I am writing a class that has many class variables. So I am declaring the variables as static in my .m file and before #implementation statement, with setters and getters for them as class methods. Is it a good idea to do this for lets say more than 10 class variables? Or is there a better alternative to do this?
Without more information that's a tough call. Technically working - yes.
I know many people don't like singletons, but maybe this is one of the good use cases for it?
Maybe you find that configuring one of those classes, or now objects, really doesn't have to be a singleton at all?
Just because there is only one instance of a given class doesn't mean in cannot be a "normal" class.
Class variables often mystify your state all over your code base and make debugging and code reuse a pain. Let alone multi threading.
Edit: Given your usecase as described in a comment to another answer, I'd go with a singleton, i.e. a 'SoundPlayer' class. '[[SoundPlayer sharedInstance] playCoolSound];' is easy, and you get proper instance variables there, too. And you can always exchange it for another class if needed (think test cases etc.).
Well, I can guarantee that the computer will have no problem with it. They're pretty good with large numbers.
Without knowing more about your situation, it's hard to say. It does sound, though, like you're potentially going about it in a way that isn't optimal. It's good that you followed your intuition and are asking about it. Perhaps you should modify your question (or ask a new one and link it here) to talk about what you really want to accomplish, and then we can help.
Related
How can I share code between classes in Objective-C, the way Traits in PHP work?
I thought of using categories, but I wondered if there is something more suitable when it wouldn't be sensible to use inheritance.
There are several ways to share code between classes and each one has its own importance, depending upon the situation:
You can use inheritance.
You can declare Global Methods.
You can put the sharable code in AppDelegate.
You can use Singleton Class and put the common code in that class. (Not preferred for sharing code but we can still do it.)
All methods have their own pros/cons. You need to study their applications and use. Hope it helps.
Depends. You should ask yourself why do you want to have the same behaviour in various classes. You can use: Inheritance or design patterns (e.g. Composite pattern).
See:
Does Objective-C support traits/mixins?
Not sure if this is the best practice, or what you mean by "sharing code" but I usually have a static class which can hold global values.
The class is static and you can access it from anywhere like this:
[dataModel getMyValue];
[dataModel setMyValue];
It only becomes an issues if you try to write to it from multiple threads, but other than that its a good way to store shared data in your app.
Sharing code in Objective-C can be done only via subclassing or doing composition.
There is no equivalent of PHP's traits here. Categories work in a little bit different way. They're are assigned to a certain class, so you can't use code from category in any class. Unless you create NSObject category, which is good idea only in rare cases. You can treat category as a class extension.
It's possible 'share' interfaces having many different protocols. But it's not exactly what you need, I guess.
I was reading the sources for LibGDX, and I saw that there are too many public fields inside classes. So I was wondering, why? Is there any advantage instead setting up the typical setters/getters for that fields?
I know I should avoid direct accessing to class' fields, but if a guy like the author of LibGDX do it, I'm starting to doubt about "what are the best practices".
You don't have to know the implementation of this class, so they make your code simpler. Also, you are sure some variables you do not want them to be changed adheres to the rules. So they make sure you don't mess up with your code.
Fairly early on in my app, when I was a lot less experienced than I am now, I wanted to spice up some transitions between view controllers with my own custom animations. Having no idea where to start, I looked around SO for a pattern like MVC that could be accessed from nearly any controller at any time, and as it turns out, a singleton was the way to go.
What I didn't realize is that there seems to be a strong and well-defended hatred of the singleton pattern, and I myself am starting to see why, but that is beside the point.
So, a while later, I decided to move my very same implementation into a category on UINavigationController (after all, it handles transitions!), kept the original classes around for comparison, and am wondering which method would work best. Having thoroughly tested both implementations, I can say without a doubt that they are equal in every way, including speed, accuracy, smoothness, frame-rate, memory usage, etc. so which one is 'better' in the sense of overall maintainability?
EDIT: after reading the well-written arguments you all have made, I have decided to use a singleton. #JustinXXVII has made the most convincing argument (IMHO), although I consider every answer here equally worthy of merit. Thank you all for your opinions, I have upvoted all answers in the question.
I believe the best option is use the category.
Because if you are already using UINavigationController, do not make sense create a new class that will only manage the transition, like you told: (after all, it handles transitions!)
This will be a better option to maintain your code, and you will be sure that the thing do what they expect to do, and if you already have an instance that do the transitions, why create another?
The design patterns, like singleton, factory, and others, need to be used with responsibility. In your case, I do not see why use a singleton, you use it only to no instantiate new objects, you do not really need to have only one instance of it, but you do it because you want only one.
I'll make the case for a singleton object. Singletons are used all over UIKit and iOS. One thing you can't do with categories is add instance variables. There are two things about this:
MVC workflows don't tolerate objects with intimate knowledge of other objects
Sometimes you just need a place to reference an object that doesn't really belong anywhere else
These things go against each other, but the added ability to be able to keep an instance variable that doesn't really have an "owner" is why I favor the singleton.
I usually have one singleton class in all of my XCode projects, which is used to store "global" objects and do mundane things that I don't want to burden my AppDelegate with.
An example would be serializing/archiving objects and unarchiving/restoring. I have to use the same method throughout several classes, I don't want to extend UIViewController with some serializing method to write and read arbitrary files. Maybe it's just my personal preference.
I also might need a quick way to lookup information in NSUserDefaults but not want to always be writing [[NSUserDefaults standardUserDefaults]stringForKey:#"blah"], so I will just declare a method in my singleton that takes a string argument.
Until now i've not really thought too much about using a category for these things. One thing is sure though, I'd rather not be instantiating a new object a hundred times to do the same task when I can have just one living object that sticks around and will take care of stuff for me. (Without burdening the AppDelegate)
I think that the real question is in "design" (as you said, both codes work fine), and by writing down your problem in simple sentences, you will find your answer :
singleton's purpose is to have only one instance of a class running in your app. So you can share things between objects. (one available to many objects)
category purpose is to extend the methods available to a class. (available to one class of objects only ! ok...objects from subclasses too)
what you really want is to make a new transition available to UINavigationController class. UINavigationController, which has already some method available to change view (present modal views, addsubviews, etc.) is built to manage views with transitions (you said it yourself, it handles transitions), all you want to do is adding another way of handling transitions for your navigation controllers thus you would preferably use a category.
My opinion is that what you want to achieve is covered by the category and by doing this you ensure that the only objects which are accessing this method are entitled to use it. With the singleton pattern, any object of any class could call your singleton and its methods (and... it could work nobody knowing how for an OS version n but your app could be broken in n+1 version).
In this implementation, for which there is no need to use a Singleton, there may be no difference at all. That doesn't mean that there isn't one.
A plastic bucket holds as much water as a metal bucket does, and it does it just as well. In that aspect there seems to be no difference between the two. However, if you try to transport something extremely hot, the plastic bucket might not do the job so well..
What I'm trying to say is, they both serve their purposes but in your case there seemed to be no difference because the task was too generic. You wanted a method that was available from multiple classes, and both solutions can do that.
In your case, however, it might be a whole of a lot simpler to use a Category. The implementation is easier and you (possibly) need less code.
But if you were to create a data manager that holds an array of objects that you ONLY want available at one place, a Category will not be up to the task. That's a typical Singleton task.
Singeltons are single-instance objects (and if made static, available from nearly everywhere). Categories are extensions to your existing classes and limited to the class it extends.
To answer your question; choose a Category.
*A subclass might also work, but has its own pros and cons
Why don't you simply create a base UIViewController subclass and extend all of your view controllers from this object? A category doesn't make sense for this purpose.
Singletons, as the name suggests, has to be used when there is a need to be exactly one object in your application. The pattern for the accessor method ensures only this requirement being a class method:
+ (MyClass*) sharedInstance
{
static MyClass *instance = nil;
if (instance == nil) instance = [[MyClass alloc] init];
return instance;
}
If implemented well, the class also ensures that its constructor is private thus nobody else can instantiate the class but the accessor method: this ensures that at any time at most one instance of the class exists. The best example of such class is UIApplication since at any time there might be only one object of this class.
The point here is that this is the only requirement towards singleton. The role of the accessor method is to ensure that there is only one instance, and not that it would provide access to that instance from everywhere. It is only a side effect of the pattern that, the accessor method being static, everybody can access this single object without having a reference (pointer) to it a priori. Unfortunately this fact is widely abused by Objective C programmers and this leads to messed up design and the hatred towards singleton pattern you mentioned. But all in all it is not the fault the singleton patter but the misuse of their accessor method.
Now turning back to your question: if you don't need static / global variables in your custom transition code (I guess you don't) then the answer is definitely go for categories. In C++ you would subclass from some parent BaseTransition class and implement your actual drawing methods. Objective C has categories (that in my opinion is another way that easily messes up the design, but they are much more convenient) where you can add custom functionality even accessing the variables of your host class. Use them whenever you can redeem singletons with them and don't use singletons when the main requirement towards your class is not that it would be only one instance of it.
Are there frequent processes which the programmer will go through? Or does everyone have different coding habits?
Often when it looks like I will be repeating some code or algorithm that I already have, I look for ways to avoid it.
A common one for me is to have need for a class that is similar in some way to a class I already have. I break the original class into a superclass (with the common functionality) and a derived class, and use the superclass as the basis for my second class.
Me and my friend had a little debate.
I had to implement a "browser process watcher" class which invokes an event whenever the browser that is being watched (let's say Internet explorer) is running.
We created a "Process watcher" class, and here starts the debate:
He said that the constructor should only accept strings (like "iexplore.exe"), and i said we should inherit "Process watcher" to create a "browser watcher" which accepts the currently used browser enum, which the constructor will "translate" it to "iexplore".
he said we should use a util function which will act as the translator.
I know both ways are valid and good, but i wonder whats the pros and cons of each, and what is suitable in our case.
Lately I've been taking the approach of "Keep it simple now, and refactor later if you need to extend it".
What you're doing right now seems pretty simple. You only really have one case that you're trying to handle. So I'd say take the simpler approach for now. In the end, if you never have to make another kind of watcher then you'll avoid the extra complexity. However, code it in a way that will make it easier to refactor later if you need to.
In the future, if you find you need another type of watcher, spend the effort then to refactor it into an inheritance (or composition, or whatever other pattern you want to follow). If your initial code is done right the refactoring should be fairly easy, so you're not really adding much extra work.
I've found this approach works fairly well for me. In the cases where I really didn't need inheritance the code stays simple. But when I really do need it I can add it in without any real problems.
Other things being equal I prefer the simpler solution (a single concrete class which takes a string as a constructor parameter) to the more complicated one (using a base class and a subclass).
Inheritance is appropriate when you want to vary behaviour: if the browser watcher will do something that the ordinary process watcher doesn't. But if you only want to vary the value of the data, then just vary the data.
If you have no other use for ProcessWatcher than to serve as the parent of BrowserWatcher than you shouldn't create it. If other Watchers are being implemented that have shared functionality that can be placed in ProcessWatcher, then you should (both are "isa" relationships so Rob's criterion is met).
It really is as simple as that. Arguing that some day you'll have other watchers is not an argument in favor of creating a separate class. It is a mental tic that you should lose ASAP.
Inheritance should only ever be used to implement an "isa" relationship.
As you can say that a "browser watcher" is a specific instance of a "process watcher" then inheritance is suitable for this architecture.
Hence, for me, having the identity of what you are watching passed through as a part of the construction of the browser watcher implementation of the "process watcher" is definitely the way to go.
Edit: More specifically, inheritance is for when you want to specialise behaviour. For example, most animals make a sound, but you could hope to provide which sound to make in a class called animal, you must wait for the specialisation.
So then we have Horse class providing a "neigh" for its sound, a Dog class providing a "bark" for its sound, etc.
HTH
cheers,
Rob
Depends on what use case you have or what god you follow.
I don't say "inheritance is evil" but generally I follow the principle "Favor composition over inheritance" to avoid excessive class hierarchies.
I agree that in most cases, simplicity over complexity is a good strategy, as long as your simplicity is not too short-sighted (ref. Herms, write code in such a way that you can easily re-factor later).
However, I also know how difficult it can be to shut up that bug in your ear that encourages a more thorough design. If you still want to favor inheritance without necessarily thinking in terms of "base class" and "subclass", you can simply define an interface (ex. IProcessWatcher) which is implemented by ProcessWatcher. When you use the ProcessWatcher object, refer to it in terms of the interface so that if you later decide to create a BrowserWatcher (or any other kind of ProcessWatcher), you can do so without forcing it to descend from ProcessWatcher, as long as it implements the IProcessWatcher interface.
Warning: Proceed with caution. It gets tempting to want to define an interface for every single object, and let's face it, that just ridiculous. =)
Ultimately, you need to find something that you're both comfortable with, since you will both have to maintain this code, and I think this might be a nice compromise, rather than simply "Inheritance or No inheritance".
Good luck!
in a very simple sentence can say:
when you need to use inheritance (subclassing) that subclass has different behaviour (not properties) than super class.