1 #import "ViewController.h"
 2
 3 @interface ViewController () <NSCacheDelegate>
 4
 5 @end
 6
 7 @implementation ViewController {
 8
 9     /// 全局缓存池
10     NSCache *_cache;
11 }
12
13 - (void)viewDidLoad {
14     [super viewDidLoad];
15
16     // 实例化缓存池
17     _cache = [[NSCache alloc] init];
18
19     // 设置缓存成本 : 以最大的缓存个数为例(最多存5个对象)
20     _cache.countLimit = 5;
21
22     // 遵守协议 : 有个唯一的代理方法,专门监听对象从cache里面移除
23     _cache.delegate = self;
24 }
25
26 /// 添加对象
27 - (IBAction)addObj:(id)sender
28 {
29     for (NSInteger i = 0; i<10; i++) {
30
31         NSString *key = [NSString stringWithFormat:@"hello_%zd",i];
32
33         NSString *obj = [NSString stringWithFormat:@"hello_%zd",i];
34         NSLog(@"add %@",obj);
35
36         [_cache setObject:obj forKey:key];
37     }
38 }
39
40 /// 读取对象
41 - (IBAction)readObj:(id)sender
42 {
43     for (NSInteger i = 0; i<10; i++) {
44
45         NSString *key = [NSString stringWithFormat:@"hello_%zd",i];
46
47         // 存进去是什么,取出来应该就是什么
48         NSString *obj = [_cache objectForKey:key];
49         NSLog(@"read %@",obj);
50     }
51 }
52
53 - (IBAction)removeAll:(id)sender
54 {
55     [_cache removeAllObjects];
56 }
57
58 /// 这个代理方法,只在cache里面有对象被移除时调用
59 - (void)cache:(NSCache *)cache willEvictObject:(id)obj
60 {
61     // obj : 就是即将被移除的对象
62     NSLog(@"移除 %@",obj);
63 }
64
65 /// NSCache的大坑 : 这个方法里面不能调用`removeAllObjects`;一旦调用了,cache就失效了
66 - (void)didReceiveMemoryWarning {
67     [super didReceiveMemoryWarning];
68
69     [_cache removeAllObjects];
70 }
71
72 @end