共用方式為

做為回呼方法，委派封送處理

  • 發行項

此範例示範如何將委派傳遞至需要函式指標的 Unmanaged 函式。 委派是可保留方法參考的類別，並且相當於型別安全函式指標或回呼函式。

注意

當您在呼叫內使用委派時，Common Language Runtime 會在該呼叫的期間防止對委派進行記憶體回收。 不過，如果 Unmanaged 函式儲存要在呼叫完成之後使用的委派，您必須手動防止記憶體回收，直到 Unmanaged 函式與委派一起完成之前。 如需詳細資訊，請參閱 HandleRef 範例和 GCHandle 範例。

Callback 範例會使用下列 Unmanaged 函式和其原始函式宣告，如下所示：

  • 從 PinvokeLib.dll 匯出的 TestCallBack。

    void TestCallBack(FPTR pf, int value);

  • 從 PinvokeLib.dll 匯出的 TestCallBack2。

    void TestCallBack2(FPTR2 pf2, char* value);

PinvokeLib.dll 是自訂的 Unmanaged 程式庫，其中包含先前所列出函式的實作。

在此範例中，NativeMethods 類別包含 TestCallBack 和 TestCallBack2 方法的 Managed 原型。 這兩種方法都會將委派當成參數傳遞給回呼函式。 委派的簽章必須符合它所參考之方法的簽章。 例如，FPtr 和 FPtr2 委派的簽章與 DoSomething 和 DoSomething2 方法相同。

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

另請參閱