How do I detect if a window of another application is open? - vb.net

Question

I am trying to detect whether or not a window is open (and being used by the user). I have used code from this forum but can't get it to work, here is what I've got:
Private Declare Function FindWindow Lib "user32" Alias "FindWindowA" _
(ByVal lpClassName As String, ByVal lpWindowName As String) As Long
Private Sub btnCheckWindow_Click(sender As Object, e As EventArgs) Handles btnCheckWindow.Click
Dim lngFindIt As Long
lngFindIt = FindWindow(vbNullString, "lkhsdlfhslfh")
If lngFindIt = 0 Then
MsgBox("It is not here")
Else
MsgBox("I found the sucker.")
End If
End Sub
Upon running the program and clicking a button I get "I found the sucker." despite definitely not having a window called "lkhsdlfhslfh" existing let alone open.
How do I fix this?

Answer 1

Your method signature is incorrect. It should return IntPtr, not Long.
Try the following:
Private Declare Function FindWindow Lib "user32" Alias "FindWindowA" _
(ByVal lpClassName As String, ByVal lpWindowName As String) As IntPtr
Private Sub btnCheckWindow_Click(sender As Object, e As EventArgs) Handles btnCheckWindow.Click
Dim result As IntPtr= FindWindow(Nothing, "lkhsdlfhslfh")
If result = IntPtr.Zero Then
MsgBox("Window not found.")
Else
MsgBox("Found it.")
End If
End Sub
Alternatively, you could use <DllImport>, which is the standard way in .NET:
<DllImport("user32.dll", SetLastError:=True, CharSet:=CharSet.Auto)>
Private Shared Function FindWindow(
ByVal lpClassName As String,
ByVal lpWindowName As String) As IntPtr
End Function
Note that unless you're dealing with an ancient program, you should probably use a Unicode charset. This means using FindWindowW (instead of FindWindowA) if you go with Declare or CharSet.Unicode if you go with <DllImport>.