Once the cell goes into edit mode, the tree displays a child control for editing and it is this control that will get mouse messages. So it's really hard to start a drag on a cell in that case. What you will need to do is somehow distinguish between when you want the cell to go into edit mode and when you want it to drag. Maybe what you can do is set the CellClickAction to SelectNodeOnly and then trap the MouseDown and MouseUp events and if the points in these two events are the same (or really close), then you know the user clicked on the cell instead of dragging, so you can call PerformAction(EnterEditMode) to force the cell to start an edit.
what if you have 2 columns. the fist is a read only text and the second is an editable checkbox. can i drag from first column and click on the second column means an edit?
In the WinGrid, I think the CellClickAction property is available on the Column. But I don't think that's the case in the tree, so you can't do it that way.
I think what you would have to do is set the CellClickAction to enter edit mode on the cell, but then handle an event of the tree like BeforeEnterEditMode, and cancel it for the column you want to be read-only.