Call Swift function with parameters from Objective C class

Question

I have a library class wrote in swift which should be used in my existing objective-c code. I have created the bridging-header and have define @class MySwiftClass in .h and import "-Swift.h" in .m

a swift class is something similar to this

@objc class MySwiftClass: NSObject {
    var firstName : String
    var lastName: String

    public init(firstName: String, lastName: String) throws {
        guard !firstName.isEmpty && !lastName.isEmpty else { throw SOME_ERROR }
        self.firstName = firstName
        self.lastName = lastName
        super.init()
    }


func methodWithParams(city: String, suburb: String) throws -> String {
        return city + suburb
    }

I have faced two problems.

Don't know how to call swift init function on the objective-c class. I have tried MySwiftClass *myClass = [MySwiftClass init];. Up to this, the app can compile. But don't know how to pass the parameters.
I also want to access myClass.methodWithParams(city:"My city", suburb:"My country") in objective-c class.

Appreciate the help!

The first thing you need is to add @objc to the methods which should be visible from Objective-C. — Martin R
– Martin R, Commented Oct 3, 2018 at 8:00

Igzar · Accepted Answer · 2018-10-03 08:07:33Z

7

You must call alloc before init call.

MySwiftClass* instance = [[MySwiftClass alloc] initWithFirstName: @"John" lastName: @"Doe"];

Mark method with @objc or use @objcMembers to make your method exposable from Objective-C code. And unfortunately you can't user throwable initializers in Objective-C.

@objcMembers class MySwiftClass: NSObject {
    var firstName : String
    var lastName: String

    public init(firstName: String, lastName: String) throws {
        guard !firstName.isEmpty && !lastName.isEmpty else { throw SOME_ERROR }
        self.firstName = firstName
        self.lastName = lastName
        super.init()
    }

    func methodWithParams(city: String, suburb: String) throws -> String {
        return city + suburb
    }
}

answered Oct 3, 2018 at 8:07

Igzar

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2 Comments

Ashley Mills Over a year ago

You can use throwable initialisers from Objective-C - the signature just has an extra NSError ** error parameter

smartsanja Over a year ago

@lgzar Thanks a lot for the detailed answer. Keep it up.

Ashley Mills · Accepted Answer · 2018-10-03 08:11:10Z

1

To instantiate an object in Objective-C…

NSError *error = NULL;
MySwiftClass *class = [[MySwiftClass alloc] initWithFirstName: @"John"
                                                     lastName: @"Smith" 
                                                        error: &error]

to call the method

[class methodWithParamsWithCity: @"My CIty" suburb: @"My suburb" error: &error];

throws in Swift appends an NSError ** error parameter in Objective-C

edited Oct 3, 2018 at 8:11

answered Oct 3, 2018 at 7:45

Ashley Mills

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3 Comments

Martin R Over a year ago

Here it would be [[MySwiftClass alloc] initWithFirstName:@"first" lastName:@"last" error:&error] since the init method throws as well.

Ashley Mills Over a year ago

This is me digging back into my 4 years old Objective-C memory - I knew that, but thought I was going crazy when testing it out it wasn't compiling. I thought maybe something had changed in the Obj-c world that had passed me by. It was the missing @objc

smartsanja Over a year ago

I have accepted lgzar's answer only because of @objcMembers.Sice I cannot accept two answers, I have given +1 to your's since both help me to resolve the problem. Thanks a lot

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