swift 代码 添加 约束 constrains

代码见下方

//不自动转换为constrains

//历史原因造成的

 //得设成false后下面添加的约谁才能生效

subView.translatesAutoresizingMaskIntoConstraints =false

//添加视图进去

view.addSubview(subView)

//创建三条约束

letsc1 = NSLayoutConstraint(

item: subView,

attribute: NSLayoutAttribute.Top,

relatedBy: NSLayoutRelation.Equal,

toItem: topLayoutGuide,

attribute: NSLayoutAttribute.Bottom,

multiplier:1,

constant:0

)

letsc2 = NSLayoutConstraint(

item: subView,

attribute: NSLayoutAttribute.Leading,

relatedBy: NSLayoutRelation.Equal,

toItem: subView.superview,

attribute: NSLayoutAttribute.Leading,

multiplier:1,

constant:0

)

letsc3 = NSLayoutConstraint(

item: subView,

attribute: NSLayoutAttribute.Trailing,

relatedBy: NSLayoutRelation.Equal,

toItem: subView.superview,

attribute: NSLayoutAttribute.Trailing,

multiplier:1,

constant:0

)

//使创建的约束生效

NSLayoutConstraint.activateConstraints([sc1,sc2,sc3])