//用pod导入库
pod 'Masonry'
* //新增约束
-(NSArray *)mas_makeConstraints:(void(^)(MASConstraintMaker *make))block;
* //更新约束
-(NSArray *)mas_updateConstraints:(void(^)(MASConstraintMaker *make))block;
* //清除之前的所有约束,从新添加最新的约束
-(NSArray *)mas_remakeConstraints:(void(^)(MASConstraintMaker *make))block;