Visual C++ .NET/Delegate/Delegate

Adding and removing Delegates

  
#include "stdafx.h"
using namespace System;
delegate void OutputMessage(String ^name);
void SayHello(String ^name){
    Console::Write("Hello there ");
    Console::WriteLine(name);
}
ref class MyClass{
public:
    static void Print1(String ^name);
    void Print2(String ^name);
    void Print3(String ^name);
};
void MyClass::Print1(System::String ^name){
    Console::Write("1 ");
    Console::WriteLine(name);
}
void MyClass::Print2(System::String ^name){
    Console::Write("2 ");
    Console::Write(name);
}
void MyClass::Print3(System::String ^name){
    Console::Write("3 ");
    Console::WriteLine(name);
}
void main(){
    OutputMessage^ say;
    say = gcnew OutputMessage(&SayHello);
    say += gcnew OutputMessage(&MyClass::Print1);
    MyClass ^computer = gcnew MyClass();
    say = say + gcnew OutputMessage(computer, &MyClass::Print2);
    say += gcnew OutputMessage(computer, &MyClass::Print3);
    say->Invoke("s1");
    say = say - gcnew OutputMessage(&MyClass::Print1);
    say -= gcnew OutputMessage(computer, &MyClass::Print3);
    say("s1");
}

Define delegate function

 
#include "stdafx.h"
using namespace System;
using namespace System::Threading;
ref class MyClass{
public:
   property String^ Value;
   MyClass(String^ s) { Value = s; }
};
delegate void DoSearch(String^, MyClass^);
ref class Database{
   IAsyncResult^ result;
   MyClass^ m_r;
   public:
      Database(String^ s) { m_r = gcnew MyClass(s); }
   void Query(String^ queryString, MyClass^ r){
       r->Value = "New Value";
   }
   void InitiateQuery(String^ queryString){
      DoSearch^ qf = gcnew DoSearch(this, &Database::Query);
      Console::WriteLine(m_r->Value);
      result = qf->BeginInvoke(queryString, m_r,gcnew AsyncCallback(this, &Database::ProcessResult),qf);
   }
   bool IsQueryCompleted(){
      return result->IsCompleted;
   }
   void ProcessResult(IAsyncResult^ result)
   {
      DoSearch^ caller = (DoSearch^) result->AsyncState;
      caller->EndInvoke(result);
      Console::WriteLine(m_r->Value);
   }
};
int main(){
   Database doc("Old Value");
   doc.InitiateQuery("SELECT * FROM Employee ");
   while (! doc.IsQueryCompleted() ){
       Thread::Sleep(100);
   }
}

delegate invocation list

 
#include "stdafx.h"
using namespace System;
delegate String^ MyDelegate();
ref class MyClass
{
   public:
   String^ f() { return "MyClass::f"; }
   String^ g() { return "MyClass::g"; }
   String^ h() { return "MyClass::h"; }
};
int main()
{
   MyDelegate^ d;
   MyClass^ r = gcnew MyClass();
   d =  gcnew MyDelegate(r, &MyClass::f);
   d = (MyDelegate^) d->Combine(d, gcnew MyDelegate(r, &MyClass::g));
   d = (MyDelegate^) d->Combine(d, gcnew MyDelegate(r, &MyClass::h));
   String^ s = d->Invoke();
   Console::WriteLine("Return value was {0}", s);
   d = (MyDelegate^) d->Remove(d, gcnew MyDelegate(r, &MyClass::g));
   s = d->Invoke();
   Console::WriteLine("Return value was {0}", s);
   for each (MyDelegate^ del in d->GetInvocationList())
   {
       s = del->Invoke();
       Console::WriteLine("Return value was {0}", s);
   }
}

delegate operators

 
#include "stdafx.h"
using namespace System;
delegate void MyDelegate();
ref class MyClass{
   public:
   void f() { Console::WriteLine("MyClass::f"); }
   void g() { Console::WriteLine("MyClass::g"); }
};
int main()
{
   MyDelegate^ d;
   MyClass^ r = gcnew MyClass();
   d += gcnew MyDelegate(r, &MyClass::f);
   d += gcnew MyDelegate(r, &MyClass::g);
   d->Invoke();
   d -= gcnew MyDelegate(r, &MyClass::g);
   d();
}