__delegate
Visual Studio .NET 2003
Defines a reference type that can be used to encapsulate a method with a specific signature.
__delegate function-declarator
Remarks
A delegate is roughly equivalent to a C++ function pointer except for the following difference:
- A delegate can only be bound to one or more methods within a __gc class.
When the compiler encounters the __delegate keyword, a definition of a __gc class is generated. This __gc class has the following characteristics:
- It inherits from System::MulticastDelegate.
- It has a constructor that takes two arguments: a pointer to a __gc class or NULL (in the case of binding to a static method) and a fully qualified method of the specified type.
- It has a method called Invoke, whose signature matches the declared signature of the delegate.
For more information on delegates and their base implementations, see 9 Delegates.
Example
In the following example, a __gc class (MyCalendar) and a delegate (GetDayOfWeek) are declared. The delegate is then bound to the different methods of MyCalendar, invoking each in turn:
// keyword__delegate.cpp
// compile with: /clr
#using <mscorlib.dll>
using namespace System;
__delegate int GetDayOfWeek();
__gc class MyCalendar
{
public:
MyCalendar() : m_nDayOfWeek(4) {}
int MyGetDayOfWeek() { Console::WriteLine("handler"); return m_nDayOfWeek; }
static int MyStaticGetDayOfWeek() { Console::WriteLine("static handler"); return 6; }
private:
int m_nDayOfWeek;
};
int main ()
{
GetDayOfWeek * pGetDayOfWeek; // declare delegate type
int nDayOfWeek;
// bind delegate to static method
pGetDayOfWeek = new GetDayOfWeek(0, &MyCalendar::MyStaticGetDayOfWeek);
nDayOfWeek = pGetDayOfWeek->Invoke();
Console::WriteLine(nDayOfWeek);
// bind delegate to instance method
MyCalendar * pcal = new MyCalendar();
pGetDayOfWeek = static_cast<GetDayOfWeek*>(Delegate::Combine(pGetDayOfWeek,
new GetDayOfWeek(pcal, &MyCalendar::MyGetDayOfWeek)));
nDayOfWeek = pGetDayOfWeek->Invoke();
Console::WriteLine(nDayOfWeek);
// delegate now bound to two methods; remove instance method
pGetDayOfWeek = static_cast<GetDayOfWeek*>(Delegate::Remove(pGetDayOfWeek,
new GetDayOfWeek(pcal, &MyCalendar::MyGetDayOfWeek)));
return 0;
}
Output
static handler 6 static handler handler 4
