I have two view controllers, one that shows some content in a list and one that renders a map. I give users the option to switch between the two by tapping a button. I'm currently using a segue for the button to switch between the two views, but because of the nature of segues I end up re-initializing the view controller each time, generating unnecessary network traffic.
I'm looking for a way to transition between these two views in such a way that the controllers are only initialized once, the first time they're invoked. Subsequent invocations of these controllers would just use whatever instance was already loaded in memory.
Is this achievable? If so, what do I use? pushViewController also ends up calling viewDidLoad on the controller being pushed onto the stack
Related
For now I have a single login view controller that hide and adds subviews dynamically based on user interaction. Is it better to have multiple UIViews with one view controller, or multiple view controllers?
The benefit of having children UIViewControllers would be if you needed to care about the view lifecycle in any of the children. For instance, if in some of your subviews (child views) you needed to know if it appeared to trigger some logic, then it would be good to use children UIViewControllers.
Another reason might be, if you wanted to use view controller transitions within your custom container, as described by Apple in the UIViewController class reference:
https://developer.apple.com/library/ios/documentation/UIKit/Reference/UIViewController_Class/index.html#//apple_ref/occ/instm/UIViewController/transitionFromViewController:toViewController:duration:options:animations:completion:
But, to me it doesn't sound like you would need this, it sounds like you would just show/hide your views, or otherwise animate them.
But if your views don't care about any of that, and just need to render UI elements, I'd say using children UIViewControllers adds additional complexity without much benefit.
This is under the assumption that either way, all your views are living on the single UIViewController's view. If you are pushing and popping view controllers inside a UINavigationController, or presenting ViewControllers modally, you definitely should use UIViewControllers for that.
Also, you definitely shouldn't put all your view code inside that single view controller. You should use subclasses of UIView, or some other mechanism of making sure you separate your components.
For example you might have:
LoginViewController - organizes and hides and shows the individual views
SignInView - shows the sign in form
RegisterView - shows the register form
...etc
Of course its better to have multiple view controllers for many reasons:
Each view controller has its own code/logic/functionality.
Better for memory management. Once you're done from a view controller, system will automatically deallocates it from memory. Using multiple views will be overload in your system when some views are not used.
Better organisation for your project. You will just present/dismiss/push/pop view controllers and pass data between each other. Instead you will deal with horrible logic for hiding and showing UIViews.
Using one view controller will have a massive amount of code which in long term the project will be an impossible mission to manage.
Having multiple view controllers is better in the sense that you would have more ease at coding them individually. Also Navigation will be good which is good for User Experience.
Memory Management will be efficient.
The MVC architecture(Model View Controller) will instead become Massive View Controller which will be a headache while debugging.
Check out this answer for more clarity. I think you are confused between ViewController and View.
Check out the accepted answer of this question in the link. Hope it helps.
About viewController's "viewDidLoad" and "viewWillAppear" methods
I am coming from a C# wpf background where you can have one ViewModel handling multiple Views. This is a great way to share data amongst unrelated views. However I can't figure out how to do the same thing in iOS, as you seem to need a Controller for each View.
What I am trying to achieve is to have a sign up sequence where the user populates 5 screens of data one by one. I was going to use a PageViewController for this and each click on Next would transfer them to the next page in the sequence. All the while, adding all their input data to a parent model object which stayed around for all five screens, at the end you can submit the whole lot to the database to sign up.
The only way I can see so far to do this is to create five separate ViewControllers, one for each screen of the sign up, and create the navigation logic to display them as you click through. However this a) seems overkill and b) means each subsequent screen and viewcontroller doesn't know about the information the user entered in the previous steps.
What is the correct way to do this in iOS?
You can do it in many ways. If you like to use UIPageViewController, you can actually have one view controller for all steps of the sign up process.
A main view controller would implement protocol UIPageViewControllerDataSource. It has two required methods, which return an instance of a content view controller. These instances can be of any UIViewController subclass, so you could have five separate view controller classes or you could have five instances of the same class.
Xcode has a project template "Page-Based Application". It might be a good sample code for you. There is one class DataViewController and it is instantiated for each page. If your case is really simple then this might be the best solution.
If you use multiple view controllers, you can pass data between them by overriding the method prepareForSegue(segue:sender:). The UIStoryboardSegue object has access to the destination view controller, you can cast it and set up the properties. (I am assuming you are using storyboards and segues.)
Another approach would be not to use UIPageViewController and implement the whole process within one view controller. There could be one view with five container subviews. Initially the first one would be shown, then the second one, and so on. This requires manual implementation of navigation between those steps, but gives a lot of flexibility. It's also more aligned with MVVM, because there is one-to-one mapping between a ViewModel and ViewController.
In general, iOS apps have lots of view controllers. It doesn't seem an overkill for me to use five in your case. It might be more code, but it's less complexity.
I have a View Controller and need to segue into another View Controller (which is customized based on what scenario I want to show). Trying to decide what is the best approach here in regards to simplicity vs efficiency
Three options I can think of:
(a) Have my View Controller segue into a View Controller that holds a View Container linked to multiple View Controllers
(b) Have my View Controller segue into a View Controller with multiple views that can be hidden and rearranged
(c) Have my View Controller segue into different View Controllers depending upon the criteria
I'm still uncertain how much each View Controller should differ from each other, but given that one View Controller might segue into another View Controller that's irrelevant for the other two scenarios, what are your guys' thoughts on the three approaches in terms of code complexity, ease of use, general efficiency in terms of speed/memory management. It's possible that the View Controllers that are being segued into might differ by just a little, but also by a lot!
I think all depends on difference between viewControllers for each scenario. BUT what I can certainly say is do not use varriant (B), because even if difference seems tiny now, as only it begins growing, your code that compose views will becomes more complicated and unreadable, at least in my case it usually happens. So, if you must show different viewControllers with same or pretty similar use (e.g. save for, show list, select item from list. go next, go previouse), try to use one viewController and load different views that are already composed. And if usage of those controllers different - use multiple controllers.
I'm using Storyboards. I need to init instance variables of UIViewController just once. viewDidLoad and awakeFromNib fire each time I open a viewController from menu (I'm using SWRevealViewController for sidebar menu as in Facebook app). Is it normal for awakeFromNib to fire many times or is it SWRevealViewController bug?
So is there some special init method or do I need to set instance variables from outside of viewController (in AppDelegate?)
EDIT:
I found this question
SWRevealViewControllerSegue, reusing Viewcontrollers
I didn't realize that each time you show a controller via segue it creates a new instance of controller. So what does it mean? Does it mean that if I have a table of data loaded from web API - it will be reloaded each time I go back and forth through segue?.. Doesn't seem very effective to me. Is it normal for iOS?
View controllers are either recreated or reused depending on the situation. When you push a view controller onto a navigation controller's stack, you almost always push a new instance. When using a tab bar controller, the view controllers it contains are often held in memory. To avoid excessive memory consumption, it makes sense that view controllers are cleaned up when possible, rather than held around.
In the case of your SWRevealViewController then yes, it sounds as though your view controller should be recreated every time. You ideally shouldn't be directly loading any data from a web API within your view controller; instead, extract your API calls and models into separate classes that you can reuse from any view controller. Then, rather than reloading the data over the network when your view controller loads, you just need to fetch the latest data from your model / store class.
I am pushing and popping from one view to the other within my App. The view is being retained in the memory so when you hit the "Back" button after pushing a view, the same screen that was before you pushed the view is retained.
For some reason, I will need to reload the parent view after popping from a child view. I need to display different content based on the actions the user taken when they were redirected to the child view.
I am using UINavigationController to navigate from one view to the other. I need it so I can easily go back and forth within the different views of the App.
The correct way to do this would be to perform your actions in viewDidAppear. Initialisation code that you write in viewDidLoad is called only once. But in viewDidAppear you can refresh your view's content every time the view is added to the window. The controller is retained in the memory for performance reasons. Removing it would hamper that factor.
Here is a stack overflow post that explains the different view* callbacks in good detail.