子类NSCache-App Singleton

我正在写一个iPhone应用程序,我想创建一个NSCache单例。

MyAppCache.h:

#import <Foundation/Foundation.h>

@interface MyAppCache : NSCache {}

+ (MyAppCache *) sharedCache;

@end

MyAppCache.m:

#import "SpotmoCache.h"

static MyAppCache *sharedMyAppCache = nil;

@implementation MyAppCache

+ (MyAppCache *) sharedCache {
    if (sharedMyAppCache == nil) {
        sharedMyAppCache = [[super allocWithZone:NULL] init];
    }
    return sharedMyAppCache; 
}

+ (id)allocWithZone:(NSZone *)zone {
    return [[self sharedCache] retain]; 
}

- (id)copyWithZone:(NSZone *)zone { 
    return self;
}

- (id)retain { 
    return self;
}

- (NSUInteger)retainCount {
    return NSUIntegerMax;  //denotes an object that cannot be released 
}

- (void)release{
    //do nothing
}

- (id)autorelease {
    return self; 
}

@end

当我想添加一些东西或从缓存中获取一些东西时,我可能会写:

#import "MyAppCache.h"

MyAppCache *theCache = [MyAppCache sharedCache];  

然后:

NSData *someData = [[theCache objectForKey: keyString] retain];

[theCache setObject: someData forKey: keyString cost: sizeof(someData)];

问题:编译器抱怨 每一行。

我可能做错了什么-知道怎么做吗?