在代码里更新autolayout布局

             //遍历view约束(高,宽)
             NSArray* constrains = self.View.constraints;
             for (NSLayoutConstraint* constraint in constrains) {
                 if (constraint.firstAttribute == NSLayoutAttributeHeight) {
                     //宽高的值
                     constraint.constant = 45.0;
                 }
             }

            //遍历view约束，找到属于子view的约束
             NSArray* constrains2 = self.view.constraints;
             for (NSLayoutConstraint* constraint in constrains2) {
                 if (constraint.secondItem == self.table) {
                     //底部距离
                     if (constraint.firstAttribute == NSLayoutAttributeBottom) {
                         constraint.constant = 0.0;

                     }
                 }
             }            

内容来自网络，并部分修改，非个人原创。