I have a viewController with two embedded viewControllers through containers. I then created outlets from the parent viewController's containers to the parent class. I want to either hide or show the containers depending on certain conditionals.
But if I simply write:
#IBOutlet var twoArmsContainer: UIView! {
didSet {
print("SETTING TWO ARM")
}
}
override func viewDidLoad() {
super.viewDidLoad()
twoArmsContainer.isHidden = true //container is nil
}
Then it crashes with twoArmsContainer being nil after the print in didSet has been triggered. How is it possible that the outlet is set, but then becomes nil? I have tried hiding it inside didSet and that works fine:
#IBOutlet var twoArmsContainer: UIView! {
didSet {
print("SETTING TWO ARM")
twoArmsContainer.isHidden = true //WORKS
}
}
What else can I say? The class I'm working in inherits from another class so there is a super.viewDidLoad. Not sure if that is relevant. I tried putting the outlets in the super class but with the same results. I also tried removing and readding the outlets again. Have never experienced this problem before. Let me know if I should show more code; perhaps the entire class. Not really sure what's relevant as I'm clueless of where to start.
Ok, so I found out what was wrong; an issue impossible to detect without access to the code, so in retrospect I should have posted both the parent class and container class. Sorry about that.
Anyway the issue was that the container viewController inherited from the parent viewController. This enabled me to share code in the two container viewControllers.
So the structure was basically this:
class WizardChooseArmViewController: WizardViewController {
...
This is the parent viewController which inherits from a base viewController. Then the container viewControllers looked like this:
final class WizardTwoArmsViewController: WizardChooseArmViewController {
...
Apparently it's a bad idea for containers to inherit from its parent, so I refactored and changed it to:
final class WizardTwoArmsViewController: WizardViewController {
...
Not quite sure why its not possible for containers to inherit from its parent. Would be great if someone could brief me.
Related
I am working on an open source tutorial using MVVM, Coordinators and RxSwift. I am constructing all the viewcontrollers and models in the coordinator. Controller has a strong reference to viewmodel and when a viewmodel is set, I would like to perform some UI related actions(using property observer didSet). The problem I am facing is that didSet is called before viewDidLoad causing a crash.
Stripped down version of ViewController:
class MessageVC: UIViewController {
var viewModel: MessageViewModel! {
didSet {
manipulateUI() // crashes
}
}
override func viewDidLoad() {
super.viewDidLoad()
manipulateUI() // works fine if setup is correct in coordinator
}
Coordinator stripped down version:
extension AppCoordinator {
convenience init() {
let rootVC = MessageVC() // actual construction from storyboard
let messages = Message.getMessages()
rootVC.viewModel = MessageViewModel(withMessage: messages)
}
My concern is that even though calling manipulateUI in viewDidLoad is working for me currently, the app will crash if I forget to set the viewModel from my co-ordinator making me think that I am using a fragile architecture. I really like updating userinterface from didSet but it is called before viewDidLoad.
I know it is a simple problem but from architecture standpoint it seems fragile. Any suggestions, improvements and comments are appreciated a lot.
I wont say that cases like this can define wether you are dealing with fragile architecture or not because view controllers has their own life cycle which differs a lot from other objects life cycle. Anyway you can easily avoid crashes here using different approaches. For example :
Approach 1:
Put a guard statement at the very beginning of your manipulateUI function so this function wont manipulate UI until both view is loaded and model is set. Then call this function on viewDidLoad method and when viewModel is set:
func manipulateUI(){
guard let viewModel = self.viewModel , isViewLoaded else {
return
}
//continue manipulation here
}
Approach 2:
Since you are not sure wether view is loaded when you set the model and don't know if views are initialized yet, you can access the views as optional properties in manipulateUI function:
func manipulateUI(){
self.someLabel?.text = self.viewModel.someText
//continue manipulation here
}
Approach 3:
Since you are using RxSwift you can always register an observer for view controller's isViewLoaded property and set the data source after you are sure that view is loaded
Crash happens because at this point
rootVC.viewModel = MessageViewModel(withMessage: messages)
view controller is not initialized.
It won't work the way you're trying to accomplish, you have to call manipulateUI() inside viewDidLoad.
I've had this working in other variations but something seems to elude me in the change from objective-c to swift as well as moving some of the setup into it's own class.
So i have:
class ViewController: UIViewController, interfaceDelegate, scrollChangeDelegate{
let scrollControl = scrollMethods()
let userinterface = interface()
override func viewDidLoad(){
super.viewDidLoad()
loadMenu("Start")
}
func loadMenu(menuName: String) {
userinterface.delegate = self
userinterface.scrollDelegate = self
userinterface.removeFromSuperview() //no impact
scrollControl.removeFromSuperview() //no impact
userinterface.configureView(menuName)
view.addSubview(scrollControl)
scrollControl.addSubview(userinterface)
}
}
This sets everything up correctly but the problem occurs when I change loadMenu() at runtime. So if the user calls loadMenu("AnotherMenu") it won't change the UIView. It will call the right functions but it won't update the view. Although if I call loadMenu("AnotherMenu") at the start, the correct menu will display. Or if I call loadMenu("Start") and then loadMenu("AnotherMenu") then the menu displayed will be "AnotherMenu". As in:
override func viewDidLoad(){
super.viewDidLoad()
loadMenu("Start")
loadMenu("AnotherMenu")
}
When I list all the subviews each time loadMenu() is called, they look correct. Even during runtime. But the display is not updated. So something isn't getting the word. I've tried disabling Auto Layout after searching for similar issues but didn't see a difference.
Try adding setNeedsDisplay() to loadMenu
Eg
func loadMenu(menuName: String) {
userinterface.delegate = self
userinterface.scrollDelegate = self
userinterface.removeFromSuperview() //no impact
scrollControl.removeFromSuperview() //no impact
userinterface.configureView(menuName)
view.addSubview(scrollControl)
scrollControl.addSubview(userinterface)
view.setNeedsDisplay()
}
setNeedsDisplay() forces the view to reload the user interface.
I didn't want to post the whole UIView class as it is long and I thought unrelated. But Dan was right that he would need to know what was going on in those to figure out the answer. So I created a dummy UIView class to stand in and intended to update the question with that. I then just put a button on the ViewController's UIView. That button was able to act on the view created by the dummy. So the problem was in the other class. Yet it was calling the methods of the ViewController and seemingly worked otherwise. So then the issue must be that its acting on an instanced version? The way the uiview class worked, it uses performSelector(). But in making these methods into their own class, I had just lazily wrote
(ViewController() as NSObjectProtocol).performSelector(selector)
when it should have been
(delegate as! NSObjectProtocol).performSelector(selector)
so that was annoying and I wasted the better part of a day on that. But thanks again for the help.
So I have a base class UIViewController called UITabBarTopLevelViewController:
class UITabBarTopLevelViewController: UIViewController {
#IBOutlet weak var uiNavItemTitle: UINavigationItem!
override func viewDidLoad() {
super.viewDidLoad()
uiNavItemTitle.titleView = CoreUtility.LogoForUINavBarGet()
// Do any additional setup after loading the view.
}
I then have two UIViewControllers that inherit from my base class and both look like this, except the second is called MyViewController2:
class MyViewController1: UITabBarTopLevelViewController {
//#IBOutlet weak var uiNavItemTitle: UINavigationItem!
override func viewDidLoad() {
super.viewDidLoad()
//uiNavItemTitle.titleView = CoreUtility.LogoForUINavBarGet()
}
I add a Navigation Bar object to each child UIViewController super view and then I CTRL drag and add a new outlet to each UIViewController child class:
And here is the second CTRL drag outlet:
These are different references, but I can comment out the #IBOutlet weak var uiNavItemTitle: UINavigationItem! in my child classes and reference one time only in the base class UITabBarTopLevelViewController, for both MyViewController1 and MyViewController2.
You can see, when I hover over the outlet circle, in my base class, it highlights both UINavigationItem in the Story Board:
I am surprised this works, its nice for me that it works because I only need to set the uiNavItemTitle.titleView for my logo one time for both views. This is what I want but there seems to be a bit of magic that I can reference multiple outlet references one time in my base class and there is no bugs or crashes.
I currently have no memory leaks or crashes and my app is working just fine and doing exactly as I desire.
Will there be any bugs with this?
Could someone explain how this is working?
Is the fact that this works, not surprising to experienced Swift developers?
That's how subclass exactly works.
You placed a UINavigationItem in the base class UITabBarTopLevelViewController through
uiNavItemTitle.titleView = CoreUtility.LogoForUINavBarGet()
Also, MyViewController1 and MyViewController2 inherit from the base class UITabBarTopLevelViewController. That's say these child viewControllers both have a UINavigationItem which inherit from their UITabBarTopLevelViewController.
This is not a bug, on the other hand, more like a topic about design pattern though. You could place all the base stuff into a base class, inherit from those classes and implement the specific detail within the child class.
HTH.
I'm writing an app that should present overlays in specific situations, like for example the lack of location services enabled for the app.
Overlay is a UIView with a UIImageView (background) a UILabel (title) and a UIButton calling a specific action. I want to use Interface Builder to set up the overlay UI but I would like to recall the overlay and show it on different UIViewControllers, depending on when the lack of location services is detected.
I have set up a custom class (subclass of UIView) to link a xib file. Code below:
class LaunchCustomScreen: UIView
{
#IBOutlet var title: UILabel!
#IBOutlet var enableLocationButton: UIButton!
#IBOutlet var waitingIndicator: UIActivityIndicatorView!
#IBOutlet var bckgroundImage: UIImageView!
func setupDefault()
{
title.text = "Location Services Required"
enableLocationButton.setTitle("Enable Location Services", forState: UIControlState.Normal)
enableLocationButton.addTarget(self,
action: "promptUserForLocation",
forControlEvents: UIControlEvents.TouchUpInside)
hideLocButton()
}
func hideLocButton()
{
enableLocationButton.hidden = true
}
func showLocButton()
{
enableLocationButton.hidden = false
}
}
Then I have created the xib file which is of Class LaunchCustomScreen and I linked the IBOutlets to all the objects in it (UILabels, UIBUtton, UIImageView)
Then I have set some global functions to be called from any other UIViewController in order to show/hide the overlay on the specific view controller and configure it with UIButton hidden or visible (it will be hidden with a waiting indicator when user location is still loading). Below related code:
func setupLaunchDefault(vc: UIViewController) -> LaunchCustomScreen
{
for aSubview in vc.view.subviews
{
if aSubview.isKindOfClass(LaunchCustomScreen)
{
NSLog("Found already a launch screen. Removing")
aSubview.removeFromSuperview()
}
}
var screen: LaunchCustomScreen = LaunchCustomScreen()
screen.setupDefault()
return screen
}
func showLaunchAskLocation(vc:UIViewController)
{
var screen = setupLaunchDefault(vc)
screen.bounds = vc.view.bounds
screen.showLocButton()
vc.view.addSubview(screen)
}
Now I'm trying if the solution works and it crashes on the setupLaunchDefault function. Reason is that even if an instance of LaunchCustomSCreen is created, the variables (title, enableLocationButton) are still nil. I though they should be non-nil thanks to the IBOutlet to the xib... what am I missing?
Thank you in advance for your help!
I have set up a custom class (subclass of UIView) to link a xib file
No, you haven't. No such "link" is possible.
what am I missing?
You're not missing anything, because you've already figured it out!
Merely creating a LaunchCustomScreen instance out of thin air (i.e. by saying LaunchCustomScreen(), as you are doing) merely creates an instance of this class. It has nothing whatever to do with the .xib (nib) file! There is no magic "link" whatever between the class and the nib! Thus, nothing happens that would cause these properties to get any value. They are, as you have rightly explained, nil.
You have designed and configured one special particular instance of LaunchCustomScreen in the nib. That is the instance whose outlets are hooked up, within the same nib. So if you want an instance of LaunchCustomScreen with hooked-up outlets, you must load the nib! Loading the nib is exactly equivalent to making an instance of what's in the nib - it is a form of instantiation. And here, it's the form of instantiation you want, because this instance is the instance you want.
So, the answer is: do not say LaunchCustomScreen() to get your LaunchCustomScreen instance (screen). Instead, load the nib to get your LaunchCustomScreen instance - and all will be well.
So, let's say your .xib file is called LaunchCustomScreen.xib. You would say:
let arr = NSBundle.mainBundle().loadNibNamed("LaunchCustomScreen", owner: nil, options: nil)
let screen = arr[0] as UIView
The first result, arr, is an array of top-level objects instantiated from the nib. The first of those objects (probably the only member of the array) is the view you are after! So you cast it to a UIView and you are ready to stick it into your interface. Since the view comes from the nib, its outlets are set, which is what you're after. You can do this as many times as you need to, to get as many "copies" of this view as you like.
I have a UIViewController (let's call it "EditViewController") which has a Container View on it (call it "ContainerView") where I switch in and out various subviews (call the one I'm most concerned with "EditDetailsView").
From the EditDetailsView I need to change the title in the navigation bar of the EditViewController. I can't seem to be able to figure out how to reference it.
From inside EditViewController I can simply make a statement like:
self.title = #"Some new title";
and it changes just fine.
But from the EditDetailsView view that is currently the subview of ContainerView nothing seems to work:
self.title = ... is obviously wrong.
super.title = ... doesn't work and seems wrong anyway.
super.super.title = ... errors out as super is not a property found on UIViewController.
Can someone please tell me how to reference the title? I'm kinda lost.
Thanks!
While digging through the parentViewController chain is possible, it is error prone and unrecommended. It is considered a bad design. Imagine you set up your view controller hierarchy in some manner, but after a few months change it a bit and now there is one level deeper. Or, you would like to use the same view controller in several different scenarios. A much better design would be to pass the new title to the container view controller using delegation. Create a delegate protocol, with a method for setting the title.
- (void)childViewController:(ChildViewController*)cvc didChangeToTitle:(NSString*)title;
I know this is an old thread, but in case someone else needs it: to avoid boilerplate code with delegation, and avoid digging into the parentViewController, I did it the other way around.
I've referenced the child view controller from the parent and got their title. So no matter which child you show, you will always get the right title.
This is in Swift 3.
So, basically, this is your parent:
class EditViewController: UIViewController {
override func viewDidLoad() {
if let child = self.childViewControllers.first {
self.title = child.title
}
}
}
And this is your child:
class ContainerView: UIViewController {
override func viewDidLoad() {
self.title = "Sbrubbles"
}
}
Another good way to avoid excess code with delegation is to use RxSwift, if you are familiar to Reactive programming.