SpriteKit - Creating a timer

Question

How can I create a timer that fires every two seconds that will increment the score by one on a HUD I have on my screen? This is the code I have for the HUD:

    @implementation MyScene
{
    int counter;
    BOOL updateLabel;
    SKLabelNode *counterLabel;
}

-(id)initWithSize:(CGSize)size
{
    if (self = [super initWithSize:size])
    {
        counter = 0;

        updateLabel = false;

        counterLabel = [SKLabelNode labelNodeWithFontNamed:@"Chalkduster"];
        counterLabel.name = @"myCounterLabel";
        counterLabel.text = @"0";
        counterLabel.fontSize = 20;
        counterLabel.fontColor = [SKColor yellowColor];
        counterLabel.horizontalAlignmentMode = SKLabelHorizontalAlignmentModeCenter;
        counterLabel.verticalAlignmentMode = SKLabelVerticalAlignmentModeBottom;
        counterLabel.position = CGPointMake(50,50); // change x,y to location you want
        counterLabel.zPosition = 900;
        [self addChild: counterLabel];
    }
}

Answer 1

In Sprite Kit do not use NSTimer, performSelector:afterDelay: or Grand Central Dispatch (GCD, ie any dispatch_... method) because these timing methods ignore a node's, scene's or the view's paused state. Moreover you do not know at which point in the game loop they are executed which can cause a variety of issues depending on what your code actually does.

The only two sanctioned ways to perform something time-based in Sprite Kit is to either use the SKScene update: method and using the passed-in currentTime parameter to keep track of time.

Or more commonly you would just use an action sequence that starts with a wait action:

id wait = [SKAction waitForDuration:2.5];
id run = [SKAction runBlock:^{
    // your code here ...
}];
[node runAction:[SKAction sequence:@[wait, run]]];

And to run the code repeatedly:

[node runAction:[SKAction repeatActionForever:[SKAction sequence:@[wait, run]]]];

Alternatively you can also use performSelector:onTarget: instead of runBlock: or perhaps use a customActionWithDuration:actionBlock: if you need to mimick the SKScene update: method and don't know how to forward it to the node or where forwarding would be inconvenient.

See SKAction reference for details.

---

UPDATE: Code examples using Swift

Swift 5

 run(SKAction.repeatForever(SKAction.sequence([
     SKAction.run( /*code block or a func name to call*/ ),
     SKAction.wait(forDuration: 2.5)
     ])))

Swift 3

let wait = SKAction.wait(forDuration:2.5)
let action = SKAction.run {
    // your code here ...
}
run(SKAction.sequence([wait,action]))

Swift 2

let wait = SKAction.waitForDuration(2.5)
let run = SKAction.runBlock {
    // your code here ...
}
runAction(SKAction.sequence([wait, run]))

And to run the code repeatedly:

runAction(SKAction.repeatActionForever(SKAction.sequence([wait, run])))

Answer 2

In Swift usable:

var timescore = Int()  
var actionwait = SKAction.waitForDuration(0.5)
            var timesecond = Int()
            var actionrun = SKAction.runBlock({
                    timescore++
                    timesecond++
                    if timesecond == 60 {timesecond = 0}
                    scoreLabel.text = "Score Time: \(timescore/60):\(timesecond)"
                })
            scoreLabel.runAction(SKAction.repeatActionForever(SKAction.sequence([actionwait,actionrun])))

Answer 3

I've taken the swift example above and added in leading zeros for the clock.

    func updateClock() {
    var leadingZero = ""
    var leadingZeroMin = ""
    var timeMin = Int()
    var actionwait = SKAction.waitForDuration(1.0)
    var timesecond = Int()
    var actionrun = SKAction.runBlock({
        timeMin++
        timesecond++
        if timesecond == 60 {timesecond = 0}
        if timeMin  / 60 <= 9 { leadingZeroMin = "0" } else { leadingZeroMin = "" }
        if timesecond <= 9 { leadingZero = "0" } else { leadingZero = "" }

        self.flyTimeText.text = "Flight Time [ \(leadingZeroMin)\(timeMin/60) : \(leadingZero)\(timesecond) ]"
    })
    self.flyTimeText.runAction(SKAction.repeatActionForever(SKAction.sequence([actionwait,actionrun])))
}

Answer 4

Here's the full code to build a timer for SpriteKit with Xcode 9.3 and Swift 4.1

In our example the score label will be incrementd by 1 every 2 seconds. Here's final result

Good, let's start!

1) The score label

First of all we need a label

class GameScene: SKScene {
    private let label = SKLabelNode(text: "Score: 0")
}

2) The score label goes into the scene

class GameScene: SKScene {

    private let label = SKLabelNode(text: "Score: 0")

    override func didMove(to view: SKView) {
        self.label.fontSize = 60
        self.addChild(label)
    }
}

Now the label is at the center of the screen. Let's run the project to see it.

Please note that at this point the label is not being updated!

3) A counter

We also want to build a counter property which will hold the current value displayed by the label. We also want the label to be updated as soon as the counter property is changed so...

class GameScene: SKScene {

    private let label = SKLabelNode(text: "Score: 0")
    private var counter = 0 {
        didSet {
            self.label.text = "Score: \(self.counter)"
        }
    }

    override func didMove(to view: SKView) {
        self.label.fontSize = 60
        self.addChild(label)

        // let's test it!
        self.counter = 123
    }
}

4) The actions

Finally we want to build an action that every 2 seconds will increment counter

class GameScene: SKScene {

    private let label = SKLabelNode(text: "Score: 0")
    private var counter = 0 {
        didSet {
            self.label.text = "Score: \(self.counter)"
        }
    }

    override func didMove(to view: SKView) {
        self.label.fontSize = 60
        self.addChild(label)
        // 1 wait action
        let wait2Seconds = SKAction.wait(forDuration: 2)
        // 2 increment action
        let incrementCounter = SKAction.run { [weak self] in
            self?.counter += 1
        }
        // 3. wait + increment
        let sequence = SKAction.sequence([wait2Seconds, incrementCounter])
        // 4. (wait + increment) forever
        let repeatForever = SKAction.repeatForever(sequence)

        // run it!
        self.run(repeatForever)
    }
}

Answer 5

The following code creates a new thread and waits 2 seconds before doing something on the main thread:

BOOL continueIncrementingScore = YES;

dispatch_async(dispatch_queue_create("timer", NULL);, ^{
    while(continueIncrementingScore) {
        [NSThread sleepForTimeInterval:2];
        dispatch_async(dispatch_get_main_queue(), ^{
            // this is performed on the main thread - increment score here

        });
    }
});

Whenever you want to stop it - just set continueIncrementingScore to NO