Gewusst wie: Verwenden von Ereignissen in C++/CLI

Artikel
10/12/2023

In diesem Artikel wird gezeigt, wie Sie eine Schnittstelle verwenden, die ein Ereignis und eine Funktion zum Aufrufen dieses Ereignisses deklariert, sowie die Klasse und den Ereignishandler, die die Schnittstelle implementieren.

Schnittstellenereignisse

Im folgenden Codebeispiel wird ein Ereignishandler hinzugefügt, das Ereignis aufgerufen, wodurch der Ereignishandler seinen Namen in die Konsole schreibt und dann den Ereignishandler entfernt.

// 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);
}

Ausgabe

EventReceiver::Handler

Benutzerdefinierte Accessormethoden

Das folgende Beispiel zeigt, wie Sie das Verhalten eines Ereignisses definieren, wenn Handler hinzugefügt oder entfernt werden und wann ein Ereignis ausgelöst wird.

// 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);
}

Ausgabe

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

Überschreiben des Standardzugriffs beim Hinzufügen, Entfernen und Auslösen von Accessoren

In diesem Beispiel wird gezeigt, wie Sie den Standardzugriff auf die Methoden zum Hinzufügen, Entfernen und Auslösen von Ereignissen außer Kraft setzen:

// 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();
}

Ausgabe

Mehrere Ereignishandler

Ein Ereignisempfänger oder ein anderer Clientcode kann einem Ereignis einen oder mehrere Handler hinzufügen.

// 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);
}

Ausgabe

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

Statische Ereignisse

Das folgende Beispiel zeigt, wie statische Ereignisse definiert und verwendet werden.

// 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);
}

Ausgabe

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

Virtuelle Ereignisse

In diesem Beispiel werden virtuelle, verwaltete Ereignisse in einer Schnittstelle und Klasse implementiert:

// 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);
}

Ausgabe

In handler H1
In handler H2 with args 1 and 2.2

Ein einfaches Ereignis kann nicht angegeben werden, um ein Basisklassenereignis außer Kraft zu setzen oder auszublenden. Sie müssen alle Accessorfunktionen des Ereignisses definieren und dann die new oder override Schlüsselwort (keyword) für jede Accessorfunktion angeben.

// 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 {}
   }
};

Abstrakte Ereignisse

Das folgende Beispiel zeigt, wie sie ein abstraktes Ereignis implementieren.

// 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");
}

Ausgabe

hi
hello from Event2

Auslösen von Ereignissen, die in einer anderen Assembly definiert sind

Ein Ereignis- und Ereignishandler kann in einer Assembly definiert und von einer anderen Assembly genutzt werden.

// 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);
   }
};

Dieser Clientcode verwendet das Ereignis:

// 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);
}

Ausgabe

hello
hello

Siehe auch

event

Freigeben über

Gewusst wie: Verwenden von Ereignissen in C++/CLI

Schnittstellenereignisse

Benutzerdefinierte Accessormethoden

Überschreiben des Standardzugriffs beim Hinzufügen, Entfernen und Auslösen von Accessoren

Mehrere Ereignishandler

Statische Ereignisse

Virtuelle Ereignisse

Abstrakte Ereignisse

Auslösen von Ereignissen, die in einer anderen Assembly definiert sind

Siehe auch

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