Setting the OnClick procedure of a Delphi button at runtime

Question

I have a program in which I need to update a database table with information entered into edit boxes, with a button at the end to do the updating. However, the form is creat

Answer 1

Event handlers must be declared exactly how the event type is defined. An OnClick event is declared as a TNotifyEvent which takes parameters (Sender: TObject). You cannot break that rule.

In your case, you can wrap your own procedure inside of the event handler, like so...

procedure TForm1.Button1Click(Sender: TObject);
begin
  UpdateDatabase(Edit1.text,Edit2.Text,Edit3.Text);
end;

Note that TNotifyEvent is a procedure "of object", which means your event handler must be declared inside of an object. In your case, the event handler should be declared inside your form (not in a global location).

Answer 2

Have you thought about descending a control from TButton with the edit controls as field members?

Here's an example that hopefully you can glean some ideas from.

  TButtonHack = class(TButton)
    fEdit1,
    fEdit2,
    fEdit3: TEdit;
  procedure Click; override;
  public
  constructor Create(AOwner: TComponent; AParent: TWinControl; Edit1, Edit2, Edit3: TEdit); Reintroduce;
end;

Constructor TButtonHack.Create(AOwner: TComponent; AParent: TWinControl;  Edit1, Edit2, Edit3: TEdit);
begin
  inherited Create(AOwner);
  Parent := AParent;
  Left := 100;
  Top := 100;
  Width := 100;
  Height := 20;
  Caption := 'ButtonHack';
  fEdit1 := Edit1;
  fEdit2 := Edit2;
  fEdit3 := Edit3;
end;

procedure TButtonHack.Click;
begin
  Inherited Click;
  Showmessage(fEdit1.text+','+ fEdit2.text+','+fEdit3.text);
end;

To test, drop a button, and three TEdits on a form.

procedure TForm1.Button1Click(Sender: TObject);
var
  ButtonHack: TButtonHack;
begin
  ButtonHack := TButtonHack.Create(Form1, Form1, Edit1, Edit2, Edit3);
end;

Whether you create the edits ahead of time or from within the TButtonHack is up to you. I've simplified it as much as possible just as an example.