Syntax to Call Swift Method from Objective-C Class

Question

I am trying to call some code in a Utilities file written in swift from an objective-c file.

Right now the class in the swift file looks like this:

class ImageClass: NSObject {
public func imageFromString(name: String?) -> UIImage? {
//code to make image

return image
}
}

I am trying to call it from the Objective-C file with:

 UIImage *myImage = [ImageClass imageFromString:@"test"];

however this is giving error:

Use of undeclared identifier 'ImageClass'

I know the Utilities file is reachable from the Objective-C file because I call other methods there though using a shared Instance.

Can anyone suggest the proper way to call the code? I actually don't care if it's a class or through a sharedInstance, I just need to be able to call it.

Edit:

As suggested by @Charles Srstka, I CMD-clicked on the #import myapp.swift file, jumped to Definition, and it shows the following in the header:

- (UIImage * _Nullable)imageFromStringWithName:(NSString * _Nullable)name SWIFT_WARN_UNUSED_RESULT;

Accordingly, I tried adding WithName (which I'd forgotten) to the invocation so I have:

 UIImage *myImage = [ImageClass imageFromStringWithName:@"test"];

but am still getting error with or without @objc before method:

No known class method for selector 'imageFromStringWithName:'

Murod Mamadjanov · Accepted Answer · 2020-07-25 07:58:40Z

8

In swift 4.2 and latest

Add this line to your "*.m" file:
```
#import "YourProjectName-Swift.h"
```

Add @objc before your function:

@objc public func imageFromString(name: String?) -> UIImage? {    
//code to make the image
return image
}

Call it inside Objective-C class:

ImageClass *imgObject = [[ImageClass alloc] init];   
UIImage *myImage = [imgObject imageFromStringWithName:@"test"];

edited Jul 25, 2020 at 7:58

Murod Mamadjanov

157 bronze badges

answered Feb 3, 2019 at 23:54

Bilal Bakhrom

16611 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

user1904273 Over a year ago

This did the job. Key was initiating the NSObject prior to invoking class method. Thanks.

Midhun Over a year ago

A note about project name, if there are spaces in the project name make sure you replace them with underscores, for example if the project name is "My Project" you need to write it as #import "My_Project-Swift.h"

Charles Srstka · Accepted Answer · 2019-02-03 19:32:51Z

1

Add this line to your Objective-C file:

#import "YourProjectName-Swift.h"

Replace YourProjectName with the name of your project. This will make all the Objective-C-compatible Swift classes in your project visible to your Objective-C code.

Note that you'll also need to add the @objc annotation to your func declataions to make the methods visible to Objective-C.

answered Feb 3, 2019 at 19:32

Charles Srstka

17.2k3 gold badges38 silver badges65 bronze badges

4 Comments

user1904273 Over a year ago

I had the import statement already. I added the @objc before public in the function line but am getting same error.

Charles Srstka Over a year ago

If you command-click on the #import line, you should be able to see the generated header file. Does your class show up in there?

user1904273 Over a year ago

I tried your suggestion which I've put into an edit above. Seems like there is a method there, but I still am not calling it correctly

Charles Srstka Over a year ago

@user1904273 Your problem was that you needed to instantiate the object (you could have called it the way you did if it were a class func instead of a regular func), but I see someone else already got that one. If you want to fix that awkward method name, though, you can declare the method as func image(string name: String?) which will show up in Objective-C as imageWithString:, or you could do func imageFromString(_ name: String?) which will show up as imageFromString:. You can also put an @objc(whateverTheHellYouWantToCallIt:) annotation on the func if you prefer.

Collectives™ on Stack Overflow

Syntax to Call Swift Method from Objective-C Class

2 Answers 2

2 Comments

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related