AutoLayout 未以编程方式更新视图 - Swift

Question

I have the following code where I'm creating and laying out everything in code. What I'm trying to do is modify the myTopContainer when a button is tapped but I can not make the width changed, only the height gets modified.

Any idea why?

func setupAutoLayout(){
    NSLayoutConstraint.activate([
        // My Container
        myTopContainer.bottomAnchor.constraint(equalTo: myButton.topAnchor, constant: -5),
        myTopContainer.heightAnchor.constraint(equalToConstant: 50),
        myTopContainer.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 15),
        myTopContainer.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: -15),

        // My Button
        myButton.widthAnchor.constraint(equalToConstant: 80),
        myButton.heightAnchor.constraint(equalToConstant: 40),
        myButton.trailingAnchor.constraint(equalTo: self.view.trailingAnchor, constant: -15),
        myButton.bottomAnchor.constraint(equalTo: self.view.bottomAnchor, constant: -400)
    ])
}


@IBAction func relayoutViews(_ sender: Any) {

    UIView.animate(withDuration: 0.5, delay: 0, options: .curveEaseIn, animations: {

        self.myTopContainer.heightAnchor.constraint(equalToConstant: 50).isActive = false
        self.myTopContainer.leadingAnchor.constraint(equalTo: self.view.leadingAnchor, constant: 15).isActive = false

        // this is working, it changes the height
        self.myTopContainer.heightAnchor.constraint(equalToConstant: 10).isActive = true
        // this is not doing anything
        self.myTopContainer.leadingAnchor.constraint(equalTo: self.myButton.trailingAnchor).isActive = true

        self.view.layoutIfNeeded()

    })
}

Answer 1

A line like this

self.myTopContainer.heightAnchor.constraint(equalToConstant: 50).isActive = false

Creates a new constraint every time. It doesn't modify the previously created constraint.

When you setupAutolayout you should save a reference to the constraints you want to later modify before actually calling NSLayoutConstraint.activate() on them. Later you can set isActive to false on them.

For example:

var someConstraint: NSLayoutConstraint?
func setupAutoLayout(){
    let aConstraint = myTopContainer.bottomAnchor.constraint(equalTo: myButton.topAnchor, constant: -5)
    someConstraint = aConstraint
    NSLayoutConstraint.activate([
        // My Container
        aConstraint
    ])
}

func editConstraint() {
    self.someConstraint?.isActive = false
}

Anyway be careful on logs when you edit constraints, it's probable that you could break something while editing. If you see those logs of broken constraint than it means that something is still wrong (even if it visually looks good, it could crash or not work properly in some other situation)

Answer 2

You're missing:

view.translatesAutoresizingMaskIntoConstraints = false