Swift callback from Objective-C

Question

In Swift application I have a ViewController, which call a new modal. This modal have as ViewController Objective-C implementation as ViewController_obj_c.

This modal is shown from Swift code and I want to call the callback property (with UIImage parameter), when the Objective-C code is done.

My callback property "signCompleteCallback" doesn't work. How can I fill a callback property from Swift and call it inside Objective-C?

SwiftViewController.swift:

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if segue.identifier == "showModalSegue" {
        if let nextVC = segue.destination as? ViewController_obj_c {

            nextVC.signCompleteCallback = #selector(self.Test)
        }
    }
}

@objc func Test(image: UIImage)
{
    debugPrint("Test method was called as callback with image parameter")
}

ViewController_obj_c.h:

@interface ViewController_obj_c : UIViewController <UIPopoverPresentationControllerDelegate>


@property SEL signCompleteCallback;

- (IBAction)Done_Clicked:(id)sender;

ViewController_obj_c.m:

- (IBAction)Done_Clicked:(UIButton *)sender
{
    UIGraphicsBeginImageContext(_dV.bounds.size);
    [_dV.layer renderInContext:UIGraphicsGetCurrentContext()];
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

   [self signCompleteCallback]; // Here is the point when I want to call me callback and as a parameter i want to send image
}

OOPer · Accepted Answer · 2018-07-06 12:13:23Z

Why don't you use Objective-C block ?

SwiftViewController.swift:

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if segue.identifier == "showModalSegue" {
        if let nextVC = segue.destination as? ViewController_obj_c {

            nextVC.signCompleteCallback = testMethod(image:) //`(image:)` is not needed when not ambiguous
        }
    }
}

func testMethod(image: UIImage) {
    debugPrint("Test method was called as callback with image parameter")
}

ViewController_obj_c.h:

@interface ViewController_obj_c : UIViewController<UIPopoverPresentationControllerDelegate>

typedef void (^signCompleteCallbackType)(UIImage * _Nonnull image); //Declare the block type

@property signCompleteCallbackType signCompleteCallback; //Declare the block property using the block type

- (IBAction)Done_Clicked:(id)sender;

@end

ViewController_obj_c.m:

- (IBAction)Done_Clicked:(UIButton *)sender
{
    UIGraphicsBeginImageContext(_dV.bounds.size);
    [_dV.layer renderInContext:UIGraphicsGetCurrentContext()];
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    self.signCompleteCallback(image);    //Use the block just like a normal function
}

Puty · Accepted Answer · 2018-07-06 11:28:26Z

I found one solution, but I'm not satisfied with him.

If someone gives a better solution I will happy for it. At this solution I don't like creating a new protocol that I have to inherit in a Swift part (create a new class or inherit it in existing SwiftViewcontroller, doesn't matter)

One way is create @protocol inside Objective-C:

@protocol ObjC_ManagerDelegate 
-(void) signCallBack: (UIImage *)image;
@end

ViewController_obj_c.h:

@interface ViewController_obj_c : UIViewController <UIPopoverPresentationControllerDelegate>

    @property (nonatomic, strong) id <ObjC_ManagerDelegate>delegate;

    - (IBAction)Done_Clicked:(id)sender;
@end

ViewController_obj_c.m:

- (IBAction)Done_Clicked:(UIButton *)sender
{
    UIGraphicsBeginImageContext(_dV.bounds.size);
    [_dV.layer renderInContext:UIGraphicsGetCurrentContext()];
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    [self.delegate signCallBack:image];
}

And the Swift part looks like this. Create a new class and inherit it from ObjC_ManagerDelegate:

class SwiftmanagerDelegate: ObjC_ManagerDelegate {
    func signCallBack(_ image: UIImage!) {
        // do something
    } 
}

and finally fill new class as a delegate

SwiftViewController.swift:

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if segue.identifier == "showModalSegue" {
        if let nextVC = segue.destination as? ViewController_obj_c {

            nextVC.delegate = SwiftmanagerDelegate()
        }
    }
}

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