In a couple of my projects I think I'm not created a great structure in many cases.
It could be a game where I've created a game board (think about chess) with a grid of 8 * 8 cells. Each cell has a gesture recognizer that relies on a subclass (cell.swift), with the game logic in a parent ViewController.
For arguments sake, let us say we want to display to the user which square they have touched.
I've found out how to do this from the subclassed UIView (obvs. create the alert in the subclassed UIView / cell.swift in this example)
UIApplication.shared.keyWindow?.rootViewController?.present(alertController, animated: true, completion: nil)
but it seems to break the structure of the app - but wouldn't it be the same accessing an action in the parent ViewController? What is the best way of approaching this>
Your rootViewController is the VC on the bottom of your stack. It's not a safe way to access the visible VC, and is rarely useful, in general (there are cases, but I doubt your app would find them useful).
What you likely want to use is a delegate pattern. Let's say the parent VC that displays your chess board (let's call this MyBoardViewController), conforms to a protocol like the following. MyView is whatever custom UIView class you're using for the chess squares:
protocol SquareAlertHandler {
func handleSquarePressed(sender : myView)
}
And add the following property to your MyView class:
weak var delegate : SquareAlertHandler?
And replace whatever event handler you're currently using, with the following (I'm assuming you're using a UIButton in IB to handle the press, and have arbitrarily named the outlet 'didPress:'):
#IBAction didPress(sender : UIButton) {
delegate?.handleSquarePressed(self)
}
Now, add the protocol to your MyBoardViewController, and define the method:
class MyBoardViewController : UIViewController, SquareAlertHandler {
... ... ...
func handleSquarePressed(sender : myView) {
// Do something to handle the press, here, like alert the user
}
... ... ...
}
And finally, wherever you create the MyView instances, assign the MyBoardViewController instance as the delegate, and you're good to go.
Depending on your Swift literacy, this may be confusing. Adding code, so that I can at least match up the class names, would help to clarify things.
Related
I have two main screens in my app, currently both just subclasses of UIViewController. These two view controllers are very similar - they both implement my custom subclass of UIView called HeaderView that is responsible for displaying information and taking user input. As it stands, this code is repetitive because the HeaderView setup is the same for both view controllers - the only difference is what happens when the user confirms the text entry in HeaderView.
To cut down on repetitive code, I am creating a class called InputViewController (a subclass of UIViewController) that houses the aspects of the two view controllers that are identical. Eventually, I want the two view controllers to subclass InputViewController instead of UIViewController.
class InputViewController: UIViewController, InputProtocol {
private let headerView = HeaderView()
override func viewDidLoad() {
super.viewDidLoad()
// layout, etc.
setupCallbacks()
}
internal func setupCallbacks() {
headerView.onUpdate = { (text: String) in
// called when user confirms text entry in headerView
self.onHeaderUpdate()
}
}
internal func onHeaderUpdate() {} // Blank function
}
setupCallbacks() and onHeaderUpdate() are methods defined in the protocol that the InputViewController conforms to. The HeaderView implements a callback closure that is handled in setupCallbacks() by headerView.onUpdate...
The protocol that InputViewController conforms to:
protocol InputProtocol {
func setupCallbacks()
func onHeaderUpdate()
}
To illustrate this, I drew up a diagram;
Since I want the subclasses of InputViewController to override the onHeaderUpdate() method, is it conventional to leave the definition of onHeaderUpdate() in InputViewController blank or is there another solution to this?
is it conventional to leave the definition of onHeaderUpdate() in InputViewController blank
Yes, that is called an abstract method. It is common to give it code that crashes deliberately, as a way of saying, “I exist only to be overridden in a subclass.”
(I should go further and say that what you are creating, a base view controller that carries out initial configurations that all subclasses must implement, is also normal.)
I have a View-Hierarchy like this:
UIViewController (SingleEventViewController)
UIScrollView (EventScrollView)
UIView (contentView)
3xUITableView (SurePeopleTV, MaybePeopleTV, NopePeopleTV (all inherited from the same UITableView)), & all other UI-Elements
The SingleEventViewController stores one Event (passed within the initializer). (All Events are stored in Core-Data).
The three UITableViews are there for displaying the users which are participating (or not or maybe) at the Event. My question is, what are the possibilities to fill the tableViews with the data and what would you recommend in which situation.
Currently I have a property parentVC: SingleEventViewController in all Subviews and get the data like this:
override func loadUsers() {
//class SurePeopleTV
guard let parentController = parentVC else { return }
users = (parentController.thisEvent.eventSureParticipants?.allObjects as! [User])
finishedLoading = true
super.loadUsers()
}
.
func applyDefaultValues() {
//class EventScrollView
guard let parent = parentVC else { return }
titleLabel.text = parent.eventName
}
I'm new to programming but I got a feeling that I should not create a parentVC reference in all of my classes.
An object should not (ideally) know about its parent - if it does they are "tightly coupled". If you change the object's parent, your code may break. In your case, your parent object must have a thisEvent property.
You want your objects to be "loosely coupled", so the object doesn't know about a specific parent object.
In Swift, the usual ways to pass information "back up the chain" is to use the delegate design pattern… https://developer.apple.com/documentation/swift/cocoa_design_patterns or to use closures.
See also https://www.andrewcbancroft.com/2015/04/08/how-delegation-works-a-swift-developer-guide/ for info on delegation
First of all, if you create a reference to the parent ViewController make sure it is weak, otherwise you can run into memory management issues.
Edit: As Ashley Mills said, delegates the way to handle this
The recommended way to pass data between ViewControllers is using something like this
Every time a segue is performed from the view controller this function is in this function is called. This code first checks what identifier the segue has, and if it is the one that you want, you can access a reference to the next view controller and pass data to it.
I'm new to Swift and I'm sure this question is pretty basic and has been asked and answered before.
I am not using storyBoard. My main viewController is created from AppDelegate via code.
I have:
a custom class defined in a model.swift file
a main viewController (from AppDelegate) that I am using as a container
3 additional viewcontrollers as subviews of the main (not each other)
all 3 subviews are displayed simultaneously each covering 1/3 of the screen (no segues)
each viewcontroller is in a separate .swift file
I want to create an instance of my custom class in the main viewController and have all 3 of the subviews be able to reference that instance.
Each of the subview view controllers need to be able to get/set instance variables and the other subviews need to be made aware of those changes.
I think I will need to use notifications to communicate the changes to the multiple subviews - but I haven't even begun to try and figure that out yet.
If this has been asked and answered before - could someone please either provide a link - or provide me with the right search terms so that I'm able to find the answer? The only found answers I've found that come close are to use segues to pass the data back and forth.
You can use delegate pattern. Below code is assuming that you are using MVVM pattern. (It is very similar for VIPER/ReSwift patterns also)
protocol DataChangedDelegate {
func refreshData()
}
// ViewModel for FirstViewController
class FirstViewModel {
var delegate: DataChangedDelegate?
var data: Any {
didSet {
delegate?.refreshData()
}
}
//rest of the things
}
//similarly other two view models will have a delegate and on data change will call the refresh method
And your view controllers should adopt this protocol
class FirstViewController: UIViewController, DataChangedDelegate {
//view controller code
//delegate code
func refreshDate() {
//tableView.reloadDate()
//collectionView.reloadDate()
//lableView.text = viewModel.data()
}
}
And where ever you create a viewControllers and add as subView, you have to set the delegate of viewModel.
let firstViewController: FirstViewController = createFirstViewController()
let firstViewModel = FirstViewModel()
firstViewModel.delegate = firstViewController
firstViewController.viewModel = firstViewModel
mainViewController.addSubView(firstViewController.view)
Similarly for all other view controllers.
Here's how I would do it:
Create a singleton class.
Configure the singleton's properties in the the main ViewController.
Use didSet to post a Notification.
Add a listener for that Notification in your additional ViewControllers.
I have some problems to use subclasses in Swift, hope someone can help me.
What I have
Two view controllers:
VC1 with just some UIButtons
EffectVC that do some animation depending on the button pressed on VC1
import UIKit
protocol viewAnimation {
func initialStateSet()
func finalStateSet()
}
class EffectVC: UIViewController {
#IBOutlet weak var mainImage: UIImageView!
override func viewDidLoad() {
super.viewDidLoad()
self.initialStateSet()
}
override func viewDidAppear(animated: Bool) {
self.finalStateSet()
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
}
func initialStateSet() {
}
func finalStateSet() {
}
}
class GrowingEffect : EffectVC, viewAnimation {
override func initialStateSet() {
// some stuff
}
override func finalStateSet() {
// other stuff
}
}
The problem
Maybe a simple question but I can't do what I want in Swift: I need to set a subclass according to the button that is pressed.
In other words I need to present subclassed view controller from my VC1 according to which button is pressed on VC1.
If I press the first button for example I want to show the VC 2 with the class GrowingEffect for use some custom stuff (this stuff must change according to the selected button).
What I tried
use IBAction for create my subclassed VC2 and show it
let storyboard = UIStoryboard(name: "Main", bundle: nil)
let destinationViewController : UIViewController = storyboard.instantiateViewControllerWithIdentifier("EffectVC") as! GrowingEffect
self.presentViewController(destinationViewController, animated: true, completion: nil)
but I got
Could not cast value of type 'ViewAnimationDemo.EffectVC'
(0x109948570) to 'ViewAnimationDemo.GrowingEffect' (0x109948650).
use PrepareForSegue
but I can't set any subclass
What I really want to do
I know there are some other solution, like not using storyboard, but now I describe exactly what I want to do, hoping this is possibile:
have only one view controller in IB (EffectVC) associate with the class EffectVC. The class EffectVC has some subclasses like GrowingEffect.
In my code I want to instantiate the view controller EffectVC with the subclass that I need: for example instantiate the view controller in IB EffectVC with the class GrowingEffect.
I know that if I have one view controller for every subclass of EffectVC I can do what I want but I don't want so many view controller in IB because they are equal, the only things that I want to change are 2 methods.
I think there are some things mixed up in your setup. You should have 2 view controllers, each set up in its file, and each present in the storyboard with its identifier. It is ok if GrowingEffect inherits from EffectVC.
What you currently do with as! GrowingEffect is actually trying to cast the UIViewController instance you get from calling instantiateViewControllerWithIdentifier("EffectVC") to GrowingEffect. This will not work, because it is of type EffectVC.
Rather, you need to call instantiateViewControllerWithIdentifier("EffectVC") if button X is pressed, and instantiateViewControllerWithIdentifier("GrowingEffect") if button Y is pressed.
EDIT
If you use storyboard, you have to instantiate view controllers using instantiateViewControllerWithIdentifier. But you can only get an instance of GrowingEffect, if it is present on the storyboard.
It is not possible to "cast" an instance of EffectVC to GrowingEffect once created.
So, you have two possibilities here:
Use storyboard and put both view controllers on it. Use instantiateViewControllerWithIdentifier to instantiate the view controller you need, depending on the button pressed.
Do not use storyboard. Then you can create the needed view controller manually and use your UINavigationController's pushViewController method to present it.
You can't cast from parent class to child class, parent class just doesn't have the capacity to know what the child is doing. You can however cast from a child to parent, so you would want to set your view controller as GrowingEffect, then cast it to Effect, but again there is no strong suit to doing this either unless some method needs the parent class and you are using the child class. It looks like you need a redesign of how you want your view controllers laid out. Now I am assuming you have 2 children, lets call GrowingEffect and ShrinkingEffect. In your designer, you set your 1 to GrowingEffect and the other to ShrinkingEffect and make sure they have unique identifiers. Then you can use your view to present an Effect, and pass in either of those objects.
I have a custom UIView (called GridView) that I initialize and then add to a ViewController (DetailViewController). GridView contains several UIButtons and I would like to know in DetailViewController when those buttons are touched. I'm new to Swift and am wondering what is the best pattern to use to get those events?
If you want to do this with notifications, use 1:
func postNotificationName(_ notificationName: String,
object notificationSender: AnyObject?)
in the method that is triggered by your button. Then, in your DetailViewController, add a listener when it is initialized with 2:
func addObserver(_ notificationObserver: AnyObject,
selector notificationSelector: Selector,
name notificationName: String?,
object notificationSender: AnyObject?)
Both functions can be called from NSNotificationCenter.defaultCenter().
Another method would be to add callbacks which you connect once you initialize the GridView in your DetailViewController. A callback is essentially a closure:
var callback : (() -> Void)?
which you can instantiate when needed, e.g.
// In DetailViewController initialization
gridView = GridView()
gridView.callback = { self.doSomething() }
In GridView you can trigger the callback like this:
func onButton()
{
callback?()
}
The callback will only execute, if unwrapping succeeds. Please ensure, that you have read Automatic Reference Counting, because these constructs may lead to strong reference cycles.
What's the difference? You can connect the callback only once (at least with the method I've showed here), but when it triggers, the receiver immediately executes its code. For notifications, you can have multiple receivers but there is some delay in event delivery.
Lets assume your GridView implementation is like as follows:
class GridView : UIView {
// Initializing buttons
let button1:UIButton = UIButton(...)
let button2:UIButton = UIButton(...)
// ...
// Adding buttons to view
self.addSubview(button1)
self.addSubview(button2)
// ...
}
Now, we will add selector methods which will be called when a button is touched. Lets assume implementation of your view controller is like as follows:
class DetailViewController : UIViewController {
let myView:GridView = GridView(...)
myView.button1.addTarget(self, action: "actionForButton1:", forControlEvents: UIControlEvents.TouchUpInside)
myView.button2.addTarget(self, action: "actionForButton2:", forControlEvents: UIControlEvents.TouchUpInside)
// ...
func actionForButton1(sender: UIButton!) {
// Your actions when button 1 is pressed
}
// ... Selectors for other buttons
}
I have to say that my example approach is not a good example for encapsulation principles of Object-Oriented Programming, but I have written like this because you are new to Swift and this code is easy to understand. If you want to prevent duplicate codes such as writing different selectors for each button and if you want to set properties of your view as private to prevent access from "outside" like I just did in DetailViewController, there are much much better solutions. I hope it just helps you!
I think you better create a class called GridView that is inherited from the UIView. Then, you can connect all you UI element with you class as IBOutlet or whatever using tag something like that. Later on, you can ask the instance of GridView in DetailViewController so that you can connect as IBAction.
Encapsulation is one of the principles of OOP.