Using XCode 10.1 / Swift 4.2.
I'm trying to assign an object that conforms to a Swift protocol to an Objective-C pointer. The following code is a minimal example that compiles and works as expected, but it gives me the following warnings:
If assigning to a local variable: Incompatible pointer types initializing 'NSObject<Animal> *__strong' with an expression of type 'id<Animal> _Nullable'
If assigning to a stored property:
Incompatible pointer types assigning to 'NSObject<Animal> *' from 'id<Animal> _Nullable'
Any idea on how to address that warning without just silencing it?
Swift code:
#objc protocol Animal {
var name: String { get }
}
#objc class Pig: NSObject, Animal {
var name: String = "pig"
}
#objc class Cow: NSObject, Animal {
var name: String = "cow"
}
#objc class Farm: NSObject {
static func getAnimal(name: String) -> Animal? {
// return some animal or nil
}
}
Objective-C code:
// This code returns a valid pointer to a Pig object
// that is usable in objective-c, but it also triggers
// the warning described above
NSObject<Animal>* animal = [Farm getAnimalWithName:#"pig"];
Specify that every Animal implementer also implements NSObject's interface: #objc protocol Animal : NSObjectProtocol
You could also change the type of the variable in ObjC to id<Animal>.
I'm writing an API in Objective-C and would like it to play nicely in Swift. I'm having trouble getting "for..in" syntax working though. I think I need to implement the Sequence protocol, but I can't find any examples doing this from Objective-C. Just referencing Sequence gives me error: no type or protocol named 'Sequence'. Is there a special #import to get access to it or something?
I tried implementing the NSFastEnumeration protocol, thinking maybe it'd magically convert to Sequence in Swift, but that didn't work.
///// Obj-C Code
#interface Foo : NSObject<NSFastEnumeration>
...
#end
///// Swift Code
var foo: Foo = Foo()
// ERROR: Type 'Foo' does not conform to protocol 'Sequence'
for y in foo {
print("Got a y.")
}
EDIT: It looks like inheriting from NSEnumerator gets me closer, but doesn't quite work either:
///// Obj-C Code
#interface Foo : NSEnumerator<NSString *>
...
#end
///// Swift Code
// ERROR: 'NSFastEnumerationIterator.Element' (aka 'Any') is not convertible to 'String'
for y: String in foo {
print("Got \(y)")
}
EDIT 2: I still don't have a good solution and have logged a bug: https://bugs.swift.org/browse/SR-2801
The Swift extension of Foundation includes some support for making classes that adopt NSFastEnumeration also support the Swift Sequence protocol... but not automatically.
One way to do it is to extend your ObjC type in Swift and pass through to the NSFastEnumerationIterator type:
extension Foo: Sequence {
public func makeIterator() -> NSFastEnumerationIterator {
return NSFastEnumerationIterator(self)
}
}
NSFastEnumerationIterator (and all forms of ObjC enumeration) are type erasing, though, so they don't provide any insight on the element type you're iterating through. That means that you can do this (after adding the above extension):
var foo: Foo = Foo()
for y in foo {
print("Got a y.")
}
... but the static type of y is always Any. If you want typed access to the members of foo, you'll need a cast or a filtered loop:
for y in foo where y is String {
print("Got \(y)")
}
Sadly, if your class adopts ObjC generics, there doesn't seem to be a way to make this work — you'll get an error "Extension of a generic Objective-C class cannot access the class's generic parameters at runtime", even if you adopt the runtime type introspection method(s) in SE-0057. For non-generic ObjC classes you're good, though.
I am writing an OS X/iOS framework in Objective-C, and I would like for the framework to be useful for developers using either Objective-C or Swift.
In normal Objective-C enums are defined like this (this example is taken directly from Apple's own UIView class reference).
typedef enum {
UIViewAnimationCurveEaseInOut,
UIViewAnimationCurveEaseIn,
UIViewAnimationCurveEaseOut,
UIViewAnimationCurveLinear
} UIViewAnimationCurve;
To make this enum Swift-friendly, my understanding is that it should be declared like this.
typedef NS_ENUM(NSInteger, UIViewAnimationCurve) {
UIViewAnimationCurve_EaseInOut,
UIViewAnimationCurve_EaseIn,
UIViewAnimationCurve_EaseOut,
UIViewAnimationCurve_Linear
};
This allows the enum to be accessed in the style of let curve: UIViewAnimationCurve = .EaseInOut from Swift.
My problem is that the NS_ENUM and underscore method produces strangely named enums when used from Objective-C. The NS_ENUM method allows dot notation to be used from Swift, but it also means that any ObjC code will need to use an underscore in the enumerated name, which is undesirable.
How can I allow dot notation for Swift while still preserving Objective-C style naming conventions for within ObjC code?
You simply follow the usual convention – no underscoring is necessary. Swift compiler is smart enough to just cut the common prefix out (the part that matches the enum type name). You do have to use an NS_ENUM for the enum to be made visible to Swift, but it's good practice anyway.
Case in point, for instance UIViewAnimationCurve is defined in an Objective-C header in just the form you describe in your first code example and works just fine in Swift:
If you define it like this:
typedef long TrafficLightColor NS_TYPED_ENUM;
TrafficLightColor const TrafficLightColorRed;
TrafficLightColor const TrafficLightColorYellow;
TrafficLightColor const TrafficLightColorGreen;
if get compiled to swift like this:
struct TrafficLightColor: RawRepresentable, Equatable, Hashable {
typealias RawValue = Int
init(rawValue: RawValue)
var rawValue: RawValue { get }
static var red: TrafficLightColor { get }
static var yellow: TrafficLightColor { get }
static var green: TrafficLightColor { get }
}
Looks like what you need, anyway take a look at: https://itunes.apple.com/us/book/using-swift-with-cocoa-and-objective-c-swift-4-1-beta/id1002624212?mt=11
I have the following swift class with a NumericType T.
#objc class MathStatistics<T: NumericType> : NSObject {
var numbers = [T]()
func sum() -> T? {
if numbers.count == 0 {
return nil
}
var sum = T(0)
for value in numbers {
sum = sum + value
}
return sum
}
}
In swift a initialize the class object as follows:
let statistics = MathStatistics<Double>()
How do I initialize the same object in Objective C?
The following line does not set the numeric type T.
MathStatistics *stats = [[MathStatistics alloc] init];
You can't. As listed in the documentation:
You’ll have access to anything within a class or protocol that’s
marked with the #objc attribute as long as it’s compatible with
Objective-C. This excludes Swift-only features such as those listed
here:
Generics
Tuples
Enumerations defined in Swift
Structures defined in Swift
Top-level functions defined in Swift
Global variables defined in Swift
Typealiases defined in Swift
Swift-style variadics
Nested types
Curried functions
You'd have to get rid of generics in your class. Then you can use it in Objective-C
I'm trying to convert some of my Obj-C class to Swift. And some other Obj-C classes still using enum in that converted class. I searched In the Pre-Release Docs and couldn't find it or maybe I missed it. Is there a way to use Swift enum in Obj-C Class? Or a link to the doc of this issue?
This is how I declared my enum in my old Obj-C code and new Swift code.
my old Obj-C Code:
typedef NS_ENUM(NSInteger, SomeEnum)
{
SomeEnumA,
SomeEnumB,
SomeEnumC
};
#interface SomeClass : NSObject
...
#end
my new Swift Code:
enum SomeEnum: NSInteger
{
case A
case B
case C
};
class SomeClass: NSObject
{
...
}
Update: From the answers. It can't be done in Swift older version than 1.2. But according to this official Swift Blog. In Swift 1.2 that released along with XCode 6.3, You can use Swift Enum in Objective-C by adding #objc in front of enum
As of Swift version 1.2 (Xcode 6.3) you can. Simply prefix the enum declaration with #objc
#objc enum Bear: Int {
case Black, Grizzly, Polar
}
Shamelessly taken from the Swift Blog
Note: This would not work for String enums or enums with associated values. Your enum will need to be Int-bound
In Objective-C this would look like
Bear type = BearBlack;
switch (type) {
case BearBlack:
case BearGrizzly:
case BearPolar:
[self runLikeHell];
}
To expand on the selected answer...
It is possible to share Swift style enums between Swift and Objective-C using NS_ENUM().
They just need to be defined in an Objective-C context using NS_ENUM() and they are made available using Swift dot notation.
From the Using Swift with Cocoa and Objective-C
Swift imports as a Swift enumeration any C-style enumeration marked with the NS_ENUM macro. This means that the prefixes to enumeration value names are truncated when they are imported into Swift, whether they’re defined in system frameworks or in custom code.
Objective-C
typedef NS_ENUM(NSInteger, UITableViewCellStyle) {
UITableViewCellStyleDefault,
UITableViewCellStyleValue1,
UITableViewCellStyleValue2,
UITableViewCellStyleSubtitle
};
Swift
let cellStyle: UITableViewCellStyle = .Default
From the Using Swift with Cocoa and Objective-C guide:
A Swift class or protocol must be marked with the #objc attribute to
be accessible and usable in Objective-C. [...]
You’ll have access to anything within a class or protocol that’s
marked with the #objc attribute as long as it’s compatible with
Objective-C. This excludes Swift-only features such as those listed
here:
Generics Tuples / Enumerations defined in Swift / Structures defined in
Swift / Top-level functions defined in Swift / Global variables defined in
Swift / Typealiases defined in Swift / Swift-style variadics / Nested types /
Curried functions
So, no, you can't use a Swift enum in an Objective-C class.
Swift 4.1, Xcode 9.4.1:
1) Swift enum must be prefixed with #objc and be Int type:
// in .swift file:
#objc enum CalendarPermission: Int {
case authorized
case denied
case restricted
case undetermined
}
2) Objective-C name is enum name + case name, eg CalendarPermissionAuthorized:
// in .m file:
// point to something that returns the enum type (`CalendarPermission` here)
CalendarPermission calPermission = ...;
// use the enum values with their adjusted names
switch (calPermission) {
case CalendarPermissionAuthorized:
{
// code here
break;
}
case CalendarPermissionDenied:
case CalendarPermissionRestricted:
{
// code here
break;
}
case CalendarPermissionUndetermined:
{
// code here
break;
}
}
And, of course, remember to import your Swift bridging header as the last item in the Objective-C file's import list:
#import "MyAppViewController.h"
#import "MyApp-Swift.h"
If you prefer to keep ObjC codes as-they-are, you could add a helper header file in your project:
Swift2Objc_Helper.h
in the header file add this enum type:
typedef NS_ENUM(NSInteger, SomeEnum4ObjC)
{
SomeEnumA,
SomeEnumB
};
There may be another place in your .m file to make a change: to include the hidden header file:
#import "[YourProjectName]-Swift.h"
replace [YourProjectName] with your project name. This header file expose all Swift defined #objc classes, enums to ObjC.
You may get a warning message about implicit conversion from enumeration type... It is OK.
By the way, you could use this header helper file to keep some ObjC codes such as #define constants.
If you (like me) really want to make use of String enums, you could make a specialized interface for objective-c. For example:
enum Icon: String {
case HelpIcon
case StarIcon
...
}
// Make use of string enum when available:
public func addIcon(icon: Icon) {
...
}
// Fall back on strings when string enum not available (objective-c):
public func addIcon(iconName:String) {
addIcon(Icon(rawValue: iconName))
}
Of course, this will not give you the convenience of auto-complete (unless you define additional constants in the objective-c environment).
After researching this, I kept finding only partial answers, so I created an entire example of a Swift App bridged to Objective C that has Swift enums used by Objective C code and Objective C enums used by Swift code. It is a simple Xcode project that you can run and experiment with. It was written using Xcode 10.3 with Swift 5.0
Example Project
In case you are trying to observe an enum which looks like this:
enum EnumName: String {
case one = "One"
case two = "Two"
}
this workaround helped me.
Observable Class:
create #objc dynamic var observable: String?
create your enum instance like this:
private var _enumName: EnumName? {
didSet {
observable = _enumName!.rawValue
}
}
Observer Class:
create private var _enumName: EnumName?
create private let _instance = ObservableClass()
create
private var _enumObserver: NSKeyValueObservation = _instance.observe(\.observable, options: .new, changeHandler: { [weak self] (_, value) in
guard let newValue = value.newValue else { return }
self?._enumName = EnumName(rawValue: period)!
})
Than's it. Now each time you change the _enumName in the observable class, an appropriate instance on the observer class will be immediately updated as well.
This is of course an oversimplified implementation, but it should give you an idea of how to observe KVO-incompatible properties.
this might help a little more
Problem statement :- I have enum in swift class, which I am accessing form other swift classes, and Now I need to access it form my one of the objective C class.
Before accessing it from objective-c class :-
enum NTCType {
case RETRYNOW
case RETRYAFTER
}
var viewType: NTCType?
Changes for accessing it from objective c class
#objc enum NTCType :Int {
case RETRYNOW
case RETRYAFTER
}
and add a function to pass it on the value
#objc func setNtc(view:NTCType) {
self.viewType = view; // assign value to the variable
}