无法从 Swift ZA2F2ED4F8EBC2CBB4C21A29DC40AB6DZ 调用目标 C class 代表

Question

My issue here is that I need the "protocolMethod" in the OldViewController.m to be called from the NewViewController.swift in a delegate fashion.

The project I'm working on was completely written in Objective C, and there's a new View Controller that was written in Swift.

The new View Controller is supposed to call a delegate method, conformed by the Objective C caller object, so the Objective C View Controller can process that call.

The app runs and the delegate is called from Swift, but never actually executed in the Objective C View Controller.

I've tried including all the sample files and the code that's supposed to be called, so here it is:

MyProtocol.h

#import <Foundation/Foundation.h>

@protocol MyProtocol <NSObject>

- (void)protocolMethod:(NSString*)input;

@end

My-Bridging-Header.h

#ifndef My_Bridging_Header_h

#define My_Bridging_Header_h

#import <UIKit/UIKit.h>

#import "OldViewController.h"

#import "MyProtocol.h"

#endif

OldViewController.h

#import <UIKit/UIKit.h>

@interface OldViewController : UIViewController

@end

OldViewController.m

@interface OldViewController ()<MyProtocol>

@end

 
@implementation OldViewController

 
//THIS IS THE PROBLEM: NEVER GETS CALLED

- (void)protocolMethod:(NSString *)input {

    NSLog(@"protocolMethod:%@", input);

}

 

- (IBAction)myButtonClicked:(UIButton *)sender {

                NewViewController *newViewController =[self.storyboard instantiateViewControllerWithIdentifier:@"NewViewController"];

                [newViewController setModalTransitionStyle:UIModalTransitionStyleCoverVertical];

                [self presentViewController:newViewController animated:YES completion:nil];

 

}

@end

NewViewController.swift

import UIKit

class NewViewController: UIViewController {

    @objc weak var myProtocol: MyProtocol?

    override func viewWillAppear(_ animated: Bool) {

        self.myProtocol?.protocolMethod("testing 123")

    }

}

Thank you for your help!

Answer 1

Call a objective-C protocol method in Objective-C class from Swift

define the protocol in Objective-c MyProtocol.h

#ifndef MyProtocol_h
#define MyProtocol_h
#import <Foundation/Foundation.h>

@protocol MyProtocol <NSObject>
@optional
- (void)protoMethod:(NSString *)input;
@end

#endif

define interface of LoginViewController.h

#import <UIKit/UIKit.h>
#import "MyProtocol.h"

@class NewViewController; //declare knowledge of swift class
@interface LoginViewController : UIViewController <MyProtocol>
// method to trigger testing manual
-(void)haveFun;
@end

define implementation of LoginViewController.m

#import "LoginViewController.h"
#import "YourProductModulName-Swift.h" // will bridge exposed swift class to objc

@implementation LoginViewController
-(void)protoMethod:(NSString*)input {
     NSLog(@"protocolMethod:%@", input);
}
- (void)haveFun {
    // did not use the storyboard to make testing simple
    // this is an @objc exposed swift class
    NewViewController *newViewController = [[NewViewController alloc] init];
    // now trigger predefined method that checks for protocol 
    [newViewController fun:self];
}
@end

now let us write a swift class that is subclassing an NSObject, here UIViewController and expose it to objc

import Foundation
import UIKit

@objc //expose class when you need to use it from Objective-C
class NewViewController: UIViewController {

    // as objc bridging is working with NSObjects,
    // we can use it instead of Any, which can't be exposed.
    @objc(foo) weak var foo : NSObject?
    
    override func viewWillAppear(_ animated: Bool) {
        // question was: how to call (id<MyProtocol>)-(void)protoMethod:
        // as we dont use storyboard for testing here..
        // nothing in here
    }
    
    // no autonaming, defined -(void)fun: instead
    @objc(fun:) func fun(protocolObj: MyProtocol) {
        let bar = protocolObj
        bar.protoMethod!("direct invokation of protoMethod")
        // ah why not, lets remember the object for later.
        foo = bar as? NSObject
        testme()
    }
    
    @objc func testme() {
        // as foo is NSObject here, check if exist
        if (foo != nil) {
            // cast foo and check for protocol
            if let loginview = foo as? MyProtocol {
                loginview.protoMethod!("PROTOCOL-LOL!")
            } else {
                print("i will allways love youuu!")
            }
        }
    }

}

now lets have some fun and use the back and forth bridged stuff. This will allocate a Objective-c class LoginViewController following <MyProtocol> and invoke -(void)haveFun method. This method will allocate a Swift Class NewViewController (important! based on NSObject) that will invoke @objc exposed swift func fun: and give self as parameter that must follow the MyProtocol. It will then invoke the protocol method of LoginViewController with a parameter NSString and store the LoginViewController object in weak var foo as NSObject . Then it will trigger internal swift testme() and use the stored foo to check again if it exists and conforms to protocol MyProtocol and invokes the protocolMethod -(void)protoMethod:(NSString*)string; again or print something if not conforming.

LoginViewController *login = [[LoginViewController alloc] init];
[login haveFun];

Don't forget the example here needs Swift bridging to Objective-C and Objective-C bridging to Swift. If that is a perfect design pattern is another talk.