[DUG] Listview problem
Jeremy North
jeremy.north at gmail.com
Fri Feb 25 17:20:05 NZDT 2011
You asking me implementation details on code I just put together in 5 mins.
OK...
a) Keyboard - well that sucks. I blame MS.
1) Initially was expecting scroll details to be handled by the record
structure. Trapping WMNotify instead of CNNotify doesn't work (just tried).
2) I thought I searched the source and couldn't find it. Guess I searched
wrong (since I had LVM_??? in the comment).
I guess the H and V scrolling thing is down to the implementor for why
they'd want to differentiate the two. You can get enough detail to
distinguish in the message received if needed.
Also it will only work with ComCtrl version 6 and above (XP+).
On Fri, Feb 25, 2011 at 2:55 PM, Jolyon Smith <jsmith at deltics.co.nz> wrote:
> A good spot, but this code doesn’t solve it either. It provides a
> universal way of handling scrollbar or mousewheel scroll notifications,
> although a bit of extra work is then required to discriminate between H vs
> V scrolling, but when I added this to my listview class it didn’t get called
> as the result of keyboard scrolling either.
>
>
>
> Couple of supplementary questions:
>
>
>
> 1. Where do you get TWMNotifyLV from? Why not just use TWMNotify ?
>
> 2. Why not use the LVN_BEGINSCROLL/LVN_ENDSCROLL constants, rather
> than literals + comments ?
>
>
>
>
>
> *From:* delphi-bounces at delphi.org.nz [mailto:delphi-bounces at delphi.org.nz]
> *On Behalf Of *Jeremy North
> *Sent:* Friday, 25 February 2011 16:21
>
> *To:* NZ Borland Developers Group - Delphi List
> *Subject:* Re: [DUG] Listview problem
>
>
>
> Don't forget "scrolling" also occurs when you use the arrow keys.
>
>
>
> My contribution (just made up then)...
>
>
>
> unit ScrollingListView;
>
>
>
> interface
>
>
>
> uses
> Windows, Messages, ComCtrls, CommCtrl, Controls;
>
>
>
> type
> TJSListView = class(TListView)
> private
> type
> TJSScrollEvent = procedure (Sender: TObject; const BeginScroll:
> Boolean) of object;
> var
> FOnEndScroll: TJSScrollEvent;
> FOnBeginScroll: TJSScrollEvent;
> protected
> procedure DoScroll(const AStart: Boolean); virtual;
> procedure CNNotify(var Message: TWMNotifyLV); message CN_NOTIFY;
> public
> property OnBeginScroll: TJSScrollEvent read FOnBeginScroll write
> FOnBeginScroll;
> property OnEndScroll: TJSScrollEvent read FOnEndScroll write
> FOnEndScroll;
> end;
>
>
>
> implementation
>
>
>
> { TJSListView }
>
>
>
> procedure TJSListView.CNNotify(var Message: TWMNotifyLV);
> begin
> if Message.NMHdr.code = -180 then // LVM_BEGINSCROLL
> begin
> DoScroll(True);
> end;
> if Message.NMHdr.code = -181 then // LVM_ENDSCROLL
> begin
> DoScroll(False);
> end;
> inherited;
> end;
>
>
>
> procedure TJSListView.DoScroll(const AStart: Boolean);
> var
> LEvent: TJSScrollEvent;
> begin
> if AStart then
> LEvent := OnBeginScroll
> else
> LEvent := OnEndScroll;
> if Assigned(LEvent) then
> LEvent(Self, AStart);
> end;
>
>
>
> end.
>
>
>
>
>
>
>
> On Fri, Feb 25, 2011 at 2:01 PM, David O'Brien <Dave at iccs.co.nz> wrote:
>
> Sorted it thanks, had mixed versions of code in the component. The events
> do fire…
>
>
>
> *From:* delphi-bounces at delphi.org.nz [mailto:delphi-bounces at delphi.org.nz]
> *On Behalf Of *Jolyon Smith
> *Sent:* Friday, 25 February 2011 3:43 p.m.
>
>
> *To:* 'NZ Borland Developers Group - Delphi List'
>
> *Subject:* Re: [DUG] Listview problem
>
>
>
> 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-bounces at delphi.org.nz [mailto:delphi-bounces at 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.
>
>
> _______________________________________________
> NZ Borland Developers Group - Delphi mailing list
> Post: delphi at delphi.org.nz
> Admin: http://delphi.org.nz/mailman/listinfo/delphi
> Unsubscribe: send an email to delphi-request at delphi.org.nz with Subject:
> unsubscribe
>
>
>
> _______________________________________________
> NZ Borland Developers Group - Delphi mailing list
> Post: delphi at delphi.org.nz
> Admin: http://delphi.org.nz/mailman/listinfo/delphi
> Unsubscribe: send an email to delphi-request at delphi.org.nz with Subject:
> unsubscribe
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://listserver.123.net.nz/pipermail/delphi/attachments/20110225/64a5f351/attachment-0001.html
More information about the Delphi
mailing list