Swift UI Navigation

three main ways (App development with swift iBook)
        using navigation controller
        using normal segues direclty link to viewcontrollers
        using segues programatically (use segue id to navigate after check conditions)

    https://developer.apple.com/library/content/referencelibrary/GettingStarted/DevelopiOSAppsSwift/ImplementNavigation.html

     A navigation controller manages transitions backward and forward through a series of view controllers. The set of view controllers managed by a particular navigation controller is called its navigation stack. The first item added to the stack becomes the root view controller and is never popped off (removed from) the navigation stack.

     add navigation controller to scene
        select scene doc
            Choose Editor > Embed In > Navigation Controller
        the story board entry point will be automatically added to navigation controller

        this will add a bar in all scenes called navigation bar. this can handle all backword and forward navigation
            to use auto back item
                add Navigation item to view. this will automatically add back arrow and click will move to back.
                the segue shoud show. not work for present as popover

            to use button add
                add bar buttons for add back and forward.
                To go back
                    dismiss(animated: true, completion: nil)
                To go forward
                    click -> control drag to relavant scene

                create super view controller and make other viewCOntrollers as children. make commont nav bar button items click event if you want and link click event with super controller function.

    using normal segues direclty link to viewcontrollers
        in this normal button use. no navigation controller. button segue link with view controller. to go back click use "Unwind Segue" way. it means
            if you want to come back second to first
                in first viewcontroller add method like
                    @IBAction func funcName(unwindSegue: UIStoryboardSegue) {}
                in secind button click+control+ drag to exit icon in viewController header. this will suggest that function, it will auto do back process.

    using segues programatically
        here we add buttons to normal way to viewcontroller. but create segeue is doing by click on firstviewController header bar yellow icon(first icon)+ control+ drag to second view controller. another segue like same wat to another viewController. remember to add segue identifier.
        then create action event to each button by normal control+click+ drag to viewcontroller. add this line to connect with each segue
             performSegue(withIdentifier: "segue_id", sender: nil)
        this way can use to check condition and open specific view controller

        to perform back event in second to first use above any way.

pass values from viewControllers
    https://stackoverflow.com/questions/5210535/passing-data-between-view-controllers?rq=1

    override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
        let secViewCtrl = segue.destination as! SecondVcViewController
        secViewCtrl.strFromFirst = "From first".
    }

    in secondvc create var
        var strFromFirst

tabviewcontroller
    drag view controller to story board and editor-> embed in -> tab bar controller
    connect other view controllers as normal way by click + control+drag

UIViewController life cycle
    https://developer.apple.com/library/content/referencelibrary/GettingStarted/DevelopiOSAppsSwift/WorkWithViewControllers.html

    viewDidLoad. - like oncreate
    viewWIllAppear. - like onresume
    ViewDidAppear
    viewWIllDisappear. - like onpause
    viewDidDisappear   - can handle ondestroy part.

    when app open
        TabFirstViewController - viewDidLoad
        TabFirstViewController - viewWillAppear
        TabFirstViewController - viewDidAppear
    swcond VC load
        TabSecondViewController - viewDidLoad
        TabFirstViewController - viewWillDisappear
        TabSecondViewController - viewWillAppear
        TabSecondViewController - viewDidAppear
        TabFirstViewController- viewDidDisappear
    back to first VC
        TabSecondViewController - viewWillDisappear
        TabFirstViewController - viewWillAppear
        TabFirstViewController - viewDidAppear
        TabSecondViewController - viewDidDisappear
    kill app in first VC
        TabFirstViewController - viewWillDisappear
        TabFirstViewController- viewDidDisappear

    what to handle viewWillDisappear vs viewDidDisappear
        when viewWillDisappear called next viewDidDisappear called. viewWillDisappear can use to hide keyboard, save edits etc. viewDidDisappear can use to stop running services etc