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iOS Introduction to Auto Layout in iOS Auto Layout in Code Using Layout Anchors

Vansh Agarwal
PLUS
Vansh Agarwal
Courses Plus Student 3,965 Points
Posted by Vansh Agarwal
Vansh Agarwal
Courses Plus Student 3,965 Points

Can someone help me with this code challenge?

When I execute the code below, I get an error message in 'Preview', saying 'swift_lint.swift:351:54: error: value of type 'UIView' has no member 'layoutMarginsGuide' greenView.leftAnchor.constraint(equalTo: view.layoutMarginsGuide.leftAnchor, constant: 8),'. I don't know why this is happening as I tried doing this on XCode and it still worked. Please help me out. Thanks!

layout.swift 
class MyViewController: UIViewController {

    let blueView = UIView()
    let greenView = UIView()

    override func viewDidLoad() {
        super.viewDidLoad()
        view.addSubview(greenView)
        view.addSubview(blueView)
    }

    override func viewWillLayoutSubviews() {
        super.viewWillLayoutSubviews()
        blueView.translatesAutoresizingMaskIntoConstraints = false
        greenView.translatesAutoresizingMaskIntoConstraints = false

        NSLayoutConstraint.activate([
            NSLayoutConstraint(item: blueView, attribute: .height, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1.0, constant: 100.0),
            NSLayoutConstraint(item: blueView, attribute: .width, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1.0, constant: 150.0),
            NSLayoutConstraint(item: blueView, attribute: .left, relatedBy: .equal, toItem: view, attribute: .leftMargin, multiplier: 1.0, constant: 8.0),
            NSLayoutConstraint(item: blueView, attribute: .top, relatedBy: .equal, toItem: self.topLayoutGuide, attribute: .bottom, multiplier: 1.0, constant: 8.0),
            NSLayoutConstraint(item: blueView, attribute: .right, relatedBy: .equal, toItem: view, attribute: .rightMargin, multiplier: 1.0, constant: -8.0)
        ])

        // Add constraint code below

           NSLayoutConstraint.activate([
            greenView.topAnchor.constraint(equalTo: blueView.bottomAnchor, constant: 8),
            greenView.leftAnchor.constraint(equalTo: view.layoutMarginsGuide.leftAnchor, constant: 8),
            greenView.rightAnchor.constraint(equalTo: view.layoutMarginsGuide.rightAnchor, constant: 8),
            greenView.heightAnchor.constraint(equalToConstant: 75)
        ])

    }
}

1 Answer

landonferrier
landonferrier
25,097 Points

Vansh,

Here is the code that I got to pass the challenge: 

class MyViewController: UIViewController {

    let blueView = UIView()
    let greenView = UIView()

    override func viewDidLoad() {
        super.viewDidLoad()
        view.addSubview(greenView)
        view.addSubview(blueView)
    }

    override func viewWillLayoutSubviews() {
        super.viewWillLayoutSubviews()
        blueView.translatesAutoresizingMaskIntoConstraints = false
        greenView.translatesAutoresizingMaskIntoConstraints = false



        NSLayoutConstraint.activate([
            NSLayoutConstraint(item: blueView, attribute: .height, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1.0, constant: 100.0),
            NSLayoutConstraint(item: blueView, attribute: .width, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1.0, constant: 150.0),
            NSLayoutConstraint(item: blueView, attribute: .left, relatedBy: .equal, toItem: view, attribute: .leftMargin, multiplier: 1.0, constant: 8.0),
            NSLayoutConstraint(item: blueView, attribute: .top, relatedBy: .equal, toItem: self.topLayoutGuide, attribute: .bottom, multiplier: 1.0, constant: 8.0),
            NSLayoutConstraint(item: blueView, attribute: .right, relatedBy: .equal, toItem: view, attribute: .rightMargin, multiplier: 1.0, constant: -8.0)
        ])

        // Add constraint code below
       NSLayoutConstraint.activate([
        greenView.bottomAnchor.constraint(equalTo: view.bottomAnchor, constant: 8),
        greenView.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 8),
        greenView.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: 8),
        greenView.heightAnchor.constraint(equalToConstant: 75.0)
        ])

    }
}

When activating the constraints, you don't need to use the layout guide to get the anchors. These can be accessed directly from the "view" property. If you have any questions, feel free to ask.