How to call Swift function with more than one parameter from Objective C class?

Question

For example I have this method in swift:

@objc class MyClass: NSObject
....
@objc class func viewWithIndex(index: Int, str: String) {
    println(index, str)
}

then i wanna call that method in my objective-c class, and i was expecting as simple as this call [MyClass viewWithIndex:10 str:@"string"]; but it doesn't work.

How do i call it? Please help.

Note: I have already a working swift function call to objective-c [MyClass showSomething]; so that means i have successfully setup necessary settings to bridge classes. Only the function that has two of more parameters is my problem. :)

Solved:

I dont know what i happened but i just restarted my mac and removed objc and it worked with the call [MyClass viewWithIndex:10 str:@"string"];. I remember reading in documentation.

Migrating Your Objective-C Code to Swift

To be accessible and usable in Objective-C, a Swift class must be a descendant of an Objective-C class or it must be marked @objc.

What doesn't work? Do you have a compile-time error or a runtime error? — Francescu
– Francescu, Commented Sep 17, 2014 at 9:48
Is your Swift class a subclass of NSObject? Compare stackoverflow.com/questions/25605677/…. — Martin R
– Martin R, Commented Sep 17, 2014 at 9:51
I have a working swift function call to objective-c class already but without a parameter or just one parameter. now i want to try two or more parameter. the error it make is No Known class method for selector viewWithIndex:str — Arnlee Vizcayno
– Arnlee Vizcayno, Commented Sep 17, 2014 at 9:59

haplo1384 · Accepted Answer · 2016-12-11 16:42:21Z

17

This worked for me in Swift 3.0

public class func viewWithIndex(_ index: Int, str: String) {
    println(index, str)
}

Adding the underscore before the first parameter in the Swift declaration allowed me to call from objective c without naming the first parameter, like this:

[MyClass viewWithIndex:10 str:@"string"]

answered Dec 11, 2016 at 16:42

haplo1384

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3 Comments

James T Snell Over a year ago

What does the underscore at the start of the method's parameters list actually do? ..viewWithIndex(_ index... I can confirm this works for me too, but what's going on here? Does this token have a name in this context?

haplo1384 Over a year ago

@JamesTSnell The _ determines whether or not the parameter name should be used when calling the method. In the example above, even calling that method from swift would look something like this: className.viewWithIndex(10, str: "test"). If the method definition had the _ before both index and str, then the method call would look like this: className.viewWithIndex(10,"test")

mohsinulhaq Over a year ago

Is it not possible to call a swift function where all parameters are named?

Jasper Blues · Accepted Answer · 2014-09-18 01:12:03Z

4

I believe you'll need to mark the function as either public (makes sense) or dynamic. Otherwise it will be a candidate for Swift's optimization (inline or vtable the method) which will make it invisible to Objective-C.

Try this:

public class func viewWithIndex(index: Int, str: String) {
    println(index, str)
}

Or this: (doesn't really make sense, but should also work)

private dynamic class func viewWithIndex(index: Int, str: String) {
    println(index, str)
}

answered Sep 18, 2014 at 1:12

Jasper Blues

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4 Comments

Arnlee Vizcayno Over a year ago

i dont know what happened but when i turned on my mac this morning and removed @objc it just work properly with the call [MyClass viewWithIndex:10 str:@"string"];

Jasper Blues Over a year ago

OK, it must be the method is already using dynamic dispatch. When its not, I've found the above approach works. . the same rules for the guide on working with KVO in Swift should apply.

Arnlee Vizcayno Over a year ago

i guess i dont need public or dynamic or etc coz i have my class subclass to NSObject.

Jasper Blues Over a year ago

As of Xcode6 beta 6, Swift can still inline/vtable methods/vars on NSObject subclasses. This definitely applies to private vars (which makes sense), but if you have a case where you want it to be private except to the Objective-C runtime, you can add the 'dynamic' modifier.

vinay kumar · Accepted Answer · 2019-10-21 06:57:00Z

1

forward declaration of your class in .h file of objective-c

@class <MySwiftClass>

import "Productname-swift.h" in obj-c .m class use

[SwiftClass storeWithData:@"Hi" password:@"secret"];

SwiftClass.swift

@objcMembers class SwiftClass{
   public class func store(data: String,password:String)->Bool{
    let saveSuccessful: Bool = KeychainWrapper.standard.set(data, forKey: password)
    return saveSuccessful;
  }
}

answered Oct 21, 2019 at 6:57

vinay kumar

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