Gör så här: Använda händelser i C++/CLI

2025-06-19

Den här artikeln visar hur du använder ett gränssnitt som deklarerar en händelse och en funktion för att anropa händelsen samt den klass- och händelsehanterare som implementerar gränssnittet.

Gränssnittshändelser

I följande kodexempel läggs en händelsehanterare till, händelsen anropas – vilket gör att händelsehanteraren skriver sitt namn till konsolen – och tar sedan bort händelsehanteraren.

// mcppv2_events2.cpp
// compile with: /clr
using namespace System;

delegate void Del(int, float);

// interface that has an event and a function to invoke the event
interface struct I {
public:
   event Del ^ E;
   void fire(int, float);
};

// class that implements the interface event and function
ref class EventSource: public I {
public:
   virtual event Del^ E;
   virtual void fire(int i, float f) {
      E(i, f);
   }
};

// class that defines the event handler
ref class EventReceiver {
public:
   void Handler(int i , float f) {
      Console::WriteLine("EventReceiver::Handler");
   }
};

int main () {
   I^ es = gcnew EventSource();
   EventReceiver^ er = gcnew EventReceiver();

   // hook the handler to the event
   es->E += gcnew Del(er, &EventReceiver::Handler);

   // call the event
   es -> fire(1, 3.14);

   // unhook the handler from the event
   es->E -= gcnew Del(er, &EventReceiver::Handler);
}

Resultat

EventReceiver::Handler

Anpassade åtkomstmetoder

Följande exempel visar hur du definierar en händelses beteende när hanterare läggs till eller tas bort och när en händelse aktiveras.

// mcppv2_events6.cpp
// compile with: /clr
using namespace System;

public delegate void MyDel();
public delegate int MyDel2(int, float);

ref class EventSource {
public:
   MyDel ^ pE;
   MyDel2 ^ pE2;

   event MyDel^ E {
      void add(MyDel^ p) {
         pE = static_cast<MyDel^> (Delegate::Combine(pE, p));
         // cannot refer directly to the event
         // E = static_cast<MyDel^> (Delegate::Combine(pE, p));   // error
      }

      void remove(MyDel^ p) {
         pE = static_cast<MyDel^> (Delegate::Remove(pE, p));
      }

      void raise() {
         if (pE != nullptr)
            pE->Invoke();
      }
   }  // E event block

   event MyDel2^ E2 {
      void add(MyDel2^ p2) {
         pE2 = static_cast<MyDel2^> (Delegate::Combine(pE2, p2));
      }

      void remove(MyDel2^ p2) {
         pE2 = static_cast<MyDel2^> (Delegate::Remove(pE2, p2));
      }

      int raise(int i, float f) {
         if (pE2 != nullptr) {
            return pE2->Invoke(i, f);
         }
         return 1;
      }
   } // E2 event block
};

public ref struct EventReceiver {
   void H1() {
      Console::WriteLine("In event handler H1");
   }

   int H2(int i, float f) {
      Console::WriteLine("In event handler H2 with args {0} and {1}", i.ToString(), f.ToString());
      return 0;
   }
};

int main() {
   EventSource ^ pE = gcnew EventSource;
   EventReceiver ^ pR = gcnew EventReceiver;

   // hook event handlers
   pE->E += gcnew MyDel(pR, &EventReceiver::H1);
   pE->E2 += gcnew MyDel2(pR, &EventReceiver::H2);

   // raise events
   pE->E();
   pE->E2::raise(1, 2.2);   // call event through scope path

   // unhook event handlers
   pE->E -= gcnew MyDel(pR, &EventReceiver::H1);
   pE->E2 -= gcnew MyDel2(pR, &EventReceiver::H2);

   // raise events, but no handlers
   pE->E();
   pE->E2::raise(1, 2.5);
}

Resultat

In event handler H1
In event handler H2 with args 1 and 2.2

Åsidosätt standardåtkomst för tilläggs-, borttagnings- och anropsmetoder

Det här exemplet visar hur du åsidosätter standardåtkomsten för metoderna lägg till, ta bort och skapa händelser:

// mcppv2_events3.cpp
// compile with: /clr
public delegate void f(int);

public ref struct E {
   f ^ _E;
public:
   void handler(int i) {
      System::Console::WriteLine(i);
   }

   E() {
      _E = nullptr;
   }

   event f^ Event {
      void add(f ^ d) {
         _E += d;
      }
   private:
      void remove(f ^ d) {
        _E -= d;
      }

   protected:
      void raise(int i) {
         if (_E) {
            _E->Invoke(i);
         }
      }
   }

   // a member function to access all event methods
   static void Go() {
      E^ pE = gcnew E;
      pE->Event += gcnew f(pE, &E::handler);
      pE->Event(17);   // prints 17
      pE->Event -= gcnew f(pE, &E::handler);
      pE->Event(17);   // no output
   }
};

int main() {
   E::Go();
}

Resultat

Flera händelsehanterare

En händelsemottagare, eller någon annan klientkod, kan lägga till en eller flera hanterare i en händelse.

// mcppv2_events4.cpp
// compile with: /clr
using namespace System;
#include <stdio.h>

delegate void ClickEventHandler(int, double);
delegate void DblClickEventHandler(String^);

ref class EventSource {
public:
   event ClickEventHandler^ OnClick;
   event DblClickEventHandler^ OnDblClick;

   void FireEvents() {
      OnClick(7, 3.14159);
      OnDblClick("Started");
   }
};

ref struct EventReceiver {
public:
   void Handler1(int x, double y) {
      System::Console::Write("Click(x={0},y={1})\n", x, y);
   };

   void Handler2(String^ s) {
      System::Console::Write("DblClick(s={0})\n", s);
   }

   void Handler3(String^ s) {
      System::Console::WriteLine("DblClickAgain(s={0})\n", s);
   }

   void AddHandlers(EventSource^ pES) {
      pES->OnClick +=
         gcnew ClickEventHandler(this,&EventReceiver::Handler1);
      pES->OnDblClick +=
         gcnew DblClickEventHandler(this,&EventReceiver::Handler2);
      pES->OnDblClick +=
         gcnew DblClickEventHandler(this, &EventReceiver::Handler3);
   }

   void RemoveHandlers(EventSource^ pES) {
      pES->OnClick -=
         gcnew ClickEventHandler(this, &EventReceiver::Handler1);
      pES->OnDblClick -=
         gcnew DblClickEventHandler(this, &EventReceiver::Handler2);
      pES->OnDblClick -=
         gcnew DblClickEventHandler(this, &EventReceiver::Handler3);
   }
};

int main() {
   EventSource^ pES = gcnew EventSource;
   EventReceiver^ pER = gcnew EventReceiver;

   // add handlers
   pER->AddHandlers(pES);

   pES->FireEvents();

   // remove handlers
   pER->RemoveHandlers(pES);
}

Resultat

Click(x=7,y=3.14159)
DblClick(s=System.Char[])
DblClickAgain(s=System.Char[])

Statiska händelser

Följande exempel visar hur du definierar och använder statiska händelser.

// mcppv2_events7.cpp
// compile with: /clr
using namespace System;

public delegate void MyDel();
public delegate int MyDel2(int, float);

ref class EventSource {
public:
   static MyDel ^ psE;
   static event MyDel2 ^ E2;   // event keyword, compiler generates add,
                               // remove, and Invoke

   static event MyDel ^ E {
      static void add(MyDel ^ p) {
         psE = static_cast<MyDel^> (Delegate::Combine(psE, p));
      }

      static void remove(MyDel^ p) {
         psE = static_cast<MyDel^> (Delegate::Remove(psE, p));
      }

      static void raise() {
         if (psE != nullptr)   //psE!=0 -> C2679, use nullptr
            psE->Invoke();
      }
   }

   static int Fire_E2(int i, float f) {
      return E2(i, f);
   }
};

public ref struct EventReceiver {
   void H1() {
      Console::WriteLine("In event handler H1");
   }

   int H2(int i, float f) {
      Console::WriteLine("In event handler H2 with args {0} and {1}", i.ToString(), f.ToString());
      return 0;
   }
};

int main() {
   EventSource^ pE = gcnew EventSource;
   EventReceiver^ pR = gcnew EventReceiver;

   // Called with "this"
   // hook event handlers
   pE->E += gcnew MyDel(pR, &EventReceiver::H1);
   pE->E2 += gcnew MyDel2(pR, &EventReceiver::H2);

   // raise events
   pE->E();
   pE->Fire_E2(11, 11.11);

   // unhook event handlers
   pE->E -= gcnew MyDel(pR, &EventReceiver::H1);
   pE->E2 -= gcnew MyDel2(pR, &EventReceiver::H2);

   // Not called with "this"
   // hook event handler
   EventSource::E += gcnew MyDel(pR, &EventReceiver::H1);
   EventSource::E2 += gcnew MyDel2(pR, &EventReceiver::H2);

   // raise events
   EventSource::E();
   EventSource::Fire_E2(22, 22.22);

   // unhook event handlers
   EventSource::E -= gcnew MyDel(pR, &EventReceiver::H1);
   EventSource::E2 -= gcnew MyDel2(pR, &EventReceiver::H2);
}

Resultat

In event handler H1
In event handler H2 with args 11 and 11.11
In event handler H1
In event handler H2 with args 22 and 22.22

Virtuella händelser

Det här exemplet implementerar virtuella, hanterade händelser i ett gränssnitt och en klass:

// mcppv2_events5.cpp
// compile with: /clr
using namespace System;

public delegate void MyDel();
public delegate int MyDel2(int, float);

// managed class that has a virtual event
ref class IEFace {
public:
   virtual event MyDel ^ E;   // declares three accessors (add, remove, and raise)
};

// managed interface that has a virtual event
public interface struct IEFace2 {
public:
   event MyDel2 ^ E2;   // declares two accessors (add and remove)
};

// implement virtual events
ref class EventSource : public IEFace, public IEFace2 {
public:
   virtual event MyDel2 ^ E2;

   void Fire_E() {
      E();
   }

   int Fire_E2(int i, float f) {
      try {
         return E2(i, f);
      }
      catch(System::NullReferenceException^) {
         return 0;   // no handlers
      }
   }
};

// class to hold event handlers, the event receiver
public ref struct EventReceiver {
   // first handler
   void H1() {
      Console::WriteLine("In handler H1");
   }

   // second handler
   int H2(int i, float f) {
      Console::WriteLine("In handler H2 with args {0} and {1}", i.ToString(), f.ToString());
      return 0;
   }
};

int main() {
   EventSource ^ pE = gcnew EventSource;
   EventReceiver ^ pR = gcnew EventReceiver;

   // add event handlers
   pE->E += gcnew MyDel(pR, &EventReceiver::H1);
   pE->E2 += gcnew MyDel2(pR, &EventReceiver::H2);

   // raise events
   pE->Fire_E();
   pE->Fire_E2(1, 2.2);

   // remove event handlers
   pE->E -= gcnew MyDel(pR, &EventReceiver::H1);
   pE->E2 -= gcnew MyDel2(pR, &EventReceiver::H2);

   // raise events, but no handlers; so, no effect
   pE->Fire_E();
   pE->Fire_E2(1, 2.5);
}

Resultat

In handler H1
In handler H2 with args 1 and 2.2

En enkel händelse kan inte anges för att åsidosätta eller dölja en basklasshändelse. Du måste definiera alla händelseåtkomstfunktioner och sedan ange nyckelordet new eller override för varje accessorfunktion.

// mcppv2_events5_a.cpp
// compile with: /clr /c
delegate void Del();

ref struct A {
   virtual event Del ^E;
   virtual event Del ^E2;
};

ref struct B : A {
   virtual event Del ^E override;   // C3797
   virtual event Del ^E2 new;   // C3797
};

ref struct C : B {
   virtual event Del ^E {   // OK
      void raise() override {}
      void add(Del ^) override {}
      void remove(Del^) override {}
   }

   virtual event Del ^E2 {   // OK
      void raise() new {}
      void add(Del ^) new {}
      void remove(Del^) new {}
   }
};

Abstrakta händelser

Följande exempel visar hur du implementerar en abstrakt händelse.

// mcppv2_events10.cpp
// compile with: /clr /W1
using namespace System;
public delegate void Del();
public delegate void Del2(String^ s);

interface struct IEvent {
public:
   // in this case, no raised method is defined
   event Del^ Event1;

   event Del2^ Event2 {
   public:
      void add(Del2^ _d);
      void remove(Del2^ _d);
      void raise(String^ s);
   }

   void fire();
};

ref class EventSource: public IEvent {
public:
   virtual event Del^ Event1;
   event Del2^ Event2 {
      virtual void add(Del2^ _d) {
         d = safe_cast<Del2^>(System::Delegate::Combine(d, _d));
      }

      virtual void remove(Del2^ _d) {
         d = safe_cast<Del2^>(System::Delegate::Remove(d, _d));
      }

      virtual void raise(String^ s) {
         if (d) {
            d->Invoke(s);
         }
      }
   }

   virtual void fire() {
      return Event1();
   }

private:
   Del2^ d;
};

ref class EventReceiver {
public:
   void func() {
      Console::WriteLine("hi");
   }

   void func(String^ str) {
      Console::WriteLine(str);
   }
};

int main () {
   IEvent^ es = gcnew EventSource;
   EventReceiver^ er = gcnew EventReceiver;
   es->Event1 += gcnew Del(er, &EventReceiver::func);
   es->Event2 += gcnew Del2(er, &EventReceiver::func);

   es->fire();
   es->Event2("hello from Event2");
   es->Event1 -= gcnew Del(er, &EventReceiver::func);
   es->Event2 -= gcnew Del2(er, &EventReceiver::func);
   es->Event2("hello from Event2");
}

Resultat

hi
hello from Event2

Utlysa händelser som definieras i en annan assembly

En händelse och en händelsehanterare kan definieras i en assembly och användas av en annan assembly.

// mcppv2_events8.cpp
// compile with: /LD /clr
using namespace System;

public delegate void Del(String^ s);

public ref class Source {
public:
   event Del^ Event;
   void Fire(String^ s) {
      Event(s);
   }
};

Den här klientkoden hanterar händelsen:

// mcppv2_events9.cpp
// compile with: /clr
#using "mcppv2_events8.dll"
using namespace System;

ref class Receiver {
public:
   void Handler(String^ s) {
      Console::WriteLine(s);
   }
};

int main() {
   Source^ src = gcnew Source;
   Receiver^ rc1 = gcnew Receiver;
   Receiver^ rc2 = gcnew Receiver;
   src -> Event += gcnew Del(rc1, &Receiver::Handler);
   src -> Event += gcnew Del(rc2, &Receiver::Handler);
   src->Fire("hello");
   src -> Event -= gcnew Del(rc1, &Receiver::Handler);
   src -> Event -= gcnew Del(rc2, &Receiver::Handler);
}

Resultat

hello
hello

Se även

händelse

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Gör så här: Använda händelser i C++/CLI

Gränssnittshändelser

Anpassade åtkomstmetoder

Åsidosätt standardåtkomst för tilläggs-, borttagnings- och anropsmetoder

Flera händelsehanterare

Statiska händelser

Virtuella händelser

Abstrakta händelser

Utlysa händelser som definieras i en annan assembly

Se även

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