React Native Modules: How to emit events from Swift code

[icedevml]

Hello,

I was reading those two tutorials and experimenting a little bit with them:
https://reactnative.dev/docs/next/the-new-architecture/turbo-modules-with-swift
https://reactnative.dev/docs/next/the-new-architecture/native-modules-custom-events

Throughout that journey I was however having some issues trying to connect the knowledge from those two guides together. Could you please advise on what kind of glue code do I need to write in order to be able to emit events from the Swift portion of the code?

I'm not too experienced with Objective-C and thus I'm not sure how to approach on exposing emitOnKeyAdded (generated by CodegenTypes.EventEmitter) to the Swift file, so that I can call emitOnKeyAdded from Swift code directly whenever some event happens.

I would be very grateful if somebody could provide an advice here.

[liamjones]

To expose ObjC stuff to Swift you need a "bridging header". If you do "New swift file" in your project in Xcode it should prompt you to set one up automatically. If it doesn't, this page has manual instructions: https://developer.apple.com/documentation/swift/importing-objective-c-into-swift

If you have one automatically imported its default contents will be:

//
//  Use this file to import your target's public headers that you would like to expose to Swift.
//

And then, as it says, you #import .h files into here if you want to expose them to Swift.

[icedevml]

I've figured that one out. Just for the record, it was something like that.

On the Objective-C side:

 - (id) init {
   if (self = [super init]) {
    storage = [NativeLocalStorage new];
    [storage setEmitOnKeyAdded:^(NSString *key, NSString *value){
      [self emitOnKeyAdded:@{@"key": key, @"value": value}];
    }];
   }
   return self;
 }

On the Swift side:

  var emitOnKeyAdded: ((NSString, NSString?) -> ())? = nil
  
  func setEmitOnKeyAdded(emitOnKeyAdded: @escaping (NSString, NSString?) -> ()) {
    self.emitOnKeyAdded = emitOnKeyAdded
  }

And then the autogenerated emit method can be accessed from the Swift code.