Enter and Leave events don’t work

I just figured it out.  I remembered a similar problem when using these controls in Visual Basic.  Only one control within the same container should be able to have focus.  In Visual Basic, I use to use separate Forms to create each pane, and that created all kinds of focus problems (since two different forms can have two different active controls).  The workaround was to place all my pane controls within different PictureBoxes on the same form.  Since they were all in the same container, only one could have focus at a time.

When working with C#, I use separate UserControls for each pane, and I never really give them a container.  To test this theory, I added each newly created pane UserControl to my main form's 'Controls' collection.  Since they all are in the same collection, only one can have focus at a time.  Sure enough, all the events fired as expected!

Here's some basic sample code from a routine on a Main Form that could set up the panes:

// User Controls used as a panes
TestPane paneControl1 = new TestPane();
TestPane paneControl2 = new TestPane();
// Add controls to main form controls collection
this.Controls.Add(paneControl1);
this.Controls.Add(paneControl2);
// Create Panes
dockingPane.CreatePane(ID_PANE_1, 100, 100, DockingDirection.DockTopOf, null);
dockingPane.CreatePane(ID_PANE_2, 100, 100, DockingDirection.DockTopOf, null);
// Note: Assign Handles in AttachPane event

No problem!

I did find an issue with this approach that I need to warn you about.  Since the AttachPane event is only fired when a pane becomes visible, this means you're controls will be unattached until the pane is visible.  In the case of grouped panes, this means the controls aren't attached until the user actually selects the pane in the tabbed group.

If you use the approach I mentioned, the controls are visible when the are added to the controls collection.  That means that unattached controls will be visible until the pane is selected for the first time.  To avoid this, you should set the visible property to false when you create the control and then, in the AttachPane event, set the visible property back to true.

An alternative to the AttachPane event would be to use the OnHandleCreated event of the items you want to add to your panes.  At that point, you could assign the handle to the proper pane and not have to wait until the user selects a pane.

Unfortunately, I don't have a sample VB app that uses this, but I'll repeat the basic concepts.

1. Create a PictureBox control on the main form that will hold the content of every pane you wish to create.  I suggest making this a control array so that you can use a single event handler for all the controls (like for the Resize event).  This also helps be assigning the PictureBox the same index as the ID you use to identify a pane.
2. Set the 'visible' property of the PictureBox to false so that it won't appear on the form prior to being attached in the 'AttachPane' event.
3. Create your panes just as you would if they were on different forms.
4. In the 'AttachPane' event of CommandBars, set the handle of each pane to the handle of the corresponding PictureBox control.

That's the basics.  I've been using C# so long that I don't recall any other tricky steps.  I hope that helps.