In my app I'm using delegates, so that I can read the data when ever it's ready.
I'm calling a delegate from two classes. Here is my code
protocol MyDelegate: class {
func getData()
}
class MyDelegateCalss {
weak var delegate: MyDelegate?
func loadData() {
// doing some actions
if(self.delegate != nil){
self.delegate!.getData!()
}
}
}
In one class I'm loading this method in tableview numberOfSections delegate method.
class A: UIViewController, MyDelegate {
func somefunc(){
let mydelegatecls : MyDelegateCalss = MyDelegateCalss()
mydelegatecls.delegate = self
mydelegatecls.loadData()
}
func getData(){
// Doing some actions
}
}
This method I'm loading from another calss.
class B: UIViewController, MyDelegate {
open func testfunc(){
let mydelegatecls : MyDelegateCalss = MyDelegateCalss()
mydelegatecls.delegate = self
mydelegatecls.loadData()
}
func getData(){
// doing some other stuff
}
}
class C: UIViewController {
func testfunc(){
let b : B = B()
b.testfunc()
}
}
Here from class A my delegate is working fine. and I'm able to see getData method is calling .
from Class B, the delegate becomes nil and unable to see getData method is called
If I make the delegate reference its working fine. But that will cause memory leak.
How can handle this case ?
Your delegate var is declared as weak. If nothing keep a strong reference on the object you assign as the delegate (implementing MyDelegate), your delegate will pass to nil as soon as the object is released (eg. the end of the scope where you instantiate it).
Some good read: https://cocoacasts.com/how-to-break-a-strong-reference-cycle/
Related
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
so I have a viewController which holds a custom view,
and that viewController class conforms to ViewProtocol
I expect when someAction method triggered in someCustomizedView
it will print " method in otherCustomizedClass called "
but it prints (" method in extension Called") instead.
The theNotOptionalMethod works just fine but not the optional method.
Is there anything that I misunderstand of protocol extension ?
Please help, been struggling for hours, thanks
protocol ViewDelegate: class {
func theNOTOptionalMethod()
}
extension ViewDelegate {
func theOptionalMethod(){
print (" method in extension Called")
}
}
class someCustomizedView: UIView {
weak var deleage: ViewDelegate?
#IBAction func someAction(sender: UIButton) {
deleage?.theOptionalMethod()
}
}
class someCustomizedVC: UIViewController, ViewDelegate {
lazy var someView: someCustomizedView = {
var v = someCustomizedView()
v.deleage = self
return v
}()
//...... someView added to controller
func theNOTOptionalMethod() {
// do nothing
}
func theOptionalMethod() {
print (" method in otherCustomizedClass called ")
}
}
That is how methods in extensions work. They hide the implementations in a class.
To create a protocol with optional methods, you need to put the optional method in the protocol definition:
protocol ViewDelegate: class {
func theNOTOptionalMethod()
func theOptionalMethod()
}
Alternatively, you can use #objc and optional modifiers:
#objc protocol MyDelegate : class{
func notOptionalMethod()
#objc optional func optionalMethod()
}
When you call optionalMethod, you need to unwrap the optional:
delegate.optionalMethod?()
In my project I have some delegates that works fine with returning data but I want to add some subview or do any anything in the delegate method on the receiving end nothing happen but the other codes that are in the same method are OK!
My other question is also realated to delegates :
This happens for some delegates. The delegate does not respond but I found a very strange fix on the web and I need to know why this happens and why this fix works!
My First View :
protocol SomeDelegate {
func someMethod()
}
class FirstViewClass {
//in init or didLoad method
var delegate: SomeDelegate?
// THIS DELEGATE WON'T WORK BUT WHEN I ADD THIS LINE IT WORKS FINE( IT STILL HAS THE ABOVE PROBLEM)
self.delegate = SecondViewClass()
//in some custom method
self.delegate?.someMethod();
}
My Second View:
class SecondViewClass : SomeDelegate {
var firstView = FirstViewClass()
// this is in init or didLoad method
firstView.delegate = self
//this is in some custom method
someMethod()
}
A simple working prototype:
protocol SomeDelegate {
func someMethod()
}
class FirstViewClass {
var delegate: SomeDelegate?
}
class SecondViewClass : SomeDelegate {
var firstView = FirstViewClass()
func someMethod() {
print("called via delegate")
}
}
var firstClass = FirstViewClass()
var secondClass = SecondViewClass()
firstClass.delegate = secondClass
firstClass.delegate?.someMethod()
I have a custom class and a view controller.
My custom class:
class ChatManager:NSObject {
func messageArrived() {
//When Message arrives I am handling it from here
//I need something like that: Viewcontroller.updateTable()
}
}
When message arrives from internet I need to update tableview in view controller. So I mean I have to call a view controller method from messageArrived method. How can I do this ?
Here is a simple example of using delegate:
declare the delegate before your chat manager class
protocol ChatManagerDelegate {
func manageMessage()
}
when the message arrived, call the delegate method to handle it.
class ChatManager: NSObject {
var delegate: ChatManagerDelegate?
func messageArrived() {
self.delegate!.manageMessage()
}
}
in your view controller, remember to set the delegate of the chat manager to self.
class ViewController: ChatManagerDelegate {
var manager = ChatManager()
manager.delegate = self
func manageMessage() {
self.updateTable()
}
}
This would be a possible implementation:
ViewController:
class ViewController: UIViewController,ChatManagerDelegate {
override func viewDidLoad() {
super.viewDidLoad()
let myChatManager = ChatManager()
myChatManager.delegate = self
}
func messageDidArrive() {
// Do Things here.
}
}
Chatmanager:
class ChatManager:NSObject {
var delegate:ChatManagerDelegate?
func messageArrived() {
//When Message arrives I am handling it from here
//I need something like that: Viewcontroller.updateTable()
}
}
Delegate-Protocol:
protocol ChatManagerDelegate{
func messageDidArrive()
}
I am trying to create a custom delegate using playground in swift. However the doSomething method is not being called through callback.
It seems that delegate?.doSomething() does not fire to the XYZ class doSomething method.
Thanks in advance!
import UIKit
#objc protocol RequestDelegate
{
func doSomething();
optional func requestPrinting(item : String,id : Int)
}
class ABC
{
var delegate : RequestDelegate?
func executerequest() {
delegate?.doSomething()
println("ok delegate method will be calling")
}
}
class XYZ : RequestDelegate
{
init()
{
var a = ABC()
a.delegate = self
}
func doSomething() {
println("this is the protocol method")
}
}
var a = ABC()
a.executerequest()
It seems that delegate?.doSomething() does not fire to the XYZ class
doSomething method.
That is correct. class ABC has an optional delegate property, but the value of
the property is nowhere set. So the delegate is nil
and therefore the optional chaining
delegate?.doSomething()
simply does nothing. Also you have defined a class XYZ but
not created any instances of that class.
If you set the delegate of a to an instance of XYZ then
it will work as expected:
var a = ABC()
a.delegate = XYZ()
a.executerequest()