SKAction等待间隔不一致

Question

I have a function that creates SpriteNode copies and move each copy along a rectangle path at a specified interval. I have a problem with this interval that the action is executed at inconsistent interval making odd gaps between sprite nodes while action is running.

var items = [SKSpriteNode]();
let item = SKSpriteNode(imageNamed: "Spaceship");

func createItem(scene: SKScene) {

    let square = UIBezierPath(rect: CGRect(x: -300, y: -150,  width: 700, height: 300));
    let follow = SKAction.follow(square.cgPath, asOffset: false, orientToPath: false, duration: 5.0);

    for i in 0..<6 {

        if let itemCopy = item.copy() as? SKSpriteNode {
            itemCopy.position = CGPoint(x: -300, y: -150);
            items.append(itemCopy);
            scene.addChild(itemCopy);
            let otherWait = SKAction.wait(forDuration: 1.0, withRange: 2.0);
            let otherSequence = SKAction.sequence([otherWait, SKAction.repeatForever(follow)]);
                itemCopy.run(otherSequence);
            }
        }
}

My understanding is that I can't rely on for loop for timing and this issue could be caused by that. Is there a way to get around this with some kind of callback function?

Answer 1

The problem here is not related to the for loop, but comes from that fact you're using wait(forDuration:withRange:) , and this is the intended behaviour. The documentation states:

Creates an action that idles for a randomized period of time.

I think you're looking for the wait(forDuration:) method and it will work just fine :)