Re: Is there a pattern for creating an object with global scope?
Re: Is there a pattern for creating an object with global scope?
- Subject: Re: Is there a pattern for creating an object with global scope?
- From: Graham Cox <email@hidden>
- Date: Sat, 13 Apr 2013 11:33:45 +1000
On 13/04/2013, at 11:30 AM, YT <email@hidden> wrote:
> Perhaps my approach is wrong. Looking for advise.
>
> So I'd like to define a Class called Preference.
>
> In main.m I'd like to create an object called myPreferences before the code line
>
> return NSApplicationMain(argc, (const char**)); is run;
>
> I assume the object myPreferences will persist the life of the program.
>
> So how can I make the ID of myPreferences known to all objects in the program?
>
> Is this even possible?
>
> OK! So I'm trying to create an object with global scope so all other objects can get and put data in it.
>
> AND OK! Its true I'm not yet a mature Objective-C programmer. Ya know one that doesn't know what I can't do.
Tip: don't reinvent the wheel. There is already a class, NSUserDefaults, which is designed for this purpose.
The use of global variables is strongly discouraged, but you can create the equivalent using a singleton object. NSUserDefaults provides this using +[NSUserDefaults standardUserDefaults] which is accessible from every part of your app at all times.
You probably don't really want to access preferences prior to running NSApplicationMain - I can't think of a sensible use case for that. Instead, just access each preference at the point where it's actually required - don't attempt to set up a whole bunch of state before anyone really needs it, it just slows down launch - do it lazily. For app-wide state, the NSApplication delegate method -applicationDidFinishLaunching is often a good place.
NSUserDefaults also provides a mechanism (-[NSUserDefaults registerDefaults]) for setting initial values for preferences from a plist resource which is useful if any of your default preferences are something other than 0/nil/NO.
--Graham
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