Owners and Parents Was: Re: [lazarus] Creating Components...

[Marc Weustink]

At 15:47 13-08-99 -0400, "Jeff Wormsley" <daworm at cdc.net> wrote:
>On 8/13/99, at 9:41 PM, Marc Weustink wrote: 
>
>>First I think the window shouldn't be created by then. Create it when it
>>has a parent (it has no graphical function anyhow) 
>>But if you have to .... 
>>You can change the parent of any window whose hwnd you know to any other
>>parent by  the winapi function SetParent:
>>
>>HWND SetParent(
>>    HWND hWndChild,	// handle of window whose parent is changing
>>    HWND hWndNewParent 	// handle of new parent window
>>   );	
>
>Ok, that's not a problem then.  But, if I shouldn't create the window until 
>it has a parent (except perhaps the MainForm???) 

Yes it depends on the window style. If is is ws_child (a control is mostly
a child) then this applies. A form is created after is is visible (!)

>then how do I know when the
>parent is set in the Interfaces code?

You don't.

>Does that mean I'll need to implement
>a new LM_xxx message, such as LM_SET_PARENT, and instead of creating the 
>window on LM_CREATE,

If I recall it correctly LM_CREATE is sent to the interface to create the
Windows/GTK/? object. You shouldn't get this message before a parent is set.

Looking at delphi, TWinControl

Assigning a parent to control results in the following actions

C.Parent := AParent --> C.SetParent(AParent) --> AParent.InsertControl(C) -->
(1 the parent is invisible) or (2 the parent is visible)

(1) --> AlignControl(C) --> AParent.GetClientRect --> a Handle is needed
--> GetHandle --> HAndleNeeded --> CreateHandle --> 

(2) --> AParent.UpdateControlState --> AParent.UpdateShowing -->
CreateHandle --> CreateWnd

I think this behaviour is not different al other platforms (since is is
just a grapical if to the user)

>instead create it on LM_SET_PARENT?  Or is that what
>LM_ADDCHILD is for?  If that is the case, though, then either what is stored
>in FComponent (currently the window handle) is inappropriate, and it is the
>contents of FComponent that are sent to LM_ADDCHILD if I remember
correctly.  

<guessing part>

FComponent was if I remember it (from this list) the HWND of that component.
I guess the LM_CREATE and LM_ADDCHILD were needed by the GTK libs ?
You first create a "Control" with LM_CREATE and then add it to a parent with
LM_ADDCHILD ??

I think if my guessings are right, in a Delphi point of view LM_ADDCHILD
and LM_CREATE are one and the same. 

</guessing part>

>
>The interaction between Owner, Parent, the contents of FComponent, and the
>LM_xxx message handling is so many balls to keep in the air at once that I
>find I drop more than I juggle!

:-))

I can imagine. This story took me more than an hour to investigate. I never
bothered about when exactly a window was created upon now.

Marc