Viele Objekttypen handlen?

[Robert_G]

Zitat von Dani:

Wenn du eine neuen Nachkommen hinzufügst, muss die GetDeviceClass Methode aktualisiert werden, aber ich sehe auch keinen Weg, das zu vermeiden

Ich schon

Delphi-Quellcode:

uses
   uDevice;

type
   TBaseDings = class
   private
      fDevice: TDevice;
   protected
      class function MatchesDevice(const aDevice: TDevice): Boolean; virtual; abstract;
      class procedure Register;
   public
      property Device: TDevice read fDevice;
      class function CreateMatchingDings(const aDevice: TDevice): TBaseDings;
      constructor Create(const aDevice: TDevice); virtual;
   end;

   TBaseDingsClass = class of TBaseDings;

implementation
uses
   Contnrs;
var
   ClassList            : TClassList;

constructor TBaseDings.Create(const aDevice: TDevice);
begin
   fDevice := aDevice;
end;

class function TBaseDings.CreateMatchingDings(const aDevice: TDevice): TBaseDings;
var
   i                    : Integer;
   BaseDingsClass       : TBaseDingsClass;
begin
   result := nil;
   for i := 0 to ClassList.Count - 1 do
   begin
      BaseDingsClass := TBaseDingsClass(ClassList[i]);
      if BaseDingsClass.MatchesDevice(aDevice) then
      begin
         result := BaseDingsClass.Create(aDevice);
         Break;
      end;
   end;
end;

class procedure TBaseDings.Register;
begin
   if ClassList.IndexOf(Self) = -1 then
      ClassList.Add(Self);
end;


initialization
   ClassList := TClassList.Create();
finalization
   ClassList.Free();
end.

und nun für jedes nur noch Gerät sowas:

Delphi-Quellcode:

uses
   uBaseDings,
   uDevice;

type
   TDings1Device = class(TDevice)
      // mööp
   end;


   TDings1 = class(TBaseDings)
   protected
      class function MatchesDevice(const aDevice: TDevice): Boolean; override;
   public
      constructor Create(const aDevice: TDevice); override;

   end;
implementation

{ TDings1 }

constructor TDings1.Create(const aDevice: TDevice);
begin
end;

class function TDings1.MatchesDevice(const aDevice: TDevice): Boolean;
begin
   Result := aDevice is TDings1Device;
end;

initialization
   // In die ClassList registrieren
   TDings1.Register;
end.

Wobei ich in dem Schritt zwichen BaseDings und Dings1 noch die eigentliche Basisklasse setzen würde, die die grundlegende Funktionalität (virtuell) bereitstellt.