dotnet windows forms: I have a listview whose contents are constantly being refreshed. When a
refresh occurs, I delete all the items and add back. I want to maintain the
scroll position before deleting all the items, and then want to restore it
once the items are added back.

I'm using P/Invoke Get/SetScrollInfo to get and restore the scroll
information. GetScrollInfo is working fine - it returns expected
information. SetScrollInfo has no effect - the scroll positions are
unchanged (both horz and vert are 0).

I also tried Get/SetScrollPos - no luck there, either.

Is this the correct way to do this? Anyone know what might be wrong?

Here's some of my code:

private void RefreshList()
{
User32.SCROLLINFO hsi = User32.GetScrollInfo((uint)
MyListView.Handle.ToInt32(), Constants.SB_HORZ);
User32.SCROLLINFO vsi = User32.GetScrollInfo((uint)
MyListView.Handle.ToInt32(), Constants.SB_VERT);

MyListView.BeginUpdate();

MyListView.Items.Clear();

// Add new items here...

User32.SetScrollInfo((uint)MyListView.Handle.ToInt32(),
Constants.SB_HORZ, false, hsi);
User32.SetScrollInfo((uint)MyListView.Handle.ToInt32(),
Constants.SB_VERT, false, vsi);

MyListView.EndUpdate();
}

public class Constants
{
public const int SB_HORZ = 0;
public const int SB_VERT = 1;
public const int SB_CTL = 2;
public const int SB_BOTH = 4;

public const int SIF_RANGE = 0x0001;
public const int SIF_PAGE = 0x0002;
public const int SIF_POS = 0x0004;
public const int SIF_DISABLENOSCROLL = 0x0008;
public const int SIF_TRACKPOS = 0x0010;
public const int SIF_ALL = (SIF_RANGE | SIF_PAGE | SIF_POS |
SIF_TRACKPOS);
}

public class User32
{
[StructLayout(LayoutKind.Sequential)]
public struct SCROLLINFO
{
public UInt32 cbSize;
public UInt32 fMask;
public Int32 nMin;
public Int32 nMax;
public UInt32 nPage;
public Int32 nPos;
public Int32 nTrackPos;
}

[DllImport("user32.dll", EntryPoint = "GetScrollInfo", SetLastError =
true)]
private static extern int GetScrollInfoWnd(uint hWnd, int nBar, ref
SCROLLINFO si);

public static SCROLLINFO GetScrollInfo(uint hWnd, int nBar)
{
SCROLLINFO si = new SCROLLINFO();

si.cbSize = (uint) System.Runtime.InteropServices.Marshal.SizeOf(si);
si.fMask = Constants.SIF_ALL;

// also tried si.fMask = Constants.SIF_PAGE | Constants.SIF_POS |
Constants.SIF_RANGE

GetScrollInfoWnd(hWnd, nBar, ref si); // returns correct data

return si;
}

[DllImport("user32.dll", EntryPoint = "SetScrollInfo", SetLastError =
true)]
private static extern int SetScrollInfoWnd(uint hWnd, int nBar, bool
bRedraw, ref SCROLLINFO si);

public static int SetScrollInfo(uint hWnd, int nBar, bool bRedraw,
SCROLLINFO si)
{
int rc = SetScrollInfoWnd(hWnd, nBar, bRedraw, ref si);

return rc; // return is 0 - presumably previous scroll position
}
}

Thanks

--
Michael Salamone [eMVP]
Entrek Software, Inc.
www.entrek.com

Unless I can solve the scroll problem, that's probably what I'm going to do.
The code is a whole lot simpler to clear and add back. And I don't know
about quicker (you have to search and update if found, and then search and
delete). But, you're right, if I write a little more code, I don't have to
worry about scrolling *and* should have an additional benefit of not being
such a litterbug creating all that garbage when clearing the listview :)
Which in the end, would be faster on the garbage collection side (should be
fewer invocations).

I may have just talked myself into it, but still would like to know how to
restore the scroll position if anyone knows.

--
Michael Salamone [eMVP]
Entrek Software, Inc.
www.entrek.com


[quoted text, click to view]

[quoted text, click to view]

Why not just overwrite your existing items (and delete any excess). It would
probably be quicker and would avoid all scrolling problems and the use of
P/Invoke