How to create a PaintBox in runtime?

[BlueIcaro]

Hello, I trying to create a TPaintBox in runtime, but It's doesn't work. Here is my code:

Code: Pascal  [Select][+][-]

1. var
2.   P :TPaintBox ;
3. begin
4.  
5.   P := TPaintBox.Create(Form1);
6.   P.Top :=10;
7.   P.Left :=10;
8.   P.Height :=50;
9.   P.Width := 100;
10.   P.Parent := Form1;
11.   p.Color :=clRed;
12.   P.Canvas.Ellipse(10,10,20,20);
13. end;  
14.  

Any idea?

/BlueIcaro

[Arbee]

Your TPaintbox P is a local variable and probably is lost when the function is done.
Make it a global variable or a variable in Form1.

[typo]

I can reproduce this.

Lazarus 0.9.30 r29749 FPC 2.4.2 i386-win32-win32/win64

[Blaazen]

Yes, Arbee is right, P should be global
and yes, code does not work.
Here on Qt widgetset I can paint on TPaintBox only inside OnPaint method.
You can use OnPaint for drawing or if you want paint in other methods then use TImage instead of TPaintBox.

[theo]

It's better to paint in the OnPaint event.

Code: Pascal  [Select][+][-]

1. ...
2. p.Color :=clRed;
3. p.OnPaint:=@PPaint;
4. end;
5.  
6. procedure TForm1.PPaint(Sender:TObject);
7. begin
8.   P.Canvas.Ellipse(10,10,20,20);
9. end;
10.  

[eny]

Or even better:

Code: Pascal  [Select][+][-]

1. procedure TForm1.PPaint(Sender: TObject);
2. begin
3.   with Sender as TPaintBox do
4.   begin
5.     Color := clRed;
6.     Canvas.Ellipse(10,10,20,20);
7.   end;
8. end;

This eliminates the necessity for having a global (worst case!!) or form variable.

[BlueIcaro]

Hello, I create a Global Var, and used de Paint Event, and it doesn't work. 
/BLueIcaro
P.D I using Lazarus 0.9.30

[Arbee]

OK ... let me give a small program that *should* work.  Then you can perhaps figure out how to implement that in your situation.

I have a simple application with only a button.  The paintbox is displayed when you click the button.

Code: [Select]

unit Unit1;

{$mode objfpc}{$H+}

interface

uses
  Classes, SysUtils, FileUtil, Forms, Controls, Graphics, Dialogs, StdCtrls, ExtCtrls;

type

  { TForm1 }

  TForm1 = class(TForm)
     Button1: TButton;
     procedure Button1Click(Sender: TObject);
     procedure FormCreate(Sender: TObject);
  private
    { private declarations }
     P : TPaintBox;
  public
    { public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.lfm}

{ TForm1 }

procedure TForm1.FormCreate(Sender: TObject);
begin
  P := TPaintBox.Create(Form1);
  P.Top :=10;
  P.Left :=10;
  P.Height :=50;
  P.Width := 100;
  P.Parent := Form1;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  p.Canvas.Pen.Color :=clRed;
  P.Canvas.Ellipse(10,10,20,20);
end;

end.

Note that I have changed the way you set the color.

[BlueIcaro]

It's work!!
/BlueIcaro

[typo]

This works too:

Code: [Select]

  P := TPaintBox.Create(Form1);
  P.Top :=10;
  P.Left :=10;
  P.Height :=50;
  P.Width := 100;
  P.Parent := Form1;

  Application.ProcessMessages;

  p.Canvas.Pen.Color :=clRed;
  P.Canvas.Ellipse(10,10,20,20);