[Swift] Using Swift Protocol in Objective-C

I have a ListView that is populated with detected device information when my scanning service has successfully scanned nearby devices. My scanning service is in Objective C and my App is in Swift, so I will have to use Swift protocol in Objective C functions.

The goal is simple: when device is found, notify the ListView controller. The ListView controller will then retrieve detected device information and then populate the ListView. Note that in the following snippet I have omitted how to populate data into ListView

If you follow the following steps you should have no problem using Swift protocol in Objective C files.

1. Declare the protocol in Swift, I have decided to create a new file called Delegate.swift for easy maintenance.

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//... @objc public protocol NotifyScanCompletionDelegate{ func NotifyScanCompletion() } //...

2. Declare swift protocol in objective c header:

1	@property (nonatomic, weak) id<NotifyScanCompletionDelegate> NotifyScanCompletion;

3. Set up the Swift protocol in the function that will be used in Objective C .m file. In my case I wish to emit a signal when I discover a device, I will setup my delegate in the deviceFound function in .m file.

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@implementation ScanDeviceClass //... //omitted //... - (void) deviceFound { NSLog(@"deviceWasAdded Callback %s", __PRETTY_FUNCTION__); [self.NotifyScamCompletion NotifyScanCompletion:self]; } @end

Reminder: don't forget to #import {name}-Swift.h to Objective C .m file

4. Extend the protocol in your Controller class and implement the delegate in the ListViewController.swift. Remember to initialize it.

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class deviceListViewController: UITableViewController, UITableViewDelegate, NotifyScanCompletionDelegate { var scanService:ScanDeviceClass! //.....omitted override func viewDidLoad() { super.viewDidLoad() scanService = ScanDeviceClass.getInstance() scanService.NotifyScanCompletion = self scanService.startScanDiscovery() } func NotifyScanCompletion(getData: AnyObject?) { populateDevicesList() println(">>>>> delegate successful <<<<<") } //.....omitted }

Now I can see a list of devices after scanning is successful, automagically.