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How to Limit Slider Movement

  • Článek

As described in About Trackbar Controls, it is possible to set off part of the trackbar range as a selection range. One purpose of a selection range might be to limit movement of the slider, making some parts of the full range off limits.

What you need to know

Technologies

Prerequisites

  • C/C++
  • Windows User Interface Programming

Instructions

Limit Slider Movement

The following example code limits movement of the slider by resetting the slider's position whenever it is moved outside the selection range.

case WM_HSCROLL:
    {
        HWND hTrackbar = GetDlgItem(hDlg, IDC_SLIDER1);
        
        if (hTrackbar == (HWND)lParam)
        {
            int newPos    = SendMessage(hTrackbar, TBM_GETPOS, 0, 0);
            int selStart  = SendMessage(hTrackbar, TBM_GETSELSTART, 0, 0);
            int selEnd    = SendMessage(hTrackbar, TBM_GETSELEND, 0, 0);
            
            if (newPos > selEnd)
            {
                SendMessage(hTrackbar, TBM_SETPOS, (WPARAM)TRUE, (LPARAM)selEnd);
            }
            
            else if (newPos < selStart)
            {
                SendMessage(hTrackbar, TBM_SETPOS, (WPARAM)TRUE, (LPARAM)selStart);
            }
        }
        
        break;
    }

Remarks

This code snippet would be part of a dialog box's Window Procedure.

Using Trackbar Controls