NullReferenceException in 3.0 branch

[damageboy]

Got this exception

Details: System.NullReferenceException: Object reference not set to an instance of an object.
   at System.Windows.Forms.Docking.DockPaneStripBase.OnMouseMove(MouseEventArgs e) in c:\projects\public\scm\dockpanelsuite.git\WinFormsUI\Docking\DockPaneStripBase.cs:line 217
   at System.Windows.Forms.Control.WmMouseMove(Message& m)
   at System.Windows.Forms.Control.WndProc(Message& m)
   at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

        protected override void OnMouseMove(MouseEventArgs e)
        {
            base.OnMouseMove(e);

            if (e.Button != MouseButtons.Left || _dragBox.Contains(e.Location)) 
                return;

            if (DockPane.DockPanel.AllowEndUserDocking && DockPane.AllowDockDragAndDrop && DockPane.ActiveContent.DockHandler.AllowEndUserDocking)
                DockPane.DockPanel.BeginDrag(DockPane.ActiveContent.DockHandler);
        }

Here's the faulty statement

[lextm]

Can you do some debugging to see which variable is null when this exception occurs? Without that piece of information, it is very hard to reproduce it.

[mehmetakifayas]

Hi lextm,
I'm having the same NullReferenceException in branch 3.0.
Bug steps to reproduce:
-Run DockSample project
-Create two dummy document (Document1, Document2)
-Dock Document2 to right of Document1
-Double click on the TabText of Document2 (to change Dockstate as float)
-Exception occurs.

[roken]

Thanks for the repro steps! This is an issue on the 3.0 branch introduced by 364bfca.

[lextm]

Added an extra check on DockPane.ActiveContent to avoid the exception. Tested and it seems to work as expected.