Has anybody heard of these...

[mark smit]

Hello All!


I was reading through Win32 Programming (Rector&Newcomer) and I came accross
page #790. Down at the bottom it has a little blurb about GetWindowLong
and GetWindowWord. The book shows some examples of constants that could
be used but I don't recall seeing these before...

GWL_HWNDNEXT
GWL_CHILD
GWL_OWNER

Does any body know how or what these are?

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Cheers

[Dominic Mitchell]

Mark,
This seems to be another one of those glaring errors in Newcomer and Rector.
As far as I can tell GWL_HWNDNEXT, GWL_CHILD and GWL_OWNER do not exist.
They seem to have mixed up GetWindow() and GetWindowLong().
For GetWindow these would be GW_CHILD, GW_HWNDNEXT, GW_OWNER.
Another error that comes to mind in that book is located on page 158 near the
end of the first paragraph. To quote them

...This means that WM_PAINT is the lowest-priority message in the system.

This is just plain wrong. The message with the lowest priority is WM_TIMER.

The following are excerpts from an essay on z-order and window hierarchy.

Microsoft Windows(tm) manages how each window relates to all other windows
in terms of visibility, ownership and parent/child relationship through a
linked list known as the window manager's list. The window manager uses
this instance information when creating, destroying or displaying a window.

The four elements within the instance information structure for a window
that are used to build the window manager's list are
1. a handle to the first child window
2. a handle to the next window in the list of child windows(the next sibling)
3. a handle to the windows parent
4. a handle to the windows owner
.
.
.
Some of the functions used to navigate the window manager's list are
GetWindowLong(hWnd, GWL_HWNDPARENT)
GetWindow - GW_CHILD, GW_HWNDFIRST, GW_HWNDLAST, GW_HWNDNEXT, GW_HWNDPREV, GW_OWNER
EnumWindows
EnumChildWindows
EnumThreadWindows
.
.
.
When a top-level window is newly created it is placed at the top of the
z-order, that is, the window is not obscured by other windows. However,
if the new window does not have the WS_EX_TOPMOST style it is placed
below windows with the WS_EX_TOPMOST style.
.
.
.
Top level windows can also own or be owned by other top level windows.
An owned window is created by passing the handle of the owner window in
the hwndParent of CreateWindowEx. An owned window is always above its
owner in the z-order. However, this rule is broken under certain
circumtances when the owned window has the WS_EX_APPWINDOW style. An
owned window is destroyed when its owner is destroy. Also, an owned
window is hidden when its owner is minimized but is not hidden when
its owner is hidden.
.
.
.
Newly created child windows are left right where they are created, at
the bottom of the z-order with respect to their siblings. This tends to
be counter-intuitive, that is why a mainstream GUI designer like VB or
delphi will manually place a newly created child control at the top of the
z-order with respect to its siblings. Compare Ed Turner's freeware designer
with VB or RapidQ.

    
Given the following sample form
   
Order created            Parent/Owner
-------------            ------------
form(hWndParent)      -> desktop    
button(hWndParent)    -> form
container(hWndParent) -> form
radio(hWndParent)     -> container
edit(hWndParent)      -> form
check(hWndParent)     -> container
    
The output from EnumChildWindows will be as follows
Child            z-order
Window         (visibility)
------         ------------
button            top
container
radio 
check
edit              bottom
    
Examples using GetWindow
   
GetWindow(hWndForm, GW_CHILD)         = hWndButton
GetWindow(hWndButton, GW_HWNDNEXT)    = hWndContainer
GetWindow(hWndButton, GW_HWNDLAST)    = hWndEdit
GetWindow(hWndContainer, GW_HWNDNEXT) = hWndEdit
GetWindow(hWndContainer, GW_CHILD)    = hWndRadio
GetWindow(hWndRadio, GW_HWNDLAST)     = hWndCheck
GetWindow(hWndRadio, GW_HWNDPREV)     = NULL
GetWindow(hWndCheck, GW_HWNDNEXT)     = NULL

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Dominic Mitchell

[This message has been edited by Dominic Mitchell (edited November 26, 2000).]

[mark smit]

Wow! thanks Dominic!


I kinda thought that it might be a typo because I tried to search
for them on the internet and it found zero pages which is very strange
in itself.



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Cheers