以编程方式使用乘数设置 centerXAnchor 约束不起作用

Question

I am trying to set a horizontal center constraint of a view with multiplier programmatically. But what I get is always a constraint with 1.0 as the multiplier. This is what I did:

private func createHalfCenteredView() {
    let newView = UIView(frame: .zero)
    newView.backgroundColor = .systemTeal
    view.addSubview(newView)
    
    newView.translatesAutoresizingMaskIntoConstraints = false
    let top = newView.topAnchor.constraint(equalTo: view.topAnchor)
    let bottom = newView.bottomAnchor.constraint(equalTo: view.bottomAnchor)
    let width = newView.widthAnchor.constraint(equalToConstant: 100)
    let center = newView.centerXAnchor.constraint(equalToSystemSpacingAfter: view.centerXAnchor,
                                                  multiplier: 0.5)
    
    NSLayoutConstraint.activate([top, bottom, width, center])
    
    newView.setNeedsUpdateConstraints()
    view.setNeedsLayout()
    view.layoutIfNeeded()
}

I tried using lessThanOrEqualToSystemSpacingAfter instead of equalToSystemSpacingAfter but it is still the same. The multiplier is always 1.0 or exactly in the middle.

Can anybody help me with this? Thanks.

Answer 1

You can't use multipliers using helpers functions, try this way

 let center = NSLayoutConstraint(item: newView, attribute: .centerX, relatedBy: .equal, toItem: view, attribute: .centerX, multiplier: 0.5, constant: 0)

Refer to answer