Does anybody know if there is a certain pattern for handling segues programmatically in a MVC way?
I would think the best way would be to work with an event system within a controller.
I want that all the view controllers connect to this navigationController instead of handling all the logic within the viewController logic itself. I want to out source this logic
In most of your view controllers, you will have access to a prepareForSegue function, with one parameter called sender.
If you kick off a segue programatically with performSegue(withIdentifier: "mySegueID", sender: yourVC) then this function will be called, and you'll be able to pass information from the sender to the new view controller.
In this function, to get a handle on the next VC, use segue.destinationViewController.
I don't know about a particular pattern but a simple way to programmatically handle transitions between 2 UIViewController could be to have a separated manager whose job is just to push/present/whatever new controllers over current, and to pop/dismiss/whatever current controllers to old ones.
The way I usually do this is by having a class we can name WorkflowManager, which will handle all transitions. Associated with this manager, you declare a WorkflowManagerComponent protocol and implement it :
protocol WorkflowManagerComponent {
var completionHandler: (hasCompleted:Bool,data:Any)->() {get set}
}
Make each UIViewController implement this, for example by calling completionHandler(true,someData) when the user taps a "next" button, or completionHandler(false,nil) when the user taps a "back" button.
Then in your workflow manager, you perform transitions to the next or previous UIViewController according to parameters sent in the completionHandler:
//init viewController1 ...
viewController1.completionHandler = onViewController1Completes
// ...
func onViewController1Completes(_ completed: Bool, data: Any) {
if hasCompleted {
//init viewController2 ...
viewController2.data = data
viewController2.completionHandler = onViewController2Completes
//Push the new vc
viewController1.navigationController.push(viewController2, animated: true)
} else {
//The vc1 was presented as a modal, dismiss it
viewController1.dismiss()
}
}
This way each UIViewController is separated from others, free off any transition logic.
Related
I have three views, each with its own view controller: VC1, VC2, VC3.
The user will frequently switch back and forth between each of the three views, both forward and backward.
Each view contains data: both shared from the previous view and data unique to that view.
When the user goes back to a View that he has already visited, the data displayed on that view needs to be retained (the same data as he saw the last time he visited that view), and not set to the default values the first time he visited the view.
In the first view controller, VC1, I am using a prepare for segue to push data from VC1 to VC2 or VC3:
override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
if segue.identifier == "segueToVC2” {
let destinationViewController: VC2 = segue.destination as! VC2;
destinationViewController.passedData1 = firstAmount
destinationViewController.passedData2 = secondAmount
destinationViewController.passedData3 = thirdAmount
} else {
let destinationViewController: VC3 = segue.destination as! VC3;
destinationViewController.passedData1 = firstAmount
destinationViewController.passedData2 = secondAmount
destinationViewController.passedData3 = thirdAmount
destinationViewController.passedData4 = fourthAmount
}
By tapping the GO BACK button on each view, I return to the previous view:
#IBAction func goBackButtonPressed(_ sender: Any) {
print("Back Button Pressed!")
self.view.window?.rootViewController?.dismiss(animated: true, completion: nil)
}
I am having trouble passing data backwards. And when I return to VC2 from VC1, data has been reset to 0. I have no segues going back from VC2 to VC1 or from VC3 to VC2. Would that be the cleanest way to pass the data back: to create another segue in Main.storyboard from VC2 to VC1 and then add another ‘if’ to my prepare for segue that checks for VC1?
I am passing ALL these variables back and forth between view controllers but only using some of them in each view controller. It seems like a waste and I don't think I am on the right track here.
Any help or suggestions?
View controllers should never store data. They are responsible for coordinating between model objects and view objects. That's their whole point. The pattern you're looking for is called MVC (Model-View-Controller) and it's a core part of iOS development.
Move your data out of the view controllers and put it into model classes. Each view controller should fetch data out of the model, and send updates into the model. The only thing the view controllers should pass between themselves is what model objects to work on, and most of the time that only needs to pass in one direction (down the stack).
Delegation can be a useful tool here, and you can also investigate "unwind segues" which are built to help you send data upstream. But again, the data you should be sending is mostly references to the model, and the model itself needs to live outside the view controllers.
It's in Objective-C, but still one of the best simple examples from Apple on MVC design is TheElements, and is worth exploring as a basis. Even without reading the Objective-C, you can see how the various pieces fit together.
I haven't studied it as much as TheElements, but Lister claims to be a good demonstration of MVC patterns in Swift using modern iOS techniques.
Why don't you call a delegate which passes the data to the view controller when you press back button.
Or if the data shared by all view controllers reflect the same value. Make a singleton class and use those values across the app.
example singleton class:
class SomeModel {
static let shared = SomeModel()
private init() {}
}
The issue I'm having is this.
I have a navigation controller with 3 viewController. In the 1st controller, I have the user select an image. This image is passed to 2nd and 3rd controller via prepareForSegue.
At the 3rd controller, I have a button that takes the user back to the 1st view controller. I explored 2 ways in doing this:
1) use performSegue, but I don't like this because it just push the 1st controller to my navigation stack. So I have this weird "Back" button at the 1st Viewcontroller now, which is not what I want. I want the app to take user directly to 1st viewcontroller without the back button.
2) I tried Poptorootviewcontroller. This solves the issue of the "back" button. But, when I pop back to the 1st viewcontroller, the user's selected image is still on screen. I want to clear this image when the user goes from the 3rd viewcontroller back to the 1st viewcontroller.
So with approach 2), how do I make sure all memory is refreshed and the image becomes nil in the 1st viewcontroller? Since I'm not using performSegue, 3rd viewcontroller does not have access to the 1st Viewcontroller.
For refresh, you'd have to clear it in viewWillAppear but I find this rather dangerous. Best you can do there is to create a new copy of the view controller everytime and Swift will take care of the rest. I don't know if you are using the storyboard but I would recommend using the class UIStoryboard and the function instiantiateViewControllerWithIdentifier("something") as! YourCustomVC
As long as you stay in the navigation stack, you'll not lose any of the current configurations of previous View Controllers.
As for passing data back to the first controller. You can either just throw it in the global scope which is the easiest way but might be difficult to know when it was updated or if the data is fresh. But you can always just:
var something: String = ""
class someView: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
something = "foo"
}
}
Something will be availabe everywhere then.
You could make a protocol and pass the delegate along the 3 view controllers. So when you are starting it you could do:
func someAction() {
let v = SomeViewController()
v.delegate = self
self.navigationController?.pushViewController(v, animated: true)
}
And then with each following view:
func someOtherAction() {
let v = SomeOtherViewController()
v.delegate = self.delegate
self.navigationController?.pushViewController(v, animated: true)
}
Although personally I find it hard to keep track of this.
Lastly you could use the NSNotificationCenter to pass an object along with all the data and catch it in a function on your first controller.
To do this you first register your VC for the action in viewDidLoad() or something:
NSNotificationCenter.defaultCenter().addObserver(self, selector: "someAction:", name: "someNotification", object: nil)
Then when you are done in the 3rd view make some object or a collection of string and send it back as follows:
NSNotificationCenter.defaultCenter().postNotificationName("someNotification", object: CustomObject())
And then lastly you'll catch it in the function "someAction"
func someAction(note: NSNotification) {
if let object = note.object as? CustomObject {
//Do something with it
}
}
Hope this helps!
Use an unwind segue which provides the functionality to unwind from the 3rd to the 1st (root) view controller.
The unwind segue is tied to an action in the root view controller. Within this action, you simply nil the image:
#IBAction func unwindToRootViewController(sender: UIStoryboardSegue)
{
let sourceViewController = sender.sourceViewController
// Pull any data from the view controller which initiated the unwind segue.
// Nil the selected image
myImageView.image = nil
}
As you can see in the action, segues also let you pass data back from the source view controller. This is a much simpler approach than needing to resort to using delegates, notifications, or global variables.
It also helps keep things encapsulated, as the third view controller should never need to know specifics about a parent view controller, or try to nil any image that belongs to another view controller.
In general, you pass details to a controller, which then acts on it itself, instead of trying to manipulate another controller's internals.
I'm new to swift and am trying to write an app with it.
I have a UIViewController that I am transitioning to. I have designed the UI in interface builder and I intend to use segues to manage the transition. However, the view controller relies on data that is passed into the view controller from the previous view controller.
If I have properties on my view controller then I will need to redefine my init method. But I wouldn't normally call the init method; it would be called for me before prepareForSegue. So I see a few possible solutions:
Make my variables optional (so I can pass them in prepareForSegue
and update the view then).
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
let viewController: EventViewController = segue.destinationViewController as! EventViewController
viewController.event = self.event
}
Manually init my view controller and present it programmatically instead.
???
Is there a third option? If not, which of the previously mentioned 2 is better practice?
There is two possible options as you mentioned:
The first one is the easiest which is to pass the data in prepareForSegue. which you don't have to care about dismissing the controller or keeping a track of inner view controllers,because storyboard will take care of it.
The second way is to set a Storyboard ID in storyboard,for the controller you need to present programmatically, which need more things to handle, like to dismiss the controller or keep track of inner presented controllers.
let nextViewControllerName = storyboard?.instantiateViewControllerWithIdentifier("Storyboard ID") as! nextViewControllerName
nextViewControllerName.event = self.event
self.presentViewController(nextViewControllerName, animated: true, completion: nil).
At the end they does the same purpose.
Note: You should always pass the data before presenting the controller.
A user is in a view controller which calls a modal. When self.dismissViewController is called on the modal, a function needs to be run on the initial view controller. This function also requires a variable passed from the modal.
This modal can be displayed from a number of view controllers, so the function cannot be directly called in a viewDidDisappear on the modal view.
How can this be accomplished in swift?
How about delegate?
Or you can make a ViewController like this:
typealias Action = (x: AnyObject) -> () // replace AnyObject to what you need
class ViewController: UIViewController {
func modalAction() -> Action {
return { [unowned self] x in
// the x is what you want to passed by the modal viewcontroller
// now you got it
}
}
}
And in modal:
class ModalViewController: UIViewController {
var callbackAction: Action?
override func viewDidDisappear(_ animated: Bool) {
let x = … // the x is what you pass to ViewController
callbackAction?(x)
}
}
Of course, when you show ModalViewController need to set callbackAction like this modal.callbackAction = modalAction() in ViewController
The answer supplied and chosen by the question asker (Michael Voccola) didn't work for me, so I wanted to supply another answer option. His answer didn't work for me because viewDidAppear does not appear to run when I dismiss the modal view.
I have a table and a modal VC that appears and takes some table input. I had no trouble sending the initial VC the modal's new variable info. However, I was having trouble getting the table to automatically run a tableView.reloadData function upon dismissing the modal view.
The answer that worked for me was in the comments above:
You likely want to do this using an unwind segue on the modal, that
way you can set up a function on the parent that gets called when it
unwinds. stackoverflow.com/questions/12561735/… – porglezomp Dec 15
'14 at 3:41
And if you're only unwinding one step (VC2 to VC1), you only need a snippet of the given answer:
Step 1: Insert method in VC1 code
When you perform an unwind segue, you need to specify an action, which
is an action method of the view controller you want to unwind to:
#IBAction func unwindToThisViewController(segue: UIStoryboardSegue) {
//Insert function to be run upon dismiss of VC2
}
Step 2: In storyboard, in the presented VC2, drag from the button to the exit icon and select "unwindToThisViewController"
After the action method has been added, you can define the unwind
segue in the storyboard by control-dragging to the Exit icon.
And that's it. Those two steps worked for me. Now when my modal view is dismissed, my table updates. Just figured I'd add this, in case anyone else's issue wasn't solved by the chosen answer.
I was able to achieve the desired result by setting a Global Variable as a boolean value from the modal view controller. The variable is initiated and made available from a struct in a separate class.
When the modal is dismissed, the viewDidAppear method on the initial view controller responds accordingly to the value of the global variable and, if needed, flips the value on the global variable.
I am not sure if this is the most efficient way from a performance perspective, but it works perfectly in my scenario.
I'm trying to make an app that uses three containers to show different content, but I'm having trouble communicating between the containers. I succeeded to use a segue to send some information at the tap of a button in one container to another container, but part of this information also has to be relayed to the third container. For this I wanted to use a delegate, but I cannot reference the right ViewController to the delegate variable.
So what I want goes as follows:
CollectionViewCell tapped, triggering segue to TableVC
TableVC receives information and updates the table
TableVC triggers delegate function in third VC
Third VC takes in some info and updates view
In the above I have managed to get 1 and 2 to work, but got stuck at 3.
I have made my protocol as follows:
protocol PurchaseDelegate {
func addToTotalAmount(product : Product)
}
In the TableVC I have declared var delegate : PurchaseDelegate? = nil and in the IBAction triggered from the segue: delegate?.addToTotalAmount(product)
In the third VC I have implemented the delegate as follows:
class thirdVC:UIViewController,PurchaseDelegate {
func addToTotalAmount(product : Product) {
println("Adding....")
}
}
All three containers are within a main VC that does some initial stuff in the application.
My problem is, that I don't know how to get a reference from thirdVC to my delegate variable in my tableVC.
Thanks in advance.
I ended up finding the solution to the problem after a bit further searching with inspiration from #Anna Dickinson.
Firstly, the containers must be ordered correctly in the storyboard. The container whose view controller implements the delegate protocol must be first in the list and then the other view controller further down.
Then, in the main view controller - the view controller for the view with the containers - the prepareForSegue function is implemented, since it will be triggered as the containers are initialized.
This all of the code remains as above, but the main view controller will be something like the following:
class MainViewController: UIViewController {
var actionVC : FirstViewController! // This is the one, that implements the delegate protocol
var tableVC : SecondViewController! // This is the one, that has a delegate variable
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
if(segue.identifier == "firstVC"){
self.actionVC = segue.destinationViewController as FirstViewController
} else if(segue.identifier == "secondVC"){
self.tableVC = segue.destinationViewController as SecondViewController
self.tableVC.delegate = self.actionVC
}
}
}
I'm not sure if the is the right, nor the best way to do this, but it works perfectly for what I need.