A WM_VSCROLL message handler works perfectly for me.
However, this will only be sent for scrollbar directed scrolling. To also
handle mousewheel scrolling you will have to implement a WM_MOUSEWHEEL
message handler (and WM_HMOUSEWHEEL if appropriate to your needs). Could
it be mouse scrolling that you are missing ?
I would also note that you will almost certainly want to distinguish between
H and V scrolling, rather than have a "universal" "some sort of scrolling
has occurred" notification. You may also wish to be able to respond both
before and after scrolling has occurred.
In my list view class I have:
TScrollNotification = (
snBeforeHScroll,
snBeforeHWheel,
snBeforeVScroll,
snBeforeWheel,
snHScroll,
snHWheel,
snVScroll,
snWheel
);
procedure TXListview.WMVScroll(var aMessage: TWMVScroll);
begin
DoScroll(snBeforeVScroll);
inherited;
DoScroll(snVScroll);
end;
procedure TXListview.WMHScroll(var aMessage: TWMHScroll);
begin
DoScroll(snBeforeHScroll);
inherited;
DoScroll(snHScroll);
end;
and similar for mousewheel messages of course, where DoScroll:
procedure TXListview.DoScroll(const aNotification: TScrollNotification);
begin
if (aNotification in [snBeforeHScroll, snBeforeVScroll, snBeforeHWheel,
snBeforeWheel]) then
CancelEdit;
if Assigned(fOnScroll) then
fOnScroll(self, aNotification);
end;
i.e. my listview also provides a facility for sub-item editing and when
scrolling occurs, the first thing I do before doing the actual scrolling is
dismiss any sub-item editor that may be active, before then firing the
OnScroll event to allow my application code to respond as it may require.
hth
From: delphi-boun...@delphi.org.nz [mailto:delphi-boun...@delphi.org.nz] On
Behalf Of David O'Brien
Sent: Friday, 25 February 2011 15:09
To: NZ Borland Developers Group - Delphi List
Subject: [DUG] Listview problem
I am working on an application (D2009) where I need to know when a TListView
is Scrolled.
I have used Application.OnMessage to look for WM_VScroll messages, but they
do not happen, also have tried creating the below which I thought should
work:
TLVScrollEvent = procedure(Sender: TObject) of object;
TICListView = class(TListView)
private
FOnScroll: TLVScrollEvent;
protected
Procedure WMVScroll( Var Msg: TMessage ); message WM_VSCROLL;
Procedure WMHScroll( Var Msg: TMessage ); message WM_HSCROLL;
property OnScroll: TLVScrollEvent read FOnScroll write FOnscroll ;
end;
procedure Register ;
implementation
procedure Register;
begin
RegisterComponents('Dave', [TICListView]);
end;
procedure TICListView.WMHScroll(var Msg: TMessage);
begin
OnScroll ;
inherited;
end;
procedure TICListView.WMVScroll(var Msg: TMessage);
begin
OnScroll ;
inherited;
end;
which also doesn't fire. I have written a list of all messages fired when
the scrollbar is moved, but there doesn't seem to be anything useful.
Anyone have a solution?
Regards,
Dave.
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