如何：定義和使用委派 (C++/CLI)

本文說明如何在 C++/CLI 中定義及取用委派。

雖然 .NET Framework 提供許多委派，但有時候您可能必須定義新的委派。

下列程式代碼範例會定義名為 MyCallback的委派。 事件處理程式碼—引發這個新委派時所呼叫的函式，必須具有的 void 傳回型別並取得 String 參考。

main 函式會使用 所 SomeClass 定義的靜態方法來具現化 MyCallback 委派。 接著，委派會變成呼叫此函式的替代方法，如將字串 「single」 傳送至委派物件所示範。 接下來，的其他實例 MyCallback 會連結在一起，然後由一個對委派對象的呼叫執行。

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

ref class SomeClass
{
public:
   static void Func(String^ str)
   {
      Console::WriteLine("static SomeClass::Func - {0}", str);
   }
};

ref class OtherClass
{
public:
   OtherClass( Int32 n )
   {
      num = n;
   }

   void Method(String^ str)
   {
      Console::WriteLine("OtherClass::Method - {0}, num = {1}",
         str, num);
   }

   Int32 num;
};

delegate void MyCallback(String^ str);

int main( )
{
   MyCallback^ callback = gcnew MyCallback(SomeClass::Func);
   callback("single");

   callback += gcnew MyCallback(SomeClass::Func);

   OtherClass^ f = gcnew OtherClass(99);
   callback += gcnew MyCallback(f, &OtherClass::Method);

   f = gcnew OtherClass(100);
   callback += gcnew MyCallback(f, &OtherClass::Method);

   callback("chained");

   return 0;
}

static SomeClass::Func - single
static SomeClass::Func - chained
static SomeClass::Func - chained
OtherClass::Method - chained, num = 99
OtherClass::Method - chained, num = 100

下一個程式代碼範例示範如何將委派與實值類別的成員產生關聯。

// mcppv2_del_mem_value_class.cpp
// compile with: /clr
using namespace System;
public delegate void MyDel();

value class A {
public:
   void func1() {
      Console::WriteLine("test");
   }
};

int main() {
   A a;
   A^ ah = a;
   MyDel^ f = gcnew MyDel(a, &A::func1);   // implicit box of a
   f();
   MyDel^ f2 = gcnew MyDel(ah, &A::func1);
   f2();
}

test
test

如何撰寫委派

您可以使用 「-「 運算子」，從撰寫的委派中移除元件委派。

// mcppv2_compose_delegates.cpp
// compile with: /clr
using namespace System;

delegate void MyDelegate(String ^ s);

ref class MyClass {
public:
   static void Hello(String ^ s) {
      Console::WriteLine("Hello, {0}!", s);
   }

   static void Goodbye(String ^ s) {
      Console::WriteLine("  Goodbye, {0}!", s);
   }
};

int main() {

   MyDelegate ^ a = gcnew MyDelegate(MyClass::Hello);
   MyDelegate ^ b = gcnew MyDelegate(MyClass::Goodbye);
   MyDelegate ^ c = a + b;
   MyDelegate ^ d = c - a;

   Console::WriteLine("Invoking delegate a:");
   a("A");
   Console::WriteLine("Invoking delegate b:");
   b("B");
   Console::WriteLine("Invoking delegate c:");
   c("C");
   Console::WriteLine("Invoking delegate d:");
   d("D");
}

輸出

Invoking delegate a:
Hello, A!
Invoking delegate b:
  Goodbye, B!
Invoking delegate c:
Hello, C!
  Goodbye, C!
Invoking delegate d:
  Goodbye, D!

將 delegate^ 傳遞至預期函式指標的原生函式

您可以從受控元件使用函式指標參數呼叫原生函式，然後原生函式可以呼叫 Managed 元件委派的成員函式。

此範例會建立匯出原生函式的.dll：

// delegate_to_native_function.cpp
// compile with: /LD
#include < windows.h >
extern "C" {
   __declspec(dllexport)
   void nativeFunction(void (CALLBACK *mgdFunc)(const char* str)) {
      mgdFunc("Call to Managed Function");
   }
}

下一個範例會取用.dll，並將委派句柄傳遞至預期函式指標的原生函式。

// delegate_to_native_function_2.cpp
// compile with: /clr
using namespace System;
using namespace System::Runtime::InteropServices;

delegate void Del(String ^s);
public ref class A {
public:
   void delMember(String ^s) {
      Console::WriteLine(s);
   }
};

[DllImportAttribute("delegate_to_native_function", CharSet=CharSet::Ansi)]
extern "C" void nativeFunction(Del ^d);

int main() {
   A ^a = gcnew A;
   Del ^d = gcnew Del(a, &A::delMember);
   nativeFunction(d);   // Call to native function
}

輸出

Call to Managed Function

將委派與 Unmanaged 函式產生關聯

若要將委派與原生函式產生關聯，您必須將原生函式包裝在Managed型別中，並宣告要透過 PInvoke叫用的函式。

// mcppv2_del_to_umnangd_func.cpp
// compile with: /clr
#pragma unmanaged
extern "C" void printf(const char*, ...);
class A {
public:
   static void func(char* s) {
      printf(s);
   }
};

#pragma managed
public delegate void func(char*);

ref class B {
   A* ap;

public:
   B(A* ap):ap(ap) {}
   void func(char* s) {
      ap->func(s);
   }
};

int main() {
   A* a = new A;
   B^ b = gcnew B(a);
   func^ f = gcnew func(b, &B::func);
   f("hello");
   delete a;
}

輸出

hello

使用未系結的委派

您可以使用未系結的委派，傳遞呼叫委派時要呼叫其函式之型別的實例。

如果您想要逐一查看集合中的物件，則取消系結委派特別有用，方法是針對 每個實例使用 ， 在關鍵詞中使用 ，並在每個實例上呼叫成員函式。

以下說明如何宣告、具現化及呼叫系結和未系結的委派：

此範例示範如何宣告、具現化及呼叫未系結的委派：

// unbound_delegates.cpp
// compile with: /clr
ref struct A {
   A(){}
   A(int i) : m_i(i) {}
   void Print(int i) { System::Console::WriteLine(m_i + i);}

private:
   int m_i;
};

value struct V {
   void Print() { System::Console::WriteLine(m_i);}
   int m_i;
};

delegate void Delegate1(A^, int i);
delegate void Delegate2(A%, int i);

delegate void Delegate3(interior_ptr<V>);
delegate void Delegate4(V%);

delegate void Delegate5(int i);
delegate void Delegate6();

int main() {
   A^ a1 = gcnew A(1);
   A% a2 = *gcnew A(2);

   Delegate1 ^ Unbound_Delegate1 = gcnew Delegate1(&A::Print);
   // delegate takes a handle
   Unbound_Delegate1(a1, 1);
   Unbound_Delegate1(%a2, 1);

   Delegate2 ^ Unbound_Delegate2 = gcnew Delegate2(&A::Print);
   // delegate takes a tracking reference (must deference the handle)
   Unbound_Delegate2(*a1, 1);
   Unbound_Delegate2(a2, 1);

   // instantiate a bound delegate to an instance member function
   Delegate5 ^ Bound_Del = gcnew Delegate5(a1, &A::Print);
   Bound_Del(1);

   // instantiate value types
   V v1 = {7};
   V v2 = {8};

   Delegate3 ^ Unbound_Delegate3 = gcnew Delegate3(&V::Print);
   Unbound_Delegate3(&v1);
   Unbound_Delegate3(&v2);

   Delegate4 ^ Unbound_Delegate4 = gcnew Delegate4(&V::Print);
   Unbound_Delegate4(v1);
   Unbound_Delegate4(v2);

   Delegate6 ^ Bound_Delegate3 = gcnew Delegate6(v1, &V::Print);
   Bound_Delegate3();
}

輸出

2
3
2
3
2
7
8
7
8
7

下一個範例示範如何使用未系結的委派和 ，在關鍵詞中 逐一查看集合中的物件，並在每個實例上呼叫成員函式。

// unbound_delegates_2.cpp
// compile with: /clr
using namespace System;

ref class RefClass {
   String^ _Str;

public:
   RefClass( String^ str ) : _Str( str ) {}
   void Print() { Console::Write( _Str ); }
};

delegate void PrintDelegate( RefClass^ );

int main() {
   PrintDelegate^ d = gcnew PrintDelegate( &RefClass::Print );

   array< RefClass^ >^ a = gcnew array<RefClass^>( 10 );

   for ( int i = 0; i < a->Length; ++i )
      a[i] = gcnew RefClass( i.ToString() );

   for each ( RefClass^ R in a )
      d( R );

   Console::WriteLine();
}

此範例會建立屬性存取子函式的未繫結委派：

// unbound_delegates_3.cpp
// compile with: /clr
ref struct B {
   property int P1 {
      int get() { return m_i; }
      void set(int i) { m_i = i; }
   }

private:
   int m_i;
};

delegate void DelBSet(B^, int);
delegate int DelBGet(B^);

int main() {
   B^ b = gcnew B;

   DelBSet^ delBSet = gcnew DelBSet(&B::P1::set);
   delBSet(b, 11);

   DelBGet^ delBGet = gcnew DelBGet(&B::P1::get);
   System::Console::WriteLine(delBGet(b));
}

輸出

11

下列範例示範如何叫用多播委派，其中一個實例已系結，一個實例未系結。

// unbound_delegates_4.cpp
// compile with: /clr
ref class R {
public:
   R(int i) : m_i(i) {}

   void f(R ^ r) {
      System::Console::WriteLine("in f(R ^ r)");
   }

   void f() {
      System::Console::WriteLine("in f()");
   }

private:
   int m_i;
};

delegate void Del(R ^);

int main() {
   R ^r1 = gcnew R(11);
   R ^r2 = gcnew R(12);

   Del^ d = gcnew Del(r1, &R::f);
   d += gcnew Del(&R::f);
   d(r2);
};

輸出

in f(R ^ r)
in f()

下一個範例示範如何建立及呼叫未系結的泛型委派。

// unbound_delegates_5.cpp
// compile with: /clr
ref struct R {
   R(int i) : m_i(i) {}

   int f(R ^) { return 999; }
   int f() { return m_i + 5; }

   int m_i;
};

value struct V {
   int f(V%) { return 999; }
   int f() { return m_i + 5; }

   int m_i;
};

generic <typename T>
delegate int Del(T t);

generic <typename T>
delegate int DelV(T% t);

int main() {
   R^ hr = gcnew R(7);
   System::Console::WriteLine((gcnew Del<R^>(&R::f))(hr));

   V v;
   v.m_i = 9;
   System::Console::WriteLine((gcnew DelV<V >(&V::f))(v) );
}

輸出

12
14

另請參閱

delegate (C++ 元件延伸模組)