iOS中的Category

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发布于 2023-11-22 08:38:17

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发布于 2023-11-22 08:38:17

文章被收录于专栏：浮躁的喧嚣

什么是Category

在OC中，扩展一个类的方式有两种：继承与分类
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

分类实现

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

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

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

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

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

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

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

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";
}

Xcode会有警告

Xcode会有警告.png

运行程序会崩溃

运行程序会崩溃.png

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];