[DUG] Listview problem

[Jeremy North]

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.
>
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