Question

请参阅以下代码：

Private Sub DataGridViewBorrowedBooks_SelectionChanged(ByVal sender As Object, ByVal e As EventArgs) Handles DataGridViewBorrowedBooks.SelectionChanged
        'DataGridViewBookDetails.DataSource = Nothing
        If DataGridViewBorrowedBooks.SelectedRows.Count = 0 Then
            Return
        End If

        Dim row = DataGridViewBorrowedBooks.SelectedRows(0)
        If row Is Nothing Then
            Return
        End If

        Dim isbn As Decimal = Integer.Parse(row.Cells("isbn").Value.ToString())

        ' Get member record from treeview control.
        Dim member = TryCast(TreeViewMembers.SelectedNode.Tag, MemberModel)

        ' Check for root node. It does not have a member record
        If member Is Nothing Then
            Return
        End If

        ' Locate order record
        For Each loan In member.Loan
            If loan.ISBN = isbn Then
                DataGridViewBookDetails.DataSource = loan.Books
                DataGridViewBookDetails.Columns("ISBN").Visible = False
                DataGridViewBookDetails.Columns("Title").DefaultCellStyle.Format = "C"
                DataGridViewBookDetails.Columns("Author").DefaultCellStyle.Format = "C"
                DataGridViewBookDetails.Columns("Price").DefaultCellStyle.Alignment = DataGridViewContentAlignment.MiddleRight
                Return
            End If
        Next loan
    End Sub

我得到的异常是：System.NullReferenceException，位于以下行：'DataGridViewBookDetails.Columns("ISBN").Visible = False

Answer 1

这里的问题是，"ISBN"集合中没有名称为Columns的列。您需要将其更改为列的实际名称，或者如果更合适，则使用索引。要查找所有列名称，您只需将其打印出来即可。它很可能映射到一个名字，一旦你看到它就会非常明显

For Each column in DataGridViewBookDetails.Columns 
  MessageBox.Show(column.Name)
Next

System.NullReferenceException绑定到DataGridView

1 个答案: