Swift 打印锚定常量值

Question

如何打印出锚点常量的值？例如：

let myButton = UIButton()
myButton.topAnchor.constraint(equalTo: view.topAnchor, constant: 5).isActive = true
myButton.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true
myButton.leadingAnchor.constraint(equalTo: view.leadingAnchor).isActive = true
myButton.trailingAnchor.constraint(equalTo: view.trailingAnchor).isActive = true
print(myButton.topAnchor.constant)//this would print 5

Answer 1

该常量用于您为锚点设置的约束。锚点没有常数。限制确实如此。因此，您需要做的是维护约束的引用并访问常量。

let myButtonTopAnchorConstraint = myButton.topAnchor.constraint(equalTo: view.topAnchor, constant: 5)
myButtonTopAnchorConstraint.isActive = true
myButton.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true
myButton.leadingAnchor.constraint(equalTo: view.leadingAnchor).isActive = true
myButton.trailingAnchor.constraint(equalTo: view.trailingAnchor).isActive = true

print(myButtonTopAnchorConstraint.constant) //Prints 5

一个视图只有一个 topAnchor，但可以有多个相对于该锚点的约束。