I have class A in file A and class B in file B. In class B, I want to access the running instance of class A, in order to run a function located in it. Both classes are connected to view controllers. I do not want to create a new instance of class A as in classAInstance = classA(), but rather access the instance of class A that my app is already running. Any help would be appreciated.
Here is part of my code in class A:
Class A {
func reloadTableView() {
self.CardsTableView.reloadData()
}
}
And here is part of my code in class B:
Class B {
#IBAction func saveButton(_ sender: UIButton) {
// here is where I want to call reloadTableView() from class A
}
}
The quick and dirty method I might use would be where you have some singleton where you can store the current instances of your classes.
Example:
class EnvironmentUtility {
private static var instance: EnvironmentUtility?
internal class func shared() -> EnvironmentUtility {
guard let currentInstance = instance else {
instance = EnvironmentUtility()
return instance!
}
return currentInstance
}
var myClassA: ClassA? = nil
var myClassB: ClassB? = nil
}
Then in the viewDidLoad (Or wherever else you like that a new instance is being made) of the those ViewControllers/Classes:
class ClassA: UIViewController {
…
override func viewDidLoad() {
…
EnvironmentUtility.shared().myClassA = self
}
…
}
Later in ClassB you could then:
class ClassB: UIViewController {
…
#IBAction func saveButton(_ sender: UIButton) {
EnvironmentUtility.shared().myClassA.reloadTable()
}
…
}
This isn’t the prettiest or Swifty-est way of doing it, but quick and dirty.
If you want to write a better solution I would suggest looking at the MVVM-C Swift architectural pattern (I use this pattern myself). In this architecture you will have access to a Coordinator that overseas viewController transitions and you can also track current instances of your ViewControllers/Classes in a much more elegant way.
Here is a crash course in MVVM-C: https://marcosantadev.com/mvvmc-with-swift/
Related
How i can pass data from First screen to Second screen provided that must use inheritance and data entered in base class should be available in second screen after push.
class FirstViewController {
var dataArray = [CustomModel]()
//methods will manupulate data
}
Then push subclass SecondViewController from class FirstViewController
class SecondViewController : FirstViewController {
print(dataArray)
}
Is this possible ? any solution to this ? I just wanted reuse most of code in many screens. Any help.
When you inherit class B with parent class A, then you can access its data members.
Here check this:
class ViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
//call show function of class B which is inherit from class A
let classB = B()
classB.showData()
}
}
class A {
var dataArray: [String] = ["ABC", "123", "XYZ"]
}
class B: A {
func showData()
{
print(dataArray)
}
}
Output:
["ABC", "123", "XYZ"]
This is basic rule of inheritance, is this what you are looking for! if not kindly explain your problem in detail.
P.S
you can also use static data members they are accessible without making object.
I'm writing because I'd like to know what's the best method to notify a change from a class to multiple ViewControllers. At the moment I'm using delegate method but I'm sure It's not the best one for this purpose. I created a class where I receive data and after a bit of processing I need to send the processed message to some ViewControllers (any one shows a piece of that message.). At the moment I have a singleton for the class and I assign its delegate to a different ViewController when I load it through a menu. What's your suggestion to do this job?
Here is an example of my actual code:
import Foundation
protocol MyClassDelegate {
func receivedData(_ sender: MyClass)
}
class MyClass: NSObject {
// create the var for delegate
var delegate: MyClassDelegate?
// save the single instance
static private var instance: MyClass {
return sharedInstance
}
private let sharedInstance = MyClass()
static func getInstance() -> MyClass {
return instance
}
func processData() {
// at the end of the process
delegate?.receivedData(self)
}
}
class Menu: UIViewController {
private var containerView: UIView!
private let myClass = Myclass.getInstance()
private var vcOne = VcOne()
private var vcTwo = VcTwo()
override func viewDidLoad() {
super.viewDidLoad()
containerView = UIVIew()
// set containerView position and dimensions
}
func selectViewController(previous: UIViewController, next: UIViewController) {
// remove actual loaded ViewController
previous.willMove(toParent: nil)
previous.view.removeFromSuperView()
previous.removeFromParent()
// assign the delegate
myClass.delegate = next
// add the new ViewController
self.addChild(next)
slef.addSubView(next.view)
next.didMove(toParent: self)
}
}
class VcOne: UIViewController, MyClassDelegate {
func receivedData(_ sender: MyClass) {
// data received
}
}
class VcTwo: UIViewController, MyClassDelegate {
func receivedData(_ sender: MyClass) {
// data received
}
}
You can use NotificationCenter https://developer.apple.com/documentation/foundation/notificationcenter to broadcast a message. or use KVO. Generally I consider notification center much easier.
simple example:
https://www.hackingwithswift.com/example-code/system/how-to-post-messages-using-notificationcenter
I'm trying to call method of Class B from class A on the button tap event. But it does not work and below is my code.
// Viewcontroller
class ViewController: UIViewController {
#IBAction func btnClicked(_ sender: Any) {
var objA = A()
objA.delegate?.TestA()
}
}
// ClassA.swift
protocol TestA {
func TestA()
}
class A {
var delegate: TestA?
}
// ClassB.swift
class B : TestA {
func TestA() {
print(" Function A from b")
}
}
When tapping a button, function TestA() does not invoke.
I even tried the code below, but it also didn't work:
var objB = B()
var objA = A()
objA.delegate = objB
Because you instantiate instance of Class A using
var objA = A()
Clearly you haven't initialised delegate property in A because its optional its default value is nil
Now when you call
objA.delegate?.TestA()
delegate is nil hence function TestA will not be called
Suggestion
Always use camelCasing for declaring names of functions. So TestA() is incorrect rather use testA()
EDIT 1:
Tested this
#IBAction func btnClicked(_ sender: Any) {
let objA = A()
let objB = B()
objA.delegate = objB
objA.delegate?.TestA()
}
This is working fine what is the issue?
The objA.delegate is never assigned to an object, so it has an initial value of nil. The ? operator avoids calling a function on a nil object.
The answer by Sandeep Bhandari is right.
Some information for better understanding of Protocol and Delegates.
TestA is a protocol and an optional var delegate is defined in class A. This setup is right. The idea behind this setup is that any user of class A, in this case class B which conforms to protocol TestA gets a callback from class A. You need to call the delegate.testA() function from within class A.
The current implementation of ViewController is not at all benefiting from defining Protocol and Delegates.
To achieve proper usage, the class A cab be modified as follows:
protocol TestA {
func testA()
}
class A {
var delegate: TestA?
func process() {
// Do something and call delegate function to report it.
delegate?.testA()
}
}
And modify ViewController as follows (copied class B for completeness):
class ViewController: UIViewController {
#IBAction func btnClicked(_ sender: Any) {
var objA = A()
var objB = B()
objA.delegate = objB
objA.process()
}
}
// ClassB.swift
class B : TestA {
func TestA() {
print(" Function A from b")
}
}
Now function implemented in class B to conform to protocol TestA will be called when process() function on objA of class A is called.
This is better use of Protocol and Delegate. Hope this helps.
I'm trying to implement SharedInstanceDelegate in App class. I have no idea why the functions under the protocol are not being called.
This is my Protocol and class.
class App {
let sharedInstance = SharedInstance.shared
init() {
self.sharedInstance.delegate = self
}
}
extension App: SharedInstanceDelegate {
func1() { } // this is not executed
func2() { }
}
protocol SharedInstanceDelegate: class {
func1()
func2()
}
class SharedInstance {
static let shared = SharedInstance()
weak var delegate: SharedInstanceDelegate?
private init() { }
func method1() {
self.delegate?.func1() // this is executed
}
}
I believe you meant to make SharedInstanceDelegate a protocol, but you've made it a class. In either case, App does not conform/inherit SharedInstanceDelegate, so it's not clear how this would even compile.
Here is how I would implement your code to work with the delegate:
class App {
let sharedInstance = SharedInstance.shared
init() {
self.sharedInstance.delegate = self
}
}
extension App: SharedInstanceDelegate {
func func1() { } // this will run now
func func2() { }
}
protocol SharedInstanceDelegate {
func func1()
func func2()
}
class SharedInstance {
static let shared = SharedInstance()
var delegate: SharedInstanceDelegate?
private init() { }
func method1() {
self.delegate?.func1() // this is executed
}
}
Still no idea why this was happening, but cleaning the project fixed this. This is very strange. I have other delegates that call successfully.
Your code could work but it depends on how you are calling func1(). Calling it like this:
let testinstance = App().sharedInstance
testinstance.delegate?.func1()
will not work because you are not holding on to the App object. In this case the App object is the delegate, but because its a weak member and no one is retaining it, it gets released right away.
If you call it like this:
let testapp = App()
testapp.sharedInstance.delegate?.func1()
it works. In this case the App object is being retained and is still around when func1() is called.
Either way the way these classes are related is confusing to me. Why have a separate SharedInstance class at all?
I am currently working on one project. It may potentially have duplicated codes in multiple controllers like below.
Controller A
class A: UIViewController, AVCaptureMetadataOutputObjectsDelegate {
// about 50~70 lines of codes
#IBAction func scanButtonTapped {
// used self (as AVCaptureMetadataOutputObjectsDelegate)
// used view
// called presentViewController(...), which is a func in UIViewController
}
}
Controller B
class B: UIViewController, AVCaptureMetadataOutputObjectsDelegate {
#IBAction func scanButtonTapped {
// will need same logic as in Controller A
}
}
My current solution is have another class C, and move the duplicated codes into it. However, if I do so, controller can cast to AVCaptureMetadataOutputObjectsDelegate, but not to UIViewController.
class C {
func btnTapped (view: UIView, controller: AnyClass) {
// logic is here
// controller can cast to AVCaptureMetadataOutputObjectsDelegate
// but controller cannot cast to UIViewController
}
}
so A and B will have
class A {
#IBAction func scanButtonTapped {
let c = C()
c.btnTapped(view, self)
}
}
My question is if it is possible to cast controller into UIViewController. OR is there another way to refactor the codes properly?
What about extend AVCaptureMetadataOutputObjectsDelegate protocol and create default implementation by protocol extension (POP approach)?
protocol ScanButtonClickable: AVCaptureMetadataOutputObjectsDelegate {
func btnTapped() // this line is optional
}
extension Clickable where Self: UIViewController {
func btnTapped() {
// logic is here
}
}
class A: UIViewController, ButtonClickable {
...
}
class B: UIViewController, ButtonClickable {
...
}
Try this:
//declare your default method to be used across classes
protocol MyProtocol {
func myFunc()
}
//provide the implementation of your default behavior here in myFunc()
extension MyProtocol {
func myFunc() {
print("Default behavior")
}
}
class A: MyProtocol {
}
class B: MyProtocol {
}
let a = A()
a.myFunc()
let b = B()
b.myFunc()
//prints
Default behavior
Default behavior