(四)关联对象

作者: dandelionYD | 来源:发表于2019-03-12 16:53 被阅读22次

(四)关联对象
Swift 为分类增加属性objc_getAssociated
iOS runtime关联对象 objc_setAssociat
关联对象
关联对象
objc_setAssociatedObject和objc_ge
iOS 关联对象
关联对象
iOS关联对象技术原理
关联对象

引言

准备:首先搭建好可以跑runtime源码的过程，参考配置运行objc4-750和使用

我们试试给category添加属性看看呢？

Animal.h
#import <Foundation/Foundation.h>
@interface Animal : NSObject
@property(nonatomic,strong)NSString * name;
@end

Animal.m
#import "Animal.h"
@implementation Animal
@end

Animal+category.h
#import "Animal.h"
@interface Animal (category)
@property(nonatomic,strong)NSString*address;
@end

Animal+category.m
#import "Animal+category.h"
@implementation Animal (category) 
@end

//此时我们发现系统会提示：
1.Property 'address' requires method 'address' to be defined - use @dynamic or provide a method implementation in this category
2.Property 'address' requires method 'setAddress:' to be defined - use @dynamic or provide a method implementation in this category

使用：main.h
#import <Foundation/Foundation.h>
#import "Animal+category.h"
#import  <objc/runtime.h>

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        Animal *animal = [[Animal alloc]init];    
        animal.name = @"啊黄";
        animal.address = @"地址"; //直接炸了
        NSLog(@"%@",animal.name);
        NSLog(@"%@",animal.address);
    }
    return 0;
}

发现：command+B 编译没有问题，
     command+R 运行就炸了

-[Animal setAddress:]: unrecognized selector sent to instance 0x1018159a0
*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[Animal setAddress:]: unrecognized selector sent to instance 0x1018159a0'
--------

至此我们发现：
 - 在分类里面添加属性（@property...），编译器只会生成set和get方法的声明，但是没有set和get方法的实现，而不会生成成员变量
 - 在分类里面是不能添加成员变量的

那怎么办呢？

其实我们可以间接的去为分类添加成员变量的

如下：

Animal+category.h
#import "Animal.h"
@interface Animal (category)
@property(nonatomic,strong)NSString*address;
@property(nonatomic,assign)int age;
@end

Animal+category.m
#import "Animal+category.h"
#import <objc/runtime.h>
@implementation Animal (category)
-(void)setAddress:(NSString *)address{
    objc_setAssociatedObject(self, @selector(address), address, OBJC_ASSOCIATION_COPY_NONATOMIC);
}
-(NSString *)address{
    return objc_getAssociatedObject(self, _cmd); ///_cmd = @selector(address)
}
-(void)setAge:(int)age{
     objc_setAssociatedObject(self, @selector(age), @(age), OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}
-(int)age{
    return [objc_getAssociatedObject(self, _cmd) intValue];
}
@end

使用：
#import <Foundation/Foundation.h>
#import "Animal+category.h"
#import  <objc/runtime.h>
int main(int argc, const char * argv[]) {
    @autoreleasepool {
        Animal *animal = [[Animal alloc]init];
        animal.name = @"啊黄";
        animal.address = @"地址";
        animal.age = 100;
        
        NSLog(@"%@",animal.name);
        NSLog(@"%@",animal.address);
        NSLog(@"%d",animal.age);   
    }
    return 0;
}
打印：
05.关联对象[22877:7181963] 啊黄
05.关联对象[22877:7181963] 地址
05.关联对象[22877:7181963] 100

可见使用【关联对象】可以添加成员变量的哟

API如下：

添加关联对象
void objc_setAssociatedObject(id object, const void *key, 
                            id value, objc_AssociationPolicy policy)                            
获得关联对象
id objc_getAssociatedObject(id object, const void *key) 

移除所有的关联对象
void objc_removeAssociatedObjects(id object) 

//文件处于:objc-runtime.mm

其中key的使用定义

static void *Mykey= &Mykey;
objc_setAssociatedObject(obj,Mykey,value,OBJC_ASSOCIATION_RETAIN_NONATOMIC)
objc_getAssociatedObject(obj,Mykey);
--------

static char Mykey;
objc_setAssociatedObject(obj,&Mykey,value,OBJC_ASSOCIATION_RETAIN_NONATOMIC)
objc_getAssociatedObject(obj,&Mykey);
--------

使用属性名作为key
objc_setAssociatedObject(obj,@"property",value,OBJC_ASSOCIATION_RETAIN_NONATOMIC)
objc_getAssociatedObject(obj,@"property");
--------

使用get方法的@selector作为key
objc_setAssociatedObject(obj,@selector(getter),value,OBJC_ASSOCIATION_RETAIN_NONATOMIC)
objc_getAssociatedObject(obj,@selector(getter));

补充：@selector(name)  返回的是某个结构体的指针（首地址）

objc_AssociationPolicy的说明
- objc_AssociationPolicy 对应的修饰符
- OBJC_ASSOCIATION_ASSIGN -----> assign
- OBJC_ASSOCIATION_RETAIN_NONATOMIC. ----->strong,nonatomic
- OBJC_ASSOCIATION_COPY_NONATOMIC ----->copy,nonatomic
- OBJC_ASSOCIATION_RETAIN ----->strong,actomic
- OBJC_ASSOCIATION_COPY ----->copy,actomic