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I have a view that is to be shown from different screens in my app. I dont want to allocate and initialize the view from each screen. I thought this could be done using two approaches:

1) Initialize the view in App Delegate and access the same from all the screens. (Note: I dont want add the view on window because my app only supports landscape orientation and this will result in lot of spaghetti code to manage the view orientation.)

2) Make the view singleton instead

Now, there has been a lot debate on whether the Singleton pattern in general is good or bad. Also, I know that using singletons for view controllers is considered as bad idea .

Is there any better approach to achieve this??

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Shri
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4 Answers4

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Using singletons is not a bad idea, it's actually a solid pattern that allows storage of fast accessible data throughout the application lifecycle. NSUserDefaults, NSFileManager, NSNotificationCenter and many other Apple default classes use singleton pattern. If your view takes up too much memory (e.g. it has a lot of heavy graphical assets on it), then you should have a class that creates that view each time you call it and loads it into memory for a period of time that the view is used in. If your view is light weight, you should create it statically and keep it alive throughout the entire App's lifecycle using singleton class.

Eugene
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Using a singleton or using a property of your app delegate are equivalent ways of accomplishing the same thing. One can also use a common structure passed to all of the "interested parties".

Which you choose is up to you -- the "ideal" choice depends on the circumstances.

Do be wary, however, of ending up with dozens or hundreds of singletons -- this usually indicates that your design is not very well thought out.

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Singletons are modern global variables so I try to avoid them unless absolutely necessary. The use of Apple's low memory globals caused all sorts of problems when porting to Carbon.

If you are maintaining libraries beware that there will be an instance of the singleton for each library so you need to be careful who is accessing them. I ran into this with the Loki singleton implementation (C++), although it would make sense that an Objective-C singleton would have the same issue.

Mark
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I have a view that is to be shown from different screens in my app. I dont want to allocate and initialize the view from each screen.

Why don't you want to create the view as you need it? Views use a lot of memory:

  • a half-screen view (240*320) on a non-retina iPhone requires 300KB just for the pixels.

  • the same view on a retina display requires 1.2MB

For that reason alone, allocating your common view only when you actually need it seems like a very good idea. There's nothing to be gained by hanging onto the view when it's not being displayed.

Caleb
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