Delphi-麻烦引用在运行时创建的对象

Question

I'm using Delphi 7. I've written some code to create buttons at runtime (I need lots of the exact same buttons in the exact same locations on every form, which is why I've decided to do that). But I'm having trouble referencing them in procedures (OnClick, to be precise). I want another form to open when a button is clicked.

unit Unit2;

interface

uses
 Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
 Dialogs, StdCtrls, jpeg, ExtCtrls;

procedure buttons(a: TForm);

type
 TForm2 = class(TForm)
  Image1: TImage;
  procedure FormShow(Sender: TObject);
  procedure Button1Click(Sender: TObject);
  procedure Button2Click(Sender: TObject);
  private
   { Private declarations }
  public
   { Public declarations }
end;

var
 Form2: TForm2; Button1, Button2, Button3, Button4: TButton;

implementation

uses Unit3, Unit4;

{$R *.dfm}

procedure buttons(a: TForm);
 begin
  Button1 := TButton.Create(a);
  Button1.Name := 'Button1';
  Button1.Left := 712;
  Button1.Top := 96;
  Button1.Width := 81;
  Button1.Height := 41;
  Button1.Visible := True;
  Button1.Parent := a;
  Button1.Enabled := False;
  Button1.Caption := 'Go forwards';
  Button2 := TButton.Create(a);
  Button2.Name := 'Button2';
  Button2.Left := 800;
  Button2.Top := 152;
  Button2.Width := 81;
  Button2.Height := 41;
  Button2.Visible := True;
  Button2.Parent := a;
  Button2.Enabled := False;
  Button2.Caption := 'Go right';
  Button3 := TButton.Create(a);
  Button3.Name := 'Button3';
  Button3.Left := 624;
  Button3.Top := 152;
  Button3.Width := 81;
  Button3.Height := 41;
  Button3.Visible := True;
  Button3.Parent := a;
  Button3.Enabled := False;
  Button3.Caption := 'Go left';
  Button4 := TButton.Create(a);
  Button4.Name := 'Button4';
  Button4.Left := 712;
  Button4.Top := 208;
  Button4.Width := 81;
  Button4.Height := 41;
  Button4.Visible := True;
  Button4.Parent := a;
  Button4.Enabled := False;
  Button4.Caption := 'Go back';
 end;


procedure TForm2.FormShow(Sender: TObject);
 begin
  buttons(Form2);
  Button1.Enabled := True;
  Button2.Enabled := True;
 end;

procedure TForm2.Button1Click(Sender: TObject);
 begin
  Form3.Show;
  Form2.Hide;
 end;

procedure TForm2.Button2Click(Sender: TObject);
 begin
  Form4.Show;
  Form2.Hide;
 end;

end.

I've declared the OnClicks in 'type', as well, as I probably should. The program runs, but the created buttons don't work, though are clickable. Ideas?

PS: I know I could've written more compact code to create all those buttons, but I didn't have time to think about it, and it is pretty much beside the point. I know it might be hard to read - all you need to know is, I set the same kinds of properties on every button - you need only look at Button1, the others are identical.

PPS: NOT a dup question to this: Delphi - Referencing Components created at Runtime . I couldn't find a solution to my problem in that one.

Answer 1

First of all you should clean up your code a bit. But it's not why your code isn't working. It's because you forgot to assign an OnClick Event to your button:

Have a look at this :

unit Unit19;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;

type
  TForm19 = class(TForm)
    procedure FormCreate(Sender: TObject);
  private
    Button1: TButton;
    Button2: TButton;
    Procedure CreateButtons;
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
  public
    { Public declarations }
  end;

var
  Form19: TForm19;

implementation

{$R *.dfm}

procedure TForm19.Button1Click(Sender: TObject);
begin
  Caption := 'Button1 Clicked';
end;

procedure TForm19.Button2Click(Sender: TObject);
begin
  Caption := 'Button2 Clicked';
end;

procedure TForm19.CreateButtons;
begin
  Button1 := TButton.Create(Self);
  Button1.Name := 'Button1';
  Button1.Left := 712;
  Button1.Top := 96;
  Button1.Width := 81;
  Button1.Height := 41;
  Button1.Visible := True;
  Button1.Parent := Self;
  Button1.Enabled := False;
  Button1.OnClick := Button1Click;

  Button1.Caption := 'Go forwards';
  Button2 := TButton.Create(Self);
  Button2.Name := 'Button2';
  Button2.Left := 800;
  Button2.Top := 152;
  Button2.Width := 81;
  Button2.Height := 41;
  Button2.Visible := True;
  Button2.Parent := Self;
  Button2.Enabled := False;
  Button2.Caption := 'Go right';
  Button2.OnClick := Button2Click;
end;

procedure TForm19.FormCreate(Sender: TObject);
begin
  CreateButtons;
end;

end.

First the cleanup: I've moved the declaration of your button up to the private part of the form that owns them.

About the owner of the button, the parameter of the constructor; It must be the form. Because when you destroy the form it will also destroy your buttons, and no memory will be leaked.

Then the missing OnClick event that is solved with this line:

Button1.OnClick := Button1Click;

I simply tell the button which procedure to be called when the user click the button.

I hope this answers you question.

Answer 2

In your situation I would use Frames. You can place all buttons on this frame, you can change the behavior by using properties, assign all needed events and put it on your form at design time or at run time