Assigning event handler during runtime results in compiler error
lazarus / 8-Other

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tcare · 2010-01-20 20:48

I am dynamically creating a TBitBtn during runtime:

NewPrintButton := TBitBtn.Create(paStatus);

I declare the OnClick event:

procedure NewPrintButtonClick(Sender: TObject);

I set the properties:

with NewPrintButton do
         begin
           Top := 5;
           Width := buPrint.Width;
           Height := buPrint.Height;
           Left := 5;       
           Glyph := buPrint.Glyph;
           Parent := paStatus;
         
I ASSIGN ITS ONCLICK EVENT HANDLER HERE:
           OnClick := NewPrintButtonClick;
          
         end;

And write the handler here:

procedure TfmMain.NewPrintButtonClick(Sender: TObject);
begin
  if Sender.ClassName = 'TBitBtn' then
     ShowMessage(TBitBtn(Sender).Name + ' was clicked!');

end;

However, when I try to compile, I get:

Error: Wrong number of parameters specified for call to
"NewPrintButtonClick"


Am I missing something?

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Zoran · 2010-01-20 20:57

Unlike Delphi, in Free Pascal you must use @ operator in front of
procedure variable. That means, instead of:

OnClick := NewPrintButtonClick;

You must write:

OnClick := @NewPrintButtonClick;

That's all. The error message about wrong number of paremeters is
misleading.

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theo · 2010-01-20 21:22

Or set delphi compatibility mode:
{$mode delphi} instead of {$mode objfpc}

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tcare · 2010-01-20 22:19

Thanks - I added the @ before the procedural variable and that did the
trick!

Theo - just out of curiosity, do you know if the {$mode delphi}
directive affects performance in any way, or does it just allow you to
use a more "Delphi-like" syntax?  Is there any additional performance
hit translations occurring at runtime by using the {$mode delphi}?

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theo · 2010-01-20 22:59

Quote from: tcare on January 20, 2010, 11:19:25 pmdo you know if the
{$mode delphi} directive affects performance in any way, or does it
just allow you to use a more "Delphi-like" syntax?

No, It does not affect performance afaik, it's a slightly less strict
syntax than mode objfpc.

http://www.freepascal.org/docs-html/prog/progap4.html#progse62.html