I'm practising how to communicate between two view controllers using protocol and delegate (in the xCode background even when I'm using protocol in my project I get the same problem, Delegate is nil), but the problem after setting everything it shows me that my delegate is nil and the sender VC does not send any data since the delegate is nil.
I have confirmed to the protocol and I have set the receiver VC as the delegate, but still can not see where the problem is.
The Protocol
protocol theCommunicationsStructionProtocol{
func dataToTransmit(Data: String)
}
The Sender VC
class TheSenderVC{
var delegate: theCommunicationsStructionProtocol?
func lookingForDelegate(){
self.delegate?.dataToTransmit(Data: "Data has been sent")
}
}
The Receiver VC
class TheReceiverVc1: theCommunicationsStructionProtocol{
var TheSenderVCObj = TheSenderVC()
func delegateLuncher(){
TheSenderVCObj.delegate = self
}
func dataToTransmit(Data: String) {
print("from VC1: \(Data)")
}
}
calling delegateLuncher() to set the delegate in the receiver VC
TheSenderVC().lookingForDelegate()
calling lookingForDelegate() from the sender VC to look for the
delegate and send it the data
TheReceiverVc1().delegateLuncher()
Note: I have tried accessing the delegate from the receiver VC using this way:
class TheReceiverVc1: theCommunicationsStructionProtocol{
var TheSenderVCObj: TheSenderVC?
func delegateLuncher(){
self.TheSenderVCObj?.delegate = self
}
func dataToTransmit(Data: String) {
print("from VC1: \(Data)")
}
}
but I still getting the same problem:
delegate is nil
Finally, I found the solution!
the problem is I was making instances of the TheSenderVC, instead of takling to the original TheSenderVC.
when I was making an object (an instance) of TheSenderVC the problem occurred! instead I have to access the original TheSenderVC, which means I have to use static :)
here is the old delegate set up
var delegate: theCommunicationsStructionProtocol?
from TheSenderVC
here is the new delegate set up
static var delegate: theCommunicationsStructionProtocol?
therefore the
func lookingForDelegate(){
self.delegate?.dataToTransmit(Data: "Data has been sent")
}
will be changed to
static func lookingForDelegate(){
self.delegate?.dataToTransmit(Data: "Data has been sent")
}
since now it includes a static property (delegate)
on the other hand, the The ReceiverVC1 should be changed from:
class TheReceiverVc1: theCommunicationsStructionProtocol{
var TheSenderVCObj = TheSenderVC()
func delegateLuncher(){
TheSenderVCObj.delegate = self
}
func dataToTransmit(Data: String) {
print("from VC1: \(Data)")
}
}
to:
class TheReceiverVc1: theCommunicationsStructionProtocol{
func delegateLuncher(){
TheSenderVC.delegate = self
}
func dataToTransmit(Data: String) {
print("from VC1: \(Data)")
}
}
accessing the delegate from the original TheSenderVC()
Where are you create the reference of TheSenderVCObj
replace var TheSenderVCObj: TheSenderVC? to var TheSenderVCObj = TheSenderVC()
let try below code:
class TheReceiverVc1: theCommunicationsStructionProtocol{
var TheSenderVCObj = TheSenderVC()
func delegateLuncher(){
self.TheSenderVCObj?.delegate = self
}
func dataToTransmit(Data: String) {
print("from VC1: \(Data)")
}
}
your TheSenderVCObj also nil according to your code.
NOTE: use proper naming conventions.
Because the TheReceiverVc1 was automatic deinit by ARC.
You need to save reference of the instance like that's:
class ViewController: UIViewController {
let theReceiverVc1: TheReceiverVc1 = TheReceiverVc1()
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
theReceiverVc1.delegateLuncher()
}
}
Also make sure when you using delegate set it as weak var:
weak var delegate: theCommunicationsStructionProtocol?
Related
I am trying to understand more protocols. I could not figure out myProtocolFunction never call and print or passing the variable as below.
I think my problem is about initialization. When I try with two viewcontroller everything is okay but MyStruct protocol instance is nil. Thanks for your help.
class ViewController: UIViewController, MyProtocol {
var myProtocolValue: String = ""
var globalInstance = "a"
override func viewDidLoad() {
super.viewDidLoad()
}
#IBAction func click(_ sender: Any) {
var myStruct = MyStruct()
myStruct.myProtocol = self
}
func myProtocolFunction(passing: String) {
globalInstance = passing
print("never print")
}
}
protocol MyProtocol {
func myProtocolFunction(passing: String)
}
struct MyStruct {
var myProtocol: MyProtocol?
init() {
makeSomething()
}
func makeSomething() {
myProtocol?.myProtocolFunction(passing: "abc")
}
}
1- You need to make
var myStruct = MyStruct() // an instance variable
#IBAction func click(_ sender: Any) {
myStruct.myProtocol = self
}
2- Also you call init before even you set myProtocol as its called when you do var myStruct = MyStruct() and at that time myProtocol is nil as its not yet set
init() {
makeSomething()
}
Check full working edit
class ViewController: UIViewController, MyProtocol {
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
}
func myProtocolFunction(passing: String) {
print(passing)
}
#IBAction func click(_ sender: Any) {
var myStruct = MyStruct(self)
}
}
protocol MyProtocol {
func myProtocolFunction(passing: String)
}
struct MyStruct {
var myProtocol: MyProtocol?
init(_ mine:MyProtocol) {
myProtocol = mine
makeSomething()
}
func makeSomething() {
myProtocol?.myProtocolFunction(passing: "abc")
}
}
Think about protocols as a type, in your struct you are basically saying
that this struct have a variable of this type ( your protocol )
and on init you are trying to call its function.
What you're missing is setting an instance of type ( your protocol )
so it can get called.
for instance :
MyStruct = MyStruct(myProtocol: ViewController())
Now your nullable protocol have a value and can call it's function in another word, protocols can't have implementation directly into them they're more like a signature contract
Read more about protocols here.
You need to create MyStruct() object out of the click action else when the scope is over your object is deinitialize.
Also, You have to call .makeSomething() function on the button click as the time of object creation delegate is nil.
var myStruct = MyStruct() // Create an instance here
#IBAction func click(_ sender: Any) {
myStruct.myProtocol = self
// Add your action
myStruct.makeSomething()
}
I am using delegates to get a string value from my modal. When the modal closes I am trying to update Label text using that string. However, I am getting error: Unexpectedly found nil while implicitly unwrapping an Optional value: file. I am not sure how to fix this. I think it's happening because the view is not yet active.
import Cocoa
class ViewControllerA: NSViewController, SomeDelegate {
#IBOutlet weak var msgLabel: NSTextField!
var s: String = "";
override var representedObject: Any? {
didSet {
// Update the view, if already loaded.
}
}
func setDetails(s: String) {
self.user = s;
print("Notified", self.s) // <-- prints: Notified hello again
msgLabel.stringValue = self.s <-- DOESN'T WORK
}
func showModal() -> Void {
msgLabel.stringValue = "hello" // <--- WORKS
let cbvc: NSViewController = {
return self.storyboard!.instantiateController(withIdentifier: "ControllerBVC")
as! NSViewController
}()
self.presentAsModalWindow(cbvc);
}
#IBAction func onBtn(_ sender: Any) {
self.showModal();
}
}
protocol SomeDelegate {
func setDetails(s: String)
}
class ViewControllerB: NSViewController {
#IBOutlet weak var textF: NSTextField!
var delegate: SomeDelegate?
override func viewDidLoad() {
super.viewDidLoad()
// Do view setup here.
let vc = ViewControllerA()
self.delegate = vc
}
#IBAction func onBtn(_ sender: Any) {
DispatchQueue.main.async {
self.delegate?.setDetails(s: self.textF.stringValue)
self.dismiss("ControllerAVC")
}
}
}
You have a number of problems.
In ViewControllerB.viewDidLoad you are assigning a new instance of ViewControllerA to the delegate property. Don't do that. Your viewDidLoad method should look like this:
override func viewDidLoad() {
super.viewDidLoad()
}
In the showModal method ViewControllerA should assign itself as the delegate on ViewControllerB before ViewControllerB it is presented.
func showModal() -> Void {
let cbvc: NSViewController = {
let vc = self.storyboard!.instantiateController(withIdentifier: "ControllerBVC")
as! ViewControllerB
vc.delegate = self
return vc
}()
self.presentAsModalWindow(cbvc);
}
In the setDetails method just assign the string to your text field directly:
func setDetails(s: String) {
msgLabel.stringValue = s
}
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
}
And just that I'm exercising the delegated pattern. I created a simple application where a delegate sends a message to UIViewController saying if you stop or start UIActivityIndicatorView. Unfortunately I get the following error: error atal: unexpectedly found nil while unwrapping an optional value.
It would seem that UIActivityIndicatorView is not initialized. I can not understand where I'm wrong.
protocol ProgressBarDelegate {
func UpdateProgressBar(progress: Bool)
}
class Dao: NSObject {
var delegate: ProgressBarDelegate?
override init() {
super.init()
//DELEGATO
//I who should I send the message? to FirstViewController
let messaggero = FirstViewController()
self.delegate = messaggero
scriviUnMessaggio(progress: true)
}
func scriviUnMessaggio(progress: Bool){
print("I'm writing a message ...")
delegate?.UpdateProgressBar(progress:progress)
}
My controller
class FirstViewController: UIViewController,ProgressBarDelegate {
#IBOutlet var activity: UIActivityIndicatorView!
func UpdateProgressBar(progress: Bool){
print("I received the message from Dao class (the delegate)")
switch progress{
case true:
// At this point I get the following error:Fatal error: unexpectedly found nil while unwrapping an Optional value
self.activity.startAnimating()
case false:
self.activity.stopAnimating()
default:
self.activity.startAnimating()
}
}
override func viewDidLoad() {
super.viewDidLoad()
let dao = Dao()
/// dao.caricamentoDati()
The problem is that you're creating a new object of FirstViewController in init of Dao. Since FirstViewController object is not created via xib/storyboard hence the outlet is not connected. That's why it's giving crash at self.activity.startAnimating()
Set the delegate to self in viewDidLoad
Change your Doa's init method as follow
class Dao: NSObject {
var delegate: ProgressBarDelegate?
init(delegate: ProgressBarDelegate) {
super.init()
//DELEGATO
//I who should I send the message? to FirstViewController
self.delegate = delegate
scriviUnMessaggio(progress: true)
}
func scriviUnMessaggio(progress: Bool){
print("I'm writing a message ...")
delegate?.UpdateProgressBar(progress:progress)
}
Then in viewDidLoad do this
override func viewDidLoad() {
super.viewDidLoad()
let dao = Dao(delegate: self)
}
I have a parent ui view controller and it has a method responsible for printing data to the console:
func printSomeData() {
print("printing some data")
}
It also has a container with embedded UITableViewController. The table itself has a pull to refresh functionality implemented and it prints the string when user pulls the table:
func refresh(refreshControl: UIRefreshControl) {
print("Refreshing!!")
refreshControl.endRefreshing()
}
Now I want to call printsomeData from the refresh method.
This is what I try:
parent UIViewController:
class MainMenu: UIViewController, printing{
func printSomeData() {
print("some date")
}
}
embedded UITableViewController:
protocol printing{
func printSomeData()
}
class MainMenuTableViewController: UITableViewController {
var delegate: printing?
func refresh(refreshControl: UIRefreshControl) {
print("Refreshing!!")
if let _ = delegate{
delegate?.printSomeData()
}
refreshControl.endRefreshing()
}
But now when I pull the table I only see Refreshing!!, there is no way I could see printing some data. What am I doing wrong?
Where are you assigning the delegate?
And write the optional method call as a single line
delegate?.printSomeData()
or like that:
if self.delegate != nil {
self.delegate!.printSomeData()
}
Inside MainMenu
override func viewDidLoad() {
super.viewDidLoad()
// tableViewController is placeholder for `MainMenuTableViewController` reference
tableViewController.delegate = self
}
If i have understand you correctly and the MainMenu has a ContainerView with MainMenuTableViewController than should this solve your problem:
class MainMenu: UIViewController, Printer {
func printSomeData() {
print("some date")
}
}
protocol Printer {
func printSomeData()
}
class MainMenuTableViewController: UITableViewController {
var printer: Printer? {
guard let printer = self.parentViewController as? Printer else {
return nil
}
return printer
}
func refresh(refreshControl: UIRefreshControl) {
print("Refreshing!!")
printer?.printSomeData()
refreshControl.endRefreshing()
}
}