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Hello Guys, good afternoon, it's still 4:25 pm where I live, I already know a lot about Delphi related to OOP, but I have one subject that I still have doubts about, which is the interface issue. My questions would be, when should I use an interface? To create my interface factory, should I create just the factory class or the class and a factory interface as well? How should I develop this knowledge and understand this concept once and for all.

Hi mates, I have something on my mind but I couldn't implement it correctly, imagine a generic interface, some classes inherited from that interface, and one method in each class with the same name, now I'm trying to use this interface type every where for different approaches but it doesn't compile correctly. Please have a look at the code if you get a chance and share your thoughts with me, I do appreciate you in advance. The question is how can I implement such an idea properly and safely? I have attached a sample project to save you time too. unit Unit1; interface uses Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics, Vcl.Controls, Vcl.Forms, Vcl.Dialogs, System.Rtti; type IMyInterface<T> = interface function DoSomething: T; end; TMyClass<T> = class(TInterfacedObject, IMyInterface<T>) function DoSomething: T; end; TForm1 = class(TForm) procedure FormCreate(Sender: TObject); private { Private declarations } function UseInterface<T>(obj: IMyInterface<T>): T; public { Public declarations } end; var Form1: TForm1; implementation {$R *.dfm} { TMyClass<T> } function TMyClass<T>.DoSomething: T; var ctx: TRttiContext; typ: TRttiType; begin ctx := TRttiContext.Create; typ := ctx.GetType(TypeInfo(T)); if typ.TypeKind = tkInteger then Result := 20 // E2010 Incompatible types: 'T' and 'Integer' else if typ.TypeKind = tkString then Result := T('Hello') // E2089 Invalid typecast else if typ.AsInstance.MetaclassType.InheritsFrom(TStringList) then Result := (typ.AsInstance.MetaclassType.InitInstance(typ) as TStringList) //E2010 Incompatible types: 'T' and 'TStringList' else Result := Default(T); ctx.Free; end; { TForm1 } function TForm1.UseInterface<T>(obj: IMyInterface<T>): T; begin Result := obj.DoSomething; end; procedure TForm1.FormCreate(Sender: TObject); var obj1: IMyInterface<Integer>; obj2: IMyInterface<String>; obj3: IMyInterface<TStringList>; begin try obj1 := TMyClass<Integer>.Create; obj2 := TMyClass<String>.Create; obj3 := TMyClass<TStringList>.Create; ShowMessage(UseInterface<Integer>(obj1).ToString); ShowMessage(UseInterface<String>(obj2)); ShowMessage(UseInterface<TStringList>(obj3).Text); except on E: Exception do Writeln('Exception: ', E.ClassName, ': ', E.Message); end; end; end. Generic Interface.zip

Hi, I'm experimenting some interface design and came up with the following: I would like to query a BaseClass instance if it supports a given interface, without freeing the class! As the example below, my great grand child class can support an interface, but I don't want to include the class definition ( great grand child class ) in the Base class.. So, by defining interfaces, I can write exactly what I want: TMyFrame = Class( TBaseFrame, {SupportedInterfaces}) In the code below procedure TForm22.Button1Click(Sender: TObject); begin if Supports( fBaseFrameClass, ISupportTask ) then (fBaseFrame as ISupportTask).CheckTask; end; No matter what overload Support method I call, fBaseFrame is freed once the method exits. Is there a way to know if my class instance supports an interface and call the corresponding method without messing ref counting and free the class instance prematurely? unit frm.main; interface uses Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics, Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls; type ISupportTask = Interface ['{3F785F20-7C44-4163-B55C-5EA267C7204E}'] function CheckTask : Boolean; end; ISupportList = Interface ['{9B7D95E1-DA96-475A-9A1C-910CAF99E5F5}'] function ListCount : Integer; End; ISupportItem = Interface ['{ACADFA2F-3500-4ACB-8049-F49FAC38EFB2}'] function SaveItem : Boolean; End; TBaseFrame = Class( TInterfacedObject ) protected fDummy : Boolean; End; TBaseFrameClass = Class of TBaseFrame; TMyFrame = Class( TBaseFrame, ISupportTask, ISupportList, ISupportItem ) public function CheckTask : Boolean; function ListCount : Integer; function SaveItem : Boolean; destructor Destroy; override; End; TForm22 = class(TForm) Button1: TButton; procedure Button1Click(Sender: TObject); procedure FormCreate(Sender: TObject); procedure FormDestroy(Sender: TObject); private { Private declarations } fBaseFrameClass : TBaseFrameClass; fBaseFrame : TBaseFrame; public { Public declarations } end; var Form22: TForm22; implementation {$R *.dfm} procedure TForm22.Button1Click(Sender: TObject); begin if Supports( fBaseFrameClass, ISupportTask ) then (fBaseFrame as ISupportTask).CheckTask; end; { TMyFrame } function TMyFrame.CheckTask: Boolean; begin Result := True; end; destructor TMyFrame.Destroy; begin fDummy := True; inherited; end; function TMyFrame.ListCount: Integer; begin Result := 42; end; function TMyFrame.SaveItem: Boolean; begin Result := False; end; procedure TForm22.FormCreate(Sender: TObject); begin fBaseFrameClass := TMyFrame; fBaseFrame := fBaseFrameClass.Create; end; procedure TForm22.FormDestroy(Sender: TObject); begin fBaseFrame.Free; end; end.

I want to get a list of interfaces registered in a Delphi 2007 application (with code from within that application) in order to check for possible duplicate GUIDs. There is a solution on GitHub which uses the System.RTTI unit, but unfortunately that unit is not available in Delphi 2007. Is it possible to do without? I also asked on StackOverflow: https://stackoverflow.com/q/54710667/49925