You know you can determine if specific applications are currently running (as shown in Section 11.8.2 ), 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?
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 Section 11.10.2 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.
To include this functionality in your own applications, follow these steps:
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.
In your code, declare an array of type acb_tagWindowInfo to hold the list of open windows, like this:
Dim atypWindowList( ) As acb_tagWindowInfo
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)
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
This example uses two functions for navigating through the hierarchy of windows. Table 11-11 describes the functions (both are aliased with the “acb_api” tag in the code).
Table 11-11. Windows API navigation functions
Function |
Purpose |
---|---|
GetDesktopHWnd |
Retrieve the window handle for the main desktop window. All applications are children of this window. |
GetWindow |
Find a window in a specified relation to a specified window. In this case, you’ll be looking for the first child window of the desktop window. |
GetWindowLong |
Retrieve one of the 32-bit pieces of information stored with a window’s structure in memory. You’ll need to retrieve the style information (using the GWL_STYLE constant) so you can tell whether a window is visible. |
GetClassName |
Retrieve the window class name for the specified window. |
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 fVisibleOnly
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 fVisibleOnly 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 fVisibleOnly Imp (WS_VISIBLE And lngStyle) Then ReDim Preserve aWI(0 To intCount) aWI(intCount).strCaption = strCaption aWI(intCount).hWnd = hWnd aWI(intCount).strClass = GetClassName(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.
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 Section 11.10.2 for information on deleting windows in this list.