为什么计时器在timer.invalidate（）之后继续运行？

Question

Making a Yatzee game. I've got 5 images and a button on the screen:

@IBOutlet var button: UIButton!
@IBOutlet var dice1: UIImageView!
@IBOutlet var dice2: UIImageView!
@IBOutlet var dice3: UIImageView!
@IBOutlet var dice4: UIImageView!
@IBOutlet var dice5: UIImageView!

The images in my assets folder are named Dice1.png, Dice2.png all the way to Dice6.png.

When the button is tapped, Int.random picks one of the six images to display.

@IBAction func button(_ sender: Any) {
    dice1.image = UIImage(named: "Dice\(Int.random(in: 1...6))")
    dice2.image = UIImage(named: "Dice\(Int.random(in: 1...6))")
    dice3.image = UIImage(named: "Dice\(Int.random(in: 1...6))")
    dice4.image = UIImage(named: "Dice\(Int.random(in: 1...6))")
    dice5.image = UIImage(named: "Dice\(Int.random(in: 1...6))")
}

Works perfect!

Here's my problem:

I'd like the dice to cycle through the images rapidly after the first tap (as if the dice are being shaken in a cup), and then when the button is tapped again they should stop cycling (as if they were rolled).

I was thinking to do this by using a timer. When the button is pressed, the timer fires every 0.1 second, displaying a different image every 0.1 second.

var timer = Timer()
var state = 0

@IBAction func button(_ sender: Any) {
    if state == 0 {
        Timer.scheduledTimer(timeInterval: 0.1, target: self, selector: #selector(roll), userInfo: nil, repeats: true)
        button.setTitle("Roll", for: UIControl.State.normal)
        state = 1
    } else {
        timer.invalidate()
        button.setTitle("Shake", for: UIControl.State.normal)
        state = 0
    }
}

@objc func roll() {
    dice1.image = UIImage(named: "Dice\(Int.random(in: 1...6))")
    dice2.image = UIImage(named: "Dice\(Int.random(in: 1...6))")
    dice3.image = UIImage(named: "Dice\(Int.random(in: 1...6))")
    dice4.image = UIImage(named: "Dice\(Int.random(in: 1...6))")
    dice5.image = UIImage(named: "Dice\(Int.random(in: 1...6))")
}

After the button is pressed the first time, the dice are all changing every 0.1 seconds and it looks cool, and the button title changes to "Roll".

When the button is pressed the second time, the button title changes back to "Shake" as is expected, but rather than stopping, the dice start changing images twice as fast, which I think means the timer is being called again, rather than timer.invalidate()

I'm stumped because each time I press the button, the title changes as expected, meaning that the variable "state" is correctly switching back and forth between 0 and 1. However, timer.invalidate() apparently isn't the way to get the dice to stop rolling.

What's a better way to do this?

Thanks in advance for any help!

Answer 1

Timer.scheduledTimer(timeInterval...)

creates a timer and runs it. The function also returns the timer that is created, but it is not stored anywhere, so you cannot invalidate it.

Your first line

var timer = Timer()

is strange. You declare a variable, and assign a Timer object that has been created without any parameters. That object is totally useless. You later call

timer.invalidate()

which invalidates this timer, which is pointless because it wasn't used anywhere anyway.

I suppose you started writing code until it compiled without errors. Here's what you should have done:

// Create an optional Timer variable, initially nil
var timer: Timer?

// Later: Store a scheduled timer
timer = Timer.scheduledTimer(timeInterval...)

// Invalidate if the timer exists and set to nil
timer?.invalidate()
timer = nil

You can also get rid of the "state" variable and just test the timer variable instead of state == 0

if timer == nil {
} else {
}