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??
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.
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.
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.
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.
Related
I want to decide if it is better to use XIBs or to designs my views completely using code.
So far I have read that when you design your views on interface builder they are pre-built, so even if they use more memory the user feels everything is faster.
People say doing everything using code is harder but I find it to be just as easy, so I want to know if anyone has experienced some real speed gains when using nibs.
What have been your experiences, advice, etc?
Thanks!
You should be able to do both -- there are times when building a view programmatically is better/easier, and times when using a .xib is better/easier. Even if you only ever do things one way, you'll run into code that does it the other, and you'll need to be able to deal with that.
If you don't know how to use IB, then building your views in code is certainly easier. That is why you should learn to use IB. Once you understand IB, it's way, way faster to put together most of the view-based UI your app will likely need. IB helps you line things up, center objects, align base lines, connect controls to their targets and actions, etc. I think it's safe to say that everyone who uses IB effectively experiences "real speed gains when using nibs."
You should know how to use both. Performance differences between the two are negligible and should not be the reason that you choose one or the other.
Many people who are new to iOS development have the misconception that nibs (.xib files) are inferior to programmatically creating your UI and that if you use IB you're not a good iOS developer. That view is 100% wrong. IB is created by Apple and in use by Apple's developers to create their own Mac OS X and iOS apps. If IB (as a tool) is good enough to be used by some of the best developers in the world, it's probably good enough for most of us.
In practice I have found that a combination of the two usually fits the bill.
In my own apps I find that .xibs are great for laying out the basics of your views quickly and they allow you to iterate very quickly while giving you a preview of what your view will look like. It's also much easier to use auto layout in a .xib file.
Then when you need to do more advanced things like add fancy animations or move views around that is what IBOutlets are for. Anything that you put into a nib can be referenced through an IBOutlet. This allows you do then programmatically make your view come to life.
Lastly, you should fully understand what a nib (.xib) is doing automagically for you. You should understand what happens when a .xib's objects are unfrozen. There are many resources on the internet to understand .xib files better.
Also, learn how to use .xibs in an encapsulated way. For example, .xibs are crazy useful for things like prototype cells and they allow you to keep your code base modular (much more so than storyboards). Also, you will require less UI code in your view controllers.
Lastly, I always say that people should think of IB/.xibs like jQuery. It's going to save you a lot of time but the best developers still know how to do everything in javascript if they have to.
Good luck and have fun!
TL;DR version
Performance is not a consideration when deciding to use .xibs or not.
Use .xibs because they give you a preview of the view you are creating and they allow you to quickly iterate
In practice most apps will use a combination of both. You will programmatically add animations or move views around but the .xibs will be a starting point
Understand fully what happens when the objects in a .xib are unfrozen
You'll be more productive but be sure you fully understand what is happening behind the scenes.
I would always use XIB files unless there was a reason not to. This allows your views to be maintained easily in the future.
Some reasons for creating the views programmatically might be:
A control needs to be resized,
repositioned or otherwise altered
depending on something else
Controls
need to be added or removed
dynamically
There may be more reasons but there are not too many.
If you programmatically create views when there is no need you make it a lot more difficult for other developers to try to figure out what the view will look like and to change it.
If you build your views programmatically, you have control over the loading of elements. e.g. you could use lazy loading, and load secondary buttons, subviews, etc. a fraction of a second after the more important elements, allowing the key parts of the UI to come up faster. You could even animate some elements into position.
If you use IB, you get guides as to proper element spacings and positioning, but you could always copy the coordinates from IB into code if you aren't changing the design that often.
For simple UI elements, you will end up with more lines of code to maintain if you create them programatically.
IB and NIBs do a lot to optimise loading/unloading of views, but it is largely oriented to minimising memory usage vs. perceived speed for the user. For example, lazy loading if anything might make the app UI slightly slower, but it should make memory usage lower. This in turn could make overall app performance better on a large application, and is very much encouraged, but it's difficult to define "performance" in a narrow way. It's also difficult to say when you should or should not use IB - there will be some times you're much better off doing it in code.
One often overlooked element to the IB or not debate is development speed, especially if you have multiple developers. On a larger team/project you'll probably have some developer(s) who specialise more in the infrastructure, business logic etc. of the app and some developer(s) who specialise more in the UI. In this case, use of IB will make it easier for them to work independently, which should make overall development more efficient.
I view IB as a core part of the development platform for iOS development. It's not the right solution in every situation but not knowing how to use IB will be a real limiting factor.
Are there any performance, development drawbacks or advantages when designing views using Interface Builder?
Often you want to use Interface Builder; there are several reasons why you would want to do this over programmatic interfaces:
it is the more accepted way of creating user interfaces, due to its simplicity and visual advantages that you can't achieve as easily by simply using code.
it helps your applications to conform to the iPhone Human Interface Guidelines, through the use of the markers etc, which Apple encourage developers to follow, in order to maintain consistency and usability across iPhone applications.
Despite this, the main reason why programmatic interfaces are sometimes more favourable over using Interface Builder is for interface elements that need to be created several times - for example, creating n UIImageViews - based on a variable that cannot be replicated in Interface Builder. Programmatic interfaces allow for this flexibility and are usually more efficient in this case.
Note that NIBs/XIBs do also take up memory, and if all of your interfaces are placed in your main NIB file, it will not only increase memory usage by your application (for resources which may not be needed instantly anyway) but it will increase loading time. That being said, however, the normal workaround to this problem is not to use programmatic interfaces, but to place different groups of interface elements in different NIB files, placing the immediately required interfaces in the main NIB file, which gets loaded when the application starts, and other groups of interface elements in other NIB files which get loaded when required.
In short, the general way to go is to use Interface Builder, except for when you need to create a variable amount of elements that cannot easily be dealt with in Interface Builder.
One drawback is that it is easy to miss wiring up an outlet or action, and troubleshooting this can be painful. Two positives are that positioning, aligning, and anchoring UI elements is much, much easier, and elements redraw themselves when the phone is rotated (which is an animation process you would otherwise need to handle yourself with programmatic elements).
Speaking for myself, I found interface builder horribly obtuse when I was trying to learn how to develop for the iPhone. The workflow you're supposed to use still doesn't make much sense to me. The interface builder is faster for finicky interface layouts than hand-coding.
The disadvantage with generating the GUI programmatically in your UIViewControllers is that you've blurred the difference between Views and Controllers in the MVC pattern. If you can keep the GUI generation to the loadView method, you can still keep a decent boundary between code the generates information and code that displays information.
In short: I much prefer generating GUIs by overriding loadView in the UIViewController subclasses.
Why did nobody mentioned translation. We have a project in 11 locales - this will give a number of nib*(#locales) - it's just not acceptable (more than a hundred nibs for a project of 10 UIs).
From what I've seen until now, generating views with XIBs is VERY easy. But since I've not been developing on iPhone a long time, I can only direct you to this article that shows a sample XIB converted to Objective-C code.
http://arstechnica.com/apple/guides/2009/04/iphone-dev-convert-xib-files-to-objective-c.ars
Interface Builder anyday! :)
I'm sure there are no significant performance gains by directly coding the view.
Never look at the Code generation of NIB using the tool. But look at the Note by apple.
Note: Although you can create an Objective-C application without using nib files, doing so is very rare and not recommended. Depending on your application, avoiding the use of nib files can involve overriding large amounts of framework behavior to achieve the same results you would get using a nib file.
This may be a foolish question.but I want to know,,,,
In my iPhone Application I have so many classes and Xib files (Like 12 to 15).Is it ok to have it like that???...
Is there any limitation for number of classes......?????.....
Does it affect the performance of the app????....
Thanks.
It is actually a good practice to keep individual xibs for individual screens.
If your application has more functionality, then obviously you would have more code.
Just make sure you organize & refactor the code properly.
As for performance, it would improve when you "lazy load" and release properly :)
Yes, it's OK to have it like that. If there is common code between the classes, it would be a good idea to extract common superclasses.
As far as performance goes, you should try to "lazy load" the views; that is, don't load a NIB until you actually need to display that view. If you try to load all NIBs at app startup, then it will take longer for the app to launch.
Been researching how to send data from one child view to another child view. The application has several views, where one is kind of real-time Settings view. Changes in settings should effect stuff inside other views.
NSUserDefaults seems to be popular, but I don't want persistent data nor automatic saving into database/file. Looks like potential slowdown, which I want to avoid.
Second popular thing is passing a reference to some common top level object into each child view. Just haven't found any tutorial, which would show me in detail how to do this... Most likely so easy, no tutorial is needed - after you figure it out once! Would appreciate, if you can point me to right direction (URL)!
Question: I'm thinking about using one "singleton object" to store "global data", access it from everywhere anytime. What could wrong with this? If I create it at e.g. appDelegate.m it should exist before anyone tries to access it, right?
I'm looking at this sample code.
I would recommend using delegates and/or notifications.
Instead of creating a new singleton in the app delegate, add the necessary data (or, even better, references to the data) in the app delegate and have the views have references to the app delegate.
You can also set up notifications so that your views can keep track of changes to the data that they display.
The beauty of a singleton is that it is automatically created when you first access it via some [singletonClass sharedInstance]. So you don't need to "create" it while launching. If it is global data that needs to be accessed from any view singleton might be the right way of doing this.
I have been programming with the iPhone SDK for some time now.
I have not been using Interface Builder. This scares me a little. I know that in effect I may be 'fighting the framework' but I do not see it that way.
I find it very easy to just instantiate my UITabBarController in my app delegate, instantiate a UINavigationController, then push and pop view controllers as I go.
Naturally I do not have an extensive knowledge of how to architect an app with XIB files because I have never done so, however I do know the general gist of it, having built some Mac apps in Cocoa using NIBs. So I am not completely ignorant.
My question is whether there is an increase in development time when choosing to lay out UITableViewControllers and UIViewControllers using XIBs rather than programmatically instantiating them and then setting up the ivars.
As I see it, both methods still require you to subclass the view controller for customization which will probably occur for the majority of your views. As well, there are still manual classes required for delegates, and the process of connecting outlets from within the XIB seems comparable to me from setting an ivar.
Or am I missing some other major point?
Thanks!
Code takes much longer to write to configure UIs than IB does.
Plus, you can hand off design to designers and let them tweak the UI.
In the end they both accomplish the same thing. You should use either one depending on the circumstances. Most of the time writing the code to create and position views, and especially maintaining it down the road, will take much longer than using IB. In a simple app for the iPhone though, this might not be true and you'd be just as well off creating everything in code. Basically, you should know how to do both, and pick the path that involves the clearest code and quickest development.
IB shines when you're using it to actually lay out views; even two or three views can be a real hassle to lay out and configure in code. I do tend to use it for tab bar and navigation controllers, and sometimes for subcontrollers (usually only if I think the user is very likely to use it), but that's more just because I'm already there so I find it convenient.
With this new version 3 OS they're announcing next week, I'm hoping Interface Builder gains some of the flexibility it has in Cocoa, where you can add palettes for your own classes and even build up complex non-view data structures (by using custom palettes). We'll have to see, though.
Don't worry too much, IMO Interface Builder is a little over-rated too.
It's definitely useful for getting things up and running quickly, or if you have an app with a lot of screens that are tedious to setup, but you're not missing much.
For the uses you outline just doing things in code is fine, and possibly even a little easier to understand.
Laying out views, or custom cells though... then you get into a ton of font/color/position setting that quickly explodes into a lot of code, hard to maintain and tweak. Much easier to adjust what you want in IB in those cases.