Unable to call an Objective C class delegate from a Swift class - objective-c

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.