Swift library using Promise, methods not visible in ObjC about promises HOT 4 CLOSED

Hi Fernando,

To make any Swift func visible for ObjC you need an @objc annotation.
Your idea of a duplicate method that you can then expose for ObjC is the right one.
Here's the pattern to follow in your Swift pod:

@objc(MyObjCClass)
public class MyClass: NSObject {
  public func fooBar() -> Promise<String> {
    // ...
    return Promise("hello world")
  }
  
  @objc(objc_fooBar)
  public func fooBar() -> Promise<String>.ObjCPromise<NSString> {
    return fooBar().asObjCPromise()
  }
}

Then use it from an ObjC target:

#import "MySwiftPod-Swift.h"

FBLPromise<NSString *> *fooBarPromise = [[MyObjCClass new] objc_fooBar];

If you have a lot of such methods in your class, you may consider moving them into a separate extension just to make the code look cleaner, like so:

public class MyClass: NSObject {
  public func fooBar() -> Promise<String> {
    // ...
    return Promise("hello world")
  }
  // ...
}

// Objective-C interface.
public extension MyClass {
  @objc(objc_fooBar)
  public func fooBar() -> Promise<String>.ObjCPromise<NSString> {
    return fooBar().asObjCPromise()
  }
  // ...
}

Let us know if you have any further questions.
Thanks.

from promises.

I'm using this approach, but can't see how to handle errors in objective c.

I use the following in swift:

Test.client.createUser(firstName: "firstname", lastName: "lastname").then { _ -> Void in
   assertionFailure("duplicate user created")
}.catch { error in
   assert(error is RequestError, "RequestError returned")
   let requestError = error as? RequestError
}

RequestError is a swift class visible in objective c

@objc(AGMRequestError)
public class RequestError

and in objective c

    [client createUserWithFirstName:@"firstname" withLastName:@"lastname"] .then(^id(AGAccessToken *accessToken) {
        XCTFail("duplicate user")
        return nil;
    })
     .catch(^(NSError *error) {
         AGMRequestError *requestError = (AGMRequestError *)error;
    });

error is of type _SwiftNativeNSError, not AGMRequestError, so I can't access any of its details

from promises.

Hi Matt,

Given your RequestError has @objc annotation, I assume it already derives from NSObject? Any chance you derive it from NSError instead? Then you can create instances of RequestError in Swift as follows: RequestError(domain: "your domain", code: 42, userInfo: nil) or with a custom constructor, and cast to AGMRequestError in Objective-C.

By the way, you may also like declaring errors as enums in Swift and conforming to CustomNSError protocol to be able to extract domain, code and userInfo everywhere. Take a look at an example.

Thanks.

from promises.

Hello,

Thank you for the suggestion. Yes RequestError derived from NSObject, and Error but I've changed it to just derive from NSError and that works - I can then cast to AGMRequestError in Objective-C.

I'll also consider conforming to CustomNSError instead. RequestError currently has a type, code, and description, but I could use userInfo for the type and description.

from promises.