I know this is old but I had a similar problem in 19.1 with SubItemColumns.  It was right after I added a custom SortComparer to a SubItemColumn.  Removing the comparer removed the error so I added a function to null the sortcompares prior to the clear and that seems to have helped as well.

Craig,

The issue that this thread was originally created for and development issue 182922 was logged for where a NullReferenceException is thrown when calling Clear on the UltraListView.Items collection was resolved and is not reproducible in 18.1.20181.177.

The call stack that Michael provided is different from the original issue and if that is what you are seeing, we need a sample to look into what is happening.

Working properly in 18.1.20181.177

The bug has resurfaced in version 17.2

I am using suspend layout, and confirmed that no event dependencies.

in previous versions was working fine, with no problems, and no changes to affected code for quite a few version updates.

If for simply clearing a list, if i make my own version of Clear, i can bypass the  bug.

However, when changing the order of items in a list, and keeping a reference to a selected item
I cannot bypass this bug.

My guess is that  you  have an internal event in infragistics source code fired by the  ulttralistview container that is trying  to  update some event items

This is really messing up a large application

--

If i add the following to step through changes

Private Sub UltraListView1_PropertyChanged(sender As Object, e As PropertyChangedEventArgs) Handles UltraListView1.PropertyChanged
MessageBox.Show(e.ChangeInfo.PropId.ToString())
End Sub

Then the bug dissapears. Of course this is not practical, but it does demonstrate that the problem exists int eh internal event handling withing your ultralistview being used in detail mode.

The only event i  am handling, is on item activated, and i have removed this to  confirm that it is not the source of the problems.

Here is a complete stack trace

Immeadiate frames on call stack: at Infragistics.Win.UltraWinListView.UltraListViewItem.get_UIElement()
at Infragistics.Win.UltraWinListView.SubItemEditorOwner.GetEditorElement(Object ownerContext)
at Infragistics.Win.EditorWithMask.ResolveAppearance(AppearanceData& appData, AppearancePropFlags& requestedProps, EmbeddableEditorOwnerBase owner, Object ownerContext)
at Infragistics.Win.EditorWithMaskEmbeddableUIElement.InitAppearance(AppearanceData& appData, AppearancePropFlags& requestedProps)
at Infragistics.Win.EditorWithMaskEmbeddableUIElement.GetImage()
at Infragistics.Win.EditorWithMaskEmbeddableUIElement.PositionChildElements()
at Infragistics.Win.UIElement.VerifyChildElements(ControlUIElementBase controlElement, Boolean recursive)
at Infragistics.Win.UIElement.VerifyChildElements(ControlUIElementBase controlElement, Boolean recursive)
at Infragistics.Win.UIElement.VerifyChildElements(ControlUIElementBase controlElement, Boolean recursive)
at Infragistics.Win.UIElement.VerifyChildElements(ControlUIElementBase controlElement, Boolean recursive)
at Infragistics.Win.UIElement.VerifyChildElements(ControlUIElementBase controlElement, Boolean recursive)
at Infragistics.Win.UIElement.VerifyChildElements(ControlUIElementBase controlElement, Boolean recursive)
at Infragistics.Win.UIElement.VerifyChildElements(Boolean recursive)
at Infragistics.Win.UltraWinListView.UltraListView.OnPropertyChanged(PropChangeInfo propChange)
at Infragistics.Win.UltraWinListView.UltraListView.OnPropertyChanged(PropertyChangedEventArgs e)
at Infragistics.Win.UltraWinListView.UltraListView.OnSubObjectPropChanged(PropChangeInfo propChange)
at Infragistics.Shared.SubObjectBase.NotifyPropChange(PropChangeInfo trigger)
at Infragistics.Win.UltraWinListView.UltraListViewItemsCollection.RemoveHelper(Int32 index, Boolean notify)
at SilverEarth.SeCommerce.WinAdmin.CatalogProductDisplayOrderControl.btnMoveUp_Click(Object sender, EventArgs e)
at System.Windows.Forms.Control.OnClick(EventArgs e)
at Infragistics.Win.Misc.UltraButtonBase.OnClick(EventArgs e)
at Infragistics.Win.Misc.UltraButton.OnMouseUp(MouseEventArgs e)
at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
at System.Windows.Forms.Control.WndProc(Message& m)
at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
Walk of Stack Frames follow

Caller: raise_UnhandledException
Class Name: WindowsFormsApplicationBase
File Name and Line: | Line # 0

Caller: OnUnhandledException
Class Name: WindowsFormsApplicationBase
File Name and Line: | Line # 0

Caller: OnThreadException
Class Name: ThreadContext
File Name and Line: | Line # 0

Caller: WndProcException
Class Name: Control
File Name and Line: | Line # 0

Caller: Callback
Class Name: NativeWindow
File Name and Line: | Line # 0

Caller: DefWndProc
Class Name: NativeWindow
File Name and Line: | Line # 0

Caller: WndProc
Class Name: UiaProviderControlNativeWindow
File Name and Line: | Line # 0

Caller: Callback
Class Name: NativeWindow
File Name and Line: | Line # 0

Caller: DefWndProc
Class Name: NativeWindow
File Name and Line: | Line # 0

Caller: WndProc
Class Name: GestureNativeWindow
File Name and Line: | Line # 0

Caller: Callback
Class Name: NativeWindow
File Name and Line: | Line # 0

Caller: DispatchMessageW
Class Name: UnsafeNativeMethods
File Name and Line: | Line # 0

Caller: DispatchMessageW
Class Name: UnsafeNativeMethods
File Name and Line: | Line # 0

Caller: System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop
Class Name: ComponentManager
File Name and Line: | Line # 0

Caller: RunMessageLoopInner
Class Name: ThreadContext
File Name and Line: | Line # 0

Caller: RunMessageLoop
Class Name: ThreadContext
File Name and Line: | Line # 0

Caller: OnRun
Class Name: WindowsFormsApplicationBase
File Name and Line: | Line # 0

Caller: DoApplicationModel
Class Name: WindowsFormsApplicationBase
File Name and Line: | Line # 0

Caller: Run
Class Name: WindowsFormsApplicationBase
File Name and Line: | Line # 0

Caller: Main
Class Name: MyApplication
File Name and Line: | Line # 0

Error: Object reference not set to an instance of an object.

Wondering if this was ever resolved? Or did it resurface. I'm still getting this error in 17.1. The workaround still works though.