WM_VSCROLL (Trackbar) notification code
The WM_VSCROLL message is sent to the owner of a vertical trackbar control when the slider changes position.
A window receives this message through its WindowProc function.
The HIWORD specifies the current position of the slider if the LOWORD is TB_THUMBPOSITION or TB_THUMBTRACK. For all other notification codes, the high-order word is zero; send the TBM_GETPOS message to determine the slider position.
The LOWORD specifies a notification code that indicates the user's interaction with the trackbar. This word can be one of the following values.
The user pressed the END key (VK_END).
The trackbar received WM_KEYUP, meaning that the user released a key that sent a relevant virtual key code.
The user clicked the channel below or to the right of the slider (VK_NEXT).
The user clicked the channel above or to the left of the slider (VK_PRIOR).
The trackbar received WM_LBUTTONUP following a TB_THUMBTRACK notification code.
The user dragged the slider.
The user pressed the HOME key (VK_HOME).
The handle to the trackbar control.
If an application processes this message, it should return zero.
The TB_THUMBTRACK code is typically used by applications that provide feedback as the user drags the scroll box.
Note that the WM_VSCROLL message carries only 16 bits of position data. Thus, applications that rely solely on WM_VSCROLL (and WM_HSCROLL) for slider position data have a practical maximum position value of 65,535.
Minimum supported client
Windows Vista [desktop apps only]
Minimum supported server
Windows Server 2003 [desktop apps only]