TabControl with DragDrop not raising MouseClick events on tabs

[NickThissen]

Hi,

I have a custom (inherited) TabControl which adds Drag/Drop functionality to it, so that one can drag the tabs around, either within the same control (to re-order them) or to and from other TabControls.

I've noticed some time ago that my TabControl however was not raising its MouseClick and MouseUp events (or actually: it is not calling its OnMouseClick and OnMouseUp methods, which comes down to the same thing).
I've been struggling with this problem for a long while and I finally figured out what is happening. I'm no closer to figuring out what to do about it though...


The problem seems related to the drag drop functionality. I have this code in the OnMouseDown method (which is raised as usual):

Protected Overrides Sub OnMouseDown(ByVal e As System.Windows.Forms.MouseEventArgs)
        MyBase.OnMouseDown(e)
 
        If e.Button = Windows.Forms.MouseButtons.Left Then
            Dim pt As Point = New Point(e.X, e.Y)
            Dim tp As Tab = Me.GetTabFromPoint(pt)
 
            If tp IsNot Nothing Then
                Me.DoDragDrop(tp, DragDropEffects.All)
            End If
        End If
    End Sub

To summarize, if the Left button is clicked, I get the TabPage under the mouse (if any) and start a DragDrop operation with the TabPage as the first argument. This causes some other code in the OnDragOver method to run which handles the re-ordering of the tabs (irrelevant code).

If I use this code, the OnMouseClick and OnMouseUp methods are never called.

If I remove the Me.DoDragDrop call, they are called as usual.


What can I do about this? I definitely want the drag drop functionality, but I also definitely want to handle the MouseClick and MouseUp events since I'm drawing close buttons on my TabPages, and without these events you can't click them...

[NickThissen]

Nobody..?

[SJWhiteley]

The mouse events are not called when a drag operation is in progress.

There are OnDragOver - which you have found - and OnDragDrop (I think, as well as OnDragEnter and OnDragLeave) that should contain information about the drag operation.

[NickThissen]

Yes, but I don't need information about the drag operation. I just need to be able to handle the OnMouseClick method to determine if the click is inside the close button rectangle (and if it is, the tab is sent a close request), and possibly the OnMouseUp event to invalidate the tab header.

I can't see any way around this at all... The MouseClick event works in such a way that it is only raised when you release the mouse, so clicking it down and holding it will not raise it (yet). Even if you move the mouse around a little before releasing it, the event is still fired only later. That is exactly the behavior I want, and it is why I can't use the MouseDown event: that will be raised as soon as the button is pressed, which is too early. The user could choose to click the close button while holding the mouse, then move the mouse back out and release it outside of the close button. In that case, the tab should not close. If I use the MouseDown event, the tab will close as soon as you press.

But this is a problem: if you press the mouse and then move it even slightly, the drag drop operation will begin... So how can I do what I want and still have the drag drop functionality?

[ForumAccount]

Nick, as SJ said, it seems the framework swallows mouse events during a drag operation. So... from what I can tell there is no managed way to do this. Try this implementation and let me know if that works:

Public Class OrderedTabControl
    Inherits TabControl
 
    '//fields
    Private draggingTab As TabPage = Nothing
 
    '//methods
    Protected Overrides Sub OnDragOver(ByVal drgevent As  _
                                       DragEventArgs)
        MyBase.OnDragOver(drgevent)
 
        drgevent.Effect = DragDropEffects.Move
 
    End Sub
 
    Protected Overrides Sub OnQueryContinueDrag(ByVal e As  _
                                                QueryContinueDragEventArgs)
        MyBase.OnQueryContinueDrag(e)
 
        If Me.draggingTab IsNot Nothing Then
 
            Dim raiseMouse = False
            Dim pt = Me.PointToClient(Control.MousePosition)
            Dim startTab = Me.GetTabRect(Me.TabPages.IndexOf(Me.draggingTab)) _
                             .Contains(pt)
            Dim otherTab = Me.GetRectangles().Any(Function(r) r.Contains(pt))
            Dim leftButton = Control.MouseButtons.Equals(MouseButtons.Left)
            Dim mouseArgs = New MouseEventArgs(Windows.Forms.MouseButtons.Left, _
                                               1, pt.X, pt.Y, 0)
 
            If Not leftButton AndAlso Not otherTab Then
                '//mouse let go outside of draggable area
                e.Action = DragAction.Cancel
                raiseMouse = True
            ElseIf Not leftButton AndAlso otherTab AndAlso Not startTab Then
                '//mouse let go in allowable area
                e.Action = DragAction.Drop
                raiseMouse = True
            ElseIf Not leftButton AndAlso startTab Then
                '//mouse let go in rectangle that it started from, cancel drag
                e.Action = DragAction.Cancel
                raiseMouse = True
            Else
                '//anything else can continue
                e.Action = DragAction.Continue
            End If
 
            If raiseMouse Then
                Me.OnMouseClick(mouseArgs)
                Me.OnMouseUp(mouseArgs)
            End If
 
        End If
 
    End Sub
 
    Protected Overrides Sub OnMouseDown(ByVal e As  _
                                        MouseEventArgs)
        MyBase.OnMouseDown(e)
        If e.Button = Windows.Forms.MouseButtons.Left Then
            Dim pt = New Point(e.X, e.Y)
            Dim tp = Me.GetTabFromPoint(pt)
 
            If tp IsNot Nothing Then
                Me.draggingTab = tp
                Me.DoDragDrop(tp, DragDropEffects.Move)
            End If
 
        End If
    End Sub
 
    Protected Overrides Sub OnMouseUp(ByVal e As  _
                                      MouseEventArgs)
        MyBase.OnMouseUp(e)
    End Sub
 
    Protected Overrides Sub OnMouseClick(ByVal e As  _
                                         MouseEventArgs)
        MyBase.OnMouseClick(e)
    End Sub
 
    '//methods
    Private Function GetRectangles() As IEnumerable(Of Rectangle)
        Return Me.TabPages.Cast(Of TabPage)() _
                          .Select(Function(t, i) Me.GetTabRect(i))
    End Function
 
    Private Function GetTabFromPoint(ByVal pt As Point) As TabPage
        Return Me.GetTabFromPoint(pt.X, pt.Y)
    End Function
 
    Private Function GetTabFromPoint(ByVal x As Integer, _
                                     ByVal y As Integer) As TabPage
 
        For i = 0 To Me.TabCount - 1
            If Me.GetTabRect(i).Contains(x, y) Then
                Return Me.TabPages(i)
            End If
        Next
 
        Return Nothing
 
    End Function
 
End Class

[NickThissen]

That looks promising. So basically you call the methods yourself. I thought of that but had no clue when to do it. I never knew about that OnQueryContinueDrag method, and now I think you have also answered a question that I hadn't even asked yet*.

I've no time to try it right now but I'll get back to you.


* The question I mean is "how do I react when a tab is dropped outside of a tabcontrol". I have been implementing the 'tab groups' feature of visual studio, where you can arrange the tabs in multiple groups (horizontally or vertically) and drag them between groups. You can create a new group by rightclicking a tab and selecting the appropriate contextmenu item, but in visual studio you can also simply drag a tab outside of any group and it will give you the option of creating a new (horizontal or vertical) group, or if a group already exists it will automatically create a new one (I think). I had no way to do that previously but this OnQueryContinueDrag seems to be the missing link!

[ForumAccount]

Nick always asks the questions that are the most fun to answer.

[NickThissen]

Oh well, that's what I do
And you always answer them quite satisfyingly. I must say I am a little scared now that you have started answering questions I haven't asked yet

[ForumAccount]

Yeah, I built an app that reads the mind of any selected VBForums user... I could sell it to you. Right now John is thinking about... eating a Big Mac??!

[SJWhiteley]

Ah, I see your problem, now.

Here's how I do it: whatever you 'drag' you have to move a certain amount before a drag operation begins. It seems that's how other draggable objects operate, so I've just mimicked that.

However, in your case, I wouldn't initiate a drag from the close button.

[NickThissen]

However, in your case, I wouldn't initiate a drag from the close button.

Why didn't I think of that lol. That's brilliant. Of course I shouldn't initiate a drag from the close button, and if I don't then the mouse events are raised as usual and the whole problem doesn't exist... I haven't tried it yet but I'm sure it will work... You're a genius