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From: ech@pegasus.ATT.COM (Edward C Horvath)
Newsgroups: comp.sys.mac.programmer
Subject: Re: scroll bar problem
Message-ID: <2739@pegasus.ATT.COM>
Date: 4 Apr 89 08:13:31 GMT
References: <2642@masada.cs.swarthmore.edu>
Distribution: usa
Organization: AT&T ISL Middletown NJ USA
Lines: 42

In article <425ca822.1285f@maize.engin.umich.edu> rpitt@caen.engin.umich.edu (Raymond Jeczen Pittman) writes:
> I am writing an application that uses multiple windows and I would
> like to know how I can access the control list in the window record
> to reference a particular controlhandle such as the scroll bars...

From article <2642@masada.cs.swarthmore.edu>, by jackiw@cs.swarthmore.edu (Nick Jackiw):
> Sure you can do it this way if you want. TheWindow^^.ControlList heads a
> linked list of all of your controls.  How do you recognize a particular
> control (e. g. horiz scroll) once you've got the ControlList?  You'll have
> to slap an identifying constant into the control's RefCon field.

> At this point you should begin to wonder how dearly you wish to stick to
> those principles of application hygene learned in CS courses...

One other "clean" solution already suggested is to put a handle to a struct
in the window's refCon.  Another method is to take a page from Apple's book
(single-inheritance OOPLs, really).  Note that WindowRecord has GrafPort as
a prefix; similarly, DialogRecord has a WindowRecord as a prefix.  Since
a Dialog "IS A" Window "IS A" GrafPort, this makes perfectly good sense.

The windowKind field is there for you to use as a tag for a "safe union."
While the WindowMgr will set that to userKind (8), any value >=8 is available
for your use.  Hence declarations like

enum { unspec = userKind,
	windowType1,... };

typedef struct {
	WindowRecord theWindow;
	/* my stuff ... */
} window1;

are perfectly reasonable; you allocate space for a window1, pass its address
to NewWindow, then set theWindow.windowKind appropriately and flesh out the
other fields.  The address of a window1 is usable as a WindowPtr or GrafPtr
in all contexts.

About the only drawback to this approach is if you want some of your windows
to be non-modal dialogs (the DialogMgr wants a windowKind of 2).  Not a
killer, but it would be nicer if we could just set and forget windowKind.

=Ned Horvath=