My code:
overide func viewDidLoad() {
NSNotificationCenter.defaultCenter().addObserver(self, selector: "activeAgain", name: UIApplicationWillEnterForegroundNotification, object:nil)
}
func activeAgain() {
println("ActiveAgain") //Comes immediately
callSeparateFunction() //Takes 5s
}
Why does the println comes immediately and the separate function call takes up to 5s? I have to call a new function when the app comes back to foreground. Thanks!
Related
In one of the view controller files in my project, there are two functions, one is called in viewdidload and another is called by Notification and observers. Those functions do exactly the same thing, and I was wondering if I get rid of one of the functions, especially the one without using #objc in front. (otherwise I get an error)
override func viewDidLoad() {
super.viewDidLoad()
configureNotifications()
displayItems()
}
func displayItems() {
fetchLiveEvents { [weak self] in
self?.applySnapshot(animatingDifferences: true)
}
}
func configureNotifications() {
NotificationCenter.default.addObserver(self, selector: #selector(updateExistingItem), name: .updateExistingItem, object: nil)
}
#objc func updateExistingItem() {
fetchLiveEvents { [weak self] in
self.applySnapshot(animatingDifferences: true)
}
}
Since I'm using the notification canter, I cannot get rid of #objc in front of updateExistingItem function. However, the updateExistingItem and displayItems are doing exactly something, so I feel it's kinda redundant and I was thinking to get rid of displayItems function from the viewDidLoad and call updateExistingItem (probably change the name) in viewdidLoad instead.
Is there any convention in Swift programming that keeps both #objc and normal function when they are doing the same thing? or is it just a personal preference and doesn't matter to leave both of them?
viewDidLoad just call once when the screen is present if you go to another screen by pushing a viewcontroller or presenting a controller and comeback to this controller the viewDidLoad didn't triggered it will never called again until the next run / terminate the app and open again.
so your function is called by the notification to run again when this screen appear.
// just called once
override func viewDidLoad() {
super.viewDidLoad()
configureNotifications()
displayItems()
}
// just called every time when you popped a viewController or tap on tab bar items using tabbar controller
override func viewWillAppear() {
super.viewDidLoad()
displayItems()
}
in your scenario may be you came back to this screen by present some other screen and do some functionality there and call the notification to be trigger on this screen so nothing will trigger if your present a screen by modal presentation style over full screen
That's why called the notification to start displaying item again
override func viewDidLoad() {
super.viewDidLoad()
configureNotifications()
displayItems()
}
// called once
func displayItems() {
fetchLiveEvents { [weak self] in
self?.applySnapshot(animatingDifferences: true)
}
}
func configureNotifications() {
NotificationCenter.default.addObserver(self, selector: #selector(updateExistingItem), name: .updateExistingItem, object: nil)
}
// called every time when you trigger notifcation
#objc func updateExistingItem() {
fetchLiveEvents { [weak self] in
self.applySnapshot(animatingDifferences: true)
}
}
I activated the proximity senzor in application and now the function is calling multiple times.
I don't know what is wrong. Can you help me?
//MARK:- Activate Proximity Sensor
func activateProximitySensor() {
proximitySenzorActionStatus = true
device.isProximityMonitoringEnabled = true
if device.isProximityMonitoringEnabled {
NotificationCenter.default.removeObserver(self, name: UIDevice.proximityStateDidChangeNotification, object: device)
NotificationCenter.default.addObserver(self, selector: #selector(proximityStateDidChange), name:UIDevice.proximityStateDidChangeNotification, object: device)
}
}
func deactivateProximitySenzor() {
proximitySenzorActionStatus = false
device.isProximityMonitoringEnabled = false
NotificationCenter.default.removeObserver(self, name: UIDevice.proximityStateDidChangeNotification, object: device)
}
The methos in now called for 3 times:
#objc func proximityStateDidChange(notification: NSNotification) {
print("proximityStateDidChange")}
I activated the senzor in
viewWillAppear
and remove in
viewWillDisappear
You need to calculate the time of flight between every occlusion of the sensor.
In my app which am writing to learn swift and iOS9, I'm trying to pause my NStimer when user double click the home button and becomes at app switcher, accoridng to programming ios9 matt neuberg, when The user double-clicks the Home button, The user can now work in the app switcher interface. If your app is frontmost, your app delegate receives this message:
applicationWillResignActive:
But my timer only pauses when I tap home button once and when I tap twice and have the app switcher, I see my timer counting, any ideas?
Try to add this lines in your AppDelegate.swift:
static let kAppDidBecomeActive = "kAppDidBecomeActive"
static let kAppWillResignActive = "kAppWillResignActive"
func applicationDidBecomeActive(application: UIApplication) {
// Your application is now the active one
// Take into account that this method will be called when your application is launched and your timer may not initialized yet
NSNotificationCenter.defaultCenter().postNotificationName("kAppDidBecomeActive", object: nil)
}
func applicationWillResignActive(application: UIApplication) {
// Home button is pressed twice
NSNotificationCenter.defaultCenter().postNotificationName("kAppWillResignActive", object: nil)
}
In addition, set your view controller as the observer to those notifications:
override func viewDidLoad() {
super.viewDidLoad()
NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(pauseGame), name: AppDelegate.kAppWillResignActive, object: nil)
NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(resumeGame), name: AppDelegate.AppDelegate.kAppDidBecomeActive, object: nil)
}
I have a view controller with a button. When the button is pressed it adds an observer, like so:
func buttonPress(sender:UIButton){
NSNotificationCenter.defaultCenter().addObserverForName("buttonPressEvent", object:nil, queue:nil, usingBlock:{(notif) -> Void in
// code
})
}
When I dismiss this view controller, and then return to it and press the button the //code is executed twice. If I go away and come back again the //code is executed three times, and so on.
What I want to do is to remove the Observer before I add it again, so this code doesn't execute twice. Ive gone through the documentation here and Ive added this line of code just above where I add the Observer:
NSNotificationCenter.defaultCenter().removeObserver(self, name:"buttonPressEvent", object:nil)
But this isnt working.
Can anyone tell me where I'm going wrong?
When you use the 'blocks' based approach to observing notifications then self isn't in fact the observer. The function returns an object which acts as the observer:
func addObserverForName(_ name: String?,
object obj: AnyObject?,
queue queue: NSOperationQueue?,
usingBlock block: (NSNotification!) -> Void) -> NSObjectProtocol
You need to keep a reference to this returned object and pass it in as the observer when you call removeObserver
It's explained well in the Apple Doc here
Implemented it like this, seems to be working fine.
override func viewDidLoad()
{
super.viewDidLoad()
AddScreenShotNotification()
}
func AddScreenShotNotification() {
NSNotificationCenter.defaultCenter().addObserver(
self,
selector: #selector(MyViewController.ScreenShotTaken),
name: UIApplicationUserDidTakeScreenshotNotification,
object: nil)
}
func ScreenShotTaken()
{
// do something
}
override func viewWillDisappear(animated: Bool) {
NSNotificationCenter.defaultCenter().removeObserver(self)
}
How can I call a function that is within an SKScene class when my app is terminated by the user?
I need to modify a value and save it to NSUserDefauts when the app is terminated.
You can register to receive a notification when your app is about to terminate. To do this, add an observer to the default notification center by
Swift 5:
NotificationCenter.default.addObserver(self, selector: #selector(saveData), name: UIApplication.willTerminateNotification, object: nil)
Swift 3/4:
// Add this to didMoveToView in your SKScene subclass
NotificationCenter.default.addObserver(self, selector: #selector(saveData), name: NSNotification.Name.UIApplicationWillTerminate, object: nil)
Add the following method to your SKScene subclass. The method will be called before the app terminates. It must be "exposed" to Objective-C by adding #objc so the notifier can use #selector().
#objc func saveData(notification:NSNotification) {
// Save your data here
print("Saving data...")
}
In Swift 3 and 4 you have something like that:
in your viewDidLoad
NotificationCenter.default.addObserver(self, selector: #selector(toDoSomething), name: NSNotification.Name.UIApplicationWillTerminate, object: nil)
and than you have that method to be called
func suspending () {
print("toDoSomething...")
}
There are a few methods in UIAppDelegate that will help you. Take a look at applicationWillTerminate(_:) and applicationWillResignActive(_:). From there you see what state your app is in and do perform the appropriate actions.