Update UIView before calling other function?

Question

I am working in Swift. When a user presses a UIButton it calls a function ButtonPressed(). I would like ButtonPressed() to do two things:

Update the UIView by removing the current buttons and texts, then uploading some new text.
Call function TimeConsumingCalculation(). TimeConsumingCalculation is the complicated part of my app and does some calculations which take about 20 seconds or so to complete.

Right now, I have the code in the basic order:

ButtonPressed(){
self.Button.removeFromSuperview()
TimeConsumingCalculation()
}

However, it will not remove the button or do any other UI updates or additions until after the TimeConsumingCalculation is complete. I have read and attempted a few guides on closures and asynchronous functions, but have had no luck. Is there a special property with UIView that is causing it to be updated last?

As a side note - I have already attempted putting all UI actions in a separate function and calling it first. It doesn't work. The time consuming function does not take any variables from the buttons or UI or anything like that.

Thanks!

`timeConsumingFunction` is blocking the main queue, You need to dispatch that function asynchronously on a background queue and provide a completion handler that it can invoke once it is done. Don't forget to dispatch any UI updates back onto the main queue — Paulw11, Jan 29 '17 at 00:50
as @Paulw11 suggest http://stackoverflow.com/questions/16283652/understanding-dispatch-async — , Jan 29 '17 at 00:52
please write `buttonPressed` (no first letter uppercase - which is reserved for class/protocol) — muescha, Jan 29 '17 at 02:15

score 1 · Accepted Answer · answered Jan 29 '17 at 00:59

1

It seems like timeConsumingCalculation() is blocking the main queue, which is in charge of UI updates. Try calling it like this instead and use the isHidden property to hide the button instead of removing it from the view completely.

ButtonPressed(){
   self.Button.isHidden = true
   DispatchQueue.global(qos: DispatchQoS.QoSClass.userInitiated).async {
      self.timeConsumingCalculation()
   }
}

here you call timeConsumingCalculation() asynchronously on a background thread. The quality of service we give it is userInitiated, read more about quality of service classes here

answered Jan 29 '17 at 00:59

MikeG

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I very much appreciate this response. It fixed the problem I was having. I was aware it was due to the asynchronous nature, but was having trouble fixing it otherwise! – user7299543 Jan 29 '17 at 01:12
if the calculation is very long you should entertain the users - otherwise about >1sec they think you app is broken or crashed. you can do this with a) spinnig loading indicator or better: b) with a process bar where the user can see how many iterations of the toal iterations are calculated. – muescha Jan 29 '17 at 02:18
or if you have some early results: present this to the user - and the user is busy to read this informations and don't get bored – muescha Jan 29 '17 at 02:19
Agreed! I have an animation called when they are waiting. – user7299543 Jan 30 '17 at 02:08

Update UIView before calling other function?

1 Answers1