You can make a method call run after a number of seconds have elapsed using
perform(_:withObject:afterDelay:), like this:
perform(#selector(yourMethodHere), with: nil, afterDelay: 1)
However, what if you change your mind, and decide you don't want
yourMethodHere() to be called? As long as you act before that timer expires, you have two options: cancel that specific delayed call, or cancel all delayed calls.
To cancel that specific method call, you need to use the method
NSObject. Provide it with a target (where the method was going to be called), as well as the same selector and object you used when calling
perform(), and it will cancel that delayed call.
// set up a delayed call… perform(#selector(yourMethodHere), with: nil, afterDelay: 1) // …then immediately cancel it NSObject.cancelPreviousPerformRequests(withTarget: self, selector: #selector(yourMethodHere), object: nil)
Being able to filter the cancellation by both selector and object means you can be very specific: "cancel the printing call for this filename."
If you've made a number of delayed calls and want to cancel them all – very helpful if you're about to leave a view controller, for example, and want to abandon any queued work – you can use this method call instead:
That will cancel every call that was queued up on
self, regardless of which selectors and objects were used.
If you're making delayed calls on a specific object, just use that object in place of
self. For example:
myObj.perform(#selector(yourMethodHere), with: nil, afterDelay: 1) NSObject.cancelPreviousPerformRequests(withTarget: myObj, selector: #selector(yourMethodHere), object: nil)
Available from iOS 4.0
Did this solution work for you? Please pass it on!
Other people are reading…
About the Swift Knowledge Base
This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.
Become a Swift guru
I wrote a book called Pro Swift that's dedicated to helping you master the Swift language, and it includes seven hours of video demonstrating each technique!