Can not find Swift Protocol declaration in Obj-C class

Question

I have created on Class in Swift and that class and its protocol I am using in Obj-C enabled project but I am getting below error while compiling my project.

cannot find protocol declaration for 'SpeechRecognizerDelegate'; did you mean 'SFSpeechRecognizerDelegate'?

Can anyone guide me on this how can I use Swift class protocol in my Obj-C class.

Here is my Swift code:

protocol SpeechRecognizerDelegate : class  {
    func speechRecognitionFinished(_ transcription:String)
    func speechRecognitionError(_ error:Error)
}


class SpeechRecognizer: NSObject, SFSpeechRecognizerDelegate {
    open weak var delegate: SpeechRecognizerDelegate?

}

Protocol use in Obj-C:

#import "ARBot-Swift.h"

@interface ChatScreenViewController : JSQMessagesViewController <SpeechRecognizerDelegate>

Let me know if required more info.

Thanks in Advance.

Answer 1

Define your Swift protocol like this inside your Swift file.

@objc protocol SpeechRecognizerDelegate: class{
  func speechRecognitionFinished(_ transcription:String)
  func speechRecognitionError(_ error:Error)
}

Create a Swift Module inside your project setting then use it. You can find here complete blog for the mix language coding.

Then use Protocol inside Objective C class,

We required to add protocol inside Objective C file -

#import "ARBot-Swift.h"

@interface ChatScreenViewController : JSQMessagesViewController <SpeechRecognizerDelegate>

---

Then you need to conform to the protocol methods -

- (void)viewDidLoad {
    [super viewDidLoad];
    SpeechRecognizer * speechRecognizer = [[SpeechRecognizer alloc] init];
    speechRecognizer.delegate = self;
}


#pragma mark - Delegate Methods
-(void)speechRecognitionFinished:(NSString *) transcription{
   //Do something here
}

-(void)speechRecognitionError:(NSError *) error{
   //Do something here
}

Answer 2

Add @objc attribute to your protocol:

@objc protocol SpeechRecognizerDelegate : class  {
    //...
}

Answer 3

Include Swift Classes in Objective-C Headers Using Forward Declarations

//MySwiftClass.swift
@objc protocol MySwiftProtocol {}
@objcMembers class MySwiftClass {}

// MyObjcClass.h
@class MySwiftClass;
@protocol MySwiftProtocol;

@interface MyObjcClass : NSObject
- (MySwiftClass *)returnSwiftClassInstance;
- (id <MySwiftProtocol>)returnInstanceAdoptingSwiftProtocol;
// ...
@end

Answer 4

in Swift:

@objc public protocol YOURSwiftDelegate {
    func viewReceiptPhoto()
    func amountPicked(selected: Int)
}

class YourClass: NSObject {
    weak var delegat: YOURSwiftDelegate?
}

in Objective-C headerFile.h

@protocol YOURSwiftDelegate;

@interface YOURController : UIViewController < YOURSwiftDelegate >

in Objective-C Implementation.m

SwiftObject * swiftObject = [SwiftObject alloc] init];
swiftObject.delegate = self

Answer 5

I had a similar issue after following (import header + Objc annotation on protocol). I got the warning when using Swift code from Objective C headers. Solved by only importing into the implementation .m files.