Check scroll visibility

Question

Is there a way to check if a vertical scrollbar is displayed on a specific ListView object?

I have Windows Forms with a listView on it, in a resize event that I would like to catch if a vertical scrollbar is visible in the list!

Answer 1

If it is WPF, there is a pattern that intercepts at the core of the solution ListView.LayoutUpdated.

If it's WinForms, you can use pinvoke and GetWindowLong ...

  static public class WndInfo
  {
    [DllImport("user32.dll", SetLastError = true)]
    static extern int GetWindowLong(IntPtr hWnd, int nIndex);

    ...
    public static bool IsWindowTopMost(IntPtr Handle)
    {
      return (GetWindowLong(Handle, GWL_EXSTYLE) & WS_EX_TOPMOST) != 0;
    }
    ...
  }

VB code exists , using GetWindowLongto check if there is a ScrollBar that you could port to C #.

Answer 2

, Winforms, , . .

public static class NativeMethods
{
    const Int32 LVM_FIRST = 0x1000;
    const Int32 LVM_SCROLL = LVM_FIRST + 20;

    [DllImport("user32")]
    static extern IntPtr SendMessage(IntPtr Handle, Int32 msg, IntPtr wParam, IntPtr lParam);


    // offset of window style value
    const int GWL_STYLE = -16;

    // window style constants for scrollbars
    const int WS_VSCROLL = 0x00200000;
    const int WS_HSCROLL = 0x00100000;

    [DllImport("user32.dll", SetLastError = true)]
    static extern int GetWindowLong(IntPtr hWnd, int nIndex);


    static ScrollBars GetControlVisibleScrollbars(Control ctl)
    {
        int wndStyle = GetWindowLong(ctl.Handle, GWL_STYLE);
        bool hsVisible = (wndStyle & WS_HSCROLL) != 0;
        bool vsVisible = (wndStyle & WS_VSCROLL) != 0;

        if(hsVisible)
            return vsVisible ? ScrollBars.Both : ScrollBars.Horizontal;
        else
            return vsVisible ? ScrollBars.Vertical : ScrollBars.None;
    }

    public static ScrollBars GetVisibleScrollbars(this ListView lv)
    {
        if(lv is null)
        {
            throw new ArgumentNullException(nameof(lv));
        }

        return GetControlVisibleScrollbars(lv);
    }


    public static ScrollBars GetVisibleScrollbars(this ScrollableControl ctl)
    {
        if(ctl is null)
        {
            throw new ArgumentNullException(nameof(ctl));
        }

        if(ctl.HorizontalScroll.Visible)
            return ctl.VerticalScroll.Visible ? ScrollBars.Both : ScrollBars.Horizontal;
        else
            return ctl.VerticalScroll.Visible ? ScrollBars.Vertical : ScrollBars.None;
    }


    private static void ScrollHorizontal(Form form, int pixelsToScroll)
    {
        SendMessage(form.Handle, LVM_SCROLL, (IntPtr)pixelsToScroll, IntPtr.Zero);
    }

    public static void EnsureVisible(this ListViewItem item, int subItemIndex, int margin=10)
    {
        if(item is null)
        {
            throw new ArgumentNullException(nameof(item));
        }

        if( subItemIndex > item.SubItems.Count - 1)
        {
            throw new IndexOutOfRangeException($"ListView {item.ListView.Name} does not have a SubItem on index {subItemIndex}");
        }

        // scroll to the item row.
        item.EnsureVisible();
        Rectangle bounds = item.SubItems[subItemIndex].Bounds;
        bounds.Width = item.ListView.Columns[subItemIndex].Width;
        ScrollToRectangle(item.ListView,bounds,margin);
    }



    private static void ScrollToRectangle(ListView listView, Rectangle bounds, int margin)
    {
        int scrollToLeft = bounds.X + bounds.Width + margin;
        if(scrollToLeft > listView.Bounds.Width)
        {
            ScrollHorizontal(listView.FindForm(),scrollToLeft - listView.Bounds.Width);
        }
        else
        {
            int scrollToRight = bounds.X - margin;
            if(scrollToRight < 0)
            {
                ScrollHorizontal(listView.FindForm(),scrollToRight);
            }
        }
    }

, , , , , :

var bar= MyListView.GetVisibleScrollbars();
while(bar== ScrollBars.Horizontal || bar== ScrollBars.Both)
{
    progressPanels.SplitterDistance += 5;
    bar = MyListView.GetVisibleScrollbars();
}

, , , DPI