Re: 'Pseudo' Singleton in Objective C
Thank you to everyone whose helped me with this problem. I now have the
solution I needed, and (as usual) I've learned a whole lot that will be useful
in the future.
As always, this is an incredibly useful resource!
On 15 Mar 2013, at 02:16, Seth Willits wrote:
> On Mar 14, 2013, at 11:22 AM, Pax wrote:
>
>> I don't really know how to describe what I'm trying to do except as a
>> 'Pseudo' Singleton. I have a class with an NSWindow, which displays
>> information. It is run by selecting an NSMenuItem called 'More
>> Information…'
>>
>> My issue is that I only want one instance of the Information class to be
>> loaded at a given time (and therefore only one information window on screen
>> at a given time). If the information window is already loaded and it is
>> then reselected from the menu then the existing window needs to be brought
>> to the front - nothing more.
>>
>> I have currently resolved it by making my class a singleton…
>
> I don't see anything to "resolve" so for the sake of clarification…
>
> There's no reason to make your class a singleton just because you only want
> one instance of it. Just don't create a second instance if you already have
> one. Your "More Information" menu item is hooked up to some controller
> already — presumably the application delegate. All that controller has to do
> is maintain and reuse a reference to your InformationWindow.
>
>
>
>> … but that's not the right answer because it means that I can't release
>> information window…
>
>
> Right. This is the reason you don't want a singleton or "pseudo" singleton.
> There's no fancy pattern needed:
>
>
> - (IBAction)showInformation:(id)sender
> {
> if (!_infoWindowController) {
> _infoWindowController = [[InformationWindowController alloc]
> init];
> [[NSNotificationCenter defaultCenter] addObserver:self
> selector:@selector(infoWindowWillClose:) name:NSWindowWillCloseNotification
> object:_infoWindowController.window];
> }
>
> [_infoWindowController showWindow:nil];
> }
>
>
> - (void)infoWindowWillClose:(NSNotification *)notification;
> {
> [[NSNotificationCenter defaultCenter] removeObserver:self
> name:NSWindowWillCloseNotification object:_infoWindowController.window];
> [_infoWindowController autorelease];
> _infoWindowController = nil;
> }
>
>
> --
> Seth Willits
>
>
>
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Re: 'Pseudo' Singleton in Objective C
Hi,
Firstly, I'm assuming the more information button is the only location
which triggers displaying/redisplaying.
if thats the case I would just store the instance of your class in a property
and make sure it will be created only once.
You can accomplish this by simply overwriting the getter method like this:
-(your class) foo {
if (!_foo) {
_foo = [[yourclass alloc]init];
}
return _foo;
}
be careful about mem managment. above is good for a retain property!
best regards,
oliver
Von meinem iPhone gesendet
Am 14.03.2013 um 19:22 schrieb Pax <45rpmli...@googlemail.com>:
> I don't really know how to describe what I'm trying to do except as a
> 'Pseudo' Singleton. I have a class with an NSWindow, which displays
> information. It is run by selecting an NSMenuItem called 'More Information…'
>
> My issue is that I only want one instance of the Information class to be
> loaded at a given time (and therefore only one information window on screen
> at a given time). If the information window is already loaded and it is then
> reselected from the menu then the existing window needs to be brought to the
> front - nothing more.
>
> I have currently resolved it by making my class a singleton - but that's not
> the right answer because it means that I can't release information window and
> its class when it gets closed, resulting in a minor leak (only minor because,
> as a singleton, the instance is only ever loaded once anyway). Even so, this
> is one leak too many - and I'be grateful if someone could tell me the correct
> way to do what I am trying to do.
>
> Currently, I am setting to be a singleton as follows:
>
> static informationWindow *singletonManager = nil;
>
> @implementation informationWindow
>
> //Code to handle singleton
> + (id)singleton
> {
>@synchronized(self)
>{
>if(singletonManager == nil)
>singletonManager = [[super allocWithZone:NULL] init];
>}
>return singletonManager;
> }
>
> + (id)allocWithZone:(NSZone *)zone
> {
>return [[self singleton] retain];
> }
>
> - (id)copyWithZone:(NSZone *)zone
> {
>return self;
> }
>
> - (id)retain
> {
>return self;
> }
>
> - (unsigned)retainCount
> {
>return UINT_MAX;
> }
>
> - (oneway void)release
> {
>
> }
>
> - (id)autorelease
> {
>return self;
> }
>
>
> I'm not using ARC. All suggestions gratefully received!
>
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Re: 'Pseudo' Singleton in Objective C
On Mar 14, 2013, at 11:22 AM, Pax wrote:
> I don't really know how to describe what I'm trying to do except as a
> 'Pseudo' Singleton. I have a class with an NSWindow, which displays
> information. It is run by selecting an NSMenuItem called 'More Information…'
>
> My issue is that I only want one instance of the Information class to be
> loaded at a given time (and therefore only one information window on screen
> at a given time). If the information window is already loaded and it is then
> reselected from the menu then the existing window needs to be brought to the
> front - nothing more.
>
> I have currently resolved it by making my class a singleton…
I don't see anything to "resolve" so for the sake of clarification…
There's no reason to make your class a singleton just because you only want one
instance of it. Just don't create a second instance if you already have one.
Your "More Information" menu item is hooked up to some controller already —
presumably the application delegate. All that controller has to do is maintain
and reuse a reference to your InformationWindow.
> … but that's not the right answer because it means that I can't release
> information window…
Right. This is the reason you don't want a singleton or "pseudo" singleton.
There's no fancy pattern needed:
- (IBAction)showInformation:(id)sender
{
if (!_infoWindowController) {
_infoWindowController = [[InformationWindowController alloc]
init];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(infoWindowWillClose:) name:NSWindowWillCloseNotification
object:_infoWindowController.window];
}
[_infoWindowController showWindow:nil];
}
- (void)infoWindowWillClose:(NSNotification *)notification;
{
[[NSNotificationCenter defaultCenter] removeObserver:self
name:NSWindowWillCloseNotification object:_infoWindowController.window];
[_infoWindowController autorelease];
_infoWindowController = nil;
}
--
Seth Willits
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Re: 'Pseudo' Singleton in Objective C
Matt Galloway's example is the one to run with IMO. http://www.galloway.me.uk/tutorials/singleton-classes/ You're pretty close though. Matt's examples and explanation should put you in the right direction. Any reason why you're not using ARC? ___ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
Re: 'Pseudo' Singleton in Objective C
On Mar 14, 2013, at 11:22 AM, Pax <45rpmli...@googlemail.com> wrote: > My issue is that I only want one instance of the Information class to be > loaded at a given time (and therefore only one information window on screen > at a given time). If the information window is already loaded and it is then > reselected from the menu then the existing window needs to be brought to the > front - nothing more. > I have currently resolved it by making my class a singleton - but that's not > the right answer because it means that I can't release information window and > its class when it gets closed, resulting in a minor leak (only minor because, > as a singleton, the instance is only ever loaded once anyway). IMHO the full belt-and-suspenders implementation of a singleton you’ve chosen — overriding alloc, retain, release, etc. — is overkill. I just implement singletons using a +sharedInstance method that looks like your +singleton. If I’m feeling paranoid I put an assertion into the -init method that the singleton doesn’t yet exist. An easy way to make a sort of “weak singleton” like what you want, is to (a) make the static singleton pointer variable non-retained, and (b) nil it out in the -dealloc method. That way your singleton object isn’t kept around permanently, and when it goes away it cleans up so that the next request will instantiate a new one. (Of course you do have to ensure that *something* retains your singleton object as long as it needs to stay around, or else it’ll get dealloced very soon after being created and lose its state. —Jens ___ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
