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List of events

Posted on 1997-12-21
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Last Modified: 2012-05-04
How do I fire events stored in a TList ?
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Question by:miv
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8 Comments
 
LVL 4

Expert Comment

by:d003303
ID: 1354325
What exactly do you mean ? Do you want to fire multiple event handlers for one event stored in a TList, or event handlers for different events stored in this list ?
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Author Comment

by:miv
ID: 1354326
option 2
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LVL 4

Expert Comment

by:d003303
ID: 1354327
Yo,

maybe you could explain a bit why you need to store the event handlers in a TList. That would help to make a better answer.
Basically it is only typecast. Lets assume that the stored event is a TNotifyEvent, here is a quick example :

   TMyObject = class(TObject)
     FEventList: TList;
     FEventCount: Integer;
     constructor Create;
     destructor Destroy; override;
     procedure SetOnClick(NewValue : TNotifyEvent);
     function GetOnClick: TNotifyEvent;
     property OnClick: TNotifyEvent read GetOnClick write SetOnClick;
   end;

constructor TMyObject.Create;
var Index : Integer;
begin
  inherited Create;
  FEventList := TList.Create;
  FEventCount := 1;
  for Index := 0 to FEventCount - 1
   do FEventList.Add(nil);
end;

destructor TMyObject.Destroy;
begin
  FEventList.Free;
  inherited Destroy;
end;

procedure TMyObject.SetOnClick(NewValue : TNotifyEvent);
begin
  FEventList[0] := @NewValue;
end;

function TMyObject.GetOnClick: TNotifyEvent;
var FEvent : TNotifyEvent;
begin
  @FEvent := FEventList[0];
  Result := FEvent;
end;

Fireing events would be like the code in GetOnClick, but better check first if the pointer is not nil.

Hope this helps,

Slash/d003303
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LVL 1

Author Comment

by:miv
ID: 1354328
Ok, I´ll try to explain exactly what I want:

I have an object which on modification of some vars need to notify all the viewers which is viewing the object.

The viewers has added their "OnReshow" event to the "NotificationList" on the object.

I want to traverse the NotificationList and fire all the events on the list.

But as the list only knows that it is containing pointers, it can´t treat them as events. Have tried typecasting, but get compiler errors everytime...
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Accepted Solution

by:
d003303 earned 200 total points
ID: 1354329
Yo,

the typecast you need is in the GetOnClick-method. This converts the pointers to the event methods.

You could also use it like

var FEvent : TNotifyEvent;
    Index : Integer;
begin
  for Index := 0 to FEventList.Count - 1 do
   if FEventList[Index] <> nil then
    begin
      @FEvent := FEventList[Index];
      FEvent(Self);
    end;
end;

to fire all events stored in FEventList.

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Author Comment

by:miv
ID: 1354330
Hi,
It was to fast to accept that answer.

The FEvent seems to pointing no where (or maybe into the ROM :-) when I fire it...

Any suggestions ?

  Michael
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Expert Comment

by:d003303
ID: 1354331
Yo,

to help you on that I need some sample code where the event list is filled, and where the events are fired.

Slash/d003330
0
 
LVL 1

Author Comment

by:miv
ID: 1354332
Hi,
It´s ok. I created a dummy object with one attribut and added that object to the list instead. That works but´s a bit of a workaround.
I can´t post my code, you´ll need apx. 70000 lines to reconstruct the error :-(

Thanks for the help anyway, you earned your points.
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