swift - 改变 NSLayoutConstraint

Question

我想改变 ScrollView 的宽度。首先，我这样做了:

var scrollWidthConstraint: NSLayoutConstraint!

然后设置它:

scrollWidthConstraint = contentView.widthAnchor.constraint(equalToConstant: CGFloat(scrollWidth()))
        scrollWidthConstraint.isActive = true

然后我想把它改成这样:

  scrollWidthConstraint = contentView.widthAnchor.constraint(equalToConstant: width)
        scrollWidthConstraint.isActive = true
        contentView.setNeedsLayout()

但是看起来我没有删除旧的约束，我在日志中看到:

"<NSLayoutConstraint:0x6000031d7160 UIView:0x7fc92c808120.width == 1333   (active)>",
    "<NSLayoutConstraint:0x6000031fcff0 UIView:0x7fc92c808120.width == 933.1   (active)>"

如何删除旧约束并更新它？

Answer 1

这个

scrollWidthConstraint = contentView.widthAnchor.constraint(equalToConstant: width)
    scrollWidthConstraint.isActive = true
    contentView.setNeedsLayout()

无论您将其重新分配给旧的约束，都会创建另一个约束，您需要

scrollWidthConstraint.constant = width
view.layoutIfNeeded()