Apps such as Instapaper and Twitterrific launch to views that aren't the root view of their navigation stacks. We know this because the initial view already has a back button. Instapaper launches one level deep (Instapaper > Read Later) and Twitterific two levels deep (Accounts > Account > All Tweets).
What's the most efficient/recommended way to achieve this behaviour using Storyboards (perhaps pushViewController:animated: or performSegueWithIdentifier:sender:) and how does one achieve this whilst taking into account the new state restoration APIs, to reduce the chance of a conflict between the view I want to present and the one the state restoration process wants to present?
You can't initiate a segue via Storyboards only, you'll have to write code. And by writing code I mean you probably want to use UINavigationController's -setViewControllers:animated: method, since segues are generally used to make nice animated transitions and not initial UI setup.
If the view controller is a second one in the hierarchy, I'd simply call UINavigationController's - (void)pushViewController:animated: (with animated:NO) from its viewDidLoad method. If it's deeper, then - (void)setViewControllers: instead of push.
Related
I am trying to create an iPhone game app with the Swift programming language using Xcode. I created the project as a single-view application, and I have been adding view controllers and connecting them up with segues as I need them, using the Storyboard.
From what I have come to understand after hours of working on this (better late than never), is that VCs do not use a stack, while a navigation controller connected to other VCs does use a stack. So, assuming there is no navigation controller being used, if I use a "show" segue from one VC to another, it won't push the proceeding VC onto the VC that initiated the segue. It will instead show it "modally".
I have a few questions regarding this.
What is occurring when I am moving between the VCs, if they are not using a stack? For instance, when I move from one VC to another, is the previous VC removed from memory, or does the memory keep taking on more and more copies of VCs as I move between them?
Since VCs cannot pop from a stack without initially having a navigation controller, is there any way to keep my app from crashing, such as a particular way to segue between VCs?
When a project is created in single-view application/tabbed application, etc., does this affect what the app will be capable of doing indefinitely, or does Xcode just create a basic template to start from? For instance, could I start off with a single-view application, but turn it into a tabbed-application? I assume the answer is yes, but confirmation is always nice.
Any information regarding these questions is greatly appreciated!
Thanks!
What is occurring when I am moving between the VCs, if they are not
using a stack? For instance, when I move from one VC to another, is
the previous VC removed from memory, or does the memory keep taking on
more and more copies of VCs as I move between them?
The previous VC stays in memory. Each new segue creates a new VC.
Since VCs cannot pop from a stack without initially having a
navigation controller, is there any way to keep my app from crashing,
such as a particular way to segue between VCs?
There is only one segue type that does not create a new VC and that is the unwind segue. You use it to return to the previous VC. Search Stack Overflow for "unwind segue" to see how to set that up.
When a project is created in single-view application/tabbed
application, etc., does this affect what the app will be capable of
doing indefinitely, or does Xcode just create a basic template to
start from? For instance, could I start off with a single-view
application, but turn it into a tabbed-application? I assume the
answer is yes, but confirmation is always nice.
The templates just start you off with the appropriate Storyboard and ViewControllers for that template type. You can easily delete or modify them to change what your application does.
What are the advantages of using segues vs managing view controllers and subviews like we did pre-iOS 5.
Pre iOS 5 I might:
Build XIB files for my various Views then do something like [myVC.view addSubView:newVC.view];
vs Segues
You get the advantage of working with storyboards and the functionality of passing data between view controllers (which was easily accomplished pre iOS 5 in multiple ways).
So to me it looks like the only advantage of using segues is that you can use storyboards and pass data between VCs.
Is that right? Or are there other advantages?
one of the down sides that can be added to Kunai Balani's answer is that it makes working with a team with version control more difficult if many people are working on the same storyboard. my svn gets really confused when 2 people make an edit on the storyboard.
if you are not working with a team then you can disregard this disadvantage
There are several advantages :
1) Communication. Storyboard (and thus use of segues) is makes it easy to understand the flow of your application. This gives other developers an ease of understanding of the structure of view controllers without looking through any code or debugging.
2) You save time by using segues. Just imagine doing push and pop everywhere all around your application. If you need to change transition (lets say modal transition animation style) for all your view-controllers you have to go and search for each and every view controller then modify it. With storyboard all of them are at one place. It's easy to modify their transition style with just modifying one attribute.
3) Ease of debugging. Lets say your application crashed during a push in navigation controllers. With story board you get the identifier for your segue which caused this. No need to follow stack trace across your UINavigation Controller.
i'm currently developing an app for both Android and iOS, thing is... I started with Android and my app has several Activities with different layouts (Screens with different GUI's, if you are not familiar with android), most of them display very different contents; maps, lists with data from databases, images, text fields with buttons and so on (And most of the time the orientation of the screen changes).
The problem comes with iOS:
How do I create more windows from IBActions? (Is this a correct approach?).
Once I create a Window, how do I create a new Interface? (Do I need another .xib file?)
If once the user finishes with one Windows, does the previous window remains in memory and can be re-opened? (Can I use a navigation tab, even though the first windows was not a using it?) This is a major problem since iPhones do not have a back button and Android relies a lot on those...
Also, if I can't split my program in several windows, wouldn't my app use a lot of memory from destroying and building views?
I'm new to Cocoa development and I have already read a book about Objective C programming (which only teaches syntax and so on), another one about simple iPhone apps (all of them were done in one window, changing the views programmatically) and I'm currently reading another one, but i'm unable to find a simple answer to my problem...
I mean I get Obj-C and how to build iPhone apps (well kind-of) but maybe the problem is that I come from a more straight forward development in Android. Each time I see an iOS project, I see it like a total mess, and the documentation in developer.apple.com doesn't help much either, I'm unable to find what I want.
Hope someone has gone through this already and is willing to point me in the right direction, thank you!
I recommend that you start with the View Controller Programming Guide at the apple developer web site. I think you will find it very helpful.
To answer your questions, you can develop each of your views independently. You depending on your purposes, developing each from a nib file could work. In the app I'm working on now, I have some that I develop programmatically and some that I bring in from NIB files. It's all up to you. The guide I mention above discusses both approaches.
Regarding loading views from button presses, you can do that. Depending on the view controller you use, it can be very easily accomplished. WIth the navigation controller, for example, you just create an instance of the view and push it onto the stack. When you're done with the view, you pop it off and your back to your previous view.
With regards to memory, that is always a concern. You might want to take a look at The Memory Management Programming Guide.
Good luck. I'm just starting out with Android development myself.
Chris already provided a great answer but there are a couple of points I want to add to adress specific questions.
iOS apps normally only have a single UIWindow. Within that window you may present multiple views.
Apps are normally organized into several logical screens worth of content, each managed by some UIViewController subclass.
Each UIViewController instance has a root view which may contain many subviews. A UIViewController's view is expected to fill its window or some frame provided by one of Apple's container view controller classes (UINavigationController, UITabBarController, UISplitViewController, and so on). You should not add one UIViewController's view as a subview of another UIViewController's view.
UIViewControllers will attempt to unload their views when the application receives a memory warning if the view is not visible. See the class' life cycle methods like -viewDidUnload. You should support and take advantage of this behavior to reduce your memory footprint. Keeping UIViewControllers in memory without their views loaded should have a minimal overhead, allows you to keep some persistent state, and each controller's view can be reloaded when needed.
Normally to transition between views a control will send a message to the current view controller (often via an IBAction binding). The current controller will then trigger a transition to another view controller. It might do so by creating a new view controller and pushing it onto the current navigation controller or presenting the new controller as a modal. It might have a reference to some existing controller and present that. It might dismiss itself from a navigation stack to reveal the previous controller. It might even pass the message up the controller's hierarchy until some parent switches the visible tab, dismisses or presents a modal, and so on.
You might also trigger smaller transitions by responding to an IBAction by adding, removing, hiding, or moving subviews of a UIViewController's root view.
Flash Builder 4.5.1 Now enables you to build one application and Compile to multiple Devices
UPDATE: Try XAMARIN, it's part of Visual Studio:
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I'm diving into iOS development and am getting familiar with navigation view controllers. I'm trying to build a simple app with a table view that allows me to add objects to it. So far, I have a table view with an add "+" button in the nav bar that allows me to load my CreateObjectView and display it modally so the user can define the new object, but when they click the save button, I don't know how to send that object data back to the parent view that created the CreateObjectView that contains the object data.
When I create the child view (CreateObjectView), I could pass into it a pointer to the current view before I push it onto the nav stack, but this just feels dirty and circular.
I was reading about protocols and delegates and I could use that approach as well, but it also feels circular.
This question seems like it would be a common design issue to any tableview-based or nav-based app, how should I probably access the view that is one level up from my current view in a nav-based iOS app?
Thanks so much in advance for all your help!
It feels circular at first, but it is the right way. Before the UINavigationController pushes the new view controller you should set the delegate to the current view controller - assuming that's the object you wish to communicate with. Of course you could set it somewhere else instead, such as to a central Core Data handler. Then when you need to communicate call the delegate with the method you have defined. I've done several navigation apps like this after seeing Apple's cookbook example, and it really works well.
I am trying to wrap my head around controllers in Cocoa Touch. The main problem is that I would like to have more than one controller “on screen” at once – I want to have a large view (with controller A) composed of smaller views controlled by their own controllers (say B). I’d like to have it this way because the division makes the code much cleaner. What’s bad is that the additional controllers (of type B) are not “first-class citizens” on the screen, for example they do not receive the autorotation queries and notifications. (And cannot easily display modal controllers, they have to send the presentModal… message to their parent controller.)
What is the difference between the A and B controllers from Cocoa viewpoint? Does the system keep some kind of pointer to the “frontmost controller”, a privileged one to which it sends notifications and such stuff? Why don’t the other controllers receive them, even though their views are on the screen? Is having multiple controllers “on screen” considered a hack? Or is it supported and I am just missing some point? Thank you.
More about the problem I am trying to solve: I am writing a simple photo browser. Photos are displayed in full screen, user can swipe left or right to change photos. The A controller takes care of the scrolling part and the B controllers take care of each photo itself.
Isolating B seemed like a good idea, since the photos are loaded from network and there is a lot that can happen, like the network might be down et cetera. In the B controller the code is fairly simple, since B only works with one particular photo. If I moved the code to the A controller, things would get messy.
The only thing I don’t like about the current solution is that I have to manually work around B not being a “first-class” controller. I have to pass some calls manually through A to B and when B wants to display a modal dialog, it has to send the presentModal… to A. Which is ugly.
There is now a first-class support for this scenario since iOS 5, it’s called controller containment.
swift controller containment
objc controller containment.
It's not closely related to the original question but important. Apple clearly states in View Controller Programming Guide that a view controller is responsible for controlling exactly one screen's content:
"Each custom view controller object you create is responsible for managing exactly one screen’s worth of content. The one-to-one correspondence between a view controller and a screen is a very important consideration in the design of your application. You should not use multiple custom view controllers to manage different portions of the same screen. Similarly, you should not use a single custom view controller object to manage multiple screens worth of content.
Note: If you want to divide a single screen into multiple areas and manage each one separately, use generic controller objects (custom objects descending from NSObject) instead of view controller objects to manage each subsection of the screen. Then use a single view controller object to manage the generic controller objects. The view controller coordinates the overall screen interactions but forwards messages as needed to the generic controller objects it manages."
However in iPad Programming Guide they also say that there may be container view controllers:
"A view controller is responsible for a single view. Most of the time, a view controller’s view is expected to fill the entire span of the application window. In some cases, though, a view controller may be embedded inside another view controller (known as a container view controller) and presented along with other content. Navigation and tab bar controllers are examples of container view controllers."
Up to my current knowledge I would not use sub-view controllers in a view controller but try to subclass NSObject and send messages to them from my main view controller.
Also check this thread:
MGSplitViewController discussion
First, and this is important, view controllers don't get "on screen" -- views do. Your "top level" controller can certainly pass along the kinds of messages you're describing to its "sub-view-controllers". In fact, this is how most apps work. Consider an app that has a tab bar, and where the views use navigation controllers. You actually have several view controllers "running" at the same time, each with its own view on screen at once -- your "root" view controller will be an instance (or subclass) of UITabBarController, which then has several nested UINavigationControllers, each which will display nested view controllers (like an instance or a subclass of UITableViewController).
You might want to read up a bit on how responder chains work. Consider a touch event. It will be generated for the view closest to the top of the stack, that can receive events, which is also underneath the tap. If that view can't handle it, it gets passed up the view hierarchy food chain until something deals with it (and then eats it).
As to the specifics of your question, on the whole, I'm not sure exactly what the strategy you describe is really doing to benefit you in terms of complexity. It depends on how exactly you're implementing things, but having separate view controllers for each little subview may require more bookkeeping code than just having one view controller that knows about all its sub-view components.
This is a pretty old question, but since I guess there are people who might face the same problem today I'd like to share my solution.
I was writing this application that had this one screen with a lot of information, pagination, controls etc. Since according to Apple's MVC documentation on the role of ViewControllers, you should not implement the logic in view itself, or access the data model directly from it, I had to choose between having a Massive ViewController with a few thousand lines of code which was both hard to maintain and debug(even with unit tests) or find a new way.
My solution was to use UIContainerView like below:
this way, you can implement each part's logic in it's own ViewController, and the parent view controller takes care of constraints and sizing of the views.
Note: This answer is just a guide to show the way, you can find a good and detailed explanation on how it works and how to implement it HERE
Actually you can make it work earlier than iOS 5, since most of us are targeting 4.x and 5.x at the same time. I've created a solution that works in both, and it works great, few apps in appstore use it :) Read my article about this or just download and use a simple class that I've created for this purpose.