protected override void WndProc(ref Message msg)
{
if (msg.Msg == Win32.WM_HSCROLL)
{
// Store the handle for use in Invalidate()
_hScrollbarHandle = msg.HWnd;
// Collect info about the position of the horizontal scrollbar
Win32.ScrollInfo si = new Win32.ScrollInfo();
si.fMask = (int)Win32.ScrollInfoMask.SIF_ALL;
si.cbSize = (uint)Marshal.SizeOf(si);
Win32.GetScrollInfo(msg.HWnd, 0, ref si);
if ((msg.WParam.ToInt32() & 0xFF) == Win32.SB_THUMBTRACK)
{
// If the user is in the middle of dragging the scrollbar, we're interested in
// the 'track' position
_scrollLeft = si.nTrackPos;
}
else
{
// Otherwise just the regular scrollbar position
_scrollLeft = si.nPos;
}
// Force repaint
base.Invalidate();
}
if(!CancelWndProc(msg))
base.WndProc(ref msg);
}
private int ScrollInfo(Win32.ScrollBarConstants fnBar)
{
Win32.ScrollInfo si = new Win32.ScrollInfo();
si.cbSize = (uint)Marshal.SizeOf(si);
si.fMask = (int)Win32.ScrollInfoMask.SIF_POS;
if (!Win32.GetScrollInfo(Handle, (int)fnBar, ref si))
return 0;
return si.nPos;
}
public new void Invalidate()
{
if (_hScrollbarHandle != IntPtr.Zero)
{
// If we've been invalidated, update our drawing code to the new horizontal scrollbar
// position (which is sometimes spontaneously reset to zero and can't be programmatically
// set to its former value) - see CA-11405.
Win32.ScrollInfo si = new Win32.ScrollInfo();
si.fMask = (int)Win32.ScrollInfoMask.SIF_ALL;
si.cbSize = (uint)Marshal.SizeOf(si);
Win32.GetScrollInfo(_hScrollbarHandle, 0, ref si);
_scrollLeft = si.nTrackPos; // often zero
}
base.Invalidate();
}