此範例示範如何將委派傳遞至期望函式指標的非受控函式。 委託是一種可以保存方法引用的類別，等同於型別安全函式指標或回調函式。
備註
當您在呼叫內使用委派時，Common Language Runtime 會保護委派，防止其在呼叫期間被垃圾回收。 不過，如果非受管函式將委派儲存在呼叫完成後使用，您必須手動防止垃圾收集，直到非受管函式使用完委派為止。 如需詳細資訊，請參閱 HandleRef 範例 和 GCHandle 範例。
Callback 範例會使用下列非受控函式，這些函式以其原始宣告顯示：
TestCallBack從 PinvokeLib.dll匯出。void TestCallBack(FPTR pf, int value);TestCallBack2從 PinvokeLib.dll匯出。void TestCallBack2(FPTR2 pf2, char* value);
PinvokeLib.dll 是自定義非受控連結庫，其中包含先前所列功能的實作。
在此範例中，類別NativeMethods包含 TestCallBack和TestCallBack2方法的管理的原型。 這兩種方法都會將委派傳遞至回調函式作為參數。 委託的簽章必須與其所參考方法的簽章一致。 例如，FPtr 和 FPtr2 委派的簽名與 DoSomething 和 DoSomething2 方法的簽名相同。
宣告原型
public delegate bool FPtr(int value);
public delegate bool FPtr2(String^ value);
private ref class NativeMethods
{
public:
// Declares managed prototypes for unmanaged functions.
[DllImport("..\\LIB\\PinvokeLib.dll")]
static void TestCallBack(FPtr^ cb, int value);
[DllImport("..\\LIB\\PinvokeLib.dll")]
static void TestCallBack2(FPtr2^ cb2, String^ value);
};
public delegate bool FPtr(int value);
public delegate bool FPtr2(string value);
internal static class NativeMethods
{
// Declares managed prototypes for unmanaged functions.
[DllImport("..\\LIB\\PinvokeLib.dll", CallingConvention = CallingConvention.Cdecl)]
internal static extern void TestCallBack(FPtr cb, int value);
[DllImport("..\\LIB\\PinvokeLib.dll", CallingConvention = CallingConvention.Cdecl)]
internal static extern void TestCallBack2(FPtr2 cb2, string value);
}
Public Delegate Function FPtr(ByVal value As Integer) As Boolean
Public Delegate Function FPtr2(ByVal value As String) As Boolean
Friend Class NativeMethods
' Declares managed prototypes for unmanaged functions.
<DllImport("..\LIB\PinvokeLib.dll", CallingConvention:=CallingConvention.Cdecl)>
Friend Shared Sub TestCallBack(
ByVal cb As FPtr, ByVal value As Integer)
End Sub
<DllImport("..\LIB\PinvokeLib.dll", CallingConvention:=CallingConvention.Cdecl)>
Friend Shared Sub TestCallBack2(
ByVal cb2 As FPtr2, ByVal value As String)
End Sub
End Class
呼叫函式
public ref class App
{
public:
static void Main()
{
FPtr^ cb = gcnew FPtr(&App::DoSomething);
NativeMethods::TestCallBack(cb, 99);
FPtr2^ cb2 = gcnew FPtr2(&App::DoSomething2);
NativeMethods::TestCallBack2(cb2, "abc");
}
static bool DoSomething(int value)
{
Console::WriteLine("\nCallback called with param: {0}", value);
// ...
return true;
}
static bool DoSomething2(String^ value)
{
Console::WriteLine("\nCallback called with param: {0}", value);
// ...
return true;
}
};
public class App
{
public static void Main()
{
FPtr cb = new FPtr(App.DoSomething);
NativeMethods.TestCallBack(cb, 99);
FPtr2 cb2 = new FPtr2(App.DoSomething2);
NativeMethods.TestCallBack2(cb2, "abc");
}
public static bool DoSomething(int value)
{
Console.WriteLine($"\nCallback called with param: {value}");
// ...
return true;
}
public static bool DoSomething2(string value)
{
Console.WriteLine($"\nCallback called with param: {value}");
// ...
return true;
}
}
Public Class App
Public Shared Sub Main()
Dim cb As FPtr = AddressOf App.DoSomething
Dim cb2 As FPtr2 = AddressOf App.DoSomething2
NativeMethods.TestCallBack(cb, 99)
NativeMethods.TestCallBack2(cb2, "abc")
End Sub
Public Shared Function DoSomething(ByVal value As Integer) As Boolean
Console.WriteLine(ControlChars.CrLf + $"Callback called with param: {value}")
' ...
Return True
End Function
Public Shared Function DoSomething2(ByVal value As String) As Boolean
Console.WriteLine(ControlChars.CrLf + $"Callback called with param: {value}")
' ...
Return True
End Function
End Class
