回呼範例
這個範例示範如何將委派傳遞至預期函式指標的 Unmanaged 函式。 委派是一種含有方法參考的類別，相當於型別安全函式指標或回呼函式 (Callback Function)。
.gif "注意事項") 注意事項 |
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當您在呼叫內使用委派時，在該呼叫期間，Common Language Runtime 會保護委派不被記憶體回收。不過，如果 Unmanaged 函式儲存在呼叫完成之後所要使用的委派，您必須在 Unmanaged 函式完成委派之前手動防止記憶體回收。如需詳細資訊，請參閱 HandleRef 範例 和 GCHandle 範例。 |
回呼範例使用下列 Unmanaged 函式，顯示其原始函式宣告：
從 PinvokeLib.dll 匯出 TestCallBack。
void TestCallBack(FPTR pf, int value);從 PinvokeLib.dll 匯出 TestCallBack2。
void TestCallBack2(FPTR2 pf2, char* value);
PinvokeLib.dll 是自訂的 Unmanaged 程式庫，包含先前列示之函式的實作。
在這個範例中，LibWrap 類別包含 TestCallBack 和 TestCallBack2 方法的 Managed 原型。 這兩個方法會將委派當成參數傳遞至回呼函式。 委派的簽章 (Signature) 必須符合它所參考的方法簽章。 例如，FPtr 和 FPtr2 委派具有相同於 DoSomething 與 DoSomething2 方法的簽章。
宣告原型
Public Delegate Function FPtr( ByVal value As Integer ) As Boolean
Public Delegate Function FPtr2( ByVal value As String[]) As Boolean
Public Class LibWrap
' Declares managed prototypes for unmanaged functions.
Declare Sub TestCallBack Lib "..\LIB\PinvokeLib.dll" ( ByVal cb _
As FPtr, ByVal value As Integer )
Declare Sub TestCallBack2 Lib "..\LIB\PinvokeLib.dll" ( ByVal cb2 _
As FPtr2, ByVal value As String[])
End Class
public delegate bool FPtr(int value);
public delegate bool FPtr2(string value);
public class LibWrap
{
// Declares managed prototypes for unmanaged functions.
[DllImport("..\\LIB\\PinvokeLib.dll")]
public static extern void TestCallBack(FPtr cb, int value);
[DllImport("..\\LIB\\PinvokeLib.dll")]
public static extern void TestCallBack2(FPtr2 cb2, String value);
}
public delegate bool FPtr(int value);
public delegate bool FPtr2(String^ value);
public ref class LibWrap
{
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);
};
呼叫函式
Public Class App
Public Shared Sub Main()
Dim cb As FPtr
cb = AddressOf App.DoSomething
Dim cb2 As FPtr2
cb2 = AddressOf App.DoSomething2
LibWrap.TestCallBack( cb, 99 )
LibWrap.TestCallBack2( cb2, "abc" )
End Sub 'Main
Public Shared Function DoSomething( ByVal value As Integer ) As Boolean
Console.WriteLine( ControlChars.CrLf + "Callback called with param: {0}", value )
' ...
Return True
End Function
Public Shared Function DoSomething2( ByVal value As String[]) As Boolean
Console.WriteLine( ControlChars.CrLf + "Callback called with param: {0}", value )
' ...
Return True
End Function
End Class
public class App
{
public static void Main()
{
FPtr cb = new FPtr(App.DoSomething);
LibWrap.TestCallBack(cb, 99);
FPtr2 cb2 = new FPtr2(App.DoSomething2);
LibWrap.TestCallBack2(cb2, "abc");
}
public static bool DoSomething(int value)
{
Console.WriteLine("\nCallback called with param: {0}", value);
// ...
return true;
}
public static bool DoSomething2( String value )
{
Console.WriteLine("\nCallback called with param: {0}", value);
// ...
return true;
}
}
public ref class App
{
public:
static void Main()
{
FPtr^ cb = gcnew FPtr(&App::DoSomething);
LibWrap::TestCallBack(cb, 99);
FPtr2^ cb2 = gcnew FPtr2(&App::DoSomething2);
LibWrap::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;
}
};