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interface class (C++/CLI and C++/CX)

  • Article

Declares an interface. For information on native interfaces, see __interface.

All runtimes

Syntax

interface_access interface class name : inherit_access base_interface {};
interface_access interface struct name : inherit_access base_interface {};

Parameters

interface_access
The accessibility of an interface outside the assembly. Possible values are public and private. private is the default. Nested interfaces can't have an interface_access specifier.

name
The name of the interface.

inherit_access
The accessibility of base_interface. The only permitted accessibility for a base interface is public (the default).

base_interface
(Optional) A base interface for interface name.

Remarks

interface struct is equivalent to interface class.

An interface can contain declarations for functions, events, and properties. All interface members have public accessibility. An interface can also contain static data members, functions, events, and properties, and these static members must be defined in the interface.

An interface defines how a class may be implemented. An interface isn't a class and classes can only implement interfaces. When a class defines a function declared in an interface, the function is implemented, not overridden. Therefore, name lookup doesn't include interface members.

A class or struct that derives from an interface must implement all members of the interface. When implementing interface name, you must also implement the interfaces in the base_interface list.

For more information, see:

For information on other CLR types, see Classes and Structs.

You can detect at compile time if a type is an interface with __is_interface_class(type). For more information, see Compiler support for type traits.

In the development environment, you can get F1 help on these keywords by highlighting the keyword (for example, interface class) and pressing F1.

Windows Runtime

Remarks

(There are no remarks for this language feature that apply to only the Windows Runtime.)

Requirements

Compiler option: /ZW

Common Language Runtime

Remarks

(There are no remarks for this language feature that apply to only the common language runtime.)

Requirements

Compiler option: /clr

Examples

The following code example demonstrates how an interface can define the behavior of a clock function.

// mcppv2_interface_class.cpp
// compile with: /clr
using namespace System;

public delegate void ClickEventHandler(int, double);

// define interface with nested interface
public interface class Interface_A {
   void Function_1();

   interface class Interface_Nested_A {
      void Function_2();
   };
};

// interface with a base interface
public interface class Interface_B : Interface_A {
   property int Property_Block;
   event ClickEventHandler^ OnClick;
   static void Function_3() { Console::WriteLine("in Function_3"); }
};

// implement nested interface
public ref class MyClass : public Interface_A::Interface_Nested_A {
public:
   virtual void Function_2() { Console::WriteLine("in Function_2"); }
};

// implement interface and base interface
public ref class MyClass2 : public Interface_B {
private:
   int MyInt;

public:
   // implement non-static function
   virtual void Function_1() { Console::WriteLine("in Function_1"); }

   // implement property
   property int Property_Block {
      virtual int get() { return MyInt; }
      virtual void set(int value) { MyInt = value; }
   }
   // implement event
   virtual event ClickEventHandler^ OnClick;

   void FireEvents() {
      OnClick(7, 3.14159);
   }
};

// class that defines method called when event occurs
ref class EventReceiver {
public:
   void OnMyClick(int i, double d) {
      Console::WriteLine("OnClick: {0}, {1}", i, d);
   }
};

int main() {
   // call static function in an interface
   Interface_B::Function_3();

   // instantiate class that implements nested interface
   MyClass ^ x = gcnew MyClass;
   x->Function_2();

   // instantiate class that implements interface with base interface
   MyClass2 ^ y = gcnew MyClass2;
   y->Function_1();
   y->Property_Block = 8;
   Console::WriteLine(y->Property_Block);

   EventReceiver^ MyEventReceiver = gcnew EventReceiver();

   // hook handler to event
   y->OnClick += gcnew ClickEventHandler(MyEventReceiver, &EventReceiver::OnMyClick);

   // invoke events
   y->FireEvents();

   // unhook handler to event
   y->OnClick -= gcnew ClickEventHandler(MyEventReceiver, &EventReceiver::OnMyClick);

   // call implemented function via interface handle
   Interface_A^ hi = gcnew MyClass2();
   hi->Function_1();
}

in Function_3

in Function_2

in Function_1

8

OnClick: 7, 3.14159

in Function_1

The following code sample shows two ways to implement functions with the same signature declared in multiple interfaces and where those interfaces are used by a class.

// mcppv2_interface_class_2.cpp
// compile with: /clr /c
interface class I {
   void Test();
   void Test2();
};

interface class J : I {
   void Test();
   void Test2();
};

ref struct R : I, J {
   // satisfies the requirement to implement Test in both interfaces
   virtual void Test() {}

   // implement both interface functions with explicit overrides
   virtual void A() = I::Test2 {}
   virtual void B() = J::Test2 {}
};

See also

Component Extensions for .NET and UWP