What caused my splitter to move? <p>I've got an issue that's doing my head in. I have a .net usercontrol with a splitcontainer control on it. The .net usercontrol is actually hosted in a control container in much older non .net legacy code (Visual Objects).</p> <p>The problem I'm having is that I'm getting a splitter_moved event firing on the splitcontainer control when the usercontrol is presented to the user, but I'm at a loss to find what's causing it to actually move. I've come across a number of curious behaviours with this interaction between the VO code and .net stuff, but I've got several other usercontrols embedded in VO container controls that work just fine. It's just this particular one that seems to be having a problem.</p> <p>The VO container controls are all identical. So are the .net usercontrols that are embedded in them (they all inherit from the same base class). This is why I'm having so much difficulty in understanding why it's just this one.</p> <p>I guess what I really want to know is how to determine what caused the splitter to move inside the splitcontainer control. The sender and eventargs aren't much help, because they all just refer to the splitcontainer control (obviously).</p> <p>Help??</p> <p>EDIT: The call stack from within the splitter_moved event handler is as follows:</p> <pre><code>00000072 0.26412687 Method: Void splitContainerMain_SplitterMoved(System.Object, System.Windows.Forms.SplitterEventArgs) 00000073 0.26649699 Method: Void OnSplitterMoved(System.Windows.Forms.SplitterEventArgs) 00000074 0.26906940 Method: Void set_SplitterDistance(Int32) 00000075 0.27223459 Method: Void ApplySplitterDistance() 00000076 0.27425244 Method: Void ResizeSplitContainer() 00000077 0.27621472 Method: Void OnLayout(System.Windows.Forms.LayoutEventArgs) 00000078 0.27813032 Method: Void PerformLayout(System.Windows.Forms.LayoutEventArgs) 00000079 0.28007442 Method: Void System.Windows.Forms.Layout.IArrangedElement.PerformLayout(System.Windows.Forms.Layout.IArrangedElement, System.String) 00000080 0.28211826 Method: Void DoLayout(System.Windows.Forms.Layout.IArrangedElement, System.Windows.Forms.Layout.IArrangedElement, System.String) 00000081 0.28451827 Method: Void OnResize(System.EventArgs) 00000082 0.28713536 Method: Void OnSizeChanged(System.EventArgs) 00000083 0.28970191 Method: Void UpdateBounds(Int32, Int32, Int32, Int32, Int32, Int32) 00000084 0.29425862 Method: Void UpdateBounds() 00000085 0.29450893 Method: Void WmWindowPosChanged(System.Windows.Forms.Message ByRef) 00000086 0.29477015 Method: Void WndProc(System.Windows.Forms.Message ByRef) 00000087 0.29508862 Method: Void WndProc(System.Windows.Forms.Message ByRef) 00000088 0.29539761 Method: Void WndProc(System.Windows.Forms.Message ByRef) 00000089 0.29568058 Method: Void WndProc(System.Windows.Forms.Message ByRef) 00000090 0.29596806 Method: Void OnMessage(System.Windows.Forms.Message ByRef) 00000091 0.29627341 Method: Void WndProc(System.Windows.Forms.Message ByRef) 00000092 0.29659048 Method: IntPtr Callback(IntPtr, Int32, IntPtr, IntPtr) 00000093 0.29688439 Method: Boolean SetWindowPos(System.Runtime.InteropServices.HandleRef, System.Runtime.InteropServices.HandleRef, Int32, Int32, Int32, Int32, Int32) 00000094 0.29714754 Method: Void SetBoundsCore(Int32, Int32, Int32, Int32, System.Windows.Forms.BoundsSpecified) 00000095 0.29755905 Method: Void SetBoundsCore(Int32, Int32, Int32, Int32, System.Windows.Forms.BoundsSpecified) 00000096 0.29781467 Method: Void System.Windows.Forms.Layout.IArrangedElement.SetBounds(System.Drawing.Rectangle, System.Windows.Forms.BoundsSpecified) 00000097 0.29814151 Method: Void xLayoutDockedControl(System.Windows.Forms.Layout.IArrangedElement, System.Drawing.Rectangle, Boolean, System.Drawing.Size ByRef, System.Drawing.Rectangle ByRef) 00000098 0.29844967 Method: System.Drawing.Size LayoutDockedControls(System.Windows.Forms.Layout.IArrangedElement, Boolean) 00000099 0.29872790 Method: Boolean xLayout(System.Windows.Forms.Layout.IArrangedElement, Boolean, System.Drawing.Size ByRef) 00000100 0.29901370 Method: Boolean LayoutCore(System.Windows.Forms.Layout.IArrangedElement, System.Windows.Forms.LayoutEventArgs) 00000101 0.29931039 Method: Boolean Layout(System.Object, System.Windows.Forms.LayoutEventArgs) 00000102 0.29965651 Method: Void OnLayout(System.Windows.Forms.LayoutEventArgs) 00000103 0.29993618 Method: Void OnLayout(System.Windows.Forms.LayoutEventArgs) 00000104 0.30027559 Method: Void OnLayout(System.Windows.Forms.LayoutEventArgs) 00000105 0.30064937 Method: Void PerformLayout(System.Windows.Forms.LayoutEventArgs) 00000106 0.30087790 Method: Void System.Windows.Forms.Layout.IArrangedElement.PerformLayout(System.Windows.Forms.Layout.IArrangedElement, System.String) 00000107 0.30116984 Method: Void DoLayout(System.Windows.Forms.Layout.IArrangedElement, System.Windows.Forms.Layout.IArrangedElement, System.String) 00000108 0.30157101 Method: Void OnResize(System.EventArgs) 00000109 0.30196688 Method: Void OnResize(System.EventArgs) 00000110 0.30212274 Method: Void OnSizeChanged(System.EventArgs) 00000111 0.30244765 Method: Void UpdateBounds(Int32, Int32, Int32, Int32, Int32, Int32) 00000112 0.30264741 Method: Void UpdateBounds() 00000113 0.30294549 Method: Void WmWindowPosChanged(System.Windows.Forms.Message ByRef) 00000114 0.30337656 Method: Void WndProc(System.Windows.Forms.Message ByRef) 00000115 0.30359614 Method: Void WndProc(System.Windows.Forms.Message ByRef) 00000116 0.30389002 Method: Void WndProc(System.Windows.Forms.Message ByRef) 00000117 0.30451524 Method: Void WndProc(System.Windows.Forms.Message ByRef) 00000118 0.30456889 Method: Void OnMessage(System.Windows.Forms.Message ByRef) 00000119 0.30483985 Method: Void WndProc(System.Windows.Forms.Message ByRef) 00000120 0.30507788 Method: IntPtr Callback(IntPtr, Int32, IntPtr, IntPtr) 00000121 0.30540919 Method: Boolean SetWindowPos(System.Runtime.InteropServices.HandleRef, System.Runtime.InteropServices.HandleRef, Int32, Int32, Int32, Int32, Int32) 00000122 0.30566931 Method: Void SetBoundsCore(Int32, Int32, Int32, Int32, System.Windows.Forms.BoundsSpecified) 00000123 0.30598581 Method: Void SetBounds(Int32, Int32, Int32, Int32, System.Windows.Forms.BoundsSpecified) 00000124 0.30637357 Method: Void set_Height(Int32) 00000125 0.30679765 Method: Void ContainerCtrl.ResizeForm(ContainerCtrl*, WTL.CRect) 00000126 0.30718428 Method: Int32 ContainerCtrl.OnSize(ContainerCtrl*, UInt32, UInt32, Int32, Int32*) 00000127 0.30755892 Method: Int32 ContainerCtrl.ProcessWindowMessage(ContainerCtrl*, HWND__*, UInt32, UInt32, Int32, Int32*, UInt32) 00000128 0.30793831 Method: Int32 ATL.CDialogImplBaseT&lt;ATL::CWindow&gt;.DialogProc(HWND__*, UInt32, UInt32, Int32) 00000129 0.30838418 Method: Int32 ATL.CAxDialogImpl&lt;ContainerCtrl,ATL::CWindow&gt;.DialogProc(HWND__*, UInt32, UInt32, Int32) 00000130 0.30881271 Method: Int32 SetWindowPos(HWND__*, HWND__*, Int32, Int32, Int32, Int32, UInt32) 00000131 0.30922171 Method: Int32 ATL.CComControlBase.IOleInPlaceObject_SetObjectRects(ATL.CComControlBase*, tagRECT*, tagRECT*) 00000132 0.30961114 Method: Int32 ATL.IOleInPlaceObjectWindowlessImpl&lt;ContainerCtrl&gt;.SetObjectRects(ATL.IOleInPlaceObjectWindowlessImpl&lt;ContainerCtrl&gt;*, tagRECT*, tagRECT*) </code></pre> <p>Edit: Ok, it looks like the resize event on the VO container control is firing on this one when it's shown to the user, but not on the others.</p> <p>Confusing much?!?</p>