使用 ViewController 中的 CGFloat 值在 Swift 中的 TabBarController 中移动视图

Question

I'm so close to just throw my laptop away. For 3 days, again, 3 days I'm looking for this specific piece of code and I cannot seem to find out how. My project became a whole commented-out-code graveyard. I would give anything for an answer. Please help me.

What I want: My ViewController has a gestureRecognizer that gets me the value eg. var fingerPos of the current finger position. Simple example:

 @objc func panGestureRecognizerHandler(_ sender: UIPanGestureRecognizer) {
        fingerPos = sender.location(in: view?.window)
}

I want to get the fingerPos position and pass it to the TabBarController . That value should then be used to move the TabBarController . For example self.view.frame.origin.y = fingerPos.y . The movement/update of the value must be continuous.

What I tried: NSNotificationCenter , didSet , Structs in combination with didSet , Various types of function passing eg.

//Function in ViewController

func IBegYouGiveMeTheValueFunction() -> CGFloat {
 return fingerPos
}


//In the TabBarController

let vc = ViewController()
self.view.frame.origin.y = vc.IBegYouGiveMeTheValueFunction()

that resulted in crashes because the "Value was found nil" even though it had a value, Adding the TabBarController as a child which resulted in a white screen on the simulator and fan spinning, Values written out of any classes (public), Trying to set the position of the TabBarController in the ViewController , literally anything I found online.

Can anyone help me with this? I would be really thankful!

Answer 1

You do not need a custom TabBarController class.

The view controllers in each tab can be accessed via the tab bar controllers .viewControllers array, so you can call funds or set properties directly.

• In your first tab view controller, track the finger position with the drag gesture.
• When it changes, get a reference to the view controller in the second tab.
• Call a func in that vc, which will, for example, update the position of a subView.

Here is a complete, simple example. Just add a UITabBarController to a Storyboard, and assign the class of the two default tab controllers to MyFirstViewController and MySecondViewController included in the following code (you don't need to add anything else... no IBOutlet or IBAction needed):

class MyFirstViewController: UIViewController {

    let statusLabel: UILabel = {
        let v = UILabel()
        v.translatesAutoresizingMaskIntoConstraints = false
        v.backgroundColor = .red
        v.textColor = .white
        v.textAlignment = .center
        v.numberOfLines = 0
        v.text = "Tracking" + "\n\n" + "Drag your finger in view..."
        return v
    }()

    var topConstraint: NSLayoutConstraint!

    override func viewDidLoad() {
        super.viewDidLoad()

        view.addSubview(statusLabel)

        topConstraint = statusLabel.topAnchor.constraint(equalTo: view.topAnchor, constant: 200.0)

        NSLayoutConstraint.activate([
            topConstraint,
            statusLabel.centerXAnchor.constraint(equalTo: view.centerXAnchor),
            statusLabel.widthAnchor.constraint(equalToConstant: 240.0),
        ])

        let pg = UIPanGestureRecognizer(target: self, action: #selector(panGestureRecognizerHandler(_:)))
        view.addGestureRecognizer(pg)

    }

    @objc func panGestureRecognizerHandler(_ sender: UIPanGestureRecognizer) {

        let fingerPos = sender.location(in: view)
        var strTmp = "Tracking Y: \(fingerPos.y)"
        topConstraint.constant = fingerPos.y

        guard let tb = self.tabBarController else {
            strTmp += "\n\n" + "Must be in a tabBarController!"
            statusLabel.text = strTmp
            return
        }

        guard let vControllers = tb.viewControllers else {
            strTmp += "\n\n" + "Could not get viewControllers from tabBarController!"
            statusLabel.text = strTmp
            return
        }

        guard vControllers.count > 1, let secondVC = vControllers[1] as? MySecondViewController else {
            strTmp += "\n\n" + "VC in second tab is not MySecondViewController!"
            statusLabel.text = strTmp
            return
        }

        // in case we have not yet navigated to the second tab
        secondVC.loadViewIfNeeded()

        // tell SecondVC to update the Y position
        secondVC.updateYPosition(at: fingerPos.y)

        strTmp += "\n\n" + "Sent!"

        statusLabel.text = strTmp

    }

}

class MySecondViewController: UIViewController {

    let statusLabel: UILabel = {
        let v = UILabel()
        v.translatesAutoresizingMaskIntoConstraints = false
        v.backgroundColor = .blue
        v.textColor = .white
        v.textAlignment = .center
        v.numberOfLines = 0
        v.text = "Have not received" + "\n\n" + "a Y update yet..."
        return v
    }()

    var topConstraint: NSLayoutConstraint!

    override func viewDidLoad() {
        super.viewDidLoad()

        view.addSubview(statusLabel)

        topConstraint = statusLabel.topAnchor.constraint(equalTo: view.topAnchor, constant: 200.0)

        NSLayoutConstraint.activate([
            topConstraint,
            statusLabel.centerXAnchor.constraint(equalTo: view.centerXAnchor),
            statusLabel.widthAnchor.constraint(equalToConstant: 240.0),
        ])

    }

    func updateYPosition(at y: CGFloat) -> Void {
        topConstraint.constant = y
        statusLabel.text = "Top contstraint constant:" + "\n\n" + "\(y)"
    }

}

When you run this, the first thing you see is the first tab:

As you tap-and-drag your finger, the top of the red label will follow:

When you select the second tab, you will see a blue label with its top at the same Y position where you dragged the red label: