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WM_HSCROLL (Trackbar) notification code

  • Článek

The WM_HSCROLL message is sent to the owner of a horizontal trackbar control when the slider changes position.

A window receives this message through its WindowProc function.

WM_HSCROLL

    WPARAM wParam
    LPARAM lParam;

Parameters

wParam

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.

Value Meaning
TB_BOTTOM
 The user pressed the END key (VK_END).
TB_ENDTRACK
 The trackbar received WM_KEYUP, meaning that the user released a key that sent a relevant virtual key code.
TB_LINEDOWN
 The user pressed the RIGHT ARROW (VK_RIGHT) or DOWN ARROW (VK_DOWN) key.
TB_LINEUP
 The user pressed the LEFT ARROW (VK_LEFT) or UP ARROW (VK_UP) key.
TB_PAGEDOWN
 The user clicked the channel below or to the right of the slider (VK_NEXT).
TB_PAGEUP
 The user clicked the channel above or to the left of the slider (VK_PRIOR).
TB_THUMBPOSITION
 The trackbar received WM_LBUTTONUP following a TB_THUMBTRACK notification code.
TB_THUMBTRACK
 The user dragged the slider.
TB_TOP
 The user pressed the HOME key (VK_HOME).

lParam

The handle to the trackbar control.

Return value

If an application processes this message, it should return zero.

Remarks

The TB_THUMBTRACK code is typically used by applications that provide feedback as the user drags the scroll box.

Note that the WM_HSCROLL message carries only 16 bits of position data. Thus, applications that rely solely on WM_HSCROLL (and WM_VSCROLL) for slider position data have a practical maximum position value of 65,535.

Requirements

Requirement Value
Minimum supported client
 Windows Vista [desktop apps only]
Minimum supported server
 Windows Server 2003 [desktop apps only]
Header
Winuser.h (include Windows.h)

See also

Reference

WM_VSCROLL