YYCache源码分析(一)

文／汉斯哈哈哈（简书作者）
原文链接：http://www.jianshu.com/p/b8dcf6634fab

iOS 开发中总会用到各种缓存，YYCache或许是你最好的选择。性能上有优势，用法也很简单。作者ibireme曾经对比过同类轮子：http://blog.ibireme.com/2015/10/26/yycache/

1.简单架构图

2.YYCache.h方法分析

@interface YYCache : NSObject
// 读取当前数据库名称
@property (copy, readonly) NSString *name;

// memoryCache内存缓存，diskCache文件缓存
@property (strong, readonly) YYMemoryCache *memoryCache;
@property (strong, readonly) YYDiskCache *diskCache;

// 可通过下面四种方法来实例化YYCache对象
- (nullable instancetype)initWithName:(NSString *)name;
- (nullable instancetype)initWithPath:(NSString *)path NS_DESIGNATED_INITIALIZER;
+ (nullable instancetype)cacheWithName:(NSString *)name;
+ (nullable instancetype)cacheWithPath:(NSString *)path;

// 禁止通过下面两个方式实例化对象
- (instancetype)init UNAVAILABLE_ATTRIBUTE;
+ (instancetype)new __attribute__((unavailable("new方法不可用，请用initWithName:")));

// 通过key判断是否缓存了某个东西，第二个法是异步执行,异步回调
- (BOOL)containsObjectForKey:(NSString *)key;
- (void)containsObjectForKey:(NSString *)key withBlock:(nullable void(^)(NSString *key, BOOL contains))block;

// 读--通过key读取缓存，第二个法是异步执行,异步回调
- (nullable id<NSCoding>)objectForKey:(NSString *)key;
- (void)objectForKey:(NSString *)key withBlock:(nullable void(^)(NSString *key, id<NSCoding> object))block;

// 增、改--缓存对象(可缓存遵从NSCoding协议的对象)，第二个法是异步执行,异步回调
- (void)setObject:(nullable id<NSCoding>)object forKey:(NSString *)key;
- (void)setObject:(nullable id<NSCoding>)object forKey:(NSString *)key withBlock:(nullable void(^)(void))block;

// 删--删除缓存
- (void)removeObjectForKey:(NSString *)key;
- (void)removeObjectForKey:(NSString *)key withBlock:(nullable void(^)(NSString *key))block;
- (void)removeAllObjects;
- (void)removeAllObjectsWithBlock:(void(^)(void))block;
- (void)removeAllObjectsWithProgressBlock:(nullable void(^)(int removedCount, int totalCount))progress
                                 endBlock:(nullable void(^)(BOOL error))end;

@end

这些语法：参考外链学习:
NS_DESIGNATED_INITIALIZER

(instancetype)new attribute((unavailable("new方法不可用，请用initWithName:")));

3.YYCache使用

// 0.初始化YYCache
YYCache *cache = [YYCache cacheWithName:@"mydb"];
// 1.缓存普通字符
[cache setObject:@"汉斯哈哈哈" forKey:@"name"];
NSString *name = (NSString *)[cache objectForKey:@"name"];
NSLog(@"name: %@", name);
// 2.缓存模型
[cache setObject:(id<NSCoding>)model forKey:@"user"];
// 3.缓存数组
NSMutableArray *array = @[].mutableCopy;
for (NSInteger i = 0; i < 10; i ++) {
    [array addObject:model];
}
// 异步缓存
[cache setObject:array forKey:@"user" withBlock:^{
    // 异步回调
    NSLog(@"%@", [NSThread currentThread]);
    NSLog(@"array缓存完成....");
}];
// 延时读取
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.3 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
    // 异步读取
    [cache objectForKey:@"user" withBlock:^(NSString * _Nonnull key, id<NSCoding>  _Nonnull object) {
        // 异步回调
        NSLog(@"%@", [NSThread currentThread]);
        NSLog(@"%@", object);
    }];
});

打印：

2016-06-09 11:35:44.069 YYCache源码分析[13546:949048] <NSThread: 0x7ffd43f14840>{number = 2, name = (null)}
2016-06-09 11:35:44.069 YYCache源码分析[13546:949048] array缓存完成....
2016-06-09 11:35:44.386 YYCache源码分析[13546:949052] <NSThread: 0x7ffd43e01900>{number = 3, name = (null)}
2016-06-09 11:35:44.386 YYCache源码分析[13546:949052] (
    "<UserModel: 0x7ffd44014310>",
    "<UserModel: 0x7ffd44014310>",
    "<UserModel: 0x7ffd44014310>",
    "<UserModel: 0x7ffd44014310>",
    "<UserModel: 0x7ffd44014310>",
    "<UserModel: 0x7ffd44014310>",
    "<UserModel: 0x7ffd44014310>",
    "<UserModel: 0x7ffd44014310>",
    "<UserModel: 0x7ffd44014310>",
    "<UserModel: 0x7ffd44014310>"
)

// 缓存实现，默认同时进行内存缓存与文件缓存
- (void)setObject:(id<NSCoding>)object forKey:(NSString *)key {
    [_memoryCache setObject:object forKey:key];
    [_diskCache setObject:object forKey:key];
}

// 如果只想内存缓存，可以直接调用`memoryCache`对象
YYCache *cache2 = [YYCache cacheWithName:@"mydb"];
[cache2.memoryCache setObject:@24 forKey:@"age"];
NSLog(@"age缓存在内存：%d", [cache2.memoryCache containsObjectForKey:@"age"]);
NSLog(@"age缓存在文件：%d", [cache2.diskCache containsObjectForKey:@"age"]);

打印：

2016-06-09 21:23:24.326 YYCache源码分析[14512:1085375] age缓存在内存：1
2016-06-09 21:23:24.326 YYCache源码分析[14512:1085375] age缓存在文件：0

4.YYCache.h tips

#if __has_include(<YYCache/YYCache.h>)
#import <YYCache/YYMemoryCache.h>
#import <YYCache/YYDiskCache.h>
#import <YYCache/YYKVStorage.h>
#elif __has_include(<YYWebImage/YYCache.h>)
#import <YYWebImage/YYMemoryCache.h>
#import <YYWebImage/YYDiskCache.h>
#import <YYWebImage/YYKVStorage.h>
#else
#import "YYMemoryCache.h"
#import "YYDiskCache.h"
#import "YYKVStorage.h"
#endif

__has_include：用来检查Frameworks是否引入某个类，
像YYWebImage已经集成YYCache,如果导入过YYWebImage则无需重新导入YYCache

NS_ASSUME_NONNULL_BEGIN
@interface YYCache : NSObject
...
- (nullable instancetype)initWithName:(NSString *)name;
...
@end
NS_ASSUME_NONNULL_END

接口中 nullable 的是少数,一般都为nonnull,为了防止写一大堆 nonnull，Foundation供了一对宏NS_ASSUME_NONNULL_BEGIN、NS_ASSUME_NONNULL_END，包在里面的对象默认加 nonnull 修饰符，如果是nullable的,只需要把 nullable 的指出来就行

- (instancetype)init UNAVAILABLE_ATTRIBUTE;
+ (instancetype)new UNAVAILABLE_ATTRIBUTE;

<p>
command+鼠标左键UNAVAILABLE_ATTRIBUTE，
发现宏定义#define UNAVAILABLE_ATTRIBUTE __attribute__((unavailable)),
__attribute__是Clang提供的一种源码注解，方便开发者向编译器表达某种要求,括号里是传达某种命令.
为方便使用，一些常用属性也被Cocoa定义成宏,
比如UNAVAILABLE_ATTRIBUTE、NS_CLASS_AVAILABLE_IOS(9_0).
unavailable告诉编译器该方法失效.
在封装单例或初始化某个类前必须做一些事时,对一些方法禁用是非常不错的选择.
还可以给个message提示:

+ (instancetype)alloc __attribute__((unavailable("alloc方法不可用，请用initWithName:")));
- (instancetype)init __attribute__((unavailable("init方法不可用，请用initWithName:")));
+ (instancetype)new __attribute__((unavailable("new方法不可用，请用initWithName:")));
- (instancetype)copy __attribute__((unavailable("copy方法不可用，请用initWithName:")));

</p>

- (nullable instancetype)initWithPath:(NSString *)path NS_DESIGNATED_INITIALIZER;

NS_DESIGNATED_INITIALIZER 这个宏并不是新面孔，可以使用它标志出像 Swift 一样的指定构造器和便捷构造器。

NS_DESIGNATED_INITIALIZER关键字意思是最终被指定的初始化方法，在interface只能用一次而且必须以init开头的方法。
在m文件中，不管init或者其他的初始化方法都要调用上面的initWithTitle方法初始化，因为我么用到了NS_DESIGNATED_INITIALIZER关键字，不知道明白没？http://www.cocoachina.com/bbs/read.php?tid-282223.html

References
http://blog.sunnyxx.com/2016/05/14/clang-attributes/
http://blog.sunnyxx.com/2015/06/12/objc-new-features-in-2015/

YYCache源码分析(一)