Let's say you're writing the IOS component of a Flutter plugin in Swift.

You have your MyFlutterPlugin.swift file open in XCode.

So that we know what we're talking about the same thing, it's the file that looks like this:

public class MyFlutterPlugin: NSObject, FlutterPlugin {

    public static func register(with registrar: FlutterPluginRegistrar) {
        let channel = FlutterMethodChannel(name: "my_flutter_plugin", binaryMessenger: registrar.messenger())
        let instance = SwiftMetronomeFlutterPlugin()
        registrar.addMethodCallDelegate(instance, channel: channel)
    }

    public func handle(_ call: FlutterMethodCall, result: @escaping FlutterResult) {

    // ...

    }

}

This file exists on disk at:

[your_plugin_project_name]/ios/classes/MyFlutterPlugin.swift

How could you add a resource, for example an audio (WAV) file, such that it could be referenced from within MyFlutterPlugin.swift?

In a normal (not Flutter) IOS app, I have accomplished this by simply dragging the WAV file into XCode where it sits alongside ViewController.swift (in the same folder), and referenced it from within the ViewController like this:

let clack_Path = Bundle.main.path(forResource: "clack", ofType: "wav")
let clack_URL = URL(fileURLWithPath: clack_Path!)

But, if I try that same approach from within MyFlutterPlugin.swift (putting the audio file alongside MyFlutterPlugin.swift), I get an error that clack_Path is null.

So where is the correct place to put the file, and how to properly reference it?

I can't find any code examples, tutorials, or documentation (at least not any that I recognize as being useful) on this specific problem. Hopefully it's actually possible to do on IOS... I've already got the resources included and working on the Android side of the plugin.