Access Cookbook, 2nd Edition [Electronic resources] نسخه متنی

Recipe 11.9 Retrieve a List of All Top-Level Windows

11.9.1 Problem

You know you can determine if
specific applications are currently running (as shown in the Solution
in Recipe 11.8), but now you'd like to obtain a list
of all the running applications. That way, you could decide, as part
of your application, what to present to your users. Is there a way to
walk through all the open main windows and build up a list?

11.9.2 Solution

Windows includes API functions that allow you to walk down and around
the tree of open windows, starting with the main desktop window. This
solution provides a function that will do that for you, filling an
array with information on each top-level window. You can then use
that array to list applications, switch to them, or close them (see
the Solution in Recipe 11.10 for information
on closing other windows).

Load and run frmListWindows from

11-09.MDB . This sample form fills a list box
with all the top-level windows and provides a button that uses the
VBA AppActivate command to display the selected window. In addition,
the "Show visible windows only"
checkbox allows you to add invisible windows to the list. Of course,
attempting to use AppActivate to switch to an
invisible window will fail. Figure 11-11 shows the
sample form in action.

Figure 11-11. frmListWindows allows you to select and display any of the top-level windows

To include this functionality in your own applications, follow these
steps:

1. Import the module basWindowList from
   

   11-09.MDB . This module includes the API
   declarations, constants, and wrapper functions that
   you'll need to list and select top-level windows.

2. In your code, declare an array of type
   acb_tagWindowInfo to hold the list of open
   windows, like this:

   Dim atypWindowList( ) As acb_tagWindowInfo

3. Call acbWindowList, passing the array to be filled
   in and a Boolean value indicating whether to show visible windows
   only. The function returns the number of windows it finds. After the
   function call, your array will have
   intCount rows, with each row containing
   information about a specific top-level window. For example, this call
   will fill the array with information about all the visible top-level
   windows:

   intCount = acbWindowList(atypWindowList( ), True)

4. In your application, decide which (if any) window
   you'd like to display, perhaps by looping through
   all the elements of the array. Use the
   AppActivate command, along with the window
   name, to activate the selected window:

   AppActivate atypWindowList(intI).strCaption

11.9.3 Discussion

This example uses several functions for
navigating through the hierarchy of windows. Table 11-11 describes the functions.

The acbWindowList function first
retrieves a handle to the main desktop window, using
GetDesktopHWnd. Once it knows that, it can find
the handle for the desktop's first child window,
using GetWindow. From then on, as long as the
handle for the current window isn't 0, the code
loops, filling in the array with information about the current window
and then moving on to the next window with the

GetWindow function. You'll note
that the loop skips windows without captions (of which there are
quite a few). Windows maintains a number of top-level hidden windows
without captions for its own use. In addition, by specifying the
blnVisibleOnly parameter for
acbWindowList, you can include or exclude
invisible windows. Windows sets up a number of invisible windows, and
you probably won't want them to show up in your
list. If you're interested, however, pass in
False for this parameter to add all the hidden
windows to your list. The code for the
acbWindowList function is as follows:

Type acb_tagWindowInfo
strCaption As String
hWnd As Long
strClass As String
End Type
Public Function acbWindowList(aWI( ) As acb_tagWindowInfo, _
ByVal blnVisibleOnly As Boolean) As Integer
' Fill an array with a list of all the currently
' open top-level windows.
Dim hWnd As Long
Dim strCaption As String
Dim intCount As Integer
Dim lngStyle As Long
' Get the desktop window and, from there, the first
' top-level window.
hWnd = acb_apiGetDesktopWindow( )
hWnd = acb_apiGetWindow(hWnd, GW_CHILD)
' Loop through all the top-level windows.
Do While hWnd <> 0
strCaption = acbGetCaption(hWnd)
If Len(strCaption) > 0 Then
' If you got a caption, add one element to the output
' array, and fill in the information (name and hWnd).
lngStyle = acb_apiGetWindowLong(hWnd, GWL_STYLE)
' The Imp operator (Implies) returns True unless
' the first condition is True and the second is False,
' so this condition will be true unless you're
' showing visible only and the window is not visible.
If blnVisibleOnly Imp (WS_VISIBLE And lngStyle) Then
ReDim Preserve aWI(0 To intCount)
aWI(intCount).strCaption = strCaption
aWI(intCount).hWnd = hWnd
aWI(intCount).strClass = CalcClassName(hWnd)
intCount = intCount + 1
End If
End If
' Move to the next top-level window.
hWnd = acb_apiGetWindow(hWnd, GW_HWNDNEXT)
Loop
' Return the number of windows.
acbWindowList = intCount
End Function

You may find it instructive to
study the code in the sample form's module. It calls
acbWindowList and then uses a list-filling
callback function to fill the list box on the form with window
captions, classes, and handles. This is a perfect example of when
you'd use such a function: you need to fill a
control with data from an array that can't be
gathered until the application is running, and the array might be too
large to fit within the character limit imposed when you call the
control's AddItem method.

Some of the windows on the list exist at the time the form is filling
its list, but are not available (the Access Immediate window, for
example). You can attempt to switch to them, but the attempt will
fail. The code attached to the checkmark button's
Click event disregards errors, so it just keeps going if an error
occurs when it tries to switch the active window. See the Solution in
Recipe 11.10 for information on deleting
windows in this list.