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。