Add delegate to custom iOS Flutter Plugin

Question

I'm working on integrating a custom iOS plugin into my Flutter app, problem is that I'm not getting delegate callbacks from the custom SDK Protocol.

I have to connect a bluetooth device to my app and I from the delegate calls I should receive the device's ID and pair it.

From the Flutter side, I can call the native functions from the customSdk: sdkInstance.scan() and there are even some internal (inside the sdk) prints with the scan results but my delegate calls are not in place.

I think I'm not correctly adding the delegate to the SDK, I can get this to work in a swift native app but not as a Flutter Plugin.

So here's more or less the code:

iOS Code

AppDelegate.swift

import UIKit
import Flutter

@UIApplicationMain
@objc class AppDelegate: FlutterAppDelegate {
  override func application(
    _ application: UIApplication,
    didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
  ) -> Bool {
    GeneratedPluginRegistrant.register(with: self)
    return super.application(application, didFinishLaunchingWithOptions: launchOptions)
  }
}

SwiftIosPlugin.swift

import Flutter
import UIKit
import CustomSDK

public class SwiftIosPlugin: NSObject, FlutterPlugin {

    let sdkInstance = CustomSDK.shared // This returns an instance of the SDK
    let channel: FlutterMethodChannel


    public static func register(with registrar: FlutterPluginRegistrar) 
      let channel = FlutterMethodChannel(name: "ios_plugin_channel", binaryMessenger: registrar.messenger())
      let instance = SwiftIosPlugin(channel)

      registrar.addMethodCallDelegate(instance, channel: channel)
      registrar.addApplicationDelegate(instance)
    }

    init (_ channel: FlutterMethodChannel) {
      self.channel = channel
      super.init()
      // In Swift, this is done in viewDidLoad()
      // Is this the correct place to do this?
      sdkInstance.addDelegate(self)

    }

public func handle(_ call: FlutterMethodCall, result: @escaping FlutterResult) {
      switch call.method {
        case "startScan":
         do {
           // This is being called and results printed
           try sdkInstance.scan()
          } catch {
            result(FlutterError(code: "400", message: "\(error)", details: nil))

          }
        case "connect":
            sdkInstance.connect(call, result)
    
        default:
          result(FlutterMethodNotImplemented)
      }
    }
}


// These should be called but are not
extension SwiftIosPlugin: CustomSDKDelegate {
    // Isn't called when scan() is executeed!
    public func onScanDevice(didScan id:String) {
        // do logic
    }

    public func onPairedDevice(didPair id:String) {
        // do logic
    }
}

score 0 · Answer 1 · answered Jan 13 '23 at 12:05

Update:

Silly thing that I hope nobody else has this trouble...

Two things to consider:

The problem was some of the delegate's functions public func onScanDevice(didScan id:String) was missing a parameter (even though there weren't any errors pointed out by Xcode).
sdkInstance.addDelegate(self) was called too early in the class "lifecycle".

Be mindful of these things and you won't have any trouble!

Add delegate to custom iOS Flutter Plugin

1 Answers1