I read quite a few questions and answers no this problem. Some are for Ojective C. Some are for iOS. The ones that were close to what I need didn't work.
I've set up a protocol for delegation. It doesn't work. The problem is that delegate variable isn't set. I need the reference to an active controller.
Delegator
protocol SwitchTabDelegate: class {
func selectTab(tab: Int)
}
class ViewController: NSViewController {
weak var delegate: SwitchTabDelegate?
override func viewDidLoad() {
super.viewDidLoad()
}
#IBAction func selectCompositions(_ sender: NSButton) {
if let delegate = self.delegate {
delegate.selectTab(tab: 2)
}
else {
print("self.delegate is nil")
}
print("delegate called")
}
}
Delegatee
class TabViewController: NSTabViewController, SwitchTabDelegate {
var viewController : ViewController?;
override func viewDidLoad() {
super.viewDidLoad()
//viewController = storyboard?.instantiateController(withIdentifier: "viewController") as? ViewController
// viewController?.delegate = self
// print(viewController)
}
func selectTab(tab: Int) {
print("In the delegate")
switchToDataTab()
}
func switchToDataTab() {
Timer.scheduledTimer(timeInterval: 0.2, target: self,
selector: #selector(switchToDataTabCont),
userInfo: nil, repeats: false)
}
func switchToDataTabCont(){
self.selectedTabViewItemIndex = 2
}
}
The delegatee is the main NSViewContoller. On the storyboard, it contains two buttons and a Container view controller. Embedded in the container view controller is the TabViewController, the delegatee. You can see in the delegatee where I tried to get a reference. It does get a reference, presumably to the newly instantiated instance. I need a reference to the original view controller that was spun up when the application started.
Answer
I added the following code to the delegator:
override func prepare(for segue: NSStoryboardSegue, sender: Any?) {
let controller = segue.destinationController as! TabViewController
self.delegate = controller as SwitchTabDelegate
}
That's not how it should work following the design pattern. The delegator should have no knowledge of the delegatee. I've spent way too much time on this issue so a hack is going to do.
When using storyboards, you want to "push" references to children when they are created vs. pulling them from an upstream controller. This is what -prepareForSegue:sender: is used for.
Related
I'm apparently designing a drag and drop dropbox which can either select files by clicking it or dragging and dropping the files on it, and I want the selected files to be visible in a table next to it. My design logic is that whenever the user selects files from an NSOpenPanel, it passes the selected file paths into the CoreData and then an array retrieves them one by one from the CoreData, and finally, update the NSTableView's content by using reloadData().
Basically, my problem is that whenever I try to call ViewController().getDroppedFiles() from DropboxButton class, I always get a Fatal error: unexpectedly found nil while unwrapping an optional value.
My ViewController.swift:
import Cocoa
class ViewController: NSViewController, NSTableViewDataSource, NSTableViewDelegate {
override func viewDidLoad() {
super.viewDidLoad()
getDroppedFiles()
}
#IBOutlet weak var DroppedFilesTableView: NSTableView!
var droppedFiles: [DroppedFiles] = [] // Core Data class definition: DroppedFiles
func numberOfRows(in tableView: NSTableView) -> Int {
return droppedFiles.count
}
func tableView(_ tableView: NSTableView, viewFor tableColumn: NSTableColumn?, row: Int) -> NSView? {
let droppedFilesCollection = droppedFiles[row]
if (tableView?.identifier)!.rawValue == "fileNameColumn" {
if let fileNameCell = tableView.makeView(withIdentifier: NSUserInterfaceItemIdentifier(rawValue: "fileNameCell")) as? NSTableCellView {
fileNameCell.textField?.stringValue = droppedFilesCollection.fileName!
return fileNameCell
}
} else if (tableView?.identifier)!.rawValue == "filePathColumn" {
if let filePathCell = tableView.makeView(withIdentifier: NSUserInterfaceItemIdentifier(rawValue: "filePathCell")) as? NSTableCellView {
filePathCell.textField?.stringValue = droppedFilesCollection.filePath!
return filePathCell
}
}
return nil
}
#IBAction func DropboxClicked(_ sender: NSButton) {
// selected file paths
for filePath in selectedFilePaths {
if let context = (NSApp.delegate as? AppDelegate)?.persistentContainer.viewContext {
let droppedFilesData = DroppedFiles(context: context)
droppedFilesData.fileName = getFileName(withPath: filePath)
droppedFilesData.filePath = filePath
do {
try context.save()
} catch {
print("Unable to save core data.")
}
}
getDroppedFiles()
}
}
func getDroppedFiles() {
if let context = (NSApp.delegate as? AppDelegate)?.persistentContainer.viewContext {
do {
try droppedFiles = context.fetch(DroppedFiles.fetchRequest())
} catch {
print("Unable to fetch core data.")
}
}
DroppedFilesTableView.reloadData() // Fatal Error: unexpectedly found nil while unwrapping an optional value (whenever I call this function in other class)
}
}
I'm using a push button (NSButton) as the dropbox (it has its own class), which can easily be clicked and also supports dragging options.
My DropboxButton.swift:
import Cocoa
class DropboxButton: NSButton {
required init?(coder: NSCoder) {
super.init(coder: coder)
registerForDraggedTypes([NSPasteboard.PasteboardType.URL, NSPasteboard.PasteboardType.fileURL])
}
override func draggingEntered(_ sender: NSDraggingInfo) -> NSDragOperation {
// some other codes
return .copy
}
override func draggingExited(_ sender: NSDraggingInfo?) {
// some other codes
}
override func draggingEnded(_ sender: NSDraggingInfo) {
// some other codes
}
override func performDragOperation(_ sender: NSDraggingInfo) -> Bool {
guard let pasteboard = sender.draggingPasteboard.propertyList(forType: NSPasteboard.PasteboardType(rawValue: "NSFilenamesPboardType")) as? NSArray,
let filePaths = pasteboard as? [String] else {
return false
}
for filePath in filePaths {
if let context = (NSApp.delegate as? AppDelegate)?.persistentContainer.viewContext {
let droppedFilesData = DroppedFiles(context: context)
droppedFilesData.fileName = getFileName(withPath: filePath)
droppedFilesData.filePath = filePath
do {
try context.save()
} catch {
print("Unable to save core data.")
}
}
ViewController().getDroppedFiles() // found nil with reloadData() in ViewController.swift
}
return true
}
}
And this is my interface and code logic:
So, how can I reloadData() for the table view in my ViewController class from another class (DropboxButton: NSButton) so that whenever the user drags and drops files into the dropbox, the table view will reload?
P.S. To get this done means a lot to me, I really need to get this fixed in a short time, is there anyone can spend some time and help me?
You need to call getDroppedFiles() on a loaded instance of ViewController.
With ViewController().getDroppedFiles() you're creating a new instance of ViewController that is not shown anywhere (so controls are not initialized resulting in the nil error).
I found this solution useful for my case.
I used observer to pass through data and call functions from other controller classes, now I understand that I was creating a new instance of ViewController which is not loaded. Here is my code:
ViewController.swift:
class ViewController: NSViewController {
// other codes
override func viewDidLoad() {
super.viewDidLoad()
NotificationCenter.default.addObserver(self, selector: #selector(getDroppedFiles), name: NSNotification.Name(rawValue: "reloadTableViewData"), object: nil)
}
#objc func getDroppedFiles() {
DroppedFilesTableView.reloadData()
}
}
DropboxButton.swift:
class DropboxButton: NSButton {
// other codes
override func performDragOperation(_ sender: NSDraggingInfo) -> Bool {
// other codes
NotificationCenter.default.post(name: NSNotification.Name(rawValue: "reloadTableViewData"), object: nil)
return true
}
}
And now, everything works perfectly, I can even add an userInfo: to pass data between files and classes.
Found a similar question to mine(this),
but my issues seems to be a bit more associated with view hierarchy.
I have a NSTextView, then as sibling views, several other NSViews on top of it.
Similar to the question linked above, I setup a tracking area, and applied the cursor as such:
class CursorChangingView: NSView {
override func updateTrackingAreas() {
let trackingArea = NSTrackingArea(rect:
}
override func cursorUpdate(event: NSEvent) {
NSCursor.arrowCursor().set()
}
}
It does seem to work when hovering, but immediately goes back to the IBeam Cursor, which is the default cursor for NSTextViews under this CursorChangingView.
Is this the proper way of applying changing the cursor when hovering over a certain NSView, and is the NSTextView under it overriding my overrriding?
All you need is to subclass a custom view, override awakeFromNib method, add the custom tracking area for [.mouseMoved, .activeAlways] events: NSTrackingArea Info there. There is no need to override resetCursorRects and/or updateTrackingAreas. All you need is to override mouseMoved method and set the desired cursor there:
Note about discardCursorRects method:
From the docs
You need never invoke this method directly
Xcode 9 • Swift 4
import Cocoa
class CursorChangingView: NSView {
override func awakeFromNib() {
addTrackingArea(NSTrackingArea(rect: bounds, options: [.activeAlways, .mouseMoved], owner: self, userInfo: nil))
wantsLayer = true
layer?.backgroundColor = NSColor.cyan.cgColor
layer?.borderColor = NSColor.black.cgColor
layer?.borderWidth = 1
}
#objc override func mouseMoved(with theEvent: NSEvent) {
NSCursor.pointingHand.set()
}
}
Sample
Thanks #Leo Dabus for your answer,
but I managed to solve it, so I will post my answer too.
In my case, for some reason, mouseEntered and mouseEntered did not work at all.
So here is my code that finally got it to work:
class CursorChangingView: NSView {
let trackingArea: NSTrackingArea?
func setupTracking() {
if self.trackingArea == nil {
self.trackingArea = NSTrackingArea(rect: self.bounds, options: NSTrackingAreaOptions.ActiveAlways | NSTrackingAreaOptions.MouseMoved | NSTrackingAreaOptions.CursorUpdate | NSTrackingAreaOptions.MouseEnteredAndExited | NSTrackingAreaOptions.ActiveInActiveApp, owner: self, userInfo: nil)
self.addTrackingArea(self.trackingArea!)
}
}
override func updateTrackingAreas() {
self.trackingArea = NSTrackingArea(rect: self.bounds, options: NSTrackingAreaOptions.ActiveAlways | NSTrackingAreaOptions.CursorUpdate | NSTrackingAreaOptions.MouseEnteredAndExited | NSTrackingAreaOptions.ActiveInActiveApp, owner: self, userInfo: nil)
self.addTrackingArea(self.trackingArea!)
}
override func resetCursorRects() {
self.discardCursorRects()
self.addCursorRect(self.bounds, cursor: NSCursor.arrowCursor())
}
override func mouseMoved(theEvent: NSEvent) {
NSCursor.arrowCursor().set()
}
}
It might be a little excessive, but worked, so will share this as my own solution.
A few important notes:
Be careful calling super on your mouseMoved or similar events, or the cursor might just get reset by the base class implementation.
Only reset your tracking area when the parent view size changes; if you try to do this by overriding layout() it's going to be happening all the time which is not great
Here's an example class that you can just use as a base class in your storyboards.
Swift 4 code:
import Cocoa
final class MouseTrackingTextView: NSTextView {
// MARK: - Lifecycle
override func awakeFromNib() {
setupTrackingArea()
}
// MARK: - Resizing
// Call this in your controller's `viewDidLayout`
// so it only gets called when the view resizes
func superviewResized() {
resetTrackingArea()
}
// MARK: - Mouse Events
override func resetCursorRects() {
addCursorRect(bounds, cursor: cursorType)
}
override func mouseMoved(with event: NSEvent) {
cursorType.set()
}
// MARK: - Private Properties
private var currentTrackingArea: NSTrackingArea?
private var cursorType: NSCursor {
return isEditable ? .iBeam : .pointingHand
}
// MARK: - Private API
private func setupTrackingArea() {
let trackingArea = NSTrackingArea(rect: bounds,
options: [.activeAlways, .mouseMoved],
owner: self, userInfo: nil)
currentTrackingArea = trackingArea
addTrackingArea(trackingArea)
}
private func resetTrackingArea() {
if let trackingArea = currentTrackingArea {
removeTrackingArea(trackingArea)
}
setupTrackingArea()
}
}
I'm trying to use a protocol / delegate in swift, and while I'm not getting any errors it seems that my delegate is not being created. It is returning nil on me, and I'm not sure why.
Here is my code
Class 1
import UIKit
protocol GameViewSliding{
func slideGameView()
}
class GameDetailsViewController: UIViewController {
var delegate:GameViewSliding?
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
#IBAction func showOptions(sender: AnyObject) {
println("button pressed")
println(delegate)
delegate?.slideGameView()
}
}
Class 2 that conforms to the protocol
import UIKit
var currentHoleNumber:Int = 0
var parThree = false;
var parFive = false;
class GameViewController: UIViewController, GameViewSliding{
var gameDetailsVC:GameDetailsViewController = GameDetailsViewController()
override func viewDidLoad() {
super.viewDidLoad()
println("inside the game class")
gameDetailsVC.delegate = self
}
func slideGameView(){
println("this is from the root controller")
}
}
The problem is likely in the code you are not showing here. In prepareForSegue you usually want to set the delegate on the destination view controller.
Essentially you are setting it on an instance of the class that you are creating, but that isn't the instance that is actually shown. So the instance that is shown has no delegate.
Remove your local var of the second controller, and the setting of the delegate in the view did load and simply set it on the destination in prepare for segue and I bet it will work perfectly.
I have been looking for an answer for this, but have only found answers for segues.
I have viewController1 with a button that segues to viewController2. There is no code for this, I set it up through Interface builder. On viewController2 I have a button that dismisses itself with
self.dismissViewControllerAnimated(true, completion, nil)
I want to pass a string from viewController2 back to viewController1 when the view is dismissed. How do I go about doing this? Also, I am using swift.
Thanks in advance!
There are two common patterns, both of which eliminate the need for viewController2 to know explicitly about viewController1 (which is great for maintainability):
Create a delegate protocol for your for viewController2 and set viewController1 as the delegate. Whenever you want to send data back to viewController1, have viewController2 send the "delegate" the data
Setup a closure as a property that allows passing the data. viewController1 would implement that closure on viewController2 when displaying viewController2. Whenever viewController2 has data to pass back, it would call the closure. I feel that this method is more "swift" like.
Here is some example code for #2:
class ViewController2 : UIViewController {
var onDataAvailable : ((data: String) -> ())?
func sendData(data: String) {
// Whenever you want to send data back to viewController1, check
// if the closure is implemented and then call it if it is
self.onDataAvailable?(data: data)
}
}
class ViewController1 : UIViewController {
func doSomethingWithData(data: String) {
// Do something with data
}
override func prepareForSegue(segue: UIStoryboardSegue!, sender: AnyObject!) {
// When preparing for the segue, have viewController1 provide a closure for
// onDataAvailable
if let viewController = segue.destinationViewController as? ViewController2 {
viewController.onDataAvailable = {[weak self]
(data) in
if let weakSelf = self {
weakSelf.doSomethingWithData(data)
}
}
}
}
}
I used the code from the first answer in a transition between controllers WITHOUT prepareForSegue and worked for me as well.
Here's the sample code.
The First View Controller:
#IBAction func dpAgendaClick(sender:UIBarButtonItem) {
///instantiating view controller with identifier
if let datePickerViewController = storyboard?.instantiateViewControllerWithIdentifier("DatePickerViewController")
as? DatePickerViewController {
///bring instantiated view controller to front
self.presentViewController(datePickerViewController, animated: true, completion: nil)
///wrapping the data returned
datePickerViewController.onDataFiltroAvailable = {[weak self]
(dataFiltro) in
if let weakSelf = self {
///use dataFiltro here
}
}
The second View Controller:
var onDataFiltroAvailable: ((dataFiltro: String) -> ())?
///private var
var dataFiltro: String = ""
///the returning data is obtained on the datePickerChanged event
#IBAction func datePickerChanged(sender: UIDatePicker) {
let dateFormatter = NSDateFormatter()
dateFormatter.dateStyle = NSDateFormatterStyle.ShortStyle
dateFormatter.dateFormat = "yyyy-MM-dd"
dataFiltro = dateFormatter.stringFromDate(datePicker.date)
}
///dismiss the controller on button click
#IBAction func dpOkClick(sender: UIButton) {
///"returning" the data
self.onDataFiltroAvailable?(dataFiltro: dataFiltro)
dismissViewControllerAnimated(true, completion: nil)
}
(Swift 2.1, Xcode 7, iOS9)
If you don't want it to be tightly coupled only between 2 ViewControllers,
You can also use the Notification Design Pattern (Post & Observe), which is mainly used to pass on the same object/information from one VC to multiple View Controllers.
For your scenario :
In VC2.swift :
#IBAction func BackBtn(sender: UIButton) {
NSNotificationCenter.defaultCenter().postNotificationName("ThisIsTheMessage", object: nil, userInfo:["ObjectBeingSent":yourObject])
}
And in VC1.swift :
override func viewDidLoad() {
super.viewDidLoad()
NSNotificationCenter.defaultCenter().addObserver(self, selector: Selector("yourFunction:"), name: "ThisIsTheMessage", object: nil)
}
func yourFunction(theNotification : NSNotification) {
if let extractInfo = theNotification.userInfo {
//code to use the object sent from VC2, by extracting the object details
}
}
Common Practise is:
Pass data forward -> Use PrepareForSegue
Pass data backward to the previous View Controller-> Protocol and Delegation
Pass data across multiple View Controllers -> Notifications : Post and Observe(observe in all the View controllers where you are using the object details)
How does one go about making a delegate, i.e. NSUserNotificationCenterDelegate in swift?
Here's a little help on delegates between two view controllers:
Step 1: Make a protocol in the UIViewController that you will be removing/will be sending the data.
protocol FooTwoViewControllerDelegate:class {
func myVCDidFinish(_ controller: FooTwoViewController, text: String)
}
Step2: Declare the delegate in the sending class (i.e. UIViewcontroller)
class FooTwoViewController: UIViewController {
weak var delegate: FooTwoViewControllerDelegate?
[snip...]
}
Step3: Use the delegate in a class method to send the data to the receiving method, which is any method that adopts the protocol.
#IBAction func saveColor(_ sender: UIBarButtonItem) {
delegate?.myVCDidFinish(self, text: colorLabel.text) //assuming the delegate is assigned otherwise error
}
Step 4: Adopt the protocol in the receiving class
class ViewController: UIViewController, FooTwoViewControllerDelegate {
Step 5: Implement the delegate method
func myVCDidFinish(_ controller: FooTwoViewController, text: String) {
colorLabel.text = "The Color is " + text
controller.navigationController.popViewController(animated: true)
}
Step 6: Set the delegate in the prepareForSegue:
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if segue.identifier == "mySegue" {
let vc = segue.destination as! FooTwoViewController
vc.colorString = colorLabel.text
vc.delegate = self
}
}
And that should work. This is of course just code fragments, but should give you the idea. For a long explanation of this code you can go over to my blog entry here:
segues and delegates
If you are interested in what's going on under the hood with a delegate I did write on that here:
under the hood with delegates
Delegates always confused me until I realized that a delegate is just a class that does some work for another class. It's like having someone else there to do all the dirty work for you that you don't want to do yourself.
I wrote a little story to illustrate this. Read it in a Playground if you like.
Once upon a time...
// MARK: Background to the story
// A protocol is like a list of rules that need to be followed.
protocol OlderSiblingDelegate: class {
// The following command (ie, method) must be obeyed by any
// underling (ie, delegate) of the older sibling.
func getYourNiceOlderSiblingAGlassOfWater()
}
// MARK: Characters in the story
class BossyBigBrother {
// I can make whichever little sibling is around at
// the time be my delegate (ie, slave)
weak var delegate: OlderSiblingDelegate?
func tellSomebodyToGetMeSomeWater() {
// The delegate is optional because even though
// I'm thirsty, there might not be anyone nearby
// that I can boss around.
delegate?.getYourNiceOlderSiblingAGlassOfWater()
}
}
// Poor little sisters have to follow (or at least acknowledge)
// their older sibling's rules (ie, protocol)
class PoorLittleSister: OlderSiblingDelegate {
func getYourNiceOlderSiblingAGlassOfWater() {
// Little sis follows the letter of the law (ie, protocol),
// but no one said exactly how she had to respond.
print("Go get it yourself!")
}
}
// MARK: The Story
// Big bro is laying on the couch watching basketball on TV.
let bigBro = BossyBigBrother()
// He has a little sister named Sally.
let sally = PoorLittleSister()
// Sally walks into the room. How convenient! Now big bro
// has someone there to boss around.
bigBro.delegate = sally
// So he tells her to get him some water.
bigBro.tellSomebodyToGetMeSomeWater()
// Unfortunately no one lived happily ever after...
// The end.
In review, there are three key parts to making and using the delegate pattern.
the protocol that defines what the worker needs to do
the boss class that has a delegate variable, which it uses to tell the worker class what to do
the worker class that adopts the protocol and does what is required
Real life
In comparison to our Bossy Big Brother story above, delegates are often used for the following practical applications:
Communication: one class needs to send some information to another class.
Code example 1: sending data from one view controller to another
Code example 2: sending text input from a custom keyboard to a text field
Customization: one class wants to allow another class to customize it.
The great part is that these classes don't need to know anything about each other beforehand except that the delegate class conforms to the required protocol.
I highly recommend reading the following two articles. They helped me understand delegates even better than the documentation did.
What is Delegation? – A Swift Developer’s Guide
How Delegation Works – A Swift Developer’s Guide
One more note
Delegates that reference other classes that they do not own should use the weak keyword to avoid strong reference cycles. See this answer for more details.
It is not that different from obj-c.
First, you have to specify the protocol in your class declaration, like following:
class MyClass: NSUserNotificationCenterDelegate
The implementation will look like following:
// NSUserNotificationCenterDelegate implementation
func userNotificationCenter(center: NSUserNotificationCenter, didDeliverNotification notification: NSUserNotification) {
//implementation
}
func userNotificationCenter(center: NSUserNotificationCenter, didActivateNotification notification: NSUserNotification) {
//implementation
}
func userNotificationCenter(center: NSUserNotificationCenter, shouldPresentNotification notification: NSUserNotification) -> Bool {
//implementation
return true
}
Of course, you have to set the delegate. For example:
NSUserNotificationCenter.defaultUserNotificationCenter().delegate = self;
I got few corrections to post of #MakeAppPie
First at all when you are creating delegate protocol it should conform to Class protocol. Like in example below.
protocol ProtocolDelegate: class {
func myMethod(controller:ViewController, text:String)
}
Second, your delegate should be weak to avoid retain cycle.
class ViewController: UIViewController {
weak var delegate: ProtocolDelegate?
}
Last, you're safe because your protocol is an optional value. That means its "nil" message will be not send to this property. It's similar to conditional statement with respondToselector in objC but here you have everything in one line:
if ([self.delegate respondsToSelector:#selector(myMethod:text:)]) {
[self.delegate myMethod:self text:#"you Text"];
}
Above you have an obj-C example and below you have Swift example of how it looks.
delegate?.myMethod(self, text:"your Text")
Here's a gist I put together. I was wondering the same and this helped improve my understanding. Open this up in an Xcode Playground to see what's going on.
protocol YelpRequestDelegate {
func getYelpData() -> AnyObject
func processYelpData(data: NSData) -> NSData
}
class YelpAPI {
var delegate: YelpRequestDelegate?
func getData() {
println("data being retrieved...")
let data: AnyObject? = delegate?.getYelpData()
}
func processYelpData(data: NSData) {
println("data being processed...")
let data = delegate?.processYelpData(data)
}
}
class Controller: YelpRequestDelegate {
init() {
var yelpAPI = YelpAPI()
yelpAPI.delegate = self
yelpAPI.getData()
}
func getYelpData() -> AnyObject {
println("getYelpData called")
return NSData()
}
func processYelpData(data: NSData) -> NSData {
println("processYelpData called")
return NSData()
}
}
var controller = Controller()
DELEGATES IN SWIFT 2
I am explaining with example of Delegate with two viewControllers.In this case, SecondVC Object is sending data back to first View Controller.
Class with Protocol Declaration
protocol getDataDelegate {
func getDataFromAnotherVC(temp: String)
}
import UIKit
class SecondVC: UIViewController {
var delegateCustom : getDataDelegate?
override func viewDidLoad() {
super.viewDidLoad()
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
#IBAction func backToMainVC(sender: AnyObject) {
//calling method defined in first View Controller with Object
self.delegateCustom?.getDataFromAnotherVC(temp: "I am sending data from second controller to first view controller.Its my first delegate example. I am done with custom delegates.")
self.navigationController?.popViewControllerAnimated(true)
}
}
In First ViewController Protocol conforming is done here:
class ViewController: UIViewController, getDataDelegate
Protocol method definition in First View Controller(ViewController)
func getDataFromAnotherVC(temp : String)
{
// dataString from SecondVC
lblForData.text = dataString
}
During push the SecondVC from First View Controller (ViewController)
let objectPush = SecondVC()
objectPush.delegateCustom = self
self.navigationController.pushViewController(objectPush, animated: true)
First class:
protocol NetworkServiceDelegate: class {
func didCompleteRequest(result: String)
}
class NetworkService: NSObject {
weak var delegate: NetworkServiceDelegate?
func fetchDataFromURL(url : String) {
delegate?.didCompleteRequest(result: url)
}
}
Second class:
class ViewController: UIViewController, NetworkServiceDelegate {
let network = NetworkService()
override func viewDidLoad() {
super.viewDidLoad()
network.delegate = self
network.fetchDataFromURL(url: "Success!")
}
func didCompleteRequest(result: String) {
print(result)
}
}
Very easy step by step (100% working and tested)
step1: Create method on first view controller
func updateProcessStatus(isCompleted : Bool){
if isCompleted{
self.labelStatus.text = "Process is completed"
}else{
self.labelStatus.text = "Process is in progress"
}
}
step2: Set delegate while push to second view controller
#IBAction func buttonAction(_ sender: Any) {
let secondViewController = self.storyboard?.instantiateViewController(withIdentifier: "secondViewController") as! secondViewController
secondViewController.delegate = self
self.navigationController?.pushViewController(secondViewController, animated: true)
}
step3: set delegate like
class ViewController: UIViewController,ProcessStatusDelegate {
step4: Create protocol
protocol ProcessStatusDelegate:NSObjectProtocol{
func updateProcessStatus(isCompleted : Bool)
}
step5: take a variable
var delegate:ProcessStatusDelegate?
step6: While go back to previous view controller call delegate method so first view controller notify with data
#IBAction func buttonActionBack(_ sender: Any) {
delegate?.updateProcessStatus(isCompleted: true)
self.navigationController?.popViewController(animated: true)
}
#IBAction func buttonProgress(_ sender: Any) {
delegate?.updateProcessStatus(isCompleted: false)
self.navigationController?.popViewController(animated: true)
}
Simple Example:
protocol Work: class {
func doSomething()
}
class Manager {
weak var delegate: Work?
func passAlong() {
delegate?.doSomething()
}
}
class Employee: Work {
func doSomething() {
print("Working on it")
}
}
let manager = Manager()
let developer = Employee()
manager.delegate = developer
manager.passAlong() // PRINTS: Working on it
Delegates are a design pattern that allows one object to send messages to another object when a specific event happens.
Imagine an object A calls an object B to perform an action. Once the action is complete, object A should know that B has completed the task and take necessary action, this can be achieved with the help of delegates!
Here is a tutorial implementing delegates step by step in swift 3
Tutorial Link
Here is real life delegate scenario
Lets make our own UITextField and UITextFieldDelegate
// THE MYSTERIOUS UITEXTFIELD
protocol UITextFieldDelegate {
func textFieldDidChange(_ textField: UITextField) -> Void
}
class UITextField {
var delegate: UITextFieldDelegate?
private var mText: String?
var text: String? {
get {
return mText
}
}
init(text: String) {
}
init() {
}
func setText(_ text: String) {
mText = text
delegate?.textFieldDidChange(self)
}
}
// HERE IS MY APP
class Main {
let textfield = UITextField()
func viewDidLoad() {
print("viewDidLoad")
textfield.delegate = self
textfield.setText("Hello")
}
}
extension Main: UITextFieldDelegate {
func textFieldDidChange(_ textField: UITextField) {
print(textField.text ?? "No string")
}
}
let main = Main()
main.viewDidLoad()
Here Simple Code Example of Delegate:
//MARK: - Protocol ShowResult
protocol ShowResult: AnyObject {
func show(value: Int)
}
//MARK: - MyOperation Class
class MyOperation {
weak var delegate: ShowResult?
func sum(fNumber: Int, sNumber: Int) {
delegate?.show(value: fNumber + sNumber)
}
}
//MARK: - ViewController Class
class ViewController: UIViewController,ShowResult {
var myOperation: MyOperation?
override func viewDidLoad() {
super.viewDidLoad()
loadMyOperation()
myOperation?.delegate = self
myOperation?.sum(fNumber: 100, sNumber: 20)
}
private func loadMyOperation() {
if myOperation == nil {
myOperation = MyOperation()
}
}
func show(value: Int) {
print("value: \(value)")
}
}
The solutions above seemed a little coupled and at the same time avoid reuse the same protocol in other controllers, that's why I've come with the solution that is more strong typed using generic type-erasure.
#noreturn public func notImplemented(){
fatalError("not implemented yet")
}
public protocol DataChangedProtocol: class{
typealias DataType
func onChange(t:DataType)
}
class AbstractDataChangedWrapper<DataType> : DataChangedProtocol{
func onChange(t: DataType) {
notImplemented()
}
}
class AnyDataChangedWrapper<T: DataChangedProtocol> : AbstractDataChangedWrapper<T.DataType>{
var base: T
init(_ base: T ){
self.base = base
}
override func onChange(t: T.DataType) {
base.onChange(t)
}
}
class AnyDataChangedProtocol<DataType> : DataChangedProtocol{
var base: AbstractDataChangedWrapper<DataType>
init<S: DataChangedProtocol where S.DataType == DataType>(_ s: S){
self.base = AnyDataChangedWrapper(s)
}
func onChange(t: DataType) {
base.onChange(t)
}
}
class Source : DataChangedProtocol {
func onChange(data: String) {
print( "got new value \(data)" )
}
}
class Target {
var delegate: AnyDataChangedProtocol<String>?
func reportChange(data:String ){
delegate?.onChange(data)
}
}
var source = Source()
var target = Target()
target.delegate = AnyDataChangedProtocol(source)
target.reportChange("newValue")
output: got new value newValue
In swift 4.0
Create a delegate on class that need to send some data or provide some functionality to other classes
Like
protocol GetGameStatus {
var score: score { get }
func getPlayerDetails()
}
After that in the class that going to confirm to this delegate
class SnakesAndLadders: GetGameStatus {
func getPlayerDetails() {
}
}
In swift 5
I am a beginner, I think this is easiest way to understand in practical scenario
Note:Any improvisations are most appreciated
protocol APIService {
func onSuccessResponse() -> AnyObject
func onFailureResponse() -> AnyObject
}
class APIHelper{
var delegate : APIService?
func postUsersDataAPI() {
//assuming API communication is success
if(success){
let _: AnyObject? = delegate?.onSuccessResponse()
}else if(failure){
let _: AnyObject? = delegate?.onFailureResponse()
}
}
func getAllUsersAPI() {
//assuming API communication is success
if(success){
let _: AnyObject? = delegate?.onSuccessResponse()
}else if(failure){
let _: AnyObject? = delegate?.onFailureResponse()
}
}
}
class ViewController:UIViewController,APIService {
func onSuccessResponse() -> AnyObject {
print("onSuccessResponse") as AnyObject
}
func onFailureResponse() -> AnyObject {
print("onFailureResponse") as AnyObject
}
#IBAction func clickBtnToPostUserData(_ sender: Any) {
let apiHelper = APIHelper()
apiHelper.delegate = self
apiHelper.postAPI()
}