I have a very general view that is created and used by multiple view controllers with 2 buttons, one of them sometimes is hidden depending on the needs.
This view delegates the tap of the two buttons.
protocol TheViewsDelegate: class {
func button1Tapped()
func button2Tapped()
}
Let's put that ViewControllerA creates this view and needs both buttons, this view controller will have to implement both delegate functions and do something inside it.
Now let's say that ViewControllerB creates the same view but just needs one of the buttons. This view controller will have to still implement button2Tapped() even though it will never be called and used.
Is there a way to handle this nicely? I imagine there's a nice solution where I don't need to implement this button2Tapped() if I don't need it.
I thought about making it optional by giving a default implementation but I don't like this solution, I like (and I think it's a good practice) the compiler giving me an error when a method it's not implement. Someone can jump into the project and not realising that he/she hasn't implement button2Tapped when needs to be implemented.
Note: This is a very simple example just to illustrate my question, but the question is more broad as in what to do when a function in a delegate is defined by controller that don't need to implement it.
I believe you want to use:
optional func
There are a couple of ways of declaring a protocol method as optional, one is using optional func which requires using #objc syntax, which a lot of programmers apparently don't like, and the other requires declaring an empty body in the extension of a protocol (which makes it optional by default).
protocol TheViewsDelegate: AnyObject {
func button1Tapped()
}
extension TheViewsDelegate {
func button2Tapped() {}
}
class SomeViewController: UIViewController, TheViewsDelegate {
func button1Tapped() {
// implement
}
}
By giving the protocol an empty body inside an extension of the protocol, that method is optional and does not need to be implemented by conforming objects.
For comparison, the alternative:
#objc protocol TheViewsDelegate: AnyObject {
func button1Tapped()
#objc optional func button2Tapped()
}
class SomeViewController: UIViewController, TheViewsDelegate {
func button1Tapped() {
// implement
}
}
Related
I was converting one of my swift project into SwiftUI. I need to convert delegtes and protocols to SwiftUI, is it allowed in SwiftUI? or any alternative methods are there? Please help me i'm so confused in SwiftUI.
I'm calling a delegate method from one of my class, then delegate method will be present in another ViewController.
//PresenterClass
protocol SplashPresenterDelegate {
func didFetchedSystemInfo(info: String)
}
class SplashPresenter: NSObject {
var delegate: SplashPresenterDelegate?
func getSystemInfo(){
self.delegate?.didFetchedSystemInfo(info: "ResponseString")
}
}
// Viewcontroller class
class myViewController: UIViewController {
.
.
.
}
extension myViewController: SplashPresenterDelegate{
func didFetchedSystemInfo(info: String){
print("delegate called")
}
}
Please help me to convert this code to SwiftUI
Typically, SwiftUI prefers the pattern of taking callbacks rather than protocol/delegates. For instance, each button in an ActionSheet has a closure that is executed when the button is tapped.
You shouldn't just convert your code over directly, though. SwiftUI, being declarative, uses different paradigms for a lot of things. For instance, you wouldn't have a didFetchInfo method, you would just assign it to a #Published variable.
Think about having "single sources of truth", where a single variable is always correct. For example, List simply takes an array and updates when the array changes, unlike UITableView where you provide the data through numberOfRows and cellForRowAt. I don't know enough about your specific project to give more detail, but those are things to think about.
I have an UIViewController with 4 UIButtons. A user can tap any of those UIButtons and an UIView pops up. I want to add an didAppear() and didDisappear() function on the classes which are holding the UIViews depending on the users action. How can I call didDisappear() without the use of an enum, for example:
func didDisappear(view: EnumViews){
switch view{
case view0: myClassWithView0.didDisappear()
case view1: myClassWithView1.didDisappear()
case view2: myClassWithView2.didDisappear()
case view3: myClassWithView3.didDisappear()
}
}
Now I get 4 times duplicate data. I know that function exists for my class with a UIView, but how to call it? I made a protocol:
protocol ViewProtocol{
func didAppear()
func didDisappear()
}
I made the classes which are holding the UIView's conform to that protocol. However I do not know how to use it, when I create the class I get the error:
'myClassWithUIView' cannot be constructed because it has no accessible
initializers
The classes are all in an array and I can identify which UIView needs to pop up from the sender.tag. Ideally, I want to have something like this:
#IBAction func bringNewUIView(_ sender: UIButton) {
let newView = myArrayOfClassesWithUIView[sender.tag]
newView.didAppear()
}
You've got many things going on here. I'll start with the easy one.
'myClassWithUIView' cannot be constructed because it has no accessible initializers
This just means you don't have an initializer for your class. So inside your myClassWithUIView implementation you need to have init. I can't really help you with building the init because I don't know how that class is structured, but I will assume this is something you know how to do anyway.
Your #IBAction seems fine. Once you have an array of your classes that seems like it should work. Edit your post if that is not the case.
Finally, for your didDisappear question, you can do something like this:
func didDisappear(view: EnumViews) {
//Check to see if this view conforms to your ViewProtocol (that's not a good name, btw)
if let myClass = view as? ViewProtocol {
//Since it does conform to ViewProtocol you can call didDisappear on it
myClass.didDisappear()
}
}
Alternatively, if you already know that the didDisappear function is always passing in a view that conforms to ViewProtocol why not just change the argument and make that easier?
func didDisappear(view: ViewProtocol) {
view.didDisappear()
}
Having my first crack at POP. In this case I want to decorate some UIViewControllers so that any that they automatically raise a 'Page viewed' analytics event.
So I created a protocol, and and extension for that protocol:
protocol ReportPageViewedEvent {
func reportPageViewed()
var pageName : String? { get set }
}
extension ReportPageViewedEvent where Self: UIViewController
{
func reportPageViewed()
{
guard let pageName = self.pageName else
{
fatalError("UIViewController implements ReportPageViewEvent protocol but did not set pageName property")
}
let eventBusiness = EventBusiness.sharedInstance
eventBusiness.logUserViewedPage(pageName)
}
}
This works as I want, if I decorate a UIViewController with ReportPageViewedEvent like this:
class HomeView: UIViewController, ReportPageViewedEvent {
I get a compiler error unless I set 'pageName' which is exactly what I want.
Where I am getting unstuck is where and how to call the actual reportPageViewed() method. I really want it to be called from viewDidLoad which means I either have to modify every 'viewDidLoad' in every controller that uses it, or subclass and call the method in the super class which defies the point of using POP in the first place.
Is there a nice way to achieve this. I can't find an example like this in any tutorial/blog.
Basically, there is always some behaviour shared by all the screens of your app. So it is appropriate to create a class called (for example) BaseViewController so all the other view controllers will inherit from it.
In BaseViewController's viewDidLoad you can call the reportPageViewed() method.
However, this approach makes the Protocol Oriented Programming not needed. Protocols are useful when you need to assign some same behaviour to objects that have nothing in common (which is not the case for app screens).
I have a swift protocol:
#objc protocol SomeDelegate {
optional func myFunction()
}
I one of my classes I did:
weak var delegate: SomeDelegate?
Now I want to check if the delegate has myFunction implemented.
In objective-c I can do:
if ([delegate respondsToSelector:#selector(myFunction)]) {
...
}
But this is not available in Swift.
Edit: This is different from: What is the swift equivalent of respondsToSelector? I focus on class protocols not on classes.
How do I check if my delegate has an optional method implemented?
Per The Swift Programming Language:
You check for an implementation of an optional requirement by writing
a question mark after the name of the requirement when it is called,
such as someOptionalMethod?(someArgument). Optional property
requirements, and optional method requirements that return a value,
will always return an optional value of the appropriate type when they
are accessed or called, to reflect the fact that the optional
requirement may not have been implemented.
So the intention is not that you check whether the method is implemented, it's that you attempt to call it regardless and get an optional back.
You can do
if delegate?.myFunction != nil {
}
I've found it successful to add an extension to the protocol that defines basic default implementation and then any class implementing the protocol need only override the functions of interest.
public protocol PresenterDelegate : class {
func presenterDidRefreshCompleteLayout(presenter: Presenter)
func presenterShouldDoSomething(presenter: Presenter) -> Bool
}
then extend
extension PresenterDelegate {
public func presenterDidRefreshCompleteLayout(presenter: Presenter) {}
public func presenterShouldDoSomething(presenter: Presenter) -> Bool {
return true
}
}
Now any class needing to conform to the PresenterDelegate protocol has all functions already implemented, so it's now optional to override it's functionality.
I normally implement it like this:
self.delegate?.myFunction?()
if the delegate methods returns a value:
var result = defaultValue
if let delegateResult = self.delegate?.myFunction?() else {
result = delegateResult
}
//do something with result
Declaration
#objc public protocol nameOfDelegate: class {
#objc optional func delegateMethod(_ varA: int, didSelect item: Item)
}
Implimetation
if let delegate = nameOfDelegate {
delegate.delegateMethod?(1, didDeselect: node)
}
I know this question is 5 years old, but I would like to share what I found. My solution works as of 2021, XCode 11+, Swift 5.
Say I wanted to figure out whether the function sign follows the GIDSignInDelegate protocol and also know what all the optional functions for GIDSignInDelegate are.
I have to look at the source code of the GIDSignIn module, and this is how.
Click on jump to definition on the main module that is imported. It will lead to a file like this:
Copy the entire line, import GoogleSignIn.GIDSignIn and paste it in the ViewController or whatever .swift file (doesn't really matter).
Within the swift file, right click on the GIDSignIn part of the import line GoogleSignIn.GIDSignIn and jump to definition. This will lead you to the actual module with all the available functions (the functions not marked optional may be stubs, which are required functions in the delegate protocol):
From this file, I can see that there is a sign function that is a stub of GIDSignInDelegate and an optional sign function that is implemented as a method overload.
I used this for GIDSignInDelegate, but you can use the same method to figure out whether any function follows any delegate protocol.
Is it possible to access and run a specific method/function from another class that can change dynamically as the app is run?
I’ll try to simplify the problem as much as possible.
SelectionPage.swift
Choose which class needs to be selected and accessed using an UIPickerView - 10 possible selections (Class1, Class2, Class3,…, Class10).
Class1.swift, Class2.swift, … Class10.swift
Each of the 10 classes has a single method that has exactly the same name but is programmed differently:
func runOnUpdate() { }
GameSceneViewController.swift
When a selection is made on the SelectionPage, the app segues to a GameSceneViewController where the specific selected function is run every time the update function is run:
override func update(currentTime: CFTimeInterval)
{
// run runOnUpdate() function here from selected class
}
Inside the update function, I would like to execute the runOnUpdate( ) function depending on which class was selected on the SelectionPage. Is this possible? Ideally I'd like to be able to assign the specific class/method in the:
override func didMoveToView(view: SKView)
so that I can access in other functions as well.
I’ve looked into lazy instantiation, creating delegates for each of the classes, #objc(Class1), arrays of [AnyClass], typealias, global variables in structs, singletons etc. but I’m unable to figure out how to make this work.
It seems like a fairly common problem so any help would be greatly appreciated! Thank you in advance!
You were correct in trying delegates as this is a case where you should make a protocol and a delegate. The protocol requires the function. From there you set the delegate property to an instance of a class that conforms to that protocol and then you call delegate?.someFunction() to call the function on the given object.
class ViewController: UIViewController {
var delegate: Updatable?
override func viewDidLoad() {
super.viewDidLoad()
let foo = Foo()
delegate = foo
delegate?.runOnUpdate() // prints do something
}
}
protocol Updatable {
func runOnUpdate()
}
class Foo: NSObject, Updatable {
func runOnUpdate() {
println("do something")
}
}