send notification from swift file and recieve in objective c file in ios

Question

I am trying to send notification from swift file to objective c. My attempt so far:

ClassA.swift

    override func viewDidLoad() {
        super.viewDidLoad()

        let containerDict:[String:AnyObject] =  ["vwConatinerFrameWidth": vwContainer.frame.size.width, "vwConatinerFrameHeight": vwContainer.frame.size.height]

        NSNotificationCenter.defaultCenter().postNotificationName("ContainerFrame", object: self, userInfo: containerDict)

        let classB = ClassB(nibName: "ClassB", bundle: nil)

        classB.willMoveToParentViewController(self)

        self.vwContainer.addSubview(classB.view)

        self.addChildViewController(classB)
        classB.didMoveToParentViewController(self)

    }

ClassB.m

- (void)viewDidLoad
{
    [super viewDidLoad];

    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(containeFrameRecieved:)
                                                 name:@"ContainerFrame"
                                               object:nil];
}

- (void)containeFrameRecieved:(NSNotification *)note {
    NSDictionary *theData = [note userInfo];

    if (theData != nil) {

        CGFloat containerFrameWidth = [[theData objectForKey:@"vwConatinerFrameWidth"] floatValue];
        CGFloat containerFrameHeight = [[theData objectForKey:@"vwConatinerFrameHeight"] floatValue];

        NSLog(@"Width:%f and Height: %f",containerFrameWidth,containerFrameHeight);
    }

}

My-Bridging-Header.h

#import "ClassB.h"

But the problem is, the value is not coming to ClassB. Can anyone tell me what is wrong with this code?

Answer 1

You are creating an object of ClassB AFTER posting the notification. So while the notif is posted, the ClassB object doesn't exist. Make sure ClassB's viewDidLoad: is called before you post the notification. Only then will ClassB be able to listen to the notif and get the value

Answer 2

Updated answer for Swift 4.1

// Notification name for swift
extension NSNotification.Name {
    static let NotificationName = Notification.Name(rawValue: "NotificationName")
}

// Notification name for Objective-C
@objc public extension NSNotification {
    public static var NotificationName: String {
        return "NotificationName"
    }
}

Posting notification in swift file

NotificationCenter.default.post(name: NSNotification.Name.NotificationName, object: nil)

Observe in objective-c file

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(selectorName:) name:NSNotification.NotificationName object:nil];