UITextView does not update during loop - ios

Question

so I have tried 2 different ways to display the timer count down on the screen.
the code will print to the console but not to the UITextView (in both loop cases) in the repeat the UITextView ends with a 0 and that is the only thing it displays other than original txt "time count".... in the case where the commented loop is implemented the UITextView only displays the 1 (end of count down)... why is it printing to the console though these commands are in the same brackets as UITextView and they repeat
the image is after running code and clicking Soft (this is spin off of app brewery egg timer)
//
// ViewController.swift
// EggTimer
//
// Created by Angela Yu on 08/07/2019.
// Copyright © 2019 The App Brewery. All rights reserved.
//
import UIKit
let softTime = 5
let medTime = 7
let hardTime = 12
class ViewController: UIViewController {
#IBOutlet weak var timerTextView: UITextView!
#IBAction func eggHardnessButton(_ sender: UIButton) {
let hardness = sender.currentTitle
func timeCountDownSoft() {
var time = 3
repeat {
time = time - 1 //repeats
timerTextView.selectAll("") // does not repeat
timerTextView.insertText("") // does not repeat
let timeWord = String(time) // repeats
timerTextView.insertText(timeWord)//does not repeat
print(time) //repeats
sleep(1) //repeats
} while time >= 1
/*for timer in stride(from: 2, to: 0 , by: -1){
let time = String(timer)
timerTextView.selectAll("")
timerTextView.insertText("")
timerTextView.insertText(time)
print(time)
sleep(1)
}*/
}
func timeCountDownMed() {
for timer in stride(from: 420, to: 0 , by: -1) {
print(timer)
sleep(1)
}
}
func timeCountDownHard() {
for timer in stride(from: 720, to: 0 , by: -1) {
print(timer)
sleep(1)
}
}
if hardness == "Soft" {
print(softTime) // does not repeat
timeCountDownSoft() // does not repeat
} else if hardness == "Medium" {
print(medTime)
timeCountDownMed()
} else {
print(hardTime)
timeCountDownHard()
}
}
}

Answer 1

You never (well, almost never) want to use sleep().
The reason your text is not updating is because you are running closed-loops that never allow UIKit to update the view.
What you want to do instead is to use a repeating Timer with a one-second interval. Each time the timer fires, decrement your counter and update the UI. When the counter reaches Zero, stop the timer.
Here's a simple example:
import UIKit
let softTime = 5
let medTime = 7
let hardTime = 12
class ViewController: UIViewController {
#IBOutlet weak var timerTextView: UITextView!
var theTimer: Timer?
#IBAction func eggHardnessButton(_ sender: UIButton) {
let hardness = sender.currentTitle
var numSeconds = 0
// set number of seconds based on button title
switch hardness {
case "Soft":
numSeconds = softTime * 60
case "Medium":
numSeconds = medTime * 60
case "Hard":
numSeconds = hardTime * 60
default:
// some other button called this func, so just return
return()
}
// stop current timer if it's running
if let t = theTimer {
if t.isValid {
t.invalidate()
}
}
// update text field with selected time
let timeWord = String(numSeconds)
self.timerTextView.text = timeWord
// start a timer with 1-second interval
theTimer = Timer.scheduledTimer(withTimeInterval: 1.0, repeats: true) { timer in
numSeconds -= 1
let timeWord = String(numSeconds)
self.timerTextView.text = timeWord
// if we've reached Zero seconds remaining
if numSeconds == 0 {
// stop the timer
timer.invalidate()
}
}
}
}

Answer 2

Several points:
When your app changes the UI, those changes do not actually get
rendered to the screen until your code returns and visits the app's
event loop. Thus, with your repeat loop, nothing will show up on in
the UI until the loop completes
Do not use sleep() on the main thread. That blocks everything, and
your app comes to a screeching halt.
If you want to update the UI once a second, set up a repeating timer
that fires once a second and do your UI updates in the timer code.