CODEWITHSUNDEEP
winapiwindowparentowner
Jon Tackabury
Jon Tackabury

Reputation: 49279

Win32 window Owner vs window Parent?

In Win32 programming, what is the difference between a window's parent and a window's owner? I thought I had it figured out, then I came across this code:

SetWindowLong(handle, GWL_HWNDPARENT, foo);

This actually sets the window's owner, not the parent - despite the GWL_HWNDPARENT being used. Are the terms parent/owner interchangeable, or is there actually a difference?

Upvotes: 57

Views: 35877

Answers (4)

Maurice Flanagan
Maurice Flanagan

Reputation: 5289

Ownership is a relationship between two top level windows while Parent is a relationship between a top level and a WS_CHILD, or a WS_CHILD and another WS_CHILD.

The parent of a button is the form it is on, while a message box is owned by the form that showed it.

Read this article from Microsoft Win32 Window Hierarchy and Styles to get a much clearer understanding of Ownership, Parenting, ZOrder, SetWindowLong, GetWindow and all the other nasty bits of the Win32 api for creating window relationships.

EDIT: Looks like Microsoft took down that content, here is another reasonable summary of Ownership / Parenting.

Upvotes: 33

Kuba hasn't forgotten Monica
Kuba hasn't forgotten Monica

Reputation: 98495

It's super easy: the code is wrong. End of story right here.

Yes, some windows may happen to react favorably to such a call - someone not knowing any better may have implemented support for it. Quoth documentation (and it's old documentation) - You must not call SetWindowLong with the GWL_HWNDPARENT index to change the parent of a child window. Instead, use the SetParent function.

So, all there's to it: you came upon buggy code, change it to SetParent or refactor to do something else, and keep going?

Upvotes: 1

osullivj
osullivj

Reputation: 351

Chen's blog post is the one to read. The key point for me is that the WS_CHILD style must be used on the child window. You can attempt to create a child window and pass the parent handle in to CreateWindow( ), but if you don't have the WS_CHILD style set the two windows will have the owner relationship, not the parent/child relationship.

Upvotes: 1

TheSmurf
TheSmurf

Reputation: 15568

Owner is the Window* responsible for a control or dialog (for example, responsible for creating/destroying the window).

Parent is the next-senior window* to a control or dialog in the window chain, but isn't actually responsible for it (doesn't necessarily care about its lifecycle, etc). A window's parent can also be its owner.

*Window vs window: Window is an actual window displayed on the screen; window is any object with a HWND (includes buttons, panels, etc).

Upvotes: 20

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