Question

Here is the code which gives me the error:

TAdvSmoothDockItems = class(TCollection)
private
  FOwner: TAdvSmoothDock;
  FOnChange: TNotifyEvent;
protected
  function GetItem(Index: Integer): TAdvSmoothDockItem; virtual; //YLM_TMS_01
  procedure SetItem(Index: Integer; const Value: TAdvSmoothDockItem); virtual; //YLM_TMS_01
  function GetOwner: TPersistent; override;
public
  constructor Create(AOwner: TAdvSmoothDock); overload; virtual;    //YLM_TMS_01
  function Add: TAdvSmoothDockItem; virtual;    //YLM_TMS_01
  function Insert(Index: Integer): TAdvSmoothDockItem; virtual;    //YLM_TMS_01
  property Items[Index: Integer]: TAdvSmoothDockItem read GetItem write SetItem; default;
  procedure Delete(Index: Integer); virtual;    //YLM_TMS_01
published
  property OnChange: TNotifyEvent read FOnChange write FOnChange;
end;


TKHAdvSmoothDockItems = class(TAdvSmoothDockItems)
  private
    FOwner: TKHAdvSmoothDock;
    FOnChange: TNotifyEvent;
  protected
    function GetItem(Index: Integer): TKHAdvSmoothDockItem; override;
    procedure SetItem(Index: Integer; const Value: TKHAdvSmoothDockItem); override;
    function GetOwner: TPersistent; override;
  public
    constructor Create(AOwner: TKHAdvSmoothDock);
    function Add: TKHAdvSmoothDockItem;
    function Insert(Index: Integer): TKHAdvSmoothDockItem;
    property Items[Index: Integer]: TKHAdvSmoothDockItem read GetItem write SetItem; default;
    procedure Delete(Index: Integer); override;
  published
    property OnChange: TNotifyEvent read FOnChange write FOnChange;
  end;

this code gives me the following error :

E2037 Declaration of ‘GetItem’ differs from previous declaration

why ? I have declared the GetItem in base-class as “Virtual” then I tried to override it in the next class (TKHAdvSmoothDockItems)…? how to fix it?

Answer 1

Because

function GetItem(Index: Integer): TAdvSmoothDockItem; virtual;

differs from

function GetItem(Index: Integer): TKHAdvSmoothDockItem; override;

the Result types need to be the same.