iOS NSCache和NSUrlCache缓存类实现示例详解

#import <Foundation/NSObject.h>
@class NSString;
@protocol NSCacheDelegate;
NS_ASSUME_NONNULL_BEGIN
API_AVAILABLE(macos(10.6), ios(4.0), watchos(2.0), tvos(9.0))
@interface NSCache <KeyType, ObjectType> : NSObject {
@private
    id _delegate;
    void *_private[5];
    void *_reserved;
}
@property (copy) NSString *name;
@property (nullable, assign) id<NSCacheDelegate> delegate;
- (nullable ObjectType)objectForKey:(KeyType)key;
- (void)setObject:(ObjectType)obj forKey:(KeyType)key; // 0 cost
- (void)setObject:(ObjectType)obj forKey:(KeyType)key cost:(NSUInteger)g;
- (void)removeObjectForKey:(KeyType)key;
- (void)removeAllObjects;
@property NSUInteger totalCostLimit;	// limits are imprecise/not strict
@property NSUInteger countLimit;	// limits are imprecise/not strict
@property BOOL evictsObjectsWithDiscardedContent;
@end
@protocol NSCacheDelegate <NSObject>
@optional
- (void)cache:(NSCache *)cache willEvictObject:(id)obj;
@end
NS_ASSUME_NONNULL_END

@interface NSCacheViewController ()<NSCacheDelegate>
@property(nonatomic,strong) NSCache *cache;
@end
@implementation NSCacheViewController
- (void)viewDidLoad {
    [super viewDidLoad];
    self.cache = [[NSCache alloc] init];
    //设置最大缓存数
    self.cache.countLimit = 5;
    //设置代理，实现代理方法，
    self.cache.delegate = self;
    self.cache.name = @"测试内存";
    for (int i=0; i<10; i++) {
        NSString *str = [NSString stringWithFormat:@"%d",i];
        [self.cache setObject:str forKey:str];
    }
    // Do any additional setup after loading the view.
}
//超出缓存部分会被释放， 收到内存警告时候系统也会释放一部分。
-(void)cache:(NSCache *)cache willEvictObject:(id)obj{
    NSLog(@"%@---%@",cache,obj);
}
@end

// `setObject:forKey:` just call this with 0 cost. Override this is enough
- (void)setObject:(id)obj forKey:(id)key cost:(NSUInteger)g {
    [super setObject:obj forKey:key cost:g];
    if (!self.config.shouldUseWeakMemoryCache) {
        return;
    }
    if (key && obj) {
        // Store weak cache
        SD_LOCK(_weakCacheLock);
        [self.weakCache setObject:obj forKey:key];
        SD_UNLOCK(_weakCacheLock);
    }
}

//
//  NSURLCacheViewController.m
//  DemoTest2022
//
//  Created by wy on 2022/10/19.
//
#import "NSURLCacheViewController.h"
@interface NSURLCacheViewController ()
//去服务器比对资源是否需要更新
@property (nonatomic, strong) NSString *lastModified;
@property (nonatomic, strong) NSString *etag;
@property(nonatomic,strong) UIImageView *imagev;
@end
@implementation NSURLCacheViewController
- (void)viewDidLoad {
    [super viewDidLoad];
    self.imagev = [[UIImageView alloc] initWithFrame:CGRectMake(0, 100, 100, 100)];
    [self.view addSubview:self.imagev];
    // Do any additional setup after loading the view.
}
-(void)requestTest{
    NSURL *url = [NSURL URLWithString:@"http://via.placeholder.com/50x50.png"];
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url cachePolicy:(NSURLRequestReloadIgnoringCacheData) timeoutInterval:15] ;
    if (self.lastModified) {
        [request setValue:self.lastModified forHTTPHeaderField:@"If-Modified-Since"];
    }
    if (self.etag) {
        [request setValue:self.etag forHTTPHeaderField:@"If-None-Match"];
    }
    [[[NSURLSession sharedSession] dataTaskWithRequest:request completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {
            if (error) {
                NSLog(@"error---%@",error);
            }else{
                NSData *tempData = data;
                NSString *responseStr = [[NSString alloc] initWithData:tempData encoding:NSUTF8StringEncoding];
                self.lastModified = [(NSHTTPURLResponse *)response  allHeaderFields][@"Last-Modified"];
                self.etag =[(NSHTTPURLResponse *)response allHeaderFields][@"etag"];
                NSLog(@"response:%@", response);
                dispatch_sync(dispatch_get_main_queue(), ^{
                    self.imagev.image = [UIImage imageWithData:tempData];
                });
            }
        }] resume] ;
}
- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event{
    [self requestTest];
}
@end

typedef NS_ENUM(NSUInteger, NSURLRequestCachePolicy)
{
    NSURLRequestUseProtocolCachePolicy = 0,
    // 从不读取缓存，但请求后将response缓存起来
    NSURLRequestReloadIgnoringLocalCacheData = 1,
    NSURLRequestReloadIgnoringLocalAndRemoteCacheData = 4,
    NSURLRequestReloadIgnoringCacheData = NSURLRequestReloadIgnoringLocalCacheData,
    // 以下两种在取缓存时，可能取到的是过期数据
    NSURLRequestReturnCacheDataElseLoad = 2,// 缓存中没有才去发起请求加载，有就不进行网络请求了
    NSURLRequestReturnCacheDataDontLoad = 3,// 缓存中没有不加载，绝不发起网络请求,缓存中没有则返回错误
    NSURLRequestReloadRevalidatingCacheData = 5,//Unimplemented
};