Just in case someone made the same stupid mistake as I did:
Check out if the method name of what you expect of being didSelect
may accidentally be gotten didDeselect
in some way. It took about two hours for me to find out ...
Swift
Short answer
Use a NotificationCenter
observer rather than viewWillAppear
.
override func viewDidLoad() {
super.viewDidLoad()
// set observer for UIApplication.willEnterForegroundNotification
NotificationCenter.default.addObserver(self, selector: #selector(willEnterForeground), name: UIApplication.willEnterForegroundNotification, object: nil)
}
// my selector that was defined above
@objc func willEnterForeground() {
// do stuff
}
Long answer
To find out when an app comes back from the background, use a NotificationCenter
observer rather than viewWillAppear
. Here is a sample project that shows which events happen when. (This is an adaptation of this Objective-C answer.)
import UIKit
class ViewController: UIViewController {
// MARK: - Overrides
override func viewDidLoad() {
super.viewDidLoad()
print("view did load")
// add notification observers
NotificationCenter.default.addObserver(self, selector: #selector(didBecomeActive), name: UIApplication.didBecomeActiveNotification, object: nil)
NotificationCenter.default.addObserver(self, selector: #selector(willEnterForeground), name: UIApplication.willEnterForegroundNotification, object: nil)
}
override func viewWillAppear(_ animated: Bool) {
print("view will appear")
}
override func viewDidAppear(_ animated: Bool) {
print("view did appear")
}
// MARK: - Notification oberserver methods
@objc func didBecomeActive() {
print("did become active")
}
@objc func willEnterForeground() {
print("will enter foreground")
}
}
On first starting the app, the output order is:
view did load
view will appear
did become active
view did appear
After pushing the home button and then bringing the app back to the foreground, the output order is:
will enter foreground
did become active
So if you were originally trying to use viewWillAppear
then UIApplication.willEnterForegroundNotification
is probably what you want.
Note
As of iOS 9 and later, you don't need to remove the observer. The documentation states:
If your app targets iOS 9.0 and later or macOS 10.11 and later, you
don't need to unregister an observer in its dealloc
method.
Best Answer
You can just call:
Individual sections and items can also be reloaded: