2019-05-31 NSCache存储对象分析

nscache,
1、对于可变的object,nacache持有的object是一个强引用, 变化原来值, objectfokey跟着变化;
2、对于不可变的object,nacache持有的object还是一个强引用
3、对于普通对象,nacache持有的object是一个强引用
4、objectforkey 返回的永远的object与原保存对象地址是相同的,修改其值,会触发cache中的值变化;

回顾一下, property属性copy,
1、对于可变string,拷贝会真的发生,两块内存(浅拷贝);
2、对于不可变string, 虽然是copy, 但是实际上是持有一个强引用, 避免开销一块新的内存!

#import "ViewController.h"
#import <objc/runtime.h>
@interface SomeModel:NSObject
@property (copy, nonatomic) NSString *hello1;
@property (strong, nonatomic) NSMutableString *hello2;
@end
@implementation SomeModel
-(NSString *)description{
   return [NSString stringWithFormat:@"1=%@,2=%@",self.hello1,self.hello2];
}
@end

@interface NSStringSub:NSString
@end
@implementation NSStringSub

-(void)dealloc{
   NSLog(@"%s-%d %s",__FILE__,__LINE__, __PRETTY_FUNCTION__);
}

@end

@interface ViewController ()
{
   NSCache*cache;
}

@end

@implementation ViewController

- (void)viewDidLoad {
   [super viewDidLoad];
   
   cache = [NSCache new];
   
}
-(void)touchesEnded:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event{
   [self test];
}


/**
nscache,
1、对于可变的object,nacache持有的object是一个强引用,   变化原来值, objectfokey跟着变化;
2、对于不可变的object,nacache持有的object还是一个强引用
3、对于普通对象,nacache持有的object是一个强引用
4、objectforkey 返回的永远的object与原保存对象地址是相同的,修改其值,会触发cache中的值变化;



回顾一下,  property属性copy,
   1、对于可变string,拷贝会真的发生,两块内存(浅拷贝);
   2、对于不可变string, 虽然是copy, 但是实际上是持有一个强引用, 避免开销一块新的内存!



*/
-(void)test{
   //    setObject
   
   //    obj
   //    The object to be stored in the cache.
   //    key
   //    The key with which to associate the value.
   
   
   
   // 1、
   NSString *string =@"12345";
   [cache setObject:string forKey:@"name"];
   NSString *stringfromcache=[cache objectForKey:@"name"];
   NSLog(@"%@", stringfromcache);
   
   //setObject, 是拷贝还是引用
   string = @"1234566778900";
   NSLog(@"%@", [cache objectForKey:@"name"]);
   
   
   // 2、
   NSMutableString *string2=@"12345".mutableCopy;
   [cache setObject:string2 forKey:@"name2"];
   //string2fromcache类型是不可变类型了????
   NSMutableString *string2fromcache =[cache objectForKey:@"name2"];
   NSLog(@"%@, %@--%@", string2fromcache, NSStringFromClass(object_getClass(string2fromcache)),NSStringFromClass(object_getClass(string2)));
   
   // 可以修改--说明操作的仍然是原保存对象的地址内容
   [string2fromcache appendString:@"asdfasdfasdf"];
   //setobject,这里是引用------, 类似于copy,如果是string,就是copy,如果是mutablestring就是strong, 就跟集合类型的属性修饰符一样;  而string属性修饰符copy,遇到string就是strong,遇到不可变就是copy,不可变拷贝的
   
   [string2 appendString:@"asdfasdfasdf"];
   // 上面2处改变, 都会修改cache里面的内容
   NSLog(@"%@", [cache objectForKey:@"name2"]);
   
   
   //    [cache setObject:@"asdfasdfads" forKey:@"name2"];
   //    NSLog(@"%@", string2);
   
   NSMutableString*value2=[cache objectForKey:@"name2"];
   NSLog(@"%s-%d %s",__FILE__,__LINE__, __PRETTY_FUNCTION__);
   
   
   // 3、
   NSStringSub*string3=[@"123132" substringFromIndex:1];
   
   [cache setObject:string3 forKey:@"name3"];
   
   
   
   // 4、
   NSMutableString*stringsub=@"123".mutableCopy;
   NSMutableArray*arr=@[@"1",@"2",@"3",stringsub].mutableCopy;
   //设置可变对象value
   [cache setObject:arr forKey:@"name4"];
   [arr addObject:@"5"];
   //返回的是不可变类型的---[cache objectForKey:@"name4"]
   NSMutableArray *arrfromcache=[cache objectForKey:@"name4"];
   NSLog(@"%@", arrfromcache);
   //此处可以修改,  修改后,会更新cache中的内容
   [arrfromcache addObject:@"123"];
   NSLog(@"%@", arrfromcache);
   NSLog(@"%@", arr);
   NSMutableArray *arrfromcache2=[cache objectForKey:@"name4"];
   NSLog(@"%@", arrfromcache2);
   
   NSMutableString*tempMustring=  [arr objectAtIndex:3];
   [tempMustring appendString:@"999999"];
   NSLog(@"%@", [cache objectForKey:@"name4"]);
   NSArray *resultarray = [cache objectForKey:@"name4"];
   NSLog(@"%@", [resultarray class]);
   NSArray *result2 =[[cache objectForKey:@"name4"] mutableCopy];
   NSMutableString*tempMustring2=  [result2 objectAtIndex:3];
   [tempMustring2 appendString:@"88888"];
   NSLog(@"%@", [cache objectForKey:@"name4"]);
   
   // 5、
   NSArray *array3=@[@"1",@"2".mutableCopy];
   [cache setObject:array3 forKey:@"name5"];
   NSMutableString*string31= array3[1];
   [string31 appendString:@"22222222"];
   NSLog(@"%@", [cache objectForKey:@"name5"]);
   
   
   // 6、
   SomeModel *obj = [SomeModel new];
   obj.hello1 = @"12345";
   obj.hello2 = @"abc".mutableCopy;
   [cache setObject:obj forKey:@"name6"];
   SomeModel *obj2= [cache objectForKey:@"name6"];
   NSLog(@"%@", obj2);
   
   obj.hello1 = @"1234567890";
   [obj.hello2 appendString:@"123456"];
   SomeModel *obj3 = [cache objectForKey:@"name6"];
   NSLog(@"%@",obj3);
}


@end