CODEWITHSUNDEEP
vb6msflexgrid
Xodarap
Xodarap

Reputation: 11849

Tooltip only shows when running from source

I have a hierarchical flexgrid control with the ToolTipText property set, and when I run from source the tooltip displays as it should. But when I compile it and run that way, the tooltip doesn't display.

I've tried to remove anything listening to MouseMove in the hopes that that would fix it, and when I add some code to put the tooltip text into a message box, it appears to be set correctly. Can anyone think of why this would be happening?

Update: It appears that the problem arises when I host the grid inside another user control. E.g.: make container.ctl, which is just a blank control but with ControlContainer = True. Then make gridholder.ctl, which is a mshfg inside of a container.ctl. Lastly, embed gridholder.ctl into some form. Tooltips on the flexgrid don't appear to show up.

I'm interested to see how reproducible this is...

Upvotes: 2

Views: 2500

Answers (2)

UnhandledExcepSean
UnhandledExcepSean

Reputation: 12804

After a bit of research, I found what I think is the underlying problem. Your user control is not implementing any method for the controls to interact with. User Controls that are Container Controls need to implement the Extender functionality. These two links are the best I've found on the subject so far.

http://www.justvb.net/obook/ch7.htm#UsingtheExtenderObject

http://msdn.microsoft.com/en-us/library/aa733622(v=vs.60).aspx

Upvotes: 0

Mike Spross
Mike Spross

Reputation: 8099

I haven't found a workaround for this issue yet, but I have a better idea of why it's happening after some testing and stepping through some of the VB6 runtime code in WinDBG.

The first interesting thing is that VB6 doesn't use the standard tooltip display mechanisms provided by Windows. For example, it doesn't use WM_NOTIFY messages to show/hide tooltips, or any of the other "standard" tooltip support described in the documentation explaining how tooltips work in Windows.

Instead, the VB6 runtime has its own way of managing and displaying tooltips. In principle, it's similar to in some ways to the standard Windows way of dealing with tooltips, but it's also different in a quite a few areas.

A breakdown of how VB6 does tooltips:

  • When a VB6 program starts, the runtime uses SetWindowsHookEx to install a mouse hook for the program's main thread.

  • The mouse hook intercepts all mouse messages sent to the program, in particular all WM_MOUSEMOUSE messages

  • Whenever the mouse hook runs, it calls an internal method in the VB6 runtime to get the object pointer (HCTL) of the control that the mouse is currently over top of. Note that this is an actual COM interface pointer, not a window handle.

  • It translates the HCTL to the corresponding window handle (HWND).

  • It checks to see if the mouse position is within that window's rectangle.

  • If so, it retrieves the ToolTipText property for the control. If this is not empty, it creates a tooltip window and displays the tooltip after a 700ms delay.

The problem with the MSHFlexGrid (and I imagine other controls that are not standard VB6 controls) is that this code doesn't retrieve the correct HCTL when you hover over the control and it's inside a custom container.

In that case, the code retrieves the HCTL of the custom container, not the HCTL of the MSHFlexGrid itself. Therefore, it retrieves the container's ToolTipText property (which is empty) and not the grid's ToolTipText, and therefore won't display a tooltip.

I'm not sure exactly why it does this, because as noted in the comments on your question, all of this works correctly if you use a PictureBox as your container.

I suspect the PictureBox has code to handle this correctly that is not included when you create your own container.

I'll update this answer with an actual workaround if I can find one. The only thing I can think right now is to somehow "sync" your container's ToolTipText property with the grid's ToolTipText property, so that when VB6 requests the container's ToolTipText, it will return the value of the grid's ToolTextTip property instead.

This is easier said than done, however, because ToolTipText is an extender property, and extender properties take precedence over properties that you write yourself that have the same name.

Upvotes: 2

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