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How to Create a Keyboard Interface for Standard Scroll Bars

  • Artikkel

Although a scroll bar control provides a built-in keyboard interface, a standard scroll bar does not. To implement a keyboard interface for a standard scroll bar, a window procedure must process the WM_KEYDOWN message and examine the virtual-key code specified by the wParam parameter. If the virtual-key code corresponds to an arrow key, the window procedure sends itself a WM_HSCROLL or WM_VSCROLL message with the low-order word of the wParam parameter set to the appropriate scroll bar request code.

For example, when the user presses the UP arrow key, the window procedure receives a WM_KEYDOWN message with wParam equal to VK_UP. In response, the window procedure sends itself a WM_VSCROLL message with the low-order word of wParam set to the SB_LINEUP request code.

What you need to know

Technologies

Prerequisites

  • C/C++
  • Windows User Interface Programming

Instructions

Create a Keyboard Interface for a Standard Scroll Bar

The following code example demonstrates how to include a keyboard interface for a standard scroll bar.

    case WM_KEYDOWN: 
    {
        WORD wScrollNotify = 0xFFFF;

        switch (wParam) 
        { 
            case VK_UP: 
                wScrollNotify = SB_LINEUP; 
                break; 
 
            case VK_PRIOR: 
                wScrollNotify = SB_PAGEUP; 
                break; 
 
            case VK_NEXT: 
                wScrollNotify = SB_PAGEDOWN; 
                break; 
 
            case VK_DOWN: 
                wScrollNotify = SB_LINEDOWN; 
                break; 
 
            case VK_HOME: 
                wScrollNotify = SB_TOP; 
                break; 
 
            case VK_END: 
                wScrollNotify = SB_BOTTOM; 
                break; 
        } 
 
        if (wScrollNotify != -1) 
            SendMessage(hwnd, WM_VSCROLL, MAKELONG(wScrollNotify, 0), 0L); 
 
        break; 
    }

Using Scroll Bars

Windows common controls demo (CppWindowsCommonControls)