[DUG] Listview problem

[Jolyon Smith]

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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