Autlo布局问题

Question

将programatacally autlo布局设置为UIView，但不设置高度约束。我无法确定问题所在。

let viewSep = UIView()
            viewSep.backgroundColor = UIColor.red
            viewSep.translatesAutoresizingMaskIntoConstraints = false
            viewInner.addSubview(viewSep)

            viewSep.leftAnchor.constraint(equalTo: viewInner.leftAnchor, constant: 10).isActive = true
            viewSep.topAnchor.constraint(equalTo: lblDate.bottomAnchor, constant: 5).isActive = true
            viewSep.rightAnchor.constraint(equalTo: viewInner.rightAnchor, constant: -10).isActive = true
            viewSep.heightAnchor.constraint(equalToConstant: 21)