swift - 设置 `constraint.isActive = false` 是否解除约束？

Question

假设我想删除一个约束，传统上我会这样做:

view.removeConstraint(constraint)

但是，现在有用于安装/卸载约束的新 isActive 方法。

如果我执行以下操作:

constraint.isActive = false

它会正确地将其从内存中删除吗？

Answer 1

是的，

constraint.isActive = false

正在做同样的事情:

viewThatOwnsConstraint.removeConstraint(constraint)

因此，如果唯一保持约束的是 View ，那么这将正确地将其从内存中删除。

---

证明如下:

let view = UIView()

weak var weakView: UIView? = nil
autoreleasepool {
  weakView = UIView()
}
assert(weakView == nil)

// Traditional way of removing constraints ensures that the constraint is deallocated

weak var weakConstraint: NSLayoutConstraint? = nil
autoreleasepool {
  weakConstraint = view.widthAnchor.constraint(equalToConstant: 10)
}
assert(weakConstraint == nil) // nothing is holding on to the constraint

autoreleasepool {
  weakConstraint = view.widthAnchor.constraint(equalToConstant: 10)
  view.addConstraint(weakConstraint!)
}
assert(weakConstraint != nil)

autoreleasepool {
  view.removeConstraint(weakConstraint!)
}
assert(weakConstraint == nil)

// New way of removing constraints:

assert(weakConstraint == nil)

autoreleasepool {
  weakConstraint = view.widthAnchor.constraint(equalToConstant: 10)
  weakConstraint!.isActive = true
}
assert(weakConstraint != nil)

autoreleasepool {
  weakConstraint!.isActive = false
}
assert(weakConstraint == nil)