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.
Related
I'm trying to create a protocol that I can use on UIViewControllers that will do some setup work when the protocol is attached to a UIViewControler. I currently have the following code.
protocol MyProtocol {
}
extension MyProtocol where Self: UIViewController {
func setup() {
print("We have successfully setup this view controller")
}
}
class MyViewController: UIViewController, MyProtocol {
override func viewDidLoad() {
super.viewDidLoad()
print("Other setup work here") // This line might or might not exist
setup() // Goal is to remove this line, so I don't forget to add it across all my view controllers
}
}
My question is, is there a way to remove the setup() call from within the viewDidLoad function? I think it'd be a lot safer to not have to call that function every time. If there is a view controller that forgets to add that one call, then the setup won't happen, and I want to try to prevent that.
There is a chance that the viewDidLoad function on the view controller that it is attached to will do other work (ex. in this example print("Other setup work here")), or there is a chance it won't do anything except for that setup call.
I'm also not completely opposed to moving that setup function call into a separate function within the view life cycle, but again those other functions in the view life cycle that get called might have other things that need to run as well, so I don't want to completely override them.
I have also considered using the init method somehow, but I think the problem with that is that the view won't have been loaded yet and therefor I can't do the proper setup work like changing a label's text and such.
I ran into a bizarre bug earlier this week and wanted to follow up to see how to prevent the root cause of the issue.
Take the following code.
//*****************************
//MAINVIEWCONTROLLER CLASS CODE
//*****************************
//Some event happens that triggers me to want to load up TestViewController.
func showViewController(){
var testController = TestViewController()
testController.someMethod("Test1")
self.navigationController?.pushViewController(testController, animated: true)
}
//*****************************
//TESTVIEWCONTROLLER CLASS CODE
//*****************************
testView:TestView!
override func viewDidLoad(){
super.viewDidLoad()
testView = TestView()
...
}
func someMethod(someData:String){
testView.name = someData //AppCrashes here because testView might be nil.
...
}
So someMethod is getting fired before TestViewController has had the chance to go through and create the testView. I'm then getting a cannot unwrap an optional value because testView is nil and I'm accessing a property on it.
Whats strange is the application I'm running probably does this exact thing in 6 different places, and 5/6 are working perfectly fine, but 1/6 is now giving me this error. I'm guessing its because of the viewDidLoad not being guaranteed to fire immediately or complete before someMethod is executed, but why then is this not happening on all 6 of the use cases.
So my main questions are:
Why does this crash happen?
What is the best practice to avoid it.
Thanks! Thoughtful answers will get up-votes as always! Let me know if any more info would be helpful.
Basically never run code in the destination controller called from the source controller which involves UI elements. Create a property, set it in the source controller and assign the value to the UI element in viewDidLoad() of the destination controller, for example:
//*****************************
//MAINVIEWCONTROLLER CLASS CODE
//*****************************
//Some event happens that triggers me to want to load up TestViewController.
func showViewController(){
var testController = TestViewController()
testController.someData = "Test1"
self.navigationController?.pushViewController(testController, animated: true)
}
//*****************************
//TESTVIEWCONTROLLER CLASS CODE
//*****************************
testView:TestView!
var someData = ""
override func viewDidLoad(){
super.viewDidLoad()
testView = TestView()
testView.name = someData
...
}
viewDidLoad is called when the ViewController completes loading in preparation to be shown, e.g. when a segue takes place or when involved in a present.
As written your code shouldn't even compile since testView is optional, but you have two options. Use optionals (in which case the view may not get the information if not called after viewDidLoad, but it won't crash) or store the passed information and update your view in viewDidLoad or viewWillAppear.
Something you might want to be aware of is viewIfLoaded
You can force the viewDidLoad method with with:
var testViewController = TestViewController()
_ = testViewController.view
testViewController.someMethod("Test")
Initializing the ViewController doesn't automatically call viewDidLoad
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'm very new to Swift, and trying to create an app where Swiping between pages works normally but also involves a change in background color based on swipe distance.
Consequently, I want to "hijack" the swipe gesture, so I can add some behavior to it. The best I can find for how to do that is this question/answer.
Translating the code from the chosen answer into Swift 3, I added the following code to my RootViewController's viewDidLoad function:
for subview in (pageViewController?.view.subviews)!{
if let coercedView = subview as? UIScrollView {
coercedView.delegate = (self as! UIScrollViewDelegate)
}
}
My impression was that the above code would let me delegate functions (such as scrollViewDidScroll to the class in which I'm writing the above code, such that I can define that function, call super.scrollViewDidScroll, and then add any other functionality I want.
Unfortunately, the above code, which doesn't throw any compilation errors, does throw an error when I try to build the app:
Could not cast value of type 'My_App.RootViewController' (0x102cbf740) to 'UIScrollViewDelegate' (0x1052b2b00).
Moreover, when I try to write override func scrollViewDidScroll in my class, I get a compilation error telling me the function doesn't exist to override, which makes me think even if I got past the error, it wouldn't get called, and this isn't the right way to handle this issue.
I'm sorry this is such a noobish question, but I'm really quite confused about the basic architecture of how to solve this, and whether I understand the given answer correctly, and what's going wrong.
Am I interpreting delegate and that answer correctly?
Am I delegating to the correct object? (Is that the right terminology here?)
Is there a better way to handle this?
Am I coercing/casting improperly? Should I instead do:
view.delegate = (SomeHandMadeViewDelegateWhichDefinesScrollViewDidScroll as! UIScrollViewDelegate)
or something similar/different (another nested casting with let coercedSelf = self as? UIScrollViewDelegate or something?
Thanks!
If I understand your question correctly, you want to catch some scroll position and stuff right ? Then do
class RootViewController {
// Your stuff
for subview in pageViewController!.view.subviews {
if let coercedView = subview as? UIScrollView {
coercedView.delegate = self
}
}
extension RootViewController : UIScrollViewDelegate {
// Your scrollView stuff there
}
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.