jj_hennessy jj_hennessy - 1 year ago 72
Swift Question

Eliminating repeats in a switch statement w/ Swift in iOS

In this small practice app I am building, the background is supposed to keep alternating colors every .25 seconds because it looks really cool. However because of the fact that I am using the "arc4random_uniform" function, it occasionally will pick the same case twice in a row, resulting in a long duration of the same color which I do not like. Any ideas on how to eliminate immediate repeats in these switch statements so that it does pick the same case twice in a row?

switch arc4random_uniform(10) {
case 0:
self.backgroundImage.backgroundColor = UIColor.redColor()
case 1:
self.backgroundImage.backgroundColor = UIColor.orangeColor()
case 2:
self.backgroundImage.backgroundColor = UIColor.yellowColor()
case 3:
self.backgroundImage.backgroundColor = UIColor.greenColor()
case 4:
self.backgroundImage.backgroundColor = UIColor.blueColor()
case 5:
self.backgroundImage.backgroundColor = UIColor.purpleColor()
case 6:
self.backgroundImage.backgroundColor = UIColor.blackColor()
case 7:
self.backgroundImage.backgroundColor = UIColor.whiteColor()
case 8:
self.backgroundImage.backgroundColor = UIColor.brownColor()
case 9:
self.backgroundImage.backgroundColor = UIColor.grayColor()
case 10:
self.backgroundImage.backgroundColor = UIColor.blackColor()

self.backgroundImage.backgroundColor = UIColor.clearColor()



Answer Source

Eli's answer will work, but regenerating random numbers in a while loop is unnecessarily inefficient. Instead, if the current random number is the same as the previous, I recommend incrementing the random number using the remainder when divided by 10 and using that number in the switch statement so that the random operation isn't repeated unnecessarily, ex:

var prevNum:UInt32 = 0

func changeColor() {
    var randomNum = arc4random_uniform(10)
    if randomNum == prevNum {
        randomNum = (randomNum+1)%10
    prevNum = randomNum

    // insert your switch statement here

Theoretically (although it's highly unlikely in practice) Eli's code can cause an infinite loop.

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