Why didn't the UI update timely when using #IBAction func? - ios

Question

Here is the code of #IBAction func
#IBAction func touchCard(_ sender: UIButton) {
flipCount += 1
if let index = buttonCollection.firstIndex(of: sender) {
game.chooseCard(at: index)
updateViewFromModel() // I set breakpoint at here
}
}
Concentration.swift file, part of model of MVC
class Concentration {
var cards = [Card]()
var numberOfPairsOfCards: Int
var identifierOfOneAndOnlyOneCard: Int? {
didSet {
print("identifierOfOneAndOnlyOneCard: \(identifierOfOneAndOnlyOneCard)")
}
}
init(numberOfPairsOfCards: Int) {
self.numberOfPairsOfCards = numberOfPairsOfCards
for _ in 0..<numberOfPairsOfCards {
let card = Card()
cards += [card, card]
}
}
func chooseCard(at Index: Int) {
print("Index: \(Index)")
if !cards[Index].isMatched {
if let matchIndex = identifierOfOneAndOnlyOneCard, matchIndex != Index {
// check if cards match
if cards[matchIndex].identifier == cards[Index].identifier {
cards[matchIndex].isMatched = true
cards[Index].isMatched = true
}
cards[Index].isFaceUp = true
identifierOfOneAndOnlyOneCard = nil
} else {
// either no cards or 2 cards are face up
for flipDownIndex in cards.indices {
cards[flipDownIndex].isFaceUp = false
}
cards[Index].isFaceUp = true
identifierOfOneAndOnlyOneCard = Index
}
}
}
}
the code of func updateViewFromModel()
Card.swift file, part of model of MVC
struct Card {
var isFaceUp: Bool = false
var isMatched: Bool = false
var identifier = getUniqueIdentifier()
static var uniqueIdentifier: Int = 0
static func getUniqueIdentifier() -> Int{
uniqueIdentifier += 1
return uniqueIdentifier
}
}
These code are part of project concentration game from CS193p.
When I traced the code step by step, I found something confusing.
As mentioned before, I set a breakpoint at the line of
updateViewFromModel() in #IBAction func touchCard(_ sender:
UIButton)
Then I clicked 'Run' button of Xcode
The iPhone simulator came out.
the default UI image without any clicking
I clicked the first 'card'(actually, a button) from left to right in the first row
Xcode reacted and the UI remained the same as default
I started debug the code with LLDB, and I stepped into func updateViewFromModel()
When I stepped over to Line 64, it showed that the isFaceUp of the first card is true because I just clicked this card.
Let's go on, I stepped over to Line 68. Line 65 and 66 must be executed! What I think is that when executing Line 65 and 66, the
UI is supposed to change.But, why didn't the UI update timely?
I finished executing the left code in func updateViewFromModel because I didn't click any other card.
Finally it came to the end of #IBAction func touchCard, the UI still remained the same as default.
I clicked 'continue program execution' button, the UI responded correctly.I felt so weird.
What I want to figure out is that at Step 9 why didn't the UI update timely.
I will appreciate your help very much!

Answer 1

When you make changes on a view, it waits for a redraw cycle, thus the view won't be updated immediately. There is nothing wrong with IBAction, you put changes elsewhere and set a break point, it won't make any difference.

Answer 2

It may be due to slow simulators as i am also facing slow simulators issue i don't know if someone else also faced this or not, I doubt your facing this issue but i am not sure.
1- There is Nothing wrong with your code update your Simulators when working with Xcode 9.2 and simulators of IOS11.
2- Give it a try on your device