Ios UISegmentedControl不起作用的程序约束

我试图使用UIKit编程约束创建一个简单的界面，其中有一行，左侧有一个UISegmentedControl，右侧有一个黄色UIView

问题是，我希望UIView延伸到视图的整个高度，但是由于某些原因，它的底部锚点不在段控制器的实际底部

这是密码

parentGuide = top.layoutMarginsGuide

let choices = UISegmentedControl(items: ["Op1", "Op2"])
choices.translatesAutoresizingMaskIntoConstraints = false
top.addSubview(choices)
choices.leadingAnchor.constraint(equalTo: parentGuide.leadingAnchor).isActive = true
choices.topAnchor.constraint(equalTo: parentGuide.topAnchor).isActive = true

let yellow = UIView()
yellow.translatesAutoresizingMaskIntoConstraints = false
top.addSubview(yellow)
yellow.backgroundColor = UIColor.yellow
yellow.trailingAnchor.constraint(equalTo: parentGuide.trailingAnchor).isActive = true
yellow.topAnchor.constraint(equalTo: parentGuide.topAnchor).isActive = true
yellow.leadingAnchor.constraint(equalTo: parentGuide.trailingAnchor, constant: -40).isActive = true
yellow.bottomAnchor.constraint(equalTo: choices.layoutMarginsGuide.bottomAnchor).isActive = true

为什么会发生这种情况？我如何修复它？

而不是

yellow.bottomAnchor.constraint(equalTo: choices.layoutMarginsGuide.bottomAnchor).isActive = true

成功

yellow.bottomAnchor.constraint(equalTo: choices.bottomAnchor).isActive = true