NSLayoutAttribute 属性参数解释

typedef NS_ENUM(NSInteger, NSLayoutRelation) {

    NSLayoutRelationLessThanOrEqual = -1,          //小于等于

    NSLayoutRelationEqual = 0,                     //等于

    NSLayoutRelationGreaterThanOrEqual = 1,        //大于等于

};

typedef NS_ENUM(NSInteger, NSLayoutAttribute) {

    NSLayoutAttributeLeft = 1,                     //左侧

    NSLayoutAttributeRight,                        //右侧

    NSLayoutAttributeTop,                          //上方

    NSLayoutAttributeBottom,                       //下方

    NSLayoutAttributeLeading,                      //首部

    NSLayoutAttributeTrailing,                     //尾部

    NSLayoutAttributeWidth,                        //宽度

    NSLayoutAttributeHeight,                       //高度

    NSLayoutAttributeCenterX,                      //X轴中心

    NSLayoutAttributeCenterY,                      //Y轴中心

    NSLayoutAttributeBaseline,                     //文本底标线

                                                                                                                                                    

    NSLayoutAttributeNotAnAttribute = 0            //没有属性

};