iOS 中的 Category

作者：NewBoy

2022 年 7 月 12 日
本文字数：3204 字
阅读完需：约 11 分钟

什么是 Category

在 OC 中，扩展一个类的方式有两种
继承
分类
可以在不修改原来类的基础上，为这个类扩充一些方法
一个庞大的类可以分模块开发

Category 的格式

通过 Category 给某类添加方法，分为声明和实现俩部分
创建 Category 时，必须给 Category 的名称加上专用前缀
创建 Category 的方法时，必须给方法名称加上专用前缀
分类声明

    @interface Person (Play)    - (void)pGotoTheCinema;    - (void)pGotoSportGame;    @end

复制代码

分类实现

    #import "Person+Play.h"    @implementation Person (Play)    - (void)pGotoTheCinema{    }    - (void)pGotoSportGame{    }    @end

复制代码

Category 的类型

Class-continuation 类型的 Category
它必须定义在其所接续的那个类的实现文件中
此分类可以声明属性，且此分类没有特定的是现实文件,其中方法都定义在主实现文件中
一般存放不需要对外公开的属性(例子中的 age)

  #import <Foundation/Foundation.h>  @interface Person : NSObject  @property (nonatomic,copy,readonly) NSString *firstName;  @property (nonatomic,copy,readonly) NSString *lastName;  @property (nonatomic,strong,readonly) NSArray *friends;  - (instancetype)initWithFristName:(NSString *)firstName withLastName:(NSString *)lastName;  @end  --------------------  #import "Person.h"  @interface Person()  @property (nonatomic,assign) NSInteger age;  @property (nonatomic,strong,readwrite) NSArray *friends;  @end  @implementation Person  - (instancetype)initWithFristName:(NSString *)firstName withLastName:(NSString *)lastName{      self = [super init];      if (self) {          _firstName = firstName;          _lastName = lastName;      }      return self;  }  @end

复制代码

如果某属性在主接口中声明为“只读”，而类内部要用 setter 方法修改此属性，那么就在 Class-continuation 分类中将其扩展为 “readwrite”（例子中的 friends）

  #import <Foundation/Foundation.h>  @interface Person : NSObject  @property (nonatomic,copy,readonly) NSString *firstName;  @property (nonatomic,copy,readonly) NSString *lastName;  @property (nonatomic,strong,readonly) NSArray *friends;
  - (instancetype)initWithFristName:(NSString *)firstName withLastName:(NSString *)lastName;  @end
  -------------------------------  #import "Person.h"  @interface Person()  @property (nonatomic,strong,readwrite) NSArray *friends;  @end
  @implementation Person  - (instancetype)initWithFristName:(NSString *)firstName withLastName:(NSString *)lastName{      self = [super init];      if (self) {          _firstName = firstName;          _lastName = lastName;      }      return self;  }  @end

复制代码

若想使类遵循的协议不为人知道，则可以在 Class-continuation 分类中声明

  #import <Foundation/Foundation.h>  @class User;  @interface APP : NSObject  @property (nonatomic,strong) User *user;  @end
  -----------------------------  #import "APP.h"  #import "User.h"  @interface APP()<UserDelegate>
  @end  @implementation APP  -(void)doSomething{      NSLog(@"dosomething");  }  @end

复制代码

普通类型的 Category

    #import "Person.h"    @interface Person (Play)    - (void)pGotoTheCinema;    - (void)pGotoSportGame;    @end    --------------    #import "Person+Play.h"    @implementation Person (Play)    - (void)pGotoTheCinema{    }    - (void)pGotoSportGame{    }    @end

复制代码

Category 的运用

在开发中，类的实现文件特别大，难于管理与维护，因此经常使用分类机制把类的实现代码划分成易于管理的小块，以便单独检视

    #import <Foundation/Foundation.h>    @interface Person : NSObject    @property (nonatomic,copy) NSString *firstName;    @property (nonatomic,copy) NSString *lastName;    @property (nonatomic,strong) NSArray *friendArray;
    - (instancetype)initWithFristName:(NSString *)firstName withLastName:(NSString *)lastName;    - (void)addPerson:(Person *)person;    - (void)removePerson:(Person *)person;    - (BOOL)isFriendWithPerson:(Person *)person;    - (void)performDayWork;    - (void)takeVacationFromWork;    - (void)gotoTheCinema;    - (void)gotoSportGame;    @end

复制代码

实现文件里，所有的方法都写在一个类，内容太多，所以我们可根据其不同功能分成多个分类

    #import <Foundation/Foundation.h>    @interface Person : NSObject    @property (nonatomic,copy) NSString *firstName;    @property (nonatomic,copy) NSString *lastName;    @property (nonatomic,strong) NSArray *friends;    - (instancetype)initWithFristName:(NSString *)firstName withLastName:(NSString *)lastName;    @end    -------------------------    #import "Person.h"    @interface Person (Work)    - (void)wPerformDayWork;    - (void)wTakeVacationFromWork;    @end    -------------------------    #import "Person.h"    @interface Person (Play)    - (void)pGotoTheCinema;    - (void)pGotoSportGame;    @end    -------------------------    #import "Person.h"    @interface Person (Friendship)    - (void)fAddPerson:(Person *)person;    - (void)fRemovePerson:(Person *)person;    - (BOOL)fIsFriendWithPerson:(Person *)person;    @end

复制代码

Category 的注意事项

Category 只能添加方法，不能添加属性。因为 Category 中的 @property，只会生成 setter/getter 的方法声明，不会生成实现及私有的成员变量（在.m 文件(Class-continuation)中的分类可以声明属性，同时也可以生成 setter、getter 方法）

  #import "Person.h"  @interface Person (Play)  @property (nonatomic,copy) NSString *playGameName;  - (void)pGotoTheCinema;  - (void)pGotoSportGame;  @end  -------------  - (void)viewDidLoad {    [super viewDidLoad];    Person *p = [[Person alloc]initWithFristName:@"firstName" withLastName:@"lastName"];    p.playGameName = @"football";}

复制代码

Xcode 会有警告

运行程序会崩溃

如果分类中有和原类中同名的方法，程序只会调用分类里的方法，如果多个分类中都有和原类中同名的方法，程序只会由编译器决定，编译器最后一个执行的方法来响应调用优先级(Category->本类->父类)

#import <Foundation/Foundation.h>@interface Person : NSObject@property (nonatomic,copy,readonly) NSString *firstName;@property (nonatomic,copy,readonly) NSString *lastName;@property (nonatomic,strong,readonly) NSArray *friends;- (instancetype)initWithFristName:(NSString *)firstName withLastName:(NSString *)lastName;- (void)run;@end------------------------------------#import "Person.h"@interface Person (Play)@property (nonatomic,copy) NSString *playGameName;- (void)pGotoTheCinema;- (void)pGotoSportGame;- (void)run;@end-------------------------------------#import "Person.h"@interface Person (Work)- (void)wPerformDayWork;- (void)wTakeVacationFromWork;- (void)run;@end-------------------------------------Person *p = [[Person alloc]initWithFristName:@"firstName" withLastName:@"lastName"];[p run];

复制代码

log:

发布于: 刚刚阅读数: 3

原文链接:【http://xie.infoq.cn/article/6dfcfd52d8bad7f08dde279ad】。文章转载请联系作者。

NewBoy

关注

虽不年少，艳阳高照 2019.04.10 加入

还未添加个人简介

发布

暂无评论

创作场景

iOS 中的 Category

什么是 Category

Category 的格式

Category 的类型

Category 的运用

Category 的注意事项

NewBoy

评论