Here is working code which runs fine in Objective-C,
[dataFetcher fetchDataWithRequest:authorizeRequest
delegate:self
didFinishSelector:#selector(didReceiveRequestToken:data:)
didFailSelector:#selector(didFailOAuth:error:)];
It is calling both methods in Objective-C.
But when I use Selector in Swift, it doesn't work.
dataFetcher?.fetchDataWithRequest(requestTokenRequest,
delegate: self,
didFinishSelector:Selector("didReceiveRequestToken:data:"),
didFailSelector: Selector("didFailOAuth:error:"))
Here the method which i'm calling,
func didReceiveRequestToken(ticket:OAServiceTicket,data:NSData){
}
I've already use solutions given on StackOverFlow but they didn't worked for me.
Thanks in Advance.
It`s good a bit change in your method:
func didReceiveRequestToken(ticket:OAServiceTicket,andData data:NSData){
}
The selector is: "didReceiveRequestToken:andData:"
Your call:
dataFetcher?.fetchDataWithRequest(requestTokenRequest,
delegate: self,
didFinishSelector:"didReceiveRequestToken:andData:",
didFailSelector:"didFailOAuth:andError:") // Make the same with this.
Be sure your code have this method.
Possibly, you are forgetting to use #objc in front of your method implementations:
#objc func didReceiveRequestToken(ticket:OAServiceTicket,data:NSData) {
....
This is required when the the target method is not defined inside of a class derived from NSObject (i.e., with pure-Swift classes).
Related
I am trying to use a selector to see if a certain protocol can perform an action. When I try it like this:
protocol Test {
func hello()
func goodBye(a: String)
}
class Tester: NSObject, Test {
override init() {}
func hello() { }
func goodBye(a: String) { }
}
let a: Test = Tester()
let result = a.responds(to: Selector("goodByeWithA:"))
In this case, result evaluates to false.
But if I add the #objc tag to the protocol, it evaluates as true.
#objc protocol Test {
func hello()
func goodBye(a: String)
}
Why is this?
On a side note, I know that it is now recommended to use the #selector syntax and to move away from using strings, but for various reasons, I have to use a string in this case.
EDIT: This only started happening once I migrated my project to Swift 4.2
By default Swift generates code that is only available to other Swift code, but if you need to interact with the Objective-C runtime – all of UIKit, for example – you need to tell Swift what to do.
That’s where the #objc attribute comes in: when you apply it to a class or method it instructs Swift to make those things available to Objective-C as well as Swift code. So, any time you want to call a method from a UIBarButtonItem or a Timer, you’ll need to mark that method using #objc so it’s exposed – both of those, and many others, are Objective-C code.
Don’t worry: if you forget to add #objc when it’s needed, your code simply won’t compile – it’s not something you can forget by accident and introduce a bug.
I'm trying to convert my project's source code from Swift 3 to Swift 4. One warning Xcode is giving me is about my selectors.
For instance, I add a target to a button using a regular selector like this:
button.addTarget(self, action: #selector(self.myAction), for: .touchUpInside)
This is the warning it shows:
Argument of '#selector' refers to instance method 'myAction()' in 'ViewController' that depends on '#objc' attribute inference deprecated in Swift 4
Add '#objc' to expose this instance method to Objective-C
Now, hitting Fix on the error message does this to my function:
// before
func myAction() { /* ... */ }
// after
#objc func myAction() { /* ... */ }
I don't really want to rename all of my functions to include the #objc mark and I'm assuming that's not necessary.
How do I rewrite the selector to deal with the deprecation?
Related question:
The use of Swift 3 #objc inference in Swift 4 mode is deprecated?
The fix-it is correct – there's nothing about the selector you can change in order to make the method it refers to exposed to Objective-C.
The whole reason for this warning in the first place is the result of SE-0160. Prior to Swift 4, internal or higher Objective-C compatible members of NSObject inheriting classes were inferred to be #objc and therefore exposed to Objective-C, therefore allowing them to be called using selectors (as the Obj-C runtime is required in order to lookup the method implementation for a given selector).
However in Swift 4, this is no longer the case. Only very specific declarations are now inferred to be #objc, for example, overrides of #objc methods, implementations of #objc protocol requirements and declarations with attributes that imply #objc, such as #IBOutlet.
The motivation behind this, as detailed in the above linked proposal, is firstly to prevent method overloads in NSObject inheriting classes from colliding with each other due to having identical selectors. Secondly, it helps reduce the binary size by not having to generate thunks for members that don't need to be exposed to Obj-C, and thirdly improves the speed of dynamic linking.
If you want to expose a member to Obj-C, you need to mark it as #objc, for example:
class ViewController: UIViewController {
#IBOutlet weak var button: UIButton!
override func viewDidLoad() {
super.viewDidLoad()
button.addTarget(self, action: #selector(foo), for: .touchUpInside)
}
#objc func foo() {
// ...
}
}
(the migrator should do this automatically for you with selectors when running with the "minimise inference" option selected)
To expose a group of members to Obj-C, you can use an #objc extension:
#objc extension ViewController {
// both exposed to Obj-C
func foo() {}
func bar() {}
}
This will expose all the members defined in it to Obj-C, and give an error on any members that cannot be exposed to Obj-C (unless explicitly marked as #nonobjc).
If you have a class where you need all Obj-C compatible members to be exposed to Obj-C, you can mark the class as #objcMembers:
#objcMembers
class ViewController: UIViewController {
// ...
}
Now, all members that can be inferred to be #objc will be. However, I wouldn't advise doing this unless you really need all members exposed to Obj-C, given the above mentioned downsides of having members unnecessarily exposed.
As Apple Official Documentation. you need to use #objc to call your Selector Method.
In Objective-C, a selector is a type that refers to the name of an
Objective-C method. In Swift, Objective-C selectors are represented by
the Selector structure, and can be constructed using the #selector
expression. To create a selector for a method that can be called from
Objective-C, pass the name of the method, such as
#selector(MyViewController.tappedButton(sender:)). To construct a selector for a property’s Objective-C getter or setter method, pass
the property name prefixed by the getter: or setter: label, such as
#selector(getter: MyViewController.myButton).
As of, I think Swift 4.2, all you need to do is assign #IBAction to your method and avoid the #objc annotation.
let tap = UITapGestureRecognizer(target: self, action: #selector(self.cancel))
#IBAction func cancel()
{
self.dismiss(animated: true, completion: nil)
}
As already mentioned in other answers, there is no way to avoid the #objc annotation for selectors.
But warning mentioned in the OP can be silenced by taking following steps:
Go to Build Settings
Search for keyword #objc
Set the value of Swift 3 #objc interface to Off
below is the screenshot that illustrates the above mentioned steps:
Hope this helps
If you need objective c members in your view controller just add #objcMembers at the top of the view controller. And you can avoid this by adding IBAction in your code.
#IBAction func buttonAction() {
}
Make sure to connect this outlet in storyboard.
I'm working on an iOS application and I'm using swift in that. For more readability and organising functions I've used extensions in my swift file.
// MARK: Class Declaration
class PaymentView
{
// Some stuffs
}
// MARK: Lifecycle methods
extension PaymentView
{
// Overriden for adding gesture recogniser
override func awakeFromNib()
{
super.awakeFromNib()
// Causes a crash when tapped on view
let tapGesture = UITapGestureRecognizer(target: self, action: Selector("paymentViewSelected:"))
self.addGestureRecognizer(tapGesture)
// Works correctly !!!
paymentViewSelected(tapGesture);
}
}
// MARK: Private Methods
extension PaymentView
{
private func paymentViewSelected(sender : UITapGestureRecognizer)
{
print("Method called")
}
}
My issue is when I tap on my view the application crashes with unrecognised selector error. If I remove that private access control specifier from the method it works perfectly.
My question is, I can call the paymentViewSelected: directly from the awakeFromNib regardless the private. But why it is crashing when used as a selector ?
According to Swift AccessControl Reference
Private access restricts the use of an entity to its own defining
source file. Use private access to hide the implementation details of
a specific piece of functionality.
But my class, extension, gesture all are in same file. I think I'm missing some basic key concept here. Please help me to understand the issue.
About Your point : I can call the paymentViewSelected: directly from the awakeFromNib regardless the private. But why it is crashing when used as a selector ?
Its because methods that are marked with private can accessible inside the class, but the object of class cannot call the method marked with private.
In your tapGesture, it is called using object of class automatically, once you tap on the view.
In this case your method is not available because it is marked with private, this is the reason of crash error unrecognised selector.
If you are calling a method from a selector and it is private they cannot be called because the method is called from outside. When you call paymentViewSelected() in the awakeFromNib it is called inside the class. However when it is called via Selector, it is called from outside. like object.paymentViewSelected(). You cannot call private method from outside.
In a custom subclass of GroupOperation, I'm trying to override operationDidFinish(). When I attempt to implement the function in my subclass, I get this error message:
Method does not override any method from its superclass
If I remove the override keyword, I get
Method 'operationDidFinish(:withErrors:)' with Objective-C selector
'operationDidFinish:withErrors:' conflicts with method
'operationDidFinish(:withErrors:)' from superclass 'GroupOperation'
with the same Objective-C selector
Weirdness. I'm pretty sure my method signature is spot on, and I'm not trying to overload an obj-c method, so all should be well. What gives?
For reference, my class looks like this:
class ServerAuthenticationOperation: GroupOperation {
// properties... initializer stuff...
override func operationDidFinish(operation: NSOperation, withErrors errors: [NSError]) {
print("I finished!")
}
}
I assume you're using Swift 2.
Objective-C does not support method overloading, so you have to select a different name for your method. Or, you can try these options:
Rename the method using the #objc(newMethodName:)
Use #nonobjc
Edit:
It seems working for the repo you provided, you can check it here. https://www.dropbox.com/s/hb07u3hyjhjuews/OverrideTest.zip?dl=0
In my code file MyItemVC.swift I have defined the following class and method:
class MyItemVC: UIViewController, UITextViewDelegate {
var timer = NSTimer()
func cycleTimer(toggleOn: Bool) {
if toggleOn == true {
// Timer calls the replaceItem method every 3 seconds
timer = NSTimer.scheduledTimerWithTimeInterval(3, target: self, selector: Selector("replaceItem"), userInfo: nil, repeats: true)
} else {
timer.invalidate() // stop the timer
}
}
}
Elsewhere in this class, I call cycleTimer(true) to start the timer and cycleTimer(false) to stop it.
Now, I also want to use the usual methods in my AppDelegate.swift code file to start and stop the timer when the app moves from active to inactive state. But I'm having trouble calling the cycleTimer method from that class.
I found an answer on Stack Overflow that suggested I could call it like this:
func applicationWillResignActive(application: UIApplication) {
MyItemVC.cycleTimer()
}
But I also need to pass in an argument. So I tried calling it like this:
func applicationWillResignActive(application: UIApplication) {
MyItemVC.cycleTimer(true)
}
But I got this error:
Cannot invoke 'cycleTimer' with an argument list of type '(Bool)'
How can I call this method from the AppDelegate methods while passing in an argument?
Thanks for the help. I realize this must be a very basic question but I'm new to programming and trying to teach myself using Swift. An answer using Swift rather than Obj-C would be greatly appreciated.
You need to use class function to be able to use it this way.
class func cycleTimer(toggleOn: Bool) {
However, I'm not sure about thread safety.
The function you have specified is not a class function. Add class keyword before func keyword.
The changed code:
class func cycleTimer
Note: In the previous versions of Swift you must use the following code (and also in C or other languages):
static func cycleTimer