Returning Strings from WinAPI in VB.Net

I know this has been covered a lot in other places, but the things is, all their examples have failed to work for me. Here I offer another method, one that worked for me.

Declare Auto Function GetWindowText Lib "user32" Alias "GetWindowTextA" (ByVal hwnd As Integer, ByVal lpString As String, ByVal cch As Integer) As Integer

This is the usual declaration of the API function GetWindowText. As we know lpString should be marshalled as a LPCSTR, but according to this article, VB.Net doesn't allow you to specify the marshaling attribute on parameters, and purportedly the above declaration works just fine.

When I tried this version of the API call, using GetWindowTextLength to determine the length of the string to be filled with spaces before passing to GetWindowText, I ended up with a bunch of non-ASCII characters. When I tried using the MarshalAs attribute, all I got was an empty string of the "correct" length.

After some exasperation I decided that since the API was expecting a pointer to a string, I might as well give one, or the closest to one, a byte array. The declaration was then:

Declare Auto Function GetWindowText Lib "user32" Alias "GetWindowTextA" (ByVal hwnd As Integer, ByVal lpByteArray As Byte(), ByVal cch As Integer) As Integer

Then:

...
Dim Ret As Integer, sByte As Byte()
Ret = GetWindowTextLength(hwnd)
If Ret > 0 Then
ReDim sByte(Ret + 1)
lret = GetWindowText(hwnd, sByte, Ret + 1)
Return System.Text.Encoding.ASCII.GetString(sByte)
End if
...

Just as a sanity check (and before I found the Encoding.ASCII.GetString function), I stepped through the function to see what was being stored in sByte. They looked to be ASCII-flavored bytes (mmmm) so I looked for a function to convert them to a string, et voila!

I was actually expecting to be required to pass the first member of the byte array as a parameter to GetWindowText, but apparently .Net did the math and converted the byte array into a pointer of sorts.

I must admit I'm a bit new to .Net (two years of actual usage) and newer to managed and unmanaged code mixing, so I can't tell you that this is the right way to do it, but this method worked where others failed.

I'm on .NET 2003, in case you were wondering.