Re: Find Topmost Window

Thanks a lot.

Alex.


-----Original Message-----
From: Technical discussion of VBCOM [mailto:[email protected]]
On Behalf Of Potter, Mark
Sent: 29 July 2002 13:13
To: [email protected]
Subject: Re: [VBCOM] Find Topmost Window


Here you go.



Win32 Window Hierarchy and Styles


Kyle Marsh
Microsoft Developer Network Technology Group

Created: September 29, 1993

Click to view or copy the Styles sample  <javascript:sample1.Click()>
application files for this technical article.


Abstract


This article describes the desktop, top-level, and child windows
provided in the Win32R versions of the MicrosoftR WindowsT operating
system and their hierarchical relationships. It explains how
applications can navigate the window structure and control the style and
appearance of a window on the desktop.


Window Hierarchy


The basic building block for displaying information in the MicrosoftR
WindowsT graphical environment is the window. Microsoft Windows manages
how each window relates to all other windows in terms of visibility,
ownership, and parent/child relationship. Windows uses this relationship
information when creating, destroying, or displaying a window. The
Windows window manager controls how windows relate to one another and
stores the relationship information it needs by linking the window
instance information of each window into a hierarchy known as the window
manager's list.

Within each window's instance information structure are four elements
that the window manager uses to build the window manager's list:


*       A handle to the window's child window



*       A handle to the next window in the list of child windows (the
next sibling)



*       A handle to the window's parent



*       A handle to the window's owner


<mk:@MSITStore:f:\Potter1\msdn\2001OCT\2001OCT\1033\techart.chm::/html/s
tyles32_1.gif>

Figure 1.

When Windows initializes, it creates a window, known as the desktop
window, that is sized to cover the entire display area and upon which
all other windows are displayed. The window manager uses the desktop
window as the top of the window manager's list. Thus, the desktop window
is the top of the window hierarchy.

Windows that form the next level of the window hierarchy are called
top-level windows. A top-level window is any window that is not a child
window. Top-level windows do not have the WS_CHILD style. The window
manager connects top-level windows to the desktop window by connecting
the top-level windows into a linked list with the head of the link list
stored in the desktop window's child window handle, and by using each
top-level window's next sibling handle to form the list. The linked list
is known as a child window list because it is attached to the child
window handle of a window. All windows connected to a child window list
are considered siblings; therefore, all top-level windows are siblings
of one another. The order of the child window list (first to last) also
denotes the top to bottom order (the Z order) of the windows as seen on
the display. The window manager uses this Z order to decide which
windows and which parts of windows are visible on the display and which
windows or parts of windows are hidden by other windows. When a window
appears on the display below another window, it appears after that
window in the child window list.

All top-level windows are also connected to the desktop window through
the parent window handle in the window instance information. Top-level
windows are connected to the desktop window as if they were child
windows of the desktop, and can be considered children of the desktop in
that parent/child navigation techniques can be used to move between a
top-level window and the desktop window.

The window manager places top-level windows at the top of the Z order
when they are created, and thus the entire window is visible. The window
manager inserts the window at the head of the desktop window's child
window list. An extended style, WS_EX_TOPMOST, controls where the window
manager places a newly created window in the window manager's list. The
window manager places windows without the WS_EX_TOPMOST style after any
windows that have the WS_EX_TOPMOST style. Thus, windows with the
WS_EX_TOPMOST style always display above windows without the
WS_EX_TOPMOST style.


<mk:@MSITStore:f:\Potter1\msdn\2001OCT\2001OCT\1033\techart.chm::/html/s
tyles32_2.gif>

Figure 2.

Another type of relationship can exist between top-level windows:
Top-level windows can own or be owned by other top-level windows. An
owned window is always above its owner in the Z order and is hidden when
its owner is minimized. Owned windows are not hidden when their owner is
hidden. Thus, if Window A owns Window B, which in turn owns Window C,
and if Window A is minimized, Window B is hidden but Window C remains
visible. An application creates an owned window relationship by passing
the window handle to the owner window in the hwndParent parameter of the
CreateWindow (or CreateWindowEx) function when the application creates
the owned window. If the window whose handle is in hwndParent is not a
top-level window, Windows finds the top-level window for the given
window and makes that top-level window the owner of the created window.
The passed-in window is stored in the owned window's instance data
parent field, and the top-level owner of the window is stored in the
owner field. Windows creates dialog boxes as owned windows unless an
application specifically declares a dialog box to be a child window.


<mk:@MSITStore:f:\Potter1\msdn\2001OCT\2001OCT\1033\techart.chm::/html/s
tyles32_3.gif>

Figure 3.

The desktop window occupies the first level of the windows hierarchy and
top-level windows occupy the second level. Child windows, which are
windows created with the WS_CHILD style, occupy all other levels. The
window manager connects child windows to their parent window in the same
way it connects top-level windows to the desktop window.


<mk:@MSITStore:f:\Potter1\msdn\2001OCT\2001OCT\1033\techart.chm::/html/s
tyles32_4.gif>

Figure 4.

Child windows are displayed within the client area of their parent. The
window manager uses the first-to-last order of the child window list to
determine the Z order of child windows. This method is the same as that
used for top-level windows. All top-level windows are displayed in the
client area of the desktop window and thus behave as if they were
children of the desktop for display purposes.


So What's Different in Win32?


The relationships among the desktop window, top-level windows, owned
windows, and child windows described in the previous section are
identical in Win32R and Win16. This ensures a high degree of
compatibility between Win16 and Win32, and allows applications that take
advantage of the windows hierarchy to work in both environments. The two
differences between the Win16 and Win32 environments involve security
and multiple threads.

Windows NTT adds a new level to the window hierarchy: Each computer that
runs Windows NT has a corresponding object called the WindowStation
object. This object forms the first level of security for a workstation
and is the source of inheritable security for all user objects. A
WindowStation object can, in turn, have any number of desktop objects.
Each desktop object is a desktop window, as described in the previous
section. Windows NT uses two desktops: One desktop handles the logon
screen, CTRL+ALT+DEL screen, locked workstation screen, and screen
saver, and the other desktop is used for the rest of the system.
Currently, applications cannot create or delete desktops.

Another difference between Win16 and Win32 involves using multiple
threads. Win16 does not support multiple threads, so the application
developer does not need to consider threading when an application
creates a window. In Win32, whenever a parent/child or owner/owned
relationship exists between windows, the threads that own the windows
share an input queue. The developer must remember that sharing an input
queue counteracts the benefits of using threads-only one thread can
process a message at any given time, while other threads sharing the
input queue must wait for GetMessage or PeekMessage to return. Wherever
possible, make sure that parent/child windows or owner/owned windows
belong to the same thread.

Win32 defines two new window types that are not part of the window
hierarchy: foreground windows and background windows. The foreground
window is the window that the user is currently working in. All other
windows are background windows. Developers should normally let the user
set the foreground window; however, Win32 does supply two functions to
handle the foreground window, SetForegroundWindow and
GetForegroundWindow.


Navigating the Window Manager's List


An application navigates the window manager's list by getting the owner,
parent, child, or next window from the window manager or by having
Windows call an application-supplied callback function for a set of
windows. The functions listed below navigate the window manager's list.


EnumChildWindows


An application can use this function to have Windows call an
application-supplied callback function for each child window of a given
window. Windows enumerates all child windows, including children of
child windows. Windows does not call the callback function for any child
windows created after EnumChildWindows is called but before it returns.


EnumThreadWindows


An application can use this function to have Windows call an
application-supplied callback function for each window belonging to a
given thread. Windows enumerates all top-level windows for a thread,
including owned and non-owned top-level windows, child windows, and
children of child windows. Windows does not call the callback function
for windows created after EnumTaskWindows is called but before it
returns.


EnumWindows


An application can use this function to have Windows call an
application-supplied callback function for each top-level window.
Windows enumerates all top-level windows, including owned and non-owned
windows. Windows does not call the callback function for any top-level
windows created after EnumWindows is called but before it returns.


FindWindow


An application can use this function to locate the first top-level
window in the Z order that matches the given class and window title. The
application can specify a particular class, a particular title, both, or
neither. If the application specifies neither a class name nor a window
title, the FindWindow function returns the top-level window, which is
the highest in the Z order. An application cannot use the FindWindow
function to locate windows farther down in the Z order after the first
matching window is found.


GetDesktopWindow


This function returns the handle to the desktop window.


GetNextWindow


Win16 defined this function separately from GetWindow (see below). Win32
does not implement this function, but the WINUSER.H header file defines
a macro that replaces calls to GetNextWindow with GetWindow.


GetParent


This function returns a handle to a given window's parent, if a parent
exists. If the window is a child window, the function returns the handle
to the parent window. If the window is a top-level window, the function
returns the handle to the window's owner, if an owner exists. To find
the handle to the window that was passed to CreateWindow or to
CreateWindowEx when an owned window was created, use
GetWindowWord(GWW_HWNDPARENT). This window handle is different from the
value returned by GetParent if the window whose handle was passed to
CreateWindow or CreateWindowEx was not a top-level window. This
situation occurs when a dialog box is created with a child window in its
hwndParent parameter to CreateWindow or CreateWindowEx.


GetThreadDesktop


This function returns the handle to the desktop for the given thread.


GetTopWindow


This function returns the given window's first child. The first child
window is always at the top of the Z order for the given window. If no
window is specified, the passed-in window handle is NULL, and this
function returns the highest top-level window in the Z order.


GetWindow


An application can use this function to navigate the window manager's
list. GetWindow takes two parameters-a handle to a window (HWND) and
fwRel (WORD)-specifying the relationship from the given window to the
desired window. The following relationships can be obtained:


*       GW_HWNDNEXT: GetWindow returns the handle to the given window's
next sibling. When an application calls GetWindow with GW_HWNDNEXT, it
receives the same result that calling GetNextWindow with GW_HWNDNEXT
returns.



*       GW_HWNDFIRST: GetWindow returns the handle to the given window's
topmost sibling in the Z order. This is the most visible sibling window.
When an application calls GetWindow with GW_HWNDFIRST, it receives the
same result that calling GetTopWindow returns.



*       GW_HWNDLAST: GetWindow returns the given window's bottommost
sibling in the Z order. This is the least visible sibling.



*       GW_HWNDPREV: GetWindow returns the handle to the given window's
previous sibling. When an application calls GetWindow with GW_HWNDPREV,
it receives the same result that calling GetNextWindow with GW_HWNDPREV
returns.



*       GW_OWNER: GetWindow returns the handle to the given window's
owner. If the given window has no owner, GetWindow returns NULL.



*       GW_CHILD: GetWindow returns the handle to the given window's
first child window. The first child window is at the top of the given
window's Z order. If the given window has no child window, the GetWindow
function returns NULL.


IsChild


IsChild takes two handles to windows as its arguments: hWndParent and
hWnd. IsChild returns TRUE if hWnd is a child or another descendant of
hWndParent. hWnd is a descendant of hWndParent if hWndParent is found by
stepping from a given window's parent to its parent, and so on. IsChild
returns FALSE if hWnd is the same as hWndParent.


Window Styles


When an application creates a window with the CreateWindow or
CreateWindowEx function, it assigns the window certain style attributes
in the dwStyle parameter. The style attributes determine the type of
window, the functionality of the window, and the initial state of the
window. Win32 contains no new, changed, or deleted styles; Win32 styles
are identical to Win16 styles.


Window Type Styles


WS_OVERLAPPED


Overlapped windows are top-level windows and are connected to the
desktop window's child windows list. Applications usually use overlapped
windows as their main window. Overlapped windows always have a caption,
even if WS_CAPTION is not specified. Because an overlapped window always
has a caption, it also always has a border. See WS_CAPTION below for
more information about border styles. Overlapped windows may own other
top-level windows or be owned by other top-level windows or both. All
overlapped windows have the WS_CLIPSIBLINGS style, even if it was not
specified.

Windows can set the initial size and position for overlapped windows. To
have Windows set the window's initial position, an application uses
CW_USEDEFAULT for the X parameter to CreateWindow or CreateWindowEx.
When an application uses CW_USEDEFAULT to set an overlapped window's
position and uses the WS_VISIBLE style to have the window visible when
it is created, Windows passes the Y parameter of CreateWindow or
CreateWindowEx to ShowWindow. Thus, when an application uses
CW_USEDEFAULT for the X parameter to CreateWindow or CreateWindowEx, the
Y parameter must be one of the following:


*       SW_HIDE



*       SW_SHOWNORMAL



*       SW_NORMAL



*       SW_SHOWMINIMIZED



*       SW_SHOWMAXIMIZED



*       SW_MAXIMIZE



*       SW_SHOWNOACTIVATE



*       SW_SHOW



*       SW_MINIMIZE



*       SW_SHOWMINNOACTIVE



*       SW_SHOWNA



*       SW_RESTORE

Usually an application should use SW_SHOW for the Y parameter because
SW_SHOW allows the proper functioning for WS_MAXIMIZE and WS_MINIMIZE
styles.

To have Windows set the window's initial size, an application uses
CW_USEDEFAULT for the nWidth parameter to CreateWindow or
CreateWindowEx. When an application uses CW_USEDEFAULT to have Windows
set the window's initial size, the nHeight parameter to CreateWindow or
CreateWindowEx is ignored.


WS_POPUP


Pop-up windows are top-level windows and are connected to the desktop
window's child windows list. Applications usually use pop-up windows for
dialog boxes. The main difference between pop-up and overlapped windows
is that pop-up windows need not have captions and overlapped windows
must have captions. When a pop-up window does not have a caption, it can
be created without a border. Pop-up windows may own other top-level
windows or be owned by other top-level windows or both. All pop-up
windows have the WS_CLIPSIBLINGS style, even if it was not specified.
Pop-up windows must not be created with the CW_USEDEFAULT value for
either the position or the size of the window. Pop-up windows that use
CW_USEDEFAULT will exist but will have no size or no position or both.


WS_CHILD


Child windows must have a parent window and are confined to the client
area of their parent. This is the major distinction between child
windows and overlapped and pop-up windows. Child window parents can be
top-level windows or other child windows. Child windows are positioned
from their parent window's upper-left corner and not from the upper-left
of the screen as are top-level windows. Child windows are clipped to the
client area of their parent. Controls in a dialog box are child windows
whose parent is the dialog box. Child windows must not be created with
the CW_USEDEFAULT value for either the position or size of the window.
Child windows that use CW_USEDEFAULT will exist but will have no size or
position or both.


Window Functional and Appearance Styles


WS_CAPTION


When this style is enabled, Windows assigns a rectangular area at the
top of the window to display the window's text or title. Overlapped
windows always have a caption. The application can assign the window's
text in the CreateWindow or CreateWindowEx function and can change the
text by calling the SetWindowText function. If a window has a caption,
it can also have a maximize box (WS_MAXIMIZEBOX), a minimize box
(WS_MINIMIZEBOX), and a System menu (WS_SYSMENU). If a window does not
have a caption, Windows does not create these elements even if they are
explicitly specified.

Windows without captions cannot have menus because the menu system
relies on the caption's existence to place the menu.

When a window has a caption, the user can move the window with a mouse.
If the window does not have a caption, the user cannot move the window
because a System menu is required to move the window and a System menu
cannot exist without the window having a caption.

Windows with captions always have either a regular single-line border or
a thick sizable border. If neither a WS_BORDER (single line) nor a
WS_THICKFRAME (sizable) border is specified, the window gets the
single-line border. The WS_CAPTION constant is actually the combination
of WS_BORDER and WS_DLGFRAME constants (WS_BORDER | WS_DLGFRAME), which
makes it impossible to distinguish between a thin border and a dialog
border for windows with captions. As a result, windows with captions
cannot have the dialog box border style unless the WS_EX_DLGMODALFRAME
extended style is used.


WS_MINIMIZEBOX


When this style is enabled, Windows places the minimize box bitmap in
the upper-right corner of the window. If a maximize box exists for the
window, Windows places the minimize button to the left of the maximize
box. The minimize box cannot exist unless the window has a caption. When
the minimize box exists, the user can minimize the window by clicking on
the minimize bitmap or by using the System menu. If the minimize box
does not exist, the user cannot minimize the window.


WS_MAXIMIZEBOX


When this style is enabled, Windows places the maximize box bitmap in
the upper-right corner of the window. The maximize box cannot exist
unless the window has a caption. When the maximize box exists, the user
can maximize the window by clicking the bitmap or by using the System
menu. If the maximize box does not exist, the user cannot maximize the
window.


WS_SYSMENU


When this style is enabled, Windows places the System menu bitmap at the
upper-left corner of the window. The System menu provides an interface
for the user to perform the following system commands:


*       Restore a minimized window



*       Move the window with the keyboard



*       Size the window with the keyboard



*       Minimize the window



*       Maximize the window



*       Close the window



*       Switch to another task

When a window has a System menu, the user can bring up the System menu
by clicking the menu bitmap, by entering the ALT+SPACEBAR combination on
the keyboard, or by clicking the window's icon when the window is
minimized. If a window does not have a System menu, the user cannot use
the keyboard to perform system commands unless the application provides
a specific keyboard interface to do so.

The System menu is also important for maximized windows that take up the
entire screen. When a maximized window that takes up the entire screen
has a System menu, the window cannot be moved until the window is
restored to its previous nonmaximized size. If the window does not have
a System menu, it can be moved without restoring the window's previous
nonmaximized size when the window is maximized to the size of the
screen. When a window is maximized to the size of the screen, Windows
disables the Move, Size, and Maximize items on the System menu to
prevent their use. Thus, when a window with a System menu is maximized
to the entire screen, it cannot be moved; when a window without a System
menu is maximized to the entire screen, it can be moved.


WS_HSCROLL


When this style is enabled, Windows places a horizontal scroll bar along
the bottom of the window. Windows does not automatically scroll the
window. For a window to allow horizontal scrolling, the window procedure
for the window must process the WM_HSCROLL messages, and the window must
be created with the WS_HSCROLL style.


WS_VSCROLL


When this style is enabled, Windows places a vertical scroll bar along
the right side of the window. Windows does not automatically scroll the
window. For a window to allow vertical scrolling, the window procedure
for the window must process the WM_VSCROLL messages, and the window must
be created with the WS_VSCROLL style.


WS_BORDER


When this style is enabled, Windows draws a single-line border around
the window. If no border style is specified, Windows uses a single-line
border for all windows that have a caption. Windows created with this
style cannot be sized with either the mouse or the keyboard.


WS_DLGFRAME


When this style is enabled, Windows draws a dialog frame, a single line,
and a thick colored line around the window. This border style is
normally associated with a dialog box, but it can be used on any window
that does not have a caption. The dialog frame style can be used for a
window with a caption only if the WS_EX_DLGMODALFRAME extended style is
specified. Windows created with this style cannot be sized with either
the mouse or the keyboard.


WS_THICKFRAME


When this style is enabled, Windows draws a sizable frame, a thick
colored line between two single lines, around the window. This border
style is usually used for an application's main window. Windows created
with this style can be sized with the mouse and through the System menu
with the keyboard.


WS_CLIPCHILDREN


This style is used on a window that has child windows and causes Windows
to clip the area that a child window occupies from the client area of
the parent. Drawing performed by the parent window does not overwrite
any of the window's child windows. Windows created without the
WS_CLIPCHILDREN style can overwrite any of the window's child windows.
Performance degrades slightly; so do not use this style if the
application does not draw to the window.


WS_CLIPSIBLINGS


When this style is enabled, Windows clips the client areas of sibling
windows from one another. Thus, a window cannot draw in the client area
of any of the window's siblings. Windows forces the WS_CLIPSIBLINGS
style on all top-level windows (pop-up and overlapped windows), so
top-level windows cannot draw on any other top-level window. By default,
Windows does not clip sibling windows, thus allowing one child window to
draw on another. Performance degrades slightly; so do not use this style
if sibling windows cannot draw over one another.


Window Initial State Styles


WS_VISIBLE


When this style is enabled, Windows makes the window visible when it is
created. By default, the application must call the ShowWindow function
to make a window visible.


WS_DISABLED


When this style is enabled, Windows creates a window that is initially
disabled. The window cannot accept user input until it is enabled. The
application must provide a method to enable the window. This style is
usually used for control windows.


WS_MAXIMIZE


When this style is enabled, Windows creates a window of maximum size. An
application can control the maximum size for the window by responding to
the WM_GETMINMAXINFO message. By default, Windows sets the maximum size
of top-level windows to be the size of the screen and the maximum size
of child windows to be the size of the child window's parent's client
area. An application must also ensure that ShowWindow is correctly
called for the WS_MAXIMIZE style to be effective.


WS_MINIMIZE (WS_ICONIC)


When this style is enabled, Windows creates a window of minimum size,
that is, an iconic window. An application must also ensure that
ShowWindow is correctly called for the WS_MINIMIZE style to be
effective.


Window Standard Styles


The Microsoft Windows Software Development Kit (SDK) supplies some
standard styles for window types. These styles are usually combinations
of the basic styles. Using them can be easier than specifying each style
individually.


WS_CHILDWINDOW


This style is equivalent to WS_CHILD. Usually, child windows should be
created with the WS_CLIPSIBLINGS style as well as with WS_CHILD or
WS_CHILDWINDOW.


WS_OVERLAPPEDWINDOW


This style is equivalent to WS_OVERLAPPED | WS_CAPTION | WS_SYSMENU |
WS_THICKFRAME | WS_MINIMIZEBOX | WS_MAXIMIZEBOX. This is the style
usually used for the main window for applications.


WS_POPUPWINDOW


This style is equivalent to WS_POPUP | WS_BORDER | WS_SYSMENU. Even
though this style includes the WS_SYSMENU style, the System menu cannot
be added to a window unless it has a caption (WS_CAPTION).


Extended Window Styles


Extended window styles were added to Windows starting with Windows
version 3.0. To create a window with extended styles, an application
must use the CreateWindowEx function instead of the CreateWindow
function.


WS_EX_DLGMODALFRAME


When this style is enabled, Windows uses a dialog border on a window
that has a caption. When used, the WS_EX_DLGMODALFRAME style overrides
the WS_BORDER and WS_THICKFRAME styles, producing a window with a dialog
frame. This extended style is normally used on dialog boxes, but it can
be used for any window to get a dialog frame.


WS_EX_NOPARENTNOTIFY


This style is used for child windows. When this style is enabled,
Windows does not send WM_NOTIFY messages to the child window's parent.
By default, Windows sends WM_NOTIFY messages to a child window's parent
when a child window is created or destroyed.

The following extended Window styles were added starting with Windows
version 3.1.


WS_EX_TOPMOST


This style applies only to top-level windows; it is ignored for child
windows. When this style is enabled, Windows places the window above any
windows that do not have the WS_EX_TOPMOST style. Beginning with Windows
version 3.1, there are two classes of top-level windows: topmost
top-level windows and top-level windows. Topmost top-level windows
always appear above top-level windows in the Z order. Top-level windows
can be made topmost top-level windows by calling the SetWindowPos
function with the handle to the window and -1 for the hwndInsertAfter
parameter. Topmost top-level windows can become regular top-level
windows by calling SetWindowPos with the window handle and 1 for the
hwndInsertAfter parameter.


WS_EX_ACCEPTFILES


Windows that can accept dragged objects must be created with this style
so that Windows can determine that the window will accept objects and
can change the drag/drop cursor as the user drags an object over the
window.


WS_EX_TRANSPARENT


The WS_EX_TRANSPARENT style makes a window transparent; that is, the
window can be seen through, and anything under the window is still
visible. Transparent windows are not transparent to mouse or keyboard
events. A transparent window receives paint messages when anything under
it changes. Transparent windows are useful for drawing drag handles on
top of other windows or for implementing "hot-spot" areas without having
to hit test because the transparent window receives click messages.

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-----Original Message-----
From: Alex Bailey [mailto:[email protected]]
Sent: Monday, July 29, 2002 6:54 AM
To: [email protected]
Subject: [VBCOM] Find Topmost Window



Slightly OT from the usual VBCOM but I would appreciate if somone could
briefly give me the API calls needed to find the top-most window in the
system.

Thanks,
Alex Bailey.

You can read messages from the VBCOM archive, unsubscribe from VBCOM, or
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