BUG: Clicking Thumb Does Not Generate SB_THUMBPOSITION Message

• Microsoft Visual C++ Cross-Development Edition for Macintosh, version 2.0

SYMPTOMS

A mouse click on the thumb in a scrollbar will not generate the SB_THUMBPOSITION message unless the thumb is dragged.

CAUSE

If a mouse click occurs in a thumb without moving it, the Macintosh Control Manager treats it as though the mouse had moved outside of the thumb before being released. As a result, a mouse click within the thumb of a scrollbar is treated as a cancelled action, so no messages are generated. Visual C++ does not override this default behavior of the Macintosh Control Manager.

RESOLUTION

To track mouse clicks in the thumb, an application can use the SB_THUMBTRACK message and track the mouse to determine if it is released while still within the thumb. Alternatively, an application can use the Macintosh function SetCtlAction to specify a callback procedure to track the thumb.

STATUS

Microsoft has confirmed this to be a problem with Visual C++ version 2.0 Cross Development Edition for Macintosh. We are researching the problem and will post new information here in the Microsoft Knowledge Base as it becomes available.

MORE INFORMATION

An application running under Windows will generate an SB_THUMBPOSITION message when a mouse click occurs in a thumb whether or not the thumb is dragged. Applications that depend on this behavior will need to implement an alternative method for tracking mouse clicks in thumbs on the Macintosh.