C1FlexGrid (WinForms) freezes for 20–40 on a large dataset unbound

C1FlexGrid (WinForms) freezes for 20–40 on a large dataset unbound

Posted by: Ranba790 on 28 October 2026, 3:11 pm EST

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  Ranba790

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  Posted 28 October 2026, 3:11 pm EST

  Hi,

  We’re using C1FlexGrid 2025v2 (C1.Win.FlexGrid.4.8, 4.8.20252.740) in a .NET Framework 4.8

  The grid is bound to a List(Of T) with about 210,000 rows × 29 columns. Loading takes about 1.2 s. the form then stopped responding for 20–43 s, and again for about 20 s after a sort. During the freeze, process memory went from about 114 MB to 451 MB.

  Stack samples of the UI thread during the freeze are all under DispatchMessageW, in UI Automation calls coming from another process:

  MS.Internal.Automation.UiaCoreProviderApi.RawUiaHostProviderFromHwnd
  System.Windows.Automation.Provider.AutomationInteropProvider.HostProviderFromHandle
  ...IRawElementProviderSimple.get_HostRawElementProvider
  System.StubHelpers.BSTRMarshaler.ConvertToNative / ObjectMarshaler.ConvertToNative
  System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW

  The PC runs several UI Automation clients (ChatGPT desktop, Windows Click to Do, TeamViewer, Logi Options+). It looks like one of them walks every cell of the grid, with each call marshalled to our UI thread.

  As a workaround we put a NativeWindow on the grid handle that returns 0 for WM_GETOBJECT with UiaRootObjectId. With that in place there is no freeze, and memory stays at about 115 MB:

  Protected Overrides Sub WndProc(ByRef m As Message)
    If m.Msg = &H3D AndAlso (m.LParam.ToInt64 And &HFFFFFFFFL) = &HFFFFFFE7L Then 'WM_GETOBJECT, UiaRootObjectId
      m.Result = IntPtr.Zero
      Exit Sub
    End If
    MyBase.WndProc(m)
  End Sub

  And that fixed the issue
  
  Questions:

  1. Is there a supported way to turn off UI Automation for a C1FlexGrid, either per grid or for the whole app?
  2. Does the FlexGrid UI Automation provider support virtualization (ItemContainer / VirtualizedItem patterns), so a client only gets the visible rows instead of every cell?

  Thanks

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  vivek.singh

  

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  Posted 29 October 2026, 5:04 am EST

  Hello,

  Thank you for providing details.

  We were able to observe a bit of a delay on our end when testing with Windows Narrator active. We are getting in touch with our development team to get their insights. Rest assured, we will update you as soon as we hear back from them.

  [Internal Tracking ID: C1WIN-35867]

  Best regards,
  
  Vivek Singh