EggTimer MVC iOS project

Controller_ViewController.swift

import UIKit

class ViewController: UIViewController {
    @IBOutlet weak var bar: UIProgressView!

    override func viewDidLoad() {
        super.viewDidLoad()
        bar.alpha = 0
    }

    @IBAction func onChoiceSelected(_ sender: UIButton) {
        if let currentTitle = sender.currentTitle, let eggTimer = MainModel.msTimers.first(where: { x in x.name == currentTitle }) {
            bar.progress = 0
            bar.alpha = 1
            let model = MainModel(
                eggTimer.msTime / 1000,
                onIncrement: { (progress: Float) in self.bar.progress = progress},
                onFinish: {self.bar.alpha = 0}
            )
            model.startTimer()
        }
    }
}

Model_EggTimer.swift

import Foundation

struct EggTimer {
    let name: String
    let msTime: Float

    init(_ name: String, _ seconds: Int) {
        self.name = name
        msTime = Float(seconds) * 1000
    }
}

Model_MainModel.swift

import Foundation

var timer = Timer()
func clearTimer() {
    timer.invalidate()
}

struct MainModel {
    static let msTimers = [
        EggTimer("Soft", 5),
        EggTimer("Medium", 8),
        EggTimer("Hard", 12)
    ]

    var seconds: Float = 0
    let initialValue: Float

    typealias IncrementCallback = (_ progress: Float) -> Void
    typealias FinishCallback = () -> Void
    let onIncrement: IncrementCallback
    let onFinish: FinishCallback
    // why need @escaping
    init (_ initialValue: Float, onIncrement: @escaping IncrementCallback, onFinish: @escaping FinishCallback) {
        clearTimer()
        self.initialValue = initialValue
        self.onIncrement = onIncrement
        self.onFinish = onFinish
    }

    func startTimer() {
        //why need to capture self?
        var this = self
        timer = Timer.scheduledTimer(withTimeInterval: 1, repeats: true) { _ in this.onTimerUpdate() }
    }

    private mutating func onTimerUpdate() {
        if seconds < initialValue {
            seconds += 1
            onIncrement(seconds / initialValue)
        } else {
            onFinish()
            clearTimer()
        }
    }
}