code OnClick event handlers for array of buttons delphi

Question

Basically what I'm trying to do is create an array of Tbutton at runtime and have OnClick event handlers for each button created. the creation of the buttons works fine and please excuse the feeble attempt at trying to get the OnClick part of things right. Have googled extensively but to no avail. i tried to follow the code at http://docwiki.embarcadero.com/RADStudio/XE5/en/Events but struggled to follow. Not sure if it is what i was looking for anyway.

  procedure this(sender:TObject);
  end;

var
  Form1: TForm1;
  x: Integer;
  y: Integer;
  p:array [1..3,1..3] of Tbutton;


implementation

{$R *.dfm}

procedure TForm1.t(Sender: TObject);

begin
for x := 1 to 3 do
  for y := 1 to 3 do
      begin
         p[x,y]:=tbutton.Create(nil);
         p[x,y].Parent:=form1;
         p[x,y].height:=Round(Height/3);
         p[x,y].Width:=Round(width/3);
         p[x,y].Left:=(x-1)*(p[x,y].Width);
         p[x,y].Top:=(y-1)*(p[x,y].height);
         p[x,y].OnClick:=this;
      end;
end;

procedure TForm1.this(sender: TObject);
begin
p[x,y].Caption:='avasfd';
end;

end.

Thanks. -Benjamin.

so what is the question?

kludg
– kludg

2013-12-05 16:54:02 +00:00
Commented Dec 5, 2013 at 16:54 — kludg
– kludg, Commented Dec 5, 2013 at 16:54
use TButton(sender).Caption := 'avasf'

teran
– teran

2013-12-05 16:55:21 +00:00
Commented Dec 5, 2013 at 16:55 — teran
– teran, Commented Dec 5, 2013 at 16:55

Ken White · Accepted Answer · 2013-12-05 18:01:15Z

2

You'll need to typecast the Sender in the event handler (it will be the button clicked):

procedure TForm1.this(sender: TObject);
begin
    (Sender as TButton).Caption := 'avasfd';
end;

BTW, this is a terrible name for an event handler. It would be much better to use something descriptive, so that later when you (or someone else) reads the code it's clear what it's for. Something like this, for instance:

procedure TForm1.ButtonFromArrayClick(Sender: TObject);

edited Dec 5, 2013 at 18:01

answered Dec 5, 2013 at 16:57

Ken White

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2 Comments

David Heffernan Over a year ago

Actually you usually want that runtime exception. So you would use (Sender as TButton).Caption := ... That way you get an error when you click on the button rather than a button that does nothing. That's generally preferable. Then you discover that your code is broken.

Ken White Over a year ago

@David: Actually, I usually just write TButton(Sender) unless I'm intentionally using the handler for different types, in which case I use is to differentiate between types. I haven't shot myself in the foot more than once or twice, and they've been rare enough that the scars have all but disappeared. :-) When it happens now, it's usually when I'm figuring out a new component or class, and make a mistake about what is sending the event. You're right, though; better advice for a newer user. Updated.

Andy_D · Accepted Answer · 2013-12-05 16:57:01Z

1

You need to cast Sender as TButton. i.e.

TButton(Sender).Caption := 'avasfd';

answered Dec 5, 2013 at 16:57

Andy_D

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