How i can pass data from First screen to Second screen provided that must use inheritance and data entered in base class should be available in second screen after push.
class FirstViewController {
var dataArray = [CustomModel]()
//methods will manupulate data
}
Then push subclass SecondViewController from class FirstViewController
class SecondViewController : FirstViewController {
print(dataArray)
}
Is this possible ? any solution to this ? I just wanted reuse most of code in many screens. Any help.
When you inherit class B with parent class A, then you can access its data members.
Here check this:
class ViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
//call show function of class B which is inherit from class A
let classB = B()
classB.showData()
}
}
class A {
var dataArray: [String] = ["ABC", "123", "XYZ"]
}
class B: A {
func showData()
{
print(dataArray)
}
}
Output:
["ABC", "123", "XYZ"]
This is basic rule of inheritance, is this what you are looking for! if not kindly explain your problem in detail.
P.S
you can also use static data members they are accessible without making object.
Related
I have class A in file A and class B in file B. In class B, I want to access the running instance of class A, in order to run a function located in it. Both classes are connected to view controllers. I do not want to create a new instance of class A as in classAInstance = classA(), but rather access the instance of class A that my app is already running. Any help would be appreciated.
Here is part of my code in class A:
Class A {
func reloadTableView() {
self.CardsTableView.reloadData()
}
}
And here is part of my code in class B:
Class B {
#IBAction func saveButton(_ sender: UIButton) {
// here is where I want to call reloadTableView() from class A
}
}
The quick and dirty method I might use would be where you have some singleton where you can store the current instances of your classes.
Example:
class EnvironmentUtility {
private static var instance: EnvironmentUtility?
internal class func shared() -> EnvironmentUtility {
guard let currentInstance = instance else {
instance = EnvironmentUtility()
return instance!
}
return currentInstance
}
var myClassA: ClassA? = nil
var myClassB: ClassB? = nil
}
Then in the viewDidLoad (Or wherever else you like that a new instance is being made) of the those ViewControllers/Classes:
class ClassA: UIViewController {
…
override func viewDidLoad() {
…
EnvironmentUtility.shared().myClassA = self
}
…
}
Later in ClassB you could then:
class ClassB: UIViewController {
…
#IBAction func saveButton(_ sender: UIButton) {
EnvironmentUtility.shared().myClassA.reloadTable()
}
…
}
This isn’t the prettiest or Swifty-est way of doing it, but quick and dirty.
If you want to write a better solution I would suggest looking at the MVVM-C Swift architectural pattern (I use this pattern myself). In this architecture you will have access to a Coordinator that overseas viewController transitions and you can also track current instances of your ViewControllers/Classes in a much more elegant way.
Here is a crash course in MVVM-C: https://marcosantadev.com/mvvmc-with-swift/
I tried to do some research but couldn't figure it out, so is it possible to create a member for the class UIViewController, or any class for that matter?
In every single one of my UIViewController subclasses I declare the data member
userdata = [NSManagedObject]()
So I was wondering if I could declare the variable "userdata" inside the actual UIViewController class, either directly or through an external file.
You can simply create a sub-class of UIViewController which has the userdata property and then derive all of your view controllers from that class instead of UIViewController
Something like:
class BaseViewController:UIViewContrller {
var userdata = [NSManagedObject]()
}
class NewViewController:BaseViewController {
// Your sub view controller implementation goes here
}
You should use extensions.
extension UIViewController {
var userData : [NSManagedObject] {
get {
return [NSManagedObject]()
}
}
}
If you don't want every UIViewController to have that property, you will have to use subclassing.
class DataViewController:UIViewContrller {
var userdata = [NSManagedObject]()
}
class NewViewController:DataViewController {
// Do something stuff to the View here
}
You can use extensions if userData is a computed property:
extension UIViewController {
var userData: [NSManagedObject] {
get { return an array from somewhere else }
set { set the value to somewhere else }
}
}
If your property is not computed but stored, you must use a subclass:
class BaseViewController: UIViewController {
var userData: [NSManagedObject] = []
}
And make every VC of yours inherit this class. The disadvantage of using this approach is that your view controllers can't inherit any other class, like UITableViewController.
So here is the best method I came up with.
Create a protocol:
protocol MyVC {
var userData: [NSManagedObject] { get set }
}
Now make every VC of yours conform to this protocol. In every VC, just start typing userData and use enter to select the right completion that Xcode provides and the property will be automatically added for you. If you forgot to do this, the compilation will fail.
TL;DR
I'm looking for an array type (var array = [TheTypeImLookingFor]()) like 'all objects that subclasses UIViewController and implements the protocol MyProtocol.
Explanation
I'm building a kind of wizard view with a container view and embedded child views (controller). No problem, this will work as long, as I have only one base type of child view controllers.
Due to the content of screens, I have now a bunch of view controllers of type MyTableViewController which is a subclass of UITableViewController and other view controllers that have regular UIViewControllers as base.
All of the view controllers have one thing in common. A default data property myData: MyObject.
I created a protocol MyProtocol that contains this property.
Now, I have to combine all this view controllers into one array to use it as wizard steps. As long as I only have to access the view controller methods (array items are type of UIViewController) I'm able to use var viewControllers = [UIViewController]() or if I wanna only access the myData property, I change the array item type to MyObject.
But the problem is, I have to access the methods from the UIViewController and from the protocol.
That's why I'm looking for an array type like 'all objects that subclasses UIViewController and implements the protocol MyProtocol.
I tried:
var viewControllers = [UIViewController: MyProtocol]() // is a dict
`var viewControllers = UIViewController where MyProtocol
`var viewControllers = UIViewController.conforms(to: MyProtocol)
...
But nothing works as expected.
As far as I know, there's currently no way to type something so that it describes anything which inherits from a given class and conforms to a given protocol.
One possible hacky workaround would be to just create a wrapper type in order to perform typecasting for you in the case that you need to treat the instance as a MyProtocol.
struct MyProtocolViewController {
let base: UIViewController
init<T : UIViewController>(_ base: T) where T : MyProtocol {
self.base = base
}
func asMyProtocol() -> MyProtocol {
return base as! MyProtocol
}
}
Now you can create a [MyProtocolViewController], and can either treat an element as a UIViewController, or a MyProtocol.
// given that ViewController and AnotherViewController conform to MyProtocol.
let viewControllers = [MyProtocolViewController(ViewController()),
MyProtocolViewController(AnotherViewController())]
for viewController in viewControllers {
print(viewController.asMyProtocol().myData)
print(viewController.base.prefersStatusBarHidden)
}
You could use protocol composition with a placeholder protocol for the class:
protocol UIViewControllerClass {}
extension UIViewController: UIViewControllerClass {}
protocol MyProtocol:class {}
class MySpecialVC:UIViewController,MyProtocol {}
var viewControllers = [UIViewControllerClass & MyProtocol]()
viewControllers.append( MySpecialVC() )
This covers the type safety part but doesn't let you access UIViewController methods without type casting. You can reduce the type casting ugliness by adding a typed property to your protocol (when it applies to the base class)
extension MyProtocol where Self: UIViewControllerClass
{
var vc:UIViewController { return self as! UIViewController }
}
// accessing the view controller's methods would then only require insertion of a property name.
viewControllers.first!.vc.view
Alternatively, you could define the UIViewController methods you need to call in the placeholder protocol but that could quickly become tiresome and redundant if you're going to use many of them.
Why not simply create :
Why not creating :
class ObservingViewController : UIViewController, MyProtocol {
}
var viewControllers : [ObservingViewController] = []
You can also create a protocol that defines all the UIViewController functions that you need. Make sure that you copy the method signature, otherwise you will have to implement the functions again.
protocol UIViewControllerInteractions {
//copy the signature from the methods you want to interact with here, e.g.
var title: String? { get set }
}
Then, you can extend your existing protocol.
protocol MyProtocol: UIViewControllerInteractions { }
Or create a new protocol that extends UIViewControllerInteractions and MyProtocol.
protocol MyProtocolViewController: UIViewControllerInteractions, MyProtocol { }
Now, when you extend your SubclassUIViewController, you still only have to add your myData because the methods in the UIViewControllerInteractions are already implemented by UIViewController (that's why we copied the method signature)
class SubclassUIViewController: MyProtocol {
var myData ...
}
You can now have an array of MyProtocol or MyProtocolViewController and also call the methods defined in UIViewControllerInteractions which will call the UIViewController methods.
var viewController: [MyProtocol] = [...]
viewController.forEach { (vc) in
print(vc.myData)
print(vc.title)
}
I had a similar issue and solved it with a custom base class. Imagine an array like:
var viewControllers: [MapViewController]
which all should extend from UIViewController and implement the following protocol:
protocol MapViewControllerDelegate {
func zoomToUser()
}
Then I've declared a base class like:
class MapViewController: UIViewController {
var delegate: MapViewControllerDelegate?
}
Caution: this class doesn't implement the above protocol but holds a property which provides the desired functionality. The next step is to define one of the UIViewController that will be added to the array:
class GoogleMapsViewController: MapViewController {
override func viewDidLoad() {
super.viewDidLoad()
delegate = self
}
}
extension GoogleMapsViewController: MapViewControllerDelegate {
func zoomToUser() {
// Place custom google maps code here
}
}
The important part is located in the viewDidLoad method. The view controller assigns itself as the delegate.
Usage:
let googleMapsViewController = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "GoogleMapsViewController") as! GoogleMapsViewController
let mapboxMapsViewController = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "MapboxMapsViewController") as! MapboxMapsViewController
let mapViewControllers: [MapViewController] = [googleMapsViewController, mapboxViewController]
for mapVC in mapViewControllers {
mapVC.delegate?.zoomToUser()
}
The benefits:
The MapViewController is like an abstract class and If I change the MapViewControllerDelegate the compiler forces me to implement the changes in the GoogleMapsViewController and in the MapboxMapsViewController.
If I need a second protocol I could just implement a second delegate property.
No type casting needed like in the other answers. Each UIViewController is still a UIViewController and provides all its methods.
I am trying to pass an object to another view controller but I get an error when I try to set the property of the view controller object.
The error is pretty informative. It says the class ViewController has no public or internal property called data. You'll have to declare a property called data in class ViewController.
class ViewController: UIViewController {
var data: String?
}
the class you have that is named ViewController needs to have a public variable named data.
Your ViewController class could look something like this:
class ViewController: UIViewController {
// This is your public accessible variable you can set during a seque
var data: String?
override func loadView() {
super.loadView()
print(self.data)
}
}
Also, your prepareForSegue function can be simplified like this
if let displayTodoVC = segue.destinationViewController as? ViewController {
displayTodoVC.data = "Hello World"
}
The ViewController is obviously missing a string variable named data.
class ViewController : UIViewController {
var data: String? // Make sure you have this defined in your view controller.
}
I would also suggest that you use a conditional unwrapping of the destinationViewController in your prepareForSegue.
prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
if let viewController = segue.destinationViewController as? ViewController {
viewController.data = "Hello World"
}
}
For future posts, please refrain from posting images of code. You should include code as text in your questions.
Happy coding :)
The Basics
Let me explain my question with an Example.
class Mother: NSObject {
var momVar:Int =5
var subClass : child(mylevel:5) // <-- ******** Error //
init(){
momVar=1000
level=1
}
func print(){
NSLog("%d",momVar);
}
func subMethod(){
subClass =child(myVar: 5) // <== Doesnt Work either
yazdir()
}
}
below child class:
class child:Mother{
var someVar:Int=1
init(myVar:Int) {
super.init()
someVar = myVar
}
}
I want to use "child" class in "Mother" class. But i got " not initialized at super.init call" error. Other view controller calls "Mother" class with "print" method such as:
#IBAction func buttonTest(sender : AnyObject) {
var mom=Mother()
mom.yazdir()
}
The question is How i can use "child" class in "Mother" class?
Thank you
this line of code is not correct syntactically as is:
var subClass : child(mylevel:5)
you need to define the type after the : (before the = if there is any) or you can use it without explicit type, like:
var subClass = child(mylevel:5)