Create window dynamically in code
lazarus / 31-LCL

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unistereo · 2015-09-03 20:04

Hi, I know this is silly, but I want to create a window strictly from
code (so without any resource file). Yes I am an old school kind of
guy.

I used the code below. It runs fine but it only shows the form with no
border nor buttons (I am on Mac OSX).

First of all, am I doing this correctly, I mean regarding the
resource-less aspect of it ?

Secondly, what is missing in order to get the full window with border
& buttons ?

Thanks in advance!

Code: [Select]program helloworld;
{$mode objfpc} {$H+}

uses Classes, Interfaces, Forms, StdCtrls, Controls;

type
  TForm1 = class(TForm)
    Button1: TButton;
  end;

var
  Form1: TForm1;

begin
  Application.Initialize;
  Form1 := TForm1.CreateNew(nil);
  Form1.Button1 := TButton.Create(Form1);
  With Form1.Button1 Do
  begin
    Parent := Form1;
    Visible := TRUE;
    Left := 10;
    Top := 10;
    Width := 100;
    Height := 100;
    Caption := 'PRESS ME';
  end;
  Form1.BorderStyle:= Controls.bsSizeable;
  Form1.show();
  Application.Run;
end.

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Leledumbo · 2015-09-04 06:47

http://wiki.lazarus.freepascal.org/LCL_Tips#Creating_a_GUI_by_code

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unistereo · 2015-09-04 12:13

Hi Thanks for replying. I have seen that page, as well as http://wiki.
freepascal.org/Form_Tutorial#Creating_a_new_form_dynamically, from
which my code is inspired.

The problem is that those pages are obsolete.

Running the source code given by those pages give the following error
at runtime:
QuoteForm resource TMyForm not found. For resourceless forms CreateNew
constructor must be used. See the global variable
RequireDerivedFormResource.
My understanding is that something has been changed at one point
regarding the use of TForm.Create / TForm.CreateNew. My knowledge of
freepascal being a whopping 2 hours I fail to grasp the exact meaning
and consequences of that transition, at least at this stage.

Yet I managed to modify the code given in the second URL to use
TForm.CreatNew rather than TForm.Create and obtain a working version,
but I just wanted to know whether what I've done was valid.

It obviously is not valid it since I don't get window borders &
buttons.

Thanks in advance,

Using FPC 3.0.1 & Lazarus 1.4 on Mac

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derek.john.evans · 2015-09-04 12:51

Your code works on Windows, but the app wont shutdown.

But, if I use:
Code: [Select]Application.CreateForm(TForm1, Form1);  // not:  Form1
:= TForm1.CreateNew(nil);   

The code shuts down correctly. Maybe this is the issue.

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Handoko · 2015-09-04 12:56

This code below works (at least for me):

Code: [Select]procedure TfrmMain.ButtonTestClick(Sender: TObject);
var
  Form1: TForm;
  Button1: TButton;
begin
  Form1 := TForm.CreateNew(nil);
    Button1 := TButton.Create(Form1);
    With Button1 Do
    begin
      Parent := Form1;
      Visible := TRUE;
      Left := 10;
      Top := 10;
      Width := 100;
      Height := 100;
      Caption := 'PRESS ME';
    end;
    Form1.BorderStyle:= bsSizeable;
    Form1.ShowModal;
    Form1.Free;
end;
Put the code above in a button OnClick event (ButtonTest).

Note:
Button1 := TButton.Create(Form1)
BorderStyle:= bsSizeable;
Use ShowModal instead of Show

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unistereo · 2015-09-04 18:44

Hi guys,

If I use Application.CreateForm(...) I get the runtime error back
("Form resource TForm1 not found. For resourceless forms CreateNew
constructor must be used. See the global variable
RequireDerivedFormResource").
I don't know why it would happen on Mac and you don't get it on
Windows.

Regarding the code posted by Handoko it works but the problem is the
same as my code : it renders a bare form with no window
borders/buttons. At least on Mac.

So to summarize, my goal was simply to run the code given at
http://wiki.lazarus.freepascal.org/Using_the_LCL_without_Lazarus

As it did not work (it produces the error above) I searched for
answers and came across http://wiki.freepascal.org/Form_Tutorial#Creat
ing_a_new_form_dynamically. I modified my code to use that way of
dynamically creating forms. It works but it does not show a full
window.

As for the reason why CreateNew must be used instead of Create on the
form, it is supposedly explained here:
http://lists.lazarus.freepascal.org/pipermail/lazarus/2011-
February/060229.html

I don't know. Maybe the simplest way to answer my question is: could
someone update the code at
http://wiki.lazarus.freepascal.org/Using_the_LCL_without_Lazarus to
make it compatible with current FPC / Lazarus ?

Thanks you all,

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Handoko · 2015-09-04 18:56

Quote from: unistereo on September 04, 2015, 08:44:06 pmRegarding the
code posted by Handoko it works but the problem is the same as my code
: it renders a bare form with no window borders/buttons. At least on
Mac.

No window and buttons? I'm not sure what you mean. Can you please post
a screenshot? I test my code, everything seems correctly running on my
Ubuntu Linux 64-bit. Could it be a bug on Mac version?

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Handoko · 2015-09-04 19:00

Here is the result on my desktop. A big "PRESS ME" button, with
resizable form's borders:

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unistereo · 2015-09-04 21:57

Okay here is a screenshot of what I got. Terminal shows code and
executed commands.

Thanks

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Handoko · 2015-09-05 02:57

Okay, I guess you mean that you can't see the small icon buttons
(minimize, maximize and close), which usually located at the title
bar.

I don't use OSX nor Carbon widgetset. I also don't write Terminal
programs. One possibility I can think is, the window buttons may
actually exist, but because the form top position is 0 (zero), you may
not able to see it. I use Ubuntu + Mate Desktop Environment (non-
Ubuntu). I often experience forms being located to high that I can't
the those window buttons.

I suggest you to test the code again but with top position added:
Form1.Top := 50;

So here is the code:
Code: [Select]procedure TfrmMain.ButtonTestClick(Sender: TObject);
var
  Form1: TForm;
  Button1: TButton;
begin
  Form1 := TForm.CreateNew(nil);
    Form1.Top := 50;
    Button1 := TButton.Create(Form1);
    With Button1 Do
    begin
      Parent := Form1;
      Visible := TRUE;
      Left := 10;
      Top := 10;
      Width := 100;
      Height := 100;
      Caption := 'PRESS ME';
    end;
    Form1.BorderStyle:= bsSizeable;
    Form1.ShowModal;
    Form1.Free;
end;
About the resource error, nothing I can comment. And about the wiki
pages, yes I found many of them aren't updated properly, we are lack
of people to do it.

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unistereo · 2015-09-05 08:00

Oh yeah you were right. Moving the window a few pixels lower indeeds
reveal the window bar and buttons.
Woah now this is rocket science

Does it respond to events in your case ?

Because I cannot move the window if I try to drag it. Looks like it
doesn't catch mouse events or something.
The only thing that works is that I can close the window.

Anyway, I don't want to waste your time on this ...

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Handoko · 2015-09-05 08:21

I used Ubuntu + Unity Desktop environment, never have such problem.
But after I switched to Ubuntu + Mate Desktop environment, I often
can't see the title bar and the buttons. So I think it's a
compatibility issue between them.

Quote from: unistereo on September 05, 2015, 10:00:40 amBecause I
cannot move the window if I try to drag it. Looks like it doesn't
catch mouse events or something.
The only thing that works is that I can close the window.

Anyway, I don't want to waste your time on this ...

I can't drag the window too, because I can't click the title bar.
Fortunately, Ubuntu users can configure shortcut for moving window to
any key combination they like. I set [Alt] + [click] to move the
window. So after the title bar appear, I can drag it (on the title
bar).

No time is wasted, everyone earned.