如何在 MacOS 上的 Swift 中使用自动布局以 x 轴为中心？

Question

Hi I'm just wanting to have a childView centered on the x axis of a NSViewController view using auto layout. I'm doing the following:

override func viewWillAppear()
{
    super.viewWillAppear()

    let childView = PagesView.init(frame: CGRect(x: 0, y: 0, width:100, height: 100))
    childView.translatesAutoresizingMaskIntoConstraints = false
    self.view.addSubview(childView)

    childView.centerXAnchor.constraint(equalTo: self.view.centerXAnchor).isActive = true
}

The childView doesn't even appear on the screen. When I remove the last line, then it gets positioned at 0,0. So something about that last line is causing it go haywire and I'm not sure why? I've used this exact same logic on iOS and it has worked fine.

Answer 1

All views should have constraints to define its location and size.

// This would create dimension constraints if your class cannot already infer them
childView.widthAnchor.constraint(equalToConstant: 100).isActive = true
childView.heightAnchor.constraint(equalToConstant: 100).isActive = true

You also need to specify a vertical anchor constraint so the view has enough information to be displayed.

childView.topAnchor.constraint(equalTo: self.view.topAnchor).isActive = true