So I have this code:
#IBAction func onStart(_ sender: Any) {
DispatchQueue(label: "SyncQueue").async{
for i in 0..<numberOfItemToDownload {
// download data from the internet this may takes longer depends on the connection speed and data being download
if isCancelled {
DispatchQueue.main.async { // dismiss the progress ViewController (displayed modally) }
break
}
}
}
}
#IBAction func onEnd(_ sender: Any) {
isCancelled = true
}
This works ok, but if the current item being download takes longer then the user taps the "End" button the "progress dialog" is not dismissed until the current item is done. This makes the "End" button not working in user's perspective.
In Android we can interrupt the AsyncTask process and end it. Is there another way to do it in Swift? like when the user taps the "End" the process should immediately stop and dismiss the "progress dialog".
GDC is not easily cancellable.
Use an NSOperation subclass then you can cancel easily and quickly.
I have a Button on First VC which is directed to two active states.
1) SecondVC
override func viewDidLoad() {
super.viewDidLoad()
subjectPickerView.dataSource = self
subjectPickerView.delegate = self
SwiftyRequest()
// Used the text from the First View Controller to set the label
}
func SwiftyRequest(){
print("SecondViewController METHOD BEGINS")
let jsonobj = UserDefaults.standard.object(forKey: "PostData")
let json = JSON(jsonobj as Any)
for i in 0 ..< json.count{
let arrayValue = json[i]["name"].stringValue
print(arrayValue)
self.subjects.append(arrayValue)
self.subjectPickerView.reloadAllComponents()
}
print(self.subjects)
}
2) IBAction of FirstVC
#IBAction func buttonPressed(_ sender: Any) {
Alamofire.request("http://localhost/AIT/attempt3.php",method: .post, parameters: ["something": semValue, "branch" : streamValue])
.responseJSON { response in
print(response.result)
if let JSON1 = response.result.value {
print("Did receive JSON data: \(JSON1)")
// JSONData.someData = JSON1 as AnyObject?
UserDefaults.standard.set(JSON1, forKey: "PostData")
UserDefaults.standard.synchronize()
}
else {
print("JSON data is nil.")
}
}
}
NOW, Whenever i pressed the button it calls the viewDidLoad of SecondVC before IBAction of FirstVC which is a bit problematic for my app! How can i decide the priority between these two function.
You have to think about what you want to happen. Clearly the Alamofire call is going to take some time. What do you want to do with the 2nd VC while that time elapses? What do you want to do if the call does not return at all?
This is a common problem when dependent on external resources. How do you manage the UI? Do you present the UI in a partial state? Do you put a popover saying something like "loading". Or do you wait for the resource to complete before presenting the 2nd VC at all?
We cannot make that decision for you, since it depends on your requirement. There are ways to implement each one, though. If the resource usually responds quickly you could show the VC in a partial state and then populate it on some kind of callback. Typically call backs are either (1) blocks (2) delegate methods or (3) notifications. There is also (less commonly) (4) KVO. You should probably research the pros and cons of each.
Context: iOS App written in Swift 3 powered by Firebase 3.0
Challenge: On my app, the user's currentScore is stored on Firebase. This user can complete/un-complete tasks (that will increase/decrease its currentScore) from several ViewControllers.
Overview of the App's architecture:
ProfileVC - where I fetch the currentUser's data from Firebase & display the currentScore.
⎿ ContainerView
⎿ CollectionViewController - users can update their score from here
⎿ DetailsVC - (when users tap on a collectionView cell) - again users can update their score from here.
Question: I need to pass the currentScore to the VCs where the score can be updated. I thought about using prepare(forSegue) in cascade but this doesn't work since it passes "nil" before the query on ProfileVC is finished.
I want to avoid having a global variable as I've been told it's bad practice.
Any thoughts would be much appreciated.
Why don't you create a function that will pull all data before you do anything else.
So in ViewDidLoad call...
pullFirebaseDataASYNC()
Function will look like below...
typealias CompletionHandler = (_ success: Bool) -> Void
func pullFirebaseDataASYNC() {
self.pullFirebaseDataFunction() { (success) -> Void in
if success {
// Perform all other functions and carry on as normal...
Firebase function may look like...
func pullFirebaseDataFunction(completionHandler: #escaping CompletionHandler) {
let refUserData = DBProvider.instance.userDataRef
refUserData.observeSingleEvent(of: .value, with: { snapshot in
if let dictionary = snapshot.value as? [String: AnyObject] {
self.userCurrentScore = dictionary["UserScore"] as! Int
completionHandler(true)
}
})
}
Then when you segue the information across...
In ProfileVC
Create 2 properties
var containerVC: ContainerVC!
var userCurrentScore = Int()
Include the below function in ProfileVC...
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if segue.identifier == "ProfileToContainerSegue" {
let destination = segue.destination as! ContainerVC
containerVC = destination
containerVC.userCurrentScore = userCurrentScore
}
}
In ContainerVC create a property
var userCurrentScore = Int()
Ways to improve could be an error message to make sure all the information is pulled from Firebase before the user can continue...
Then the information can be segued across the same way as above.
Try instantiation, first embed a navigation controller to your first storyboard, and then give a storyboardID to the VC you are going to show.
let feedVCScene = self.navigationController?.storyboard?.instantiateViewController(withIdentifier: "ViewControllerVC_ID") as! ViewController
feedVCScene.scoreToChange = current_Score // scoreToChange is your local variable in the class
// current_Score is the current score of the user.
self.navigationController?.pushViewController(feedVCScene, animated: true)
PS:- The reason why instantiation is much healthier than a modal segue storyboard transfer , it nearly removes the memory leaks that you have while navigating to and fro, also avoid's stacking of the VC's.
I am trying to switch view controllers after a user successfully logs in to their account, but it is not working correctly. I cant use a segue directly because if the login button is clicked it will go to that view controller regardless if the information is correct or not. I have tried everything that I know of with no success. This is the code I am trying.
#IBAction func loginTapped(sender: AnyObject) {
let username = usernameField.text
let password = passwordField.text
if username.isEmpty || password.isEmpty {
var emptyFieldsError:UIAlertView = UIAlertView(title: "Please try again", message: "Please fill in all the fields we can get you logged in to your account.", delegate: self, cancelButtonTitle: "Try again")
emptyFieldsError.show()
}
PFUser.logInWithUsernameInBackground(username, password:password) {
(user: PFUser?, error: NSError?) -> Void in
if user != nil {
self.performSegueWithIdentifier("Klikur", sender: self)
} else {
if let errorString = error!.userInfo?["error"] as? String {
self.errorMessage = errorString
}
self.alertView("Please try again", message: "The username password combiation you have given us does not match our records, please try again.", buttonName: "Try again")
}
}
}
I have the storyboard ID set to "Test" and it is not switching view controller when the correct information is entered. Can somebody help me resolve my problem?
[Assuming that your code is not crashing, but rather just failing to segue]
At least one problem is:
self.performSegueWithIdentifier("Test", sender: self)
should be:
dispatch_async(dispatch_get_main_queue()) {
[unowned self] in
self.performSegueWithIdentifier("Test", sender: self)
}
Remember that all UI operations must be performed on the main thread's queue. You can prove to yourself you're on the wrong thread by checking:
NSThread.isMainThread() // is going to be false in the PF completion handler
ADDENDUM
If there's any chance self might become nil, such as getting dismissed or otherwise deallocated because it's not needed, you should capture self weakly as [weak self] not unowned, and use safe unwrapping: if let s = self { s.doStuff() } or optional chaining: self?.doStuff(...)
ADDENDUM 2
This seems to be a popular answer so it's important to mention this newer alternative here:
NSOperationQueue.mainQueue().addOperationWithBlock {
[weak self] in
self?.performSegueWithIdentifier("Test", sender: self)
}
Note, from https://www.raywenderlich.com/76341/use-nsoperation-nsoperationqueue-swift:
NSOperation vs. Grand Central Dispatch (GCD)
GCD [dispatch_* calls] is a lightweight way to represent units of work that are going to be executed concurrently.
NSOperation adds a little extra overhead compared to GCD, but you can add dependency among various operations and re-use, cancel or suspend them.
ADDENDUM 3
Apple hides the single-threaded rule here:
NOTE
For the most part, use UIKit classes only from your app’s main thread.
This is particularly true for classes derived from UIResponder or that
involve manipulating your app’s user interface in any way.
SWIFT 4
DispatchQueue.main.async(){
self.performSegue(withIdentifier: "Test", sender: self)
}
Reference:
https://developer.apple.com/documentation/uikit
Make sure you're putting your:
self.performSegue(withIdentifier: ..., ...)
in viewDidAppear or later. It won't work in viewWillAppear or viewDidLoad.
I've got the same problem with login issue. probably we do the same tutorial. After naming your segue identifier you need to replace:
performSegueWithIdentifier("Klikur", sender: self)
with:
dispatch_async(dispatch_get_main_queue()){
self.performSegueWithIdentifier("Klikur", sender: self)
}
type of seque needs to be set as "show (e.g. Push)" in the storyboard segue.
Hope it will work.
The segue identifier that you pass to performSegueWithIdentifier(_:sender:) must exactly match the ID you've given the segue in the storyboard. I assume that you have a segue between the login view controller and the success view controller, which is as it should be; if not, ctrl+drag from the first to the second view controller, then select the segue's icon in the storyboard and set its ID to Klikur. Don't perform the navigation on the button click, as one commenter said, because that defeats the main purpose of having segues, which is to give a visual indication of the application flow in the storyboard.
EDIT: Here's the code for a login view controller:
import UIKit
class ViewController: UIViewController {
#IBOutlet weak var usernameField: UITextField!
#IBOutlet weak var passwordField: UITextField!
#IBAction func attemptLogin(sender: AnyObject) {
if !usernameField!.text!.isEmpty && !passwordField!.text!.isEmpty {
performSegueWithIdentifier("Klikur", sender: self)
}
}
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
if "Klikur" == segue.identifier {
// Nothing really to do here, since it won't be fired unless
// shouldPerformSegueWithIdentifier() says it's ok. In a real app,
// this is where you'd pass data to the success view controller.
}
}
}
And a screenshot of the segue properties that I'm talking about:
swift 3.x
DispatchQueue.main.async(){
self.performSegue(withIdentifier: "Klikur", sender: self)
}
DispatchQueue.main.async() {
self.performSegue(withIdentifier: "GoToHomeFromSplash", sender: self)`
}
Check to make sure you are running the perform segue on a visible view controller.
This is an edge case, but my perform segue failed when I attempted to run it on the view controller belonging to my UIPageViewController that was not currently visible. It also failed if I attempted to do the segue on all view controllers belonging to my UIPageViewController, including the view controller currently visible. The fix was to track which view controller was currently visible in my UIPageViewController, and only perform the segue on that view controller.
An example in a login. When you have success in your login after clicking a button (Action) you can use:
self.performSegue(withIdentifier: "loginSucess", sender: nil)
But if you are launching the app and you got the credentials from your keychain you need to use this as a part of the theard:
DispatchQueue.main.async(){
self.performSegue(withIdentifier: "sessionSuccess", sender: nil)
}
I am trying to pass a string value from a ViewController to another:
#IBAction func unwindToMasterViewController(segue: UIStoryboardSegue) {
let viewController:MyViewController = segue.sourceViewController as! MyViewController
sprite = viewController.sp //sp is NSString declared in MyViewController
print("the string is \(viewController.sp)")// nothing happens!!!
}
I can see that sp IS NOT nil in my log before "leaving" MyViewController.
Is there a better way to do this?
EDIT:
I think I may know the issue:
In log the #IBAction func unwindToMasterViewController(segue: UIStoryboardSegue) is called before I get the string value from MyViewController.
The order the log appears is:
"the string is "
and then the print from MyViewController with the actual value:
"sp is testString"
How do I solve this?
I did this and it worked for me
#IBAction func cancelButtonTapped(sender: UIButton) {
self.dismissViewControllerAnimated(true, completion: nil)
let VC = ViewController()
let string = VC.sp
println(string)
delegate?.addTaskCanceled!("task canceled")
}
and in the main VC I had this at the top:
let sp:NSString = "Test"
Ok. Here's the solution in case anyone else come across this.
The problem was (as suspected) that the segue was called BEFORE I could pass the value to the NSString. That was because I was using the unwind segue connected straight from IB to the MasterView.
I had to delete the unwind segue and do it programmatically when my UITbleViewCell was tapped (didSelectRowAtIndexPath).
Then the right sequence of events unfold:
Get the value from cell and then execute the segue.
That way the value was passed to the MasterViewController as expected.
It goes beyond me why this happened or what is the reason to call the unwind segue before the action is called, but Apple works in mysterious ways...