How to properly manage groups of sprites onscreen

问题

I'm building my first game in Swift and I wanted to know how to go about handling multiple on screen sprites at once. My game pushes sprites on to screen with addChild continuously, so there are many active at once. I realized that I didn't have a proper way of simultaneously affecting all of them- like if I wanted to affect a physics property of all enemy sprites at once. So far I created an empty array var enemySprites = [enemyType1]() at the begining of GameScene and have been appending the sprite instances to it instead of using addChild to draw them directly to the scene. However, I'm not able to simply loop through and draw them to screen with:

    for enemy in enemySprites{
        addChild(enemy)
    }

this bit of code is in the override func update(currentTime: CFTimeInterval) function, so maybe I'm just misplacing it? Any help on how to go about this would be great!

回答1:

Sam,

Here's some sample code to update enemies when your lives reach 0:

First, we set a property observer on the lives property so we can call a function when you lose all lives:

var lives = 3 {
    didSet {
        if lives == 0 {
        updateEnemies()
    }
}

And then a function to enumerate over all the enemies and change each one's velocity to (0, 0):

func update enemies() {
        enumerateChildNodesWithName("type1") {
            node, stop in
            let enemy = node as! SKSpriteNode
            enemy.physicsBody?.velocity = CGVector(dx: 0, dy: 0)
        }
}

回答2:

Instead of use update method, you could use a timer. From sources:

public class func scheduledTimerWithTimeInterval(ti: NSTimeInterval, target aTarget: AnyObject, selector aSelector: Selector, userInfo: AnyObject?, repeats yesOrNo: Bool) -> NSTimer

So if you follow Apple guide, it will be for example:

NSTimer.scheduledTimerWithTimeInterval(0.5, target: self, selector: Selector("spawnAlien:"), userInfo: myParameter, repeats: true)

func spawnAlien(timer : NSTimer) {
      if let myUserInfo = timer.userInfo {
         print(myUserInfo) // a parameters passed to help you to the alien creation
      }
      timer.invalidate()
}

BUT according to Whirlwind I agree with him and with LearnCocos2d work, sprite-kit don't work well with timers (as explained in the link by LearnCocos2d) and the better way, especially as you say you develop your first game, it's to use SKAction, a combination of actions to achieve the similar behavior obtained by NSTimer.

I've think about a function or an extension, let me know if it's work as expected:

extension SKAction {
   class func scheduledTimerWithTimeInterval(time:NSTimeInterval, selector: Selector, repeats:Bool)->SKAction {
      let call = SKAction.customActionWithDuration(0.0) { node, _ in
          node.performSelector(selector)
      }
      let wait = SKAction.waitForDuration(time)
      let seq = SKAction.sequence([wait,call])
      let callSelector = repeats ? SKAction.repeatActionForever(seq) : seq
      return callSelector
   } 
}

Usage:

let spawn = SKAction.scheduledTimerWithTimeInterval(time, selector: #selector(GenericArea.spawnAlien), repeats: true)
self.runAction(spawn,withKey: "spawnAlien")

来源：https://stackoverflow.com/questions/38728823/how-to-properly-manage-groups-of-sprites-onscreen

标签

ios

swift

sprite-kit