Tutorial by Examples

An interface is declared like a class, but without access modifiers (public, private, ...). Also, no definitions are allowed, so variables and constants can't be used. Interfaces should always have an Unique Identifier, which can be generated by pressing Ctrl + Shift + G. IRepository = interface ...

Classes can implement more than one interface, as opposed to inheriting from more than one class (Multiple Inheritance) which isn't possible for Delphi classes. To achieve this, the name of all interfaces must be added comma-separated behind the base class. Of course, the implementing class must al...

Interfaces can inherit from each other, exactly like classes do, too. An implementing class thus has to implement functions of the interface and all base interfaces. This way, however, the compiler doesn't know that the implenting class also implements the base interface, it only knows of the interf...

Since the declaration of variables in interfaces isn't possible, the "fast" way of defining properites (property Value: TObject read FValue write FValue;) can't be used. Instead, the Getter and setter (each only if needed) have to be declared in the interface, too. IInterface = interface(...