How to choose from an array of sprites in swift - ios

Question

So basically I am looking to choose one of the 4 different coloured balls at random to come into the scene which each have an animation, physics properties and movement & spacing that I have already coded. I am not sure exactly how to make the array then choose at random from the array of the 4 coloured balls so that I have one ball chosen at random to come into the scene.
To make it more clear what I'm asking here's some code (I only use two balls in this code so you don't have to read as much):
var moveandremove = SKAction() < this is in my ballScene.swift
The spawn runBlock is inside didMovetoView
let spawn = SKAction.runBlock({
() in
self.allballs()
})
let delay = SKAction.waitForDuration(2.0)
let SpawnDelay = SKAction.sequence([spawn, delay])
let spawndelayforever = SKAction.repeatActionForever(SpawnDelay)
self.runAction(spawndelayforever)
let distance = CGFloat(brnball.frame.width * 20 + brnball.frame.width)
let moveball = SKAction.moveByX(-distance, y: 0, duration: NSTimeInterval(0.003 * distance))
let removeball = SKAction.removeFromParent()
moveandremove = SKAction.sequence([moveball])
}
func allballs() {
TextureAtlasblk = SKTextureAtlas(named: "blkball")
for i in 1...TextureAtlasblk.textureNames.count{
var Name = "blkball_\(i)"
blkarray.append(SKTexture(imageNamed: Name))
}
blkball = SKSpriteNode(imageNamed: "blkball_1")
blkball.position = CGPoint(x: CGRectGetMidX(self.frame) + 100, y: CGRectGetMidY(self.frame))
blkball.zPosition = 7
blkball.setScale(0.1)
self.addChild(blkball)
blkball.runAction(SKAction.repeatActionForever(SKAction.animateWithTextures(blkarray, timePerFrame: 0.2)))
//brownball
TextureAtlasbrn = SKTextureAtlas(named: "brnball")
for i in 1...TextureAtlasbrn.textureNames.count{
var Name = "brnball_\(i)"
brnarray.append(SKTexture(imageNamed: Name))
}
brnball = SKSpriteNode(imageNamed: "brnball_1")
brnball.position = CGPoint(x: CGRectGetMidX(self.frame) + 50, y: CGRectGetMidY(self.frame))
brnball.zPosition = 7
brnball.setScale(0.1)
self.addChild(brnball)
brnball.runAction(SKAction.repeatActionForever(SKAction.animateWithTextures(brnarray, timePerFrame: 0.2)))
Here is my terrible starting point at trying to make an array to choose from each ball (this is inside my allballs() function):
var ballarray: NSMutableArray = [blkball, brnball, yelball, bluball]
runAction(moveandremove)
I am new to swift and pretty hopeless, would be awesome if someone could help me out :)
Thanks

Answer 1

It's hard for me to find the array that you're talking about in your code. But nevertheless, I can still show you how.
Let's say we have an [Int]:
let ints = [10, 50, 95, 48, 77]
And we want to get a randomly chosen element of that array.
As you may already know, you use the subscript operator with the index of the element to access an element in the array, e.g. ints[2] returns 95. So if you give a random index to the subscript, a random item in the array will be returned!
Let's see how can we generate a random number.
The arc4random_uniform function returns a uniformly distributed random number between 0 and one less the parameter. Note that this function takes a UInt32 as a parameter and the return value is of the same type. So you need to do some casting:
let randomNumber = Int(arc4random_uniform(UInt32(ints.count)))
With randomNumber, we can access a random element in the array:
let randomItem = ints[randomNumber]
Try to apply this technique to your situation.
Here's a generic method to do this as well:
func randomItemInArray<T> (array: [T]) -> T? {
if array.isEmpty {
return nil
}
let randomNumber = Int(arc4random_uniform(UInt32(array.count)))
return array[randomNumber]
}
Note that if the array passed in is empty, it returns nil.

Answer 2

You could make and extension for Array that returns a random element.
extension Array {
func randomElement() -> Element {
let i = Int(arc4random_uniform(UInt32(count - 1)))
return self[i]
}
}
You could take that a step further and allow a function to be applied directly to a random element.
mutating func randomElement(perform: (Element) -> Element) {
let i = Int(arc4random_uniform(UInt32(count - 1)))
self[i] = perform(self[i])
}
You can use this function when using an array of reference types.
func randomElement(perform: (Element) -> ()) {
let i = Int(arc4random_uniform(UInt32(count - 1)))
perform(self[i])
}