Reputation: 1874
im currently playing around with events. But unfortunately latebinding in VBA doesn't support Events. So I'm using AddressOf. Within Access/Excel (my App) it works fine (see link)
Calling from C# the Text is returning "??" instead of the correct text
Thanks, Andi
public delegate void CallbackMsg(string msg, int unused1, int unused2, int unused3);
[ComVisible(true)]
public void TestProcess(int callback)
{
CallbackMsg x = (CallbackMsg)Marshal.GetDelegateForFunctionPointer(new IntPtr(callback), typeof(CallbackMsg));
x.Invoke("Hello Office", 0, 0, 0);
System.Windows.Forms.MessageBox.Show("Test DOTNET");
}
Upvotes: 2
Views: 832
Reputation: 2775
The strings used internally inside VB are neither C-style null-terminated strings nor "standard" Unicode strings. They are a special structure named BSTR (Basic Strings).
C# has a way of working with them through the Marshal class, so the C# code will look like this:
public delegate void CallbackMsg(IntPtr bstrMsg, int unused1, int unused2, int unused3);
[ComVisible(true)]
public void TestProcess(int callback)
{
IntPtr ptrBSTR = Marshal.StringToBSTR("Hello Office");
CallbackMsg x = (CallbackMsg)Marshal.GetDelegateForFunctionPointer(new IntPtr(callback), typeof(CallbackMsg));
x.Invoke(ptrBSTR, 2, 4, 6);
Marshal.FreeBSTR(ptrBSTR); //MUST free it
}
I tested this with Excel 2010, but I think it would be the same with other VBA products. The VBA code looks like this:
Public Sub CallbackMsg(ByVal s As String, ByVal unused1 As Long, ByVal unused2 As Long, ByVal unused3 As Long)
Debug.Print "This string came from C#: "; s
Debug.Print unused1, unused2, unused3
End Sub
Sub TestComVisbl()
Dim o As Object
Set o = CreateObject("ComVisbl.Class1")
Call o.TestProcess(AddressOf CallbackMsg)
End Sub
Upvotes: 2