Singleton Class Implementation

uSpSingleton.pas

unit uSpSingleton;

interface

uses
  System.SysUtils;

type

// 1. Add this unit to your project, then save-as a new unit file
// 2. Place cursor on TSpSingleton and press Ctrl+Shift+E to rename class
// 3. Place cursor on SpSingleton and press Ctrl+Shift+E to rename global var
// 4. Update { xxx } throughout unit with updated class name
// 5. Add custom code to your new singleton class and access via the global var

  { xxx }
  TSpSingleton = class
  private
    class var Instance: TSpSingleton;
    procedure DoFree;
    class constructor Create;
    class destructor Destroy;
  public
    class function Create: TSpSingleton;
    class procedure Destroy;
    class procedure Free;
    procedure Test;
  end;

var
  SpSingleton: TSpSingleton = nil;

implementation

class constructor TSpSingleton.Create;
begin
  SpSingleton := TSpSingleton.Create;
end;

class destructor TSpSingleton.Destroy;
begin
  if TSpSingleton.Instance <> nil then
  begin
    TSpSingleton.Instance.DoFree;
  end;  
end;

procedure TSpSingleton.DoFree;
begin
  if Instance <> nil then
  begin
    inherited Free;
    Instance := nil;
  end;
end;

class function TSpSingleton.Create: TSpSingleton;
begin
  if (Instance = nil) then
    Instance:= inherited Create as Self;
  result:= Instance;
end;

class procedure TSpSingleton.Destroy;
begin
 raise Exception.Create('Calling Destry is not allowed');
end;

class procedure TSpSingleton.Free;
begin
 raise Exception.Create('Calling Free is not allowed');
end;

procedure TSpSingleton.Test;
begin
  WriteLn('this is a test');
end;

end.