NSLayoutConstraint 约束

// 关闭autoresizing 不关闭否则程序崩溃

webView.translatesAutoresizingMaskIntoConstraints =false

//高约束

            let hight:NSLayoutConstraint = NSLayoutConstraint(item: webView, attribute: NSLayoutAttribute.height , relatedBy:NSLayoutRelation.equal, toItem:nil, attribute:NSLayoutAttribute.notAnAttribute, multiplier:0.0, constant:  900)
            webView.superview!.addConstraint(hight)

        //上边约束

            let top:NSLayoutConstraint = NSLayoutConstraint(item: webView, attribute: NSLayoutAttribute.top , relatedBy:NSLayoutRelation.equal, toItem:webView.superview, attribute:NSLayoutAttribute.top, multiplier:1.0, constant: 0)
            webView.superview!.addConstraint(top)

        //下边约束

            let bottom:NSLayoutConstraint = NSLayoutConstraint(item: webView, attribute: NSLayoutAttribute.bottom, relatedBy:NSLayoutRelation.equal, toItem:webView.superview, attribute:NSLayoutAttribute.bottom, multiplier:1.0, constant: 0)        
            webView.superview!.addConstraint(bottom)//父控件添加约束

        //左边约束

            let left:NSLayoutConstraint = NSLayoutConstraint(item: webView, attribute: NSLayoutAttribute.left, relatedBy:NSLayoutRelation.equal, toItem:webView.superview, attribute:NSLayoutAttribute.left, multiplier:1.0, constant: 0)
            webView.superview!.addConstraint(left)//父控件添加约束

        //右边约束

            let right:NSLayoutConstraint = NSLayoutConstraint(item: webView, attribute: NSLayoutAttribute.right, relatedBy:NSLayoutRelation.equal, toItem:webView.superview, attribute:NSLayoutAttribute.right, multiplier:1.0, constant: 0)
            webView.superview!.addConstraint(right)//父控件添加约束