I have a functionality throughout my application. Now i need to call a specific function inside one view controller for some particular condition. So i tried to call, but it fails
main.swift
CommandLine.unsafeArgv.withMemoryRebound(to: UnsafeMutablePointer<Int8>.self, capacity: Int(CommandLine.argc))
{ argv in
_ = UIApplicationMain(CommandLine.argc, argv, NSStringFromClass(MyClass.self), NSStringFromClass(AppDelegate.self))
}
MyClass.swift
class MyClass: UIApplication {
func resetIdleTimer() {
}
}
MyViewController.swift
class MyViewController: UIViewController {
MyClass.resetIdleTimer(); //this causes error in
}
I need to call resetIdleTimer() inside MyViewController?
Check this code, You can call it from anywhere.
if let obj = MyClass.shared as? MyClass {
obj.resetIdleTimer()
}
For ex. You can call in view controller
class MyViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
if let obj = MyClass.shared as? MyClass {
obj.resetIdleTimer()
}
}
}
Related
Ideally, I want to create a BaseViewController class that takes in a protocol type (of a delegate) and have a weak variable as the delegate. Something like this:
class BaseViewController<Delegate: AnyObject> {
weak var delegate: Delegate?
init(delegate: Delegate) {
self.delegate = delegate
super.init(...)
}
}
And then inherit from a view controller like so:
protocol MyDelegate: AnyObject {
func funcA()
func funcB()
}
class SomeViewController: BaseViewController<MyDelegate> {
func doSomething() {
delegate?.funcA()
}
}
This doesn't work as the compiler complains:
'BaseViewController' requires that 'MyDelegate' be a class type
How can I work this around to achieve what I need?
Thanks in advance :)
Thats because in swift protocols doesn't confirm to them selves, you can't use "MyProtocol" as concrete type confirming to protocol "MyDelegate"
What you can rather do is
protocol MyDelegate: AnyObject {
func funcA()
func funcB()
}
class BaseViewController<Delegate: MyDelegate> {
weak var delegate: Delegate?
init(delegate: Delegate) {
self.delegate = delegate
super.init(...)
//keeping OPs code as is
}
}
class SomeOtherDelegateClass: MyDelegate {
func funcA() {
//some code here
}
func funcB() {
//some code here
}
}
class SomeViewController: BaseViewController<SomeOtherDelegateClass> {
func doSomething() {
self.delegate?.funcA()
}
}
EDIT 1:
As OP mentioned in comment, he is trying to introduce a generic property in BaseViewController that will simply hold a weak reference to any instance whose class is decided/declared by Child classes of BaseViewController using generics, I am simplifying the above answer a bit
Try this
protocol MyDelegate {
func funcA()
func funcB()
}
class BaseViewController<Delegate> where Delegate: AnyObject {
weak var delegate: Delegate?
init(delegate: Delegate) {
self.delegate = delegate
super.init(...)
//keeping OPs code as is
}
}
class SomeOtherDelegateClass: MyDelegate {
func funcA() {
//some code here
}
func funcB() {
//some code here
}
}
class SomeViewController: BaseViewController<SomeOtherDelegateClass> {
func doSomething() {
self.delegate?.funcA()
}
}
protocol MyDelegate2 {
func funcABCD()
}
class SomeOtherDelegateClass2: MyDelegate2 {
func funcABCD() {
//some code here
}
}
class SomeViewController2: BaseViewController<SomeOtherDelegateClass2> {
func doSomething() {
self.delegate?.funcABCD()
}
}
TBH, I really dont see much of benefit of this design! Probably you need to revisit the code structure and see if you can come up with better code structure :)
You should set your delegate as a constraint for the generic type T in BaseViewController:
protocol MyDelegate: AnyObject {
func funcA()
func funcB()
}
class Delegated1: MyDelegate {
func funcA() { print("A1") }
func funcB() {}
}
class Delegated2: MyDelegate {
func funcA() { print("A2") }
func funcB() {}
}
class BaseViewController<T: MyDelegate>: UIViewController {
var delegate: T?
func doSomething() {
delegate?.funcA()
}
}
class SomeViewController1: BaseViewController<Delegated1> {}
class SomeViewController2: BaseViewController<Delegated2> {}
class TestClass {
let viewController1: SomeViewController1 = {
let viewController = SomeViewController1(nibName: nil, bundle: nil)
viewController.delegate = .init()
return viewController
}()
let viewController2: SomeViewController2 = {
let viewController = SomeViewController2(nibName: nil, bundle: nil)
viewController.delegate = .init()
return viewController
}()
// prints:
// A1
// A2
func myFunc() {
viewController1.doSomething()
viewController2.doSomething()
}
}
Struggling to learn the basics of passing data via delegates. I am trying to pass a string from my viewController to my viewController2 and print it. I am getting the error:
"Type ViewController2 has no member delagate" in my view controller 2.
I cannot figure out where I have gone wrong.
viewController 1:
protocol datadelagate {
func printThisString(string: String)
}
class ViewController: UIViewController {
var delegate: datadelagate?
override func viewDidLoad() {
delegate?.printThisString(string: "This was passed from first controller to second controller")
}
}
This is my viewController 2:
class ViewController2: UIViewController, datadelagate {
func printThisString(string: String) {
print(string)
}
override func viewDidLoad() {
super.viewDidLoad()
ViewController2.delagate = self
print(String.self)
}
}
If you want ViewController2 to print some value from ViewController, you might have to do it this way:
protocol datadelagate {
func printThisString(string: String)
func getStringFromVC1() -> String
}
class ViewController: UIViewController, datadelagate {
let someString: String = "From VC1"
func printThisString(string: String) {
print(string)
}
func getStringFromVC1() -> String {
return someString
}
override func viewDidLoad() {
ViewController2.delagate = self
}
}
class ViewController2: UIViewController {
var delegate: datadelagate?
override func viewDidLoad() {
super.viewDidLoad()
//This is how something from VC2 is sent to VC1's scope.
delegate?.printThisString(string: "Calling the delegate to print something from ViewController2 on first ViewController")
//The below call gets you some value from VC1. (This is what you wanted, I belive...)
print(delegate?.getStringFromVC1())
}
}
Now for some explanation:
For simple understanding, assume a delegate as a person who does some specific job (protocol).
You have a `delegate'
You ask your delegate to work with your friend, and your friend acknowledges. (assigns your delegate by You.delegate = self, where self is your friend)
Now, through your delegate, you can do something with your friend, by asking your delegate to do some job (defined in protocol).
EDIT
The code above won't work, as non-static data members are trying to be accessed without creating an instance
Working code
import UIKit
class ViewController2: UIViewController {
static let sharedInstance = ViewController2()
weak var delegate: DataDelagate?
override func viewDidLoad() {
super.viewDidLoad()
//This is how something from VC2 is sent to VC1's scope.
delegate?.printThis(string: "Calling the delegate to print something from ViewController2 on first ViewController")
//The below call gets you some value from VC1. (This is what you wanted, I belive...)
print(delegate?.getStringFromVC1() ?? "s")
}
}
class ViewController: UIViewController {
static let sharedInstance = ViewController2()
var someString: String = "From VC1"
override func viewDidLoad() {
super.viewDidLoad()
ViewController2.sharedInstance.delegate = self
}
}
extension ViewController: DataDelagate {
func printThis(string: String) {
print(string)
}
func getStringFromVC1() -> String {
return someString
}
}
protocol DataDelagate: AnyObject {
func printThis(string: String)
func getStringFromVC1() -> String
}
I have a class
class SomeViewController<T: SomeViewModel>: UIViewController, UICollectionViewDelegate, UICollectionViewDataSource { ... }
And another class:
class AnotherViewController: UIViewController {
private weak var someVC: UIViewController?
...
func someFunc() {
if someVC is SomeViewController { ... } // attempt 1
// or
if let vc = someVC as? SomeViewController { ... } // attempt 1
...
}
...
}
I need to see if someVC is a SomeViewController so that I can access an instance variable that has nothing to do with the generic type. However, when doing a check via either attempt 1 or attempt 2, the check always fails and my inner code never executes. How do I see if it is of a type, but not specific generic type e.g. I don't have to put the type of SomeViewModel?
EDIT: Added more code for clarity.
This doesn't work because Swift wants to know the type of the generic. If you just want to access a property without dealing with the generic, you can extract that to a protocol.
protocol SomethingThatHasFoo {
var foo: String { get }
}
class SomeViewController<T>: UIViewController, SomethingThatHasFoo {
let foo = "foo"
}
class AnotherViewController {
private weak var someVC: UIViewController?
func someFunc() {
if let vc = someVC as? SomethingThatHasFoo {
print(vc.foo)
}
}
}
Here is an example that works:
class SomeViewModel{}
class A: SomeViewModel{}
class SomeViewController<T: SomeViewModel> : UIViewController{}
class AnotherViewController {
private weak var someVC: UIViewController?
init(vc: SomeViewController<A>) {
someVC = vc
}
func someFunc() {
if someVC is SomeViewController<A> {
print("\(String(describing: someVC))")
}
if let vc = someVC as? SomeViewController<A> {
print("\(vc)")
}
}
Then you have to initialize it like this:
let someVC = SomeViewController<A>()
let anotherVC = AnotherViewController.init(vc: someVC)
anotherVC.someFunc()
Hope that answered your question
I am writing my iOS Application in Swift 3.
I have a UIViewController extension, where I have to check if the controller instance responds to a method. Below is the code that I a trying out.
extension UIViewController {
func myMethod() {
if self.responds(to: #selector(someMethod)) {
}
}}
Here the responds(to:) method throws a compile time error
Use of unresolved identifier "someMethod".
I read in another post, we have to use self inside the selector argument, but even that is throwing some error.
A simple workaround:
#objc protocol SomeMethodType {
func someMethod()
}
extension UIViewController {
func myMethod() {
if self.responds(to: #selector(SomeMethodType.someMethod)) {
//...
self.perform(#selector(SomeMethodType.someMethod))
// or
(self as AnyObject).someMethod?()
//...
}
}
}
A little more Swifty way:
protocol SomeMethodType {
func someMethod()
}
//For all classes implementing `someMethod()`.
extension MyViewController: SomeMethodType {}
//...
extension UIViewController {
func myMethod() {
if let someMethodSelf = self as? SomeMethodType {
//...
someMethodSelf.someMethod()
//...
}
}
}
Create a protocol which requires someMethod()
protocol Respondable {
func someMethod()
}
And a protocol extension which affects only UIViewController instances
extension Respondable where Self : UIViewController {
func myMethod() {
someMethod()
}
}
Adopt the protocol to some of the view controllers
class VC1 : UIViewController, Respondable {
func someMethod() { print("Hello") }
}
class VC2 : UIViewController {}
class VC3 : UIViewController {}
Now call the method in the extension
let vc1 = VC1()
vc1.myMethod() // "Hello"
Otherwise you get a compiler error:
let vc3 = VC3()
vc3.myMethod() // error: value of type 'VC3' has no member 'myMethod'
Swift 4 answer:
If the selector is written as a string you won't get that error.
extension UIViewController {
func myMethod() {
if self.responds(to: "someMethod")) {
}
}
}
And then in the viewcontroller (dont forget the #objc):
#objc func someMethod() -> Void {}
I have a viewcontroller class ViewController with collectionView. Also I have singleton class FacebookManager for fetching data from facebook.
What I want to do is to run a method in facebook class and then call a method in ViewController to reload collectionView.
I tried to make a reference to ViewController in Facebook manager by setting
class FacebookManager {
static let sharedInstance = FacebookManager()
var vc:ViewController?
}
Then setting in ViewController
class ViewController: {
func viewDidLoad() {
FacebookManager.sharedInstance.vc = self
}
}
And then calling in FacebookManager
func myMethod() {
vc.collectionView.reloadData()
}
But this doesn't work.
How to do this properly?
To provide communication between two or multiple classes there are two method that are recommended.
1) Delegation
2) Notification
In your given code to implement delegation method we have to create protocol and delegate property in FacebookManager. And assign view controller as a delegate to FacebookManger
Example:
protocol FacebookManagerDelegate: class {
func refreshData()
}
class FacebookManager {
var weak delegate:FacebookManagerDelegate?
func myMethod() {
delegate?.refreshData()
}
}
class ViewController: FacebookManagerDelegate {
ViewDidLoad() {
FacebookManager.sharedInstance.delegate = self
}
func refreshData() {
self.collectionView.reloadData()
}
}
But you are using singleton class therefore in future multiple class would be using this class and if you want to notify multiple classes use Notification method, which pretty easy to implement and should be use in singleton class
Post notification in FacebookManger whenever you want to notify:
class FacebookManager {
func myMethod() {
NSNotificationCenter.defaultCenter().postNotificationName(notificationName, object: nil)
}
}
class ViewController {
ViewDidLoad() {
NSNotificationCenter.defaultCenter().addObserver(self, selector:#selector(reloadData(_:)), name: NotificationName, object: nil)
}
deinit {
NSNotificationCenter.defaultCenter().removeObserver(self)
}
func reloadData(notification: NSNotification) {
self.collectionView.reloadData()
}
}