Year 返回当前年份，它出现在 detailsview 文本框“PlantYear”中。我尝试使用上面的代码插入值。

感谢您的帮助。

Answer 1

很可能 FindControl 实际上并没有找到控件。明智的做法是检查以确保它确实找到了您想要找到的内容：

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