XCode 6 - Delay iterations in a loop? - xcode

Question

I am testing a basic animation using a while loop. When the user touches a start button, an image randomly appears with every click of the button. I then placed the same code within a while loop and the image does not seem to move. I am thinking that it is just moving too fast through the iterations and therefore appears to not be moving. So, is there a way, simple or otherwise, that I can delay the speed of the loop so I can see a transition to some degree? I'm thinking that the speed of the loop is what is doing this, as text is instantly outputted to the label, thus I know the loop is working at least. Here is what I have...
#IBAction func btnStart(sender: AnyObject) {
isMoving = true
var i = 0
while (i != 200) //arbitrary number of iterations chosen for this example
{
var x = arc4random_uniform(400)
var y = arc4random_uniform(400)
myButton.center = CGPointMake(CGFloat(x), CGFloat(y));
++i
lblHitAmount.text = String(i) //200 appears instantaneously in label, loop is working
}
}
EDIT:
var timer = NSTimer()
var counter = 0
timer = NSTimer.scheduledTimerWithTimeInterval(0.5, target: self, selector: Selector("tolabel"), userInfo: nil, repeats: true)
var i = 0
while (i != 800)
{
var x = arc4random_uniform(400)
var y = arc4random_uniform(400)
btnBug.center = CGPointMake(CGFloat(x), CGFloat(y));
++counter
++i
//lblHitAmount.text = String(i)
}
func tolabel(){
lblHitAmount.text = String(counter++)
}

Answer 1

So to understand why you are getting this behavior, you need to understand the idea of the run loop. Every app has a run loop that is essentially an infinite loop. Each iteration of the loop, it does a number of things. Two of the primary things are handling events (like tapping a button) and updating the GUI. The GUI is updated only once per run loop.
Your event handling code (for tapping btnStart), is run inside a single run loop iteration. No matter how long you delay your loop (say 10 minutes), the GUI will remain frozen until it finishes and then only display the last value the text was set to. This is why you get freezes in apps and programs. They have something running inside a single iteration of the run loop not allowing the execution to return to updating the GUI.
If you want to update the text periodically, you should look into NSTimer. You can setup a timer that repeats every X seconds and each time the timer is fired it will be executed in a different iteration of the run loop allowing the GUI to be updated with the intermediate values:
#IBAction func btnStart(sender: AnyObject) {
NSTimer.scheduleTimerWithTimeInterval(0.5, target: self, selector: "updateText:", userInfo: nil, repeats: false)
}
func updateText(timer: NSTimer) {
// do something to update lblHitAmount.text
// if you want to execute this again run:
NSTimer.scheduleTimerWithTimeInterval(0.5, target: self, selector: "updateText:", userInfo: nil, repeats: false)
// if you are done with the "loop" don't call scheduleTimerWithTimeInterval again.
}