Get at another Window's list box.

[JoshT]

How hard is it to get at a ListBox on another Window? Here's the catch: I'm communicating with a hardware device via API calls to a pseudo-driver DLL provided by the HW manufacturer, and they supplied a (poorly documented) .bas file with the "declares" for that DLL. I can synchronously call one of the functions, which displays a "connecting" window for 20 or more seconds, following by a window with a list box containing variable names of what the HW device is monitoring. When the user clicks close on that window, the function returns the value selected in the list box to me in a string buffer. The problem is the user needs to pick quite a few of the variable names, and since each call to the function can take up to a couple of minutes for each connection to the device, I'd like to just get at those variable names once, filter them, load them into a list box on a form I created, then let the user pick from there.

How feasible is this "user-friendlyness" tweak? I have the program working smoothly, and I'd like to make it as easy for the user as possible, but I don't want to spend too much time on it if its not worth it.

[crispin]

Hi JoshT,

Heres what I use:

Option Explicit
Option Base 0
Private Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal hWnd As Long, ByVal wMsg As Long, ByVal wParam As Long, lParam As Any) As Long
Private Declare Function FindWindowEx Lib "user32" Alias "FindWindowExA" (ByVal hWnd1 As Long, ByVal hWnd2 As Long, ByVal lpsz1 As String, ByVal lpsz2 As String) As Long
Private Declare Function SendMessageByStr& Lib "user32" Alias "SendMessageA" _
 (ByVal hWnd As Long, ByVal wMsg As Long, ByVal wParam As Long, ByVal _
  lParam As String)
Private Const LB_GETCOUNT = &H18B
Private Const LB_GETTEXT = &H189

Public Sub GetListBox()
Dim lhWnd&
Dim ltxthWnd&
Dim ltChars&
Dim aLBoxItems() As String
lhWnd = FindWindowEx(0&, 0&, vbNullString, "API Viewer - C:\Program Files\Microsoft Visual Studio\Common\Tools\Winapi\Win32api.txt")
If lhWnd Then
    ltxthWnd = FindWindowEx(lhWnd, 0&, "ThunderRT6ListBox", vbNullString)
    If ltxthWnd Then
        Call ReturnList(ltxthWnd, aLBoxItems)
End If
Else
          
End If
End Sub

Public Sub ReturnList(hWnd As Long, ByRef sList() As String)
Dim iCount%
Dim lRet&
Dim lItems&
Dim sBuff$
sBuff = String(256, " ")
lItems = SendMessage(hWnd, LB_GETCOUNT, 0, 0)
For iCount = 0 To lItems - 1
    ReDim Preserve sList(iCount)
    lRet = SendMessageByStr(hWnd, LB_GETTEXT, iCount, sBuff)
    sList(iCount) = Trim(sBuff)
Next iCount
End Sub

[JoshT]

ltxthWnd = FindWindowEx(lhWnd, 0&, "ThunderRT6ListBox", vbNullString)

Thunder* class names are VB, right? The classname for a standard listbox would just be "LISTBOX", right?

Thanks, crispin, that'll get me started. Now, I'm gonna have to get this to run on a separate thread...

[JoshT]

Okay, I got this working. I'm using an API Timer to force a seperate thread. Now, my problem is that my app finds the ListBox and the Window while it is hidden and there's nothing in the ListBox...