How to share functions in Delphi?

Question

For example, I have a couple of functions written for my form. Now, I need the exact same functions in another form. So, how can I share them between the two forms? Please, provide a simple example if possible.

Answer 1

Don't put them in your form. Separate them and put them in a common unit, and add that unit to the uses clause where you need access to them.

Here's a quick example, but you can see many of the Delphi RTL units (for instance, SysUtils) that do this. (You should learn to use the VCL/RTL source and the demo apps that are included in Delphi; they could answer many of the questions you've posted more quickly than waiting for an answer here.)

SharedFunctions.pas:

unit 
  SharedFunctions;

interface

uses
  SysUtils;  // Add other units as needed

function DoSomething: string;

implementation

function DoSomething: string;
begin
  Result := 'Something done';
end;

end.

UnitA.pas

unit
  YourMainForm;

uses
  SysUtils;

interface

type
  TMainForm = class(TForm)   
    procedure FormShow(Sender: TObject);
    // other stuff
  end;

implementation

uses
  SharedFunctions;

procedure TMainForm.FormShow(Sender: TObject);
begin
  ShowMessage(DoSomething());
end;

end.

In more recent versions of Delphi than Delphi 7, you can create the functions/methods in a record instead:

unit
  SharedFunctions;

interface

uses
  SysUtils;

type
  TSharedFunctions = record
  public
    class function DoSomething: string;
  end;

implementation

function TSharedFunctions.DoSomething: string;
begin
  Result := 'Something done';
end;

end;

UnitB.pas

unit
  YourMainForm;

uses
  SysUtils;

interface

type
  TMainForm = class(TForm)   
    procedure FormShow(Sender: TObject);
    // other stuff
  end;

implementation

uses
  SharedFunctions;

procedure TMainForm.FormShow(Sender: TObject);
begin
  ShowMessage(TSharedFunctions.DoSomething());
end;

end.