更改NSLayoutConstraint

Question

我想更改滚动视图的宽度。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：

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

但是，我似乎没有删除旧的约束，我在日志中看到：

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

如何删除旧的约束并更新它？

Answer 1

这

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

创建另一个约束，不管您是否将其重新分配给旧约束，您需要

scrollWidthConstraint.constant = width
view.layoutIfNeeded()