On Thu, 12 Mar 2015, aradeonas wrote:
Here an example for you:
type
{ IFile }
IFile = interface
function GetName: string;
procedure SetName(AValue: string);
property Name: string read GetName write SetName;
end;
TFileList=specialize TFPGList<IFile>;
{ TVideoFile }
TVideoFile = class(TInterfacedPersistent, IFile)
private
FName: string;
FWidth: integer;
function GetName: string;
procedure SetName(AValue: string);
public
property Name: string read GetName write SetName;
property Width: integer read FWidth write FWidth;
end;
You should make IVideofile with GetIWidth and so on.
{ TAudioFile }
TAudioFile = class(TInterfacedPersistent, IFile)
private
FName: string;
FArtist: string;
function GetName: string;
procedure SetName(AValue: string);
public
property Name: string read GetName write SetName;
property Artist: string read FArtist write FArtist;
end;
Here you should make IAudioFile with GetArtist and so on.
var
Form1: TForm1;
implementation
{$R *.lfm}
{ TAudioFile }
function TAudioFile.GetName: string;
begin
Result:=FName;
end;
procedure TAudioFile.SetName(AValue: string);
begin
FName:=AValue;
end;
{ TVideoFile }
function TVideoFile.GetName: string;
begin
Result:=FName;
end;
procedure TVideoFile.SetName(AValue: string);
begin
FName:=AValue;
end;
{ TForm1 }
procedure TForm1.FormCreate(Sender: TObject);
var
V1,V2:TVideoFile;
A1,A2:TAudioFile;
Fl:TFileList;
begin
Fl:=TFileList.Create;
V1:=TVideoFile.Create;
V1.Name:='V';
V1.Width:=100;
A1:=TAudioFile.Create;
A1.Name:='A';
A1.Artist:='Art';
FL.Add(V1);
FL.Add(A1);
V2:=TVideoFile(FL.Items[0]);
A2:=TAudioFile(Fl.Items[1]);
ShowMessage(V2.Name);
ShowMessage(A2.Name);
end;
What you think?
If you use interfaces all the way as suggested above, you can get one interface,
and then query for the others as well with the IUnknown interface. then there is no need to access the objects.
Your problem is that you mix an interface with a non-interface approach.
Michael.
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