asp.net - 当我尝试添加插入值到 asp.net 详细信息 View 中时，我得到 "Object reference not set to an instance of an object"

Question

如何修复“对象引用未设置到对象实例”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

获取年份返回当前年份，它显示在详细信息 View 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

FindControl 很可能实际上并未找到该控件。明智的做法是进行检查以确保它确实找到了您想要查找的内容:

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