I have a swift protocol having following delegate method
#objc public protocol CuteDelegate: NSObjectProtocol {
#objc func myCuteFunc(name: NSString)
}
I have declared delegate object in swift as well
weak var delegate : CuteDelegate?
In my objective C controller where I am implementing the above delegate method is as follows
-(void)myCuteFunc:(NSString* )name{
}
But while calling the method in swift controller
self.delegate?.myCuteFunc(name: str as NSString)
I get unrecognized selector sent to instance
Any clue what's the issue
You need to account for the first arguments's name:
Either:
Make your Objective-C function -(void)myCuteFuncWithName:(NSString* )name
Or:
Change your protocol to #objc func myCuteFunc(_ name: NSString) and call it with self.delegate?.myCuteFunc(str)
This is just an artifact of the way Objective-C function names work vs. the way Swift names its arguments. Objective-C has no way of naming the first argument (which is usually described by the function name), so if Swift has a label for the first argument, the convention used is to add With plus the argument name (with the argument name capitalized) to the function name. By adding _, you make the first argument unnamed and that translates better to the Objective-C naming convention.
Related
Is there a way to fix a name of the method implemented in Swift for Objective-C?
A Swift method
static func convert(foo: Foo) -> Bar
in Objective-C becomes
+ (Bar *)convertWithFoo:(Foo *)foo;
while a desired name is
+ (Bar *)convertFoo:(Foo *)foo; // without `With`
Going from Objective-C to Swift I would use the CF_SWIFT_NAME() or NS_SWIFT_NAME() macros.
Yes, you can achieve that with a #objc attribute:
#objc(convertFoo:)
static func convert(foo: Foo) -> Bar { ... }
From "Attributes" in the Swift reference:
The objc attribute optionally accepts a single attribute argument, which consists of an identifier. Use this attribute when you want to expose a different name to Objective-C for the entity the objc attribute applies to. You can use this argument to name classes, enumerations, enumeration cases, protocols, methods, getters, setters, and initializers.
I have to implement this method in a DataSource protocol of an Objective-C library
(nullable id<SomeClass>)someMethod;
I am trying to implement it in my class in Swift, specifically, the AppDelegate, with what I believe keeps equal the signature
extension AppDelegate: LIBDataSource {
#objc func someMethod<T: SomeClass>() -> T? {
return nil // temporary
}
}
The problem is that
As it is, I have a warning and an error. The error says Method cannot be marked #objc because it has generic parameters (the warning below is also shown)
If I remove #objc, the warning says Non-#objc method 'someMethod()' cannot satisfy optional requirement of #objc protocol LIBDataSource
Is there a way to implement a generic Obj-C method of a Obj-C protocol in Swift? Or do I have to do a separate Objective-C class to accomplish this?
The syntax
id<SomeClass>
is nothing to do with lightweight generics, it means "any Objective-C class as long as it conforms the protocol SomeClass". Your method doesn't need to be generic but it does need to return an object that conforms to the SomeClass protocol. It's signature should probably be something like
func someMethod() -> SomeClass?
We are in the process of migrating existing classes from Objective-C to Swift. In a view controller class I am implementing a protocol and attempting to add the view controller as a delegate of an object contained within it. When I try to add 'self' as the object's delegate in Swift I get the following compile error:
Cannot call value of non-function type '((ListenerProtocol) -> Void)?
Here is the existing implementation in Obj-C
#interface SomeViewController : UIViewController <ListenerProtocol> ...
And adding the class as the listener (delegate)
[manager addListener:self];
This works without any problems. But the Swift version fails in what seems like the same code. Here is the Swift version of the same call:
#objc class SomeSwiftViewController: UIViewController, ListenerProtocol ...
And the call to 'addListener'
manager?.addListener(self)
I have verified successfully that 'self' is a ListenerProtocol object at runtime by checking:
if self.conformsToProtocol(ListenerProtocol){
// ...
}
In the object containing the delegate property the addListener method is defined in Objective-C as follows:
- (void)addListener:(id<ListenerProtocol>)listener {
// ...
}
The Swift class completely implements all of the methods defined in ListenerProtocol. I can't understand why this doesn't work in Swift. Can anyone make a suggestion? Thanks!
The problem is not with ListenerProtocol, it's with the protocol that manager implements. Judging by the type, addListener appears to be provided as an optional method. Notice the question mark at the end of the function type:
((ListenerProtocol) -> Void)?
This usually happens with (actually, I think that it only happens with) Objective-C optional protocol methods.
You should be able to write manager?.addListener?(self) or manager?.addListener!(self).
I have some swift function in a swift object of type Helper that returns an object of class Parameter. Parameter is defined as:
class Parameter { }
And my function like this:
func getParameter() -> Parameter { }
When accessing the methods from Helper only those that don't return anything show up. However, getParameter is uncallable. My assumption is that its return type is invisible to Obj-C. Must Parameter extend NSObject in order to work?
If you want to have your Swift classes available to Objective-C, they must inherit from an Objective-C bridged class. That's why your ViewControllers are always available, and for free-standing classes, you must make their superclass NSObject. You can also specifically note in code they are bridged by marking them: #objc class Parameter: NSObject{}
I have the following protocol definition:
#objc protocol PersonDataStore {
func findPersonWithId(remoteId: String, completionBlock: ((Person) -> Void)!)
// ...
}
The error I get is that the second parameter cannot be represented in Objective-C. I researched the blocks/closures topic but I have a hard time getting my head around it since it is so conceptually different.
Is this just a matter of syntax or is it really not possible to define an Objective-C protocol with a closure in Swift?
I believe your problem is that your class Person is not a subclass of NSObject. Add #objc to the declaration of your Person class or make it a subclass of NSObject and your protocol definition should work.