将委托作为回调方法进行封送

  • 项目

此示例演示如何将委托传递给需要函数指针的非托管函数。 委托是可以容纳方法引用的类，等效于类型安全函数指针或回调函数。

备注

在调用内使用委托时，公共语言运行时防止在该调用的持续时间内对委托执行垃圾回收。 但是，如果非托管函数存储了该委托，以便在调用完成后使用，则必须手动防止垃圾回收，直到非托管函数结束对该委托的使用为止。 有关详细信息，请参阅 HandleRef 示例和 GCHandle 示例。

回调示例使用以下非托管函数（与其原始函数声明一同显示）：

  • TestCallBack 从 PinvokeLib.dll 导出。

    void TestCallBack(FPTR pf, int value);

  • TestCallBack2 从 PinvokeLib.dll 导出。

    void TestCallBack2(FPTR2 pf2, char* value);

PinvokeLib.dll 是一种自定义的非托管库，包含上述函数的实现。

在此示例中，NativeMethods 类包含 TestCallBack 和 TestCallBack2 方法的托管原型。 这两种方法都作为参数将委托传递给回调函数。 委托的签名必须匹配它引用的方法的签名。 例如，FPtr 和 FPtr2委托的签名与 DoSomething 和 DoSomething2 方法相同。

声明原型

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

调用函数

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

请参阅