Programming in Delphi sins #1

In this serie I will tell you, what we find a sin, in Delphi programming.

Using auto create forms and datamodules
Standard Delphi will create automatically all forms and datamodules for you. This gives you a headstart when you are first learning Delphi, but in the end it will give you a headache!

Sooner or later you begin to wonder where that 'Form1' object is coming from. (It is in fact a variable in the interface section of his own unit)
Other issues:

1. Your program becomes slower, consuming more memory then needed with many forms created.
2. Bugs will be harder to track, because you just can not know the state of all your forms and datamodules. Code could run, without you knowing about it.
   
   

Solution:
Turn off auto creation of forms in the options Dialog-VCL Designer tab, and create your forms/datamodules when you need them, and free it when you are done with it. In existing projects remove those forms from the auto create forms list in the project options.

Create a form when you need it, using your own variable:

procedure TForm5.Button1Click(Sender: TObject);
var
  MyForm : TForm3;
begin
  MyForm := TForm3.Create(self);
  try
    MyForm.ShowModal;
  finally
    MyForm.Free;
  end;
end;

Remove the 'global' var in unit of the newly created forms and datamodules, you just don't need them:

unit Unit3;

interface

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

type
  TForm3 = class(TForm)
  private
    { Private declarations }
  public
    { Public declarations }
  end;

//Remove this global var, which is 
//the instance that is created with
//the auto create forms option turned on
var
  Form3: TForm3;
//--

implementation

{$R *.dfm}

end.