I am having a multiple UIViewController embedded in a UITabbarController.
These are connected by Relationship Segues.
The starting point, VC1 initially loads data and is then processed to a "detail" view.
Whenever I change tabs and go back to VC1, the application gets stuck, as viewDidLoad is not called.
Is there a way to trigger a function each time VC1 is segued to?
the application gets stuck, as viewDidLoad is not called
The application is not stuck. It is working perfectly. viewDidLoad is called when a view controller is created and loads its view. That only happens once in the life of the view controller. When you leave a view controller and come back to it, it is still there (i.e. it is not being created from scratch), so naturally viewDidLoad is not called.
If your goal is to hear about the fact that the tab bar controller is switching to VC1, give the tab bar controller a delegate and implement tabBarController(_:didSelect:) or similar.
Even better, configure things so that there is no need to do this. If there is common data that is accessed by both view controllers, architect things so that a view controller sends new data up to a data controller and the data controller broadcasts news of the change down to all view controllers that need to know this.
Related
I'm looking into the viewDidLoad and viewDidAppear methods to better understand what they both do and I came across an article which uses the example of a banking application to explain how these methods work:
Consider a banking application that shows your current balance. A user
can tap on a button, which presents a list of nearby ATMs in a modal
view controller. In order to get the list of nearby ATMs, the
application must make a core location and web service request.
In this situation, a programmer could get away with requesting the
list of nearby ATMs from the server in viewDidLoad. The view
controller is only presented once, both viewDidLoad and
viewWillAppear: will be called back to back and only once for that
particular view controller instance. The net effect of the code in
either of these two methods will be the same.
But this is a bad idea. Consider what would happen if you wanted to
move the ATM view controller into a tab bar controller. Now, the ATM
view controller – with its ATM fetching code in viewDidLoad only
fetches the list of ATMs once. So you are in Atlanta on Tuesday, open
up your application to look for an ATM, then check your balance. Then
you travel to New York on Wednesday, re-open the banking application,
and you only see ATMs in Atlanta. The view was already loaded, no need
to call viewDidLoad and now you’re looking at stale data.
Sadly, I still don't fully understand how/why both viewDidLoad and viewWillAppear will be called 'back to back', or what adding the ATM view controller to a tab bar controller means in terms of these methods.
viewDidLoad method will call only once a life time of viewController and that is when viewController object will first load in memory.
where as viewWillAppear method will call every time when a view will appear to screen or you can say will be topViewController...
Explanation:
Consider you have tab based app with two tabs. Tab1 associated with viewController1 and tab2 is associated with viewController2. Now when you will run your app and you will see tab one is selected and viewController1 is on view and you want to change to tab2, when you will tap on tab2 then tabVieController2's object will create and load to memory first time hence its viewDidLoad method will call, and soon after that it will appear to window and viewWillAppear will also get call.
Now if you you try changing tabs by click on them only viewWillAppear methods will get called for both, as they are in memory already.
It simple, viewDidLoad get called when the view is load in, either via NIB, storyboard or with the loadView method. The viewWillAppear: is called when the view is presented.
When a view is added to a tab bar it only gets load once, thus the viewDidLoad will only be called once. But if the user switch to an other tab and back to the same view the viewDidLoad will not be called. This is because the view is already loaded.
However the viewWillAppear: is called in both cases just before the view is shown. Thus this will be called when the user first opens the tab and when it switches back to that tab.
I think they are referring to the fact that the view is loaded every time the modal view controller appears (thus the data is constantly refreshed) but only once when it is part of tab bar (only loaded on app launch). Kind of a whacky example to explain the methods though.
You might want to read up on the view controller lifecycle to know when to implement what in which method:
Responding to Display-Related Notifications
View Loading and Unloading
Is there a way to send data between ViewControllers without using segues?
Specifically I have two ViewControllers embedded in a TabBarViewController. One is called PlayingCardViewController and the other is called HighScoreViewController. I want to pass a class HighScore from PlayingCardViewController to HighScoreViewController. I want to transfer the data from PlayingCardViewController as soon as I press the redeal button in PlayingCardViewController but I don't want to transition to the HighScoreViewController as that would be jarring for the player.
I thought about using segues and holding the HighScores in an array and passing that to all the VC's that PlayingCardViewController is connected to but I realized that that seems overly complicated and there must be a simpler way to pass the data upon hitting the redeal button.
Some relevant links
Passing Data between View Controllers
I'm just going to do this with bullet points:
You could implement a custom tab bar controller (your own UITabBarController subclass), and use this instead of a basic UITabBarController.
Your PlayingCardViewController could have its own delegate protocol/property.
The delegate protocol could define a method like playingCardVC:didSetHighScore:.
Your tab bar controller would be the PlayingCardViewController's delegate.
The tab bar controller could keep a reference to the HighScoreViewController.
When your tab bar controller gets the playingCardVC:didSetHighScore:, it could pass whatever you want to your HighScoreViewController.
Is it bad practice to skip view controllers in a navigation stack?
In my example I have a UINavigationController (which is being presented modally) with three UIViewControllers (firstViewController, secondViewController and thirdViewController), most of the time the user will be accessing firstViewController, maybe tapping a row which will then load secondViewController and so on, but what if in some circumstances I want to load the second or third view controllers immediately but still keep the first view controller in the stack, so that the user can still go back to the firstViewController.
I can do this but it doesn't feel right - is this something I should avoid doing?
Yes, it's called deep-linking, and it's perfectly fine. It's quite commonly done for things like coming from an external URL or push notification.
FIRST SCENARIO:
I have two view controllers
VC1 has a button, and a label
VC2 has a button, and a text field
theres a modal segue between VC1 -> VC2
when I run this segue, we set VC1, as the delegate for VC2.
We go to VC2, fill out the text field, hit the button, and VC2 is dismissed.
some delegated method is run on VC1, and VC1.label is filled in.
question: is there any way to do this without dismissing VC2.. for example, if VC2.button just modal segues us back, or slides us back to VC1 im assuming it re initializes the viewcontroller and the label wont be changed. do you always have to dismiss the view controller
SCENARIO 2:
again, two view controllers.
this time its reversed.. so i have
VC1 with a textfield and a button
VC2 with a label and a button
soo now we fill out VC1, and we expect it to show up on VC2. But without a segue, they have no relationship. is there any way to pass data between VCs using delegation without one initial segue? Is this segue requirement to use delegation something specific to view controllers? Im assuming it is because in other cases we just instantiate objects, and use their delegate methods. but with view controllers we want to reference one that is already created, and not instantiate a second one.
note: im using story boards
1) You could do it without dismissing VC2, but it's not a good idea. You don't want to segue "back" to one, because, as you surmised, you're actually creating a new instance of VC1, and then if you segue again to VC2, you're creating a new instance of that too. You will keep piling up more and more instance of the two controllers and none will ever be deallocated.
2) Again, your instincts are correct -- you need to somehow get a reference to the instance of VC2 that your putting on screen in order to set yourself as delegate. You don't have to have a segue to do that, you could create the second controller in code and do a manual push or presentViewController, but that's functionally, the same as doing a segue.
Sorry, dont fully understand what you want .. but here is my take.
FIRST SCENARIO:
Why would you need to update the view that isnt on screen ?
Just update in viewWillAppear.
Otherwise you can have the delegate update it when you finish editing that textfield.
SCENARIO 2:
You need a link between the view controllers, use segues makes easy, set as delegate and pass along the info. Why make it harder than it needs to be
Many things have delegates, textfields etc, you are just saying this class / obj will do something for something else.
There are many youTubes about delegates, ie
http://www.youtube.com/watch?v=eNmZEXNQheE
For more info see this stack post - it covers everything you need to know
Passing Data between View Controllers
I've seen this question a couple of times but never really answered. I'm wondering if there is an acceptable/clean way to dismiss all launched view controllers and return to the initial view controller when using storyboards (say from an action within a spawned view controller).
I know how to use delegates, but, I'd prefer to not have my initial view controller implement delegates for every possible spawned view controller. Instead, I'd just like a home button that cleans everything up and returns to the initial view controller from anywhere in the app.
Thoughts?
EDIT: Just for clarity, assume I am NOT using UINavigation Controllers.
EDIT2: Is it possible to just access the methods of the "initial view controller" from anywhere in the app like you might do with the appDelegate?
This should do it at any point. Just stick it in an IBAction and hook it up to a button :)
[self.navigationController popToRootViewController];
I ended up using a singleton. Seems to work quite well.
On the initial load of the initial view controller, I set the view controller as the singleton's property. I can then execute the following code in any action method on any view controller in the app to dismiss all view controllers and return to the initial view controller.
initialViewControllerManager *ivcManager = [initialViewControllerManager sharedInstance];
LPViewController *ivc = ivcManager.initalViewController;
[ivc dismissModalViewControllerAnimated:YES];
May not be the "right" answer, but, seems to work. And, given the complexity of my scenes, relying exclusively on UINavigationControllers would be very complicated.