DataGridView row headings disappear on tabpage2?

Question

Public Class Form1


  Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    'DEMONSTRATES Tabcontrol/datagridview rowheading bug
    Dim tbc As New TabControl

    Dim tbp1 As New TabPage("Tab1")
    Dim dgv1 As New DataGridView
    tbp1.Controls.Add(dgv1)
    dgv1.Dock = DockStyle.Fill

    Dim tbp2 As New TabPage("Tab2")
    Dim dgv2 As New DataGridView
    tbp2.Controls.Add(dgv2)
    dgv2.Dock = DockStyle.Fill

    tbc.TabPages.Add(tbp1)
    tbc.TabPages.Add(tbp2)

    Me.Controls.Add(tbc)
    tbc.Dock = DockStyle.Fill
    LoadDGV(dgv1)
    LoadDGV(dgv2)
    'Why do the row headers show up on the tabpage1 datagridview, but not the tabpage2 datagridview?
  End Sub

  Sub LoadDGV(ByVal dgv As DataGridView)
    Dim dtb As New DataTable
    dtb.Columns.Add("Col1", GetType(String))
    dtb.Columns.Add("Col2", GetType(String))
    dtb.Columns.Add("Col3", GetType(String))
    dtb.Rows.Add("1", "2", "3")
    dtb.Rows.Add("4", "5", "6")
    dtb.Rows.Add("7", "8", "9")
    With dgv
      .DataSource = dtb
      .Rows(0).HeaderCell.Value = "Row0"
      .Rows(1).HeaderCell.Value = "Row1"
      .Rows(2).HeaderCell.Value = "Row2"
      .RowHeadersWidth = 100
    End With
  End Sub
End Class

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David Streeter

Answer 1

Hi David,

Thank you for your valuable feedback.

The cause of this issue is, the DataGridView is not updated while DataGridView is hidden/invisible. You can check the following similar cases for some instruction  and workarounds.
http://social.msdn.microsoft.com/Forums/en-US/winformsdatacontrols/thread/b4f5079c-c8f1-4a2d-a476-8cbef1e0debb
http://social.msdn.microsoft.com/forums/en-US/winformsdatacontrols/thread/44e13cb2-15e2-4b40-b8ed-9adb80e9b6c7/

One workaround:
Use the TabControl's SelectedIndexChanged event - this is called everytime when a TabPage within the TabControl is selected. And create a sub that redraws the DataGridView or try the DataGridView.Invalidate() method.

Public Sub Tab_Changes(ByVal sender As System.Object, ByVal e As System.EventArgs)
        ' use this sub to track if a tab is selected in the tab control & force a row and column redraw
        Dim tabC As TabControl
        Dim dgvChart As DataGridView
        Dim strTab As String

        'cast to TabControl to work with
        If TypeOf sender Is TabControl Then
            tabC = DirectCast(sender, TabControl)

            'cast to DGV to work with
            If TypeOf tabC.TabPages(tabC.SelectedIndex).Controls(dgvChart.Name) Is DataGridView Then
                dgvChart = DirectCast(tabC.TabPages(tabC.SelectedIndex).Controls(DataGridView1.Name), DataGridView)

                'Invalidate the tabpage's dgv
                dgvChart.Invalidate()

                ' OR call a bespoke sub called Sub_DGVRedraw(Byval dgvInput as DataGridView) that will redraw the headers
                Sub_DGVRedraw(dgvChart)

            End If
        End If
    End Sub

Best regards,

Martin Xie

MSDN Subscriber Support in Forum

If you have any feedback on our support, please contact [e-mail]

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Answer 2

David,

Probably they would not call it a bug but known behaviour.

I call this a bug.

        Me.Controls.Add(tbc)
        tbc.Dock = DockStyle.Fill
        LoadDGV(dgv1)
        tbc.SelectTab(1)
        LoadDGV(dgv2)
        'Why do the row headers show up on the tabpage1 datagridview, but not the tabpage2 datagridview?

The Tabpages have the bad habbit that things are not done when the page is not visible.

Nevertheless, if I did found it, I would report it on

Connect.Microsoft.Com

as a bug

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Success
Cor

Answer 3

I don't think this is a redraw issue. The .HeaderCell.Value property for the second datagridview is being set to Nothing.

See following code (adds to msgbox calls to above code):

Public Class Form1

  Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    'DEMONSTRATES Tabcontrol/datagridview rowheading bug
    Dim tbc As New TabControl

    Dim tbp1 As New TabPage("Tab1")
    Dim dgv1 As New DataGridView
    tbp1.Controls.Add(dgv1)
    dgv1.Dock = DockStyle.Fill

    Dim tbp2 As New TabPage("Tab2")
    Dim dgv2 As New DataGridView
    tbp2.Controls.Add(dgv2)
    dgv2.Dock = DockStyle.Fill

    tbc.TabPages.Add(tbp1)
    tbc.TabPages.Add(tbp2)

    Me.Controls.Add(tbc)
    tbc.Dock = DockStyle.Fill
    LoadDGV(dgv1)
    LoadDGV(dgv2)

    MsgBox("dgv1.Rows(0).HeaderCell.Value=" & dgv1.Rows(0).HeaderCell.Value.ToString) 'works
    MsgBox("dgv2.Rows(0).HeaderCell.Value=" & dgv2.Rows(0).HeaderCell.Value.ToString) 'throws "object reference not set" error

  End Sub

  Sub LoadDGV(ByVal dgv As DataGridView)
    Dim dtb As New DataTable
    dtb.Columns.Add("Col1", GetType(String))
    dtb.Columns.Add("Col2", GetType(String))
    dtb.Columns.Add("Col3", GetType(String))
    dtb.Rows.Add("1", "2", "3")
    dtb.Rows.Add("4", "5", "6")
    dtb.Rows.Add("7", "8", "9")
    With dgv
      .DataSource = dtb
      .Rows(0).HeaderCell.Value = "Row0"
      .Rows(1).HeaderCell.Value = "Row1"
      .Rows(2).HeaderCell.Value = "Row2"
      .RowHeadersWidth = 100
    End With
  End Sub
End Class

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David Streeter

Answer 4

Thanks Cor, that work-around (selecting the second tab before filling it) works, and is simpler than DirectCast.

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David Streeter