Quickly updating UIView background color in Swift? - ios

Question

I have an array of times for when the background color of a UIView should change colors. The array holds values from 0-10000ms, where each index is the duration between the first change and the current change. I have implemented a loop to execute the tasks at the scheduled times, and using print statements, it seems to be working. However, the background color only changes to the last color instead of changing continuously.
I believe this is because the background color does not update until the loop is done. Is this correct, and if so, how can I fix this?
sendingView.backgroundColor = UIColor.black
let startingTime = getCurrentMillis()
var found = false
for time in receivingMsgData {
while(!found) {
let curDuration = getCurrentMillis() - startingTime
if curDuration > time {
if(sendingView.backgroundColor == UIColor.black) {
sendingView.backgroundColor = UIColor.white
print("playing at \(getCurrentMillis()-startingTime) turning white")
} else {
sendingView.backgroundColor = UIColor.black
print("playing at \(getCurrentMillis()-startingTime) turning black")
}
found = true
}
}
found = false
}

Answer 1

Try something like this
DispatchQueue.global(qos: .userInitiated).async {
let delay:TimeInterval = 0.01 // Seconds
for index in 0..<100 {
if index % 2 == 0 {
Thread.sleep(forTimeInterval: delay)
DispatchQueue.main.async {
self.view.backgroundColor = UIColor.white
print("white")
}
}else{
Thread.sleep(forTimeInterval: delay)
DispatchQueue.main.async {
self.view.backgroundColor = UIColor.black
print("black")
}
}
}
}
Do your action in async thread and change the color on main thread
You doing to much in main thread causing it to hang, aslo put some delay so that user can view the animation
try something like this in your case
let delay:TimeInterval = 0.01 // Seconds
sendingView.backgroundColor = UIColor.black
let startingTime = getCurrentMillis()
var found = false
DispatchQueue.global(qos: .userInitiated).async {
for time in receivingMsgData {
while(!found) {
let curDuration = getCurrentMillis() - startingTime
if curDuration > time {
if(sendingView.backgroundColor == UIColor.black) {
Thread.sleep(forTimeInterval: delay)
DispatchQueue.main.async {
sendingView.backgroundColor = UIColor.white
print("playing at \(getCurrentMillis()-startingTime) turning white")
}
} else {
Thread.sleep(forTimeInterval: delay)
DispatchQueue.main.async {
sendingView.backgroundColor = UIColor.black
print("playing at \(getCurrentMillis()-startingTime) turning black")
}
}
found = true
}
}
found = false
}
}

Answer 2

The code you posted either blocks the main thread or the operation is not on the main thread when setting the color. Both of the situations will most likely result in no changes until the execution of the whole loop is done or after some time even.
When you are dealing with data that are scheduled at some time which may be irrelevant to the speed of the screen update you need to give the color on demand when the screen will refresh.
In your case I would suggest using a display link CADisplayLink which is designed to trigger whenever the screen should refresh. You can even get the current time value since the beginning from the display link itself. That elapsed time can be used the same way you are already using curDuration in your code. Assuming that the rest of the code works fine that is.

Answer 3

I believe this is because the background color does not update until the loop is done. Is this correct
Yes, it is. Drawing doesn't happen until all your code on the main thread finishes and the CATransaction is committed. You would need to do one of two things:
Run your time-consuming code on a background thread, coming to the main thread only to talk to the interface and set the color.
Use some form of delay to get off the main thread long enough to let drawing take place before continuing with your "loop".