Delphi – use a closure on an event handler (ie, TButton OnClick)

delphidelphi-2009

If I try to use a closure on an event handler the compiler complains with :

Incompatible types: "method pointer and regular procedure"

which I understand.. but is there a way to use a clouser on method pointers? and how to define if can?

eg :

Button1.Onclick = procedure( sender : tobject ) begin ... end;

Thanks!

Best Answer

@Button1.OnClick := pPointer(Cardinal(pPointer( procedure (sender: tObject) 
begin 
  ((sender as TButton).Owner as TForm).Caption := 'Freedom to anonymous methods!' 

end )^ ) + $0C)^;

works in Delphi 2010

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VCL/FMX event handlers are tied to specific objects at runtime. When assigning your event handler, you need to replace the class typename with an object pointer. That object will be the event handler's Self pointer when the event is triggered later on:

New_Button.OnClick := Self.GoodbyeClick ;

Or simply:

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On a side note - when creating the Button, that code is inside of a TForm1 instance method, so you should be using the Self object pointer instead of the global Form1 object pointer:

New_Button := TButton.Create( Self );
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You are misunderstanding what .strip() does. It removes any of the characters found in the string you pass. From the str.strip() documentation:

The chars argument is a string specifying the set of characters to be removed.

emphasis mine; the word set there is crucial.

Because chars is treated as a set, .strip() will remove all s, e, r, v, i, c, C, h, k and _ characters from the start and end of your input string. So the e and r characters from the end of your input string were also removed; those characters are part of the set.

To remove a string from the start or end, use slicing instead:

if a.startswith('serviceCheck_'):
    a = a[len('serviceCheck_'):]

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