UIWebView的缓存：LocalSubstitutionCache

转自：http://www.iliunian.com/2513.html

这里介绍一个非常好的缓存类：LocalSubstitutionCache

参考：http://www.cocoawithlove.com/2010/09/substituting-local-data-for-remote.html

继承与：NSURLCache，先来简单介绍一下：

NSURLRequest需要一个缓存参数来说明它请求的url何如缓存数据的，我们先看下它的CachePolicy类型。

1、NSURLRequestUseProtocolCachePolicy NSURLRequest默认的cache policy，使用Protocol协议定义。

2、NSURLRequestReloadIgnoringCacheData 忽略缓存直接从原始地址下载。

3、NSURLRequestReturnCacheDataElseLoad 只有在cache中不存在data时才从原始地址下载。

4、NSURLRequestReturnCacheDataDontLoad 只使用cache数据，如果不存在cache，请求失败;用于没有建立网络连接离线模式;

5、NSURLRequestReloadIgnoringLocalAndRemoteCacheData：忽略本地和远程的缓存数据，直接从原始地址下载，与NSURLRequestReloadIgnoringCacheData类似。

6、NSURLRequestReloadRevalidatingCacheData:验证本地数据与远程数据是否相同，如果不同则下载远程数据，否则使用本地数据。

NSURLCache还提供了很多方法，来方便我们实现应用程序的缓存机制。大家可以研究下文档说明。

今天说的LocalSubstitutionCache是对NSURLCache的一个继承，加了一些方便调用的方法，内存缓存时间和硬盘缓存时间等。

• Cache Html页面
• Cache 图片等元素

1

//设置使用自定义Cache机制
LocalSubstitutionCache *cache = [[[LocalSubstitutionCache alloc] init] autorelease];
[cache setMemoryCapacity:4 * 1024 * 1024];
[cache setDiskCapacity:10 * 1024 * 1024];
[NSURLCache setSharedURLCache:cache];

没有DEMO，我简单的把工程中使用的代码贴出来，很简单只有两行：

- (id)initWithURL:(NSURL*)pageURL {

    if(self = [super init]) {
        self.URL = pageURL;
        LocalSubstitutionCache *urlCache = [[LocalSubstitutionCache alloc] initWithMemoryCapacity:20 * 1024 * 1024
                                                                                     diskCapacity:200 * 1024 * 1024
                                                                                         diskPath:nil
                                                                                        cacheTime:0];
        [LocalSubstitutionCache setSharedURLCache:urlCache];
    }

    return self;
}

为避免内存告急：

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    LocalSubstitutionCache *urlCache = (LocalSubstitutionCache *)[NSURLCache sharedURLCache];
    [urlCache removeAllCachedResponses];
}

附LocalSubstitutionCache的代码，该代码有一处错误已经修正，这是我修改过的仅供参考：
LocalSubstitutionCache.h

//
//  LocalSubstitutionCache.h
//  yeeyanHD
//
//  Created by liunian on 13-8-2.
//  Copyright (c) 2013年 liunian. All rights reserved.
//

#import <Foundation/Foundation.h>

@interface LocalSubstitutionCache : NSURLCache

@property(nonatomic, assign) NSInteger cacheTime;
@property(nonatomic, retain) NSString *diskPath;
@property(nonatomic, retain) NSMutableDictionary *responseDictionary;

- (id)initWithMemoryCapacity:(NSUInteger)memoryCapacity diskCapacity:(NSUInteger)diskCapacity diskPath:(NSString *)path cacheTime:(NSInteger)cacheTime;

@end

LocalSubstitutionCache.m

//
//  LocalSubstitutionCache.m
//  yeeyanHD
//
//  Created by liunian on 13-8-2.
//  Copyright (c) 2013年 liunian. All rights reserved.
//

#import "LocalSubstitutionCache.h"
#import "Util.h"

@interface LocalSubstitutionCache(private)

- (NSString *)cacheFolder;
- (NSString *)cacheFilePath:(NSString *)file;
- (NSString *)cacheRequestFileName:(NSString *)requestUrl;
- (NSString *)cacheRequestOtherInfoFileName:(NSString *)requestUrl;
- (NSCachedURLResponse *)dataFromRequest:(NSURLRequest *)request;
- (void)deleteCacheFolder;

@end
@implementation LocalSubstitutionCache
@synthesize cacheTime = _cacheTime;
@synthesize diskPath = _diskPath;
@synthesize responseDictionary = _responseDictionary;

- (id)initWithMemoryCapacity:(NSUInteger)memoryCapacity diskCapacity:(NSUInteger)diskCapacity diskPath:(NSString *)path cacheTime:(NSInteger)cacheTime {
    if (self = [self initWithMemoryCapacity:memoryCapacity diskCapacity:diskCapacity diskPath:path]) {
        self.cacheTime = cacheTime;
        if (path)
            self.diskPath = path;
        else
            self.diskPath = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject];

        self.responseDictionary = [NSMutableDictionary dictionaryWithCapacity:0];
    }
    return self;
}

- (NSCachedURLResponse *)cachedResponseForRequest:(NSURLRequest *)request {
    if ([request.HTTPMethod compare:@"GET"] != NSOrderedSame) {
        return [super cachedResponseForRequest:request];
    }

    return [self dataFromRequest:request];
}

- (void)removeAllCachedResponses {
    [super removeAllCachedResponses];

    [self deleteCacheFolder];
}

- (void)removeCachedResponseForRequest:(NSURLRequest *)request {
    [super removeCachedResponseForRequest:request];

    NSString *url = request.URL.absoluteString;
    NSString *fileName = [self cacheRequestFileName:url];
    NSString *otherInfoFileName = [self cacheRequestOtherInfoFileName:url];
    NSString *filePath = [self cacheFilePath:fileName];
    NSString *otherInfoPath = [self cacheFilePath:otherInfoFileName];
    NSFileManager *fileManager = [NSFileManager defaultManager];
    [fileManager removeItemAtPath:filePath error:nil];
    [fileManager removeItemAtPath:otherInfoPath error:nil];
}

#pragma mark - custom url cache

- (NSString *)cacheFolder {
    return @"URLCACHE";
}

- (void)deleteCacheFolder {
    NSString *path = [NSString stringWithFormat:@"%@/%@", self.diskPath, [self cacheFolder]];
    NSFileManager *fileManager = [NSFileManager defaultManager];
    [fileManager removeItemAtPath:path error:nil];
}

- (NSString *)cacheFilePath:(NSString *)file {
    NSString *path = [NSString stringWithFormat:@"%@/%@", self.diskPath, [self cacheFolder]];
    NSFileManager *fileManager = [NSFileManager defaultManager];
    BOOL isDir;
    if ([fileManager fileExistsAtPath:path isDirectory:&isDir] && isDir) {

    } else {
        [fileManager createDirectoryAtPath:path withIntermediateDirectories:YES attributes:nil error:nil];
    }
    return [NSString stringWithFormat:@"%@/%@", path, file];
}

- (NSString *)cacheRequestFileName:(NSString *)requestUrl {
    return [Util md5Hash:requestUrl];
}

- (NSString *)cacheRequestOtherInfoFileName:(NSString *)requestUrl {
    return [Util md5Hash:[NSString stringWithFormat:@"%@-otherInfo", requestUrl]];
}

- (NSCachedURLResponse *)dataFromRequest:(NSURLRequest *)request {
    NSString *url = request.URL.absoluteString;
    NSString *fileName = [self cacheRequestFileName:url];
    NSString *otherInfoFileName = [self cacheRequestOtherInfoFileName:url];
    NSString *filePath = [self cacheFilePath:fileName];
    NSString *otherInfoPath = [self cacheFilePath:otherInfoFileName];
    NSDate *date = [NSDate date];

    NSFileManager *fileManager = [NSFileManager defaultManager];
    if ([fileManager fileExistsAtPath:filePath]) {
        BOOL expire = false;
        NSDictionary *otherInfo = [NSDictionary dictionaryWithContentsOfFile:otherInfoPath];

        if (self.cacheTime > 0) {
            NSInteger createTime = [[otherInfo objectForKey:@"time"] intValue];
            if (createTime + self.cacheTime < [date timeIntervalSince1970]) {
                expire = true;
            }
        }

        if (expire == false) {

            NSData *data = [NSData dataWithContentsOfFile:filePath];
            NSURLResponse *response = [[NSURLResponse alloc] initWithURL:request.URL
                                                                MIMEType:[otherInfo objectForKey:@"MIMEType"]
                                                   expectedContentLength:data.length
                                                        textEncodingName:[otherInfo objectForKey:@"textEncodingName"]];
            NSCachedURLResponse *cachedResponse = [[NSCachedURLResponse alloc] initWithResponse:response data:data];
            return cachedResponse;
        } else {
            [fileManager removeItemAtPath:filePath error:nil];
            [fileManager removeItemAtPath:otherInfoPath error:nil];
        }
    }

    __block NSCachedURLResponse *cachedResponse = nil;
    //sendSynchronousRequest请求也要经过NSURLCache
    id boolExsite = [self.responseDictionary objectForKey:url];
    if (boolExsite == nil) {
        [self.responseDictionary setValue:[NSNumber numberWithBool:TRUE] forKey:url];

        [NSURLConnection sendAsynchronousRequest:request queue:[[NSOperationQueue alloc] init] completionHandler:^(NSURLResponse *response, NSData *data,NSError *error)
         {
             [self.responseDictionary removeObjectForKey:url];

             if (error) {
                 NSLog(@"error : %@", error);
                 NSLog(@"not cached: %@", request.URL.absoluteString);
                 cachedResponse = nil;
             }
         if (response) {
             //save to cache
             NSDictionary *dict = [NSDictionary dictionaryWithObjectsAndKeys:[NSString stringWithFormat:@"%f", [date timeIntervalSince1970]], @"time",
                                   response.MIMEType, @"MIMEType",
                                   response.textEncodingName, @"textEncodingName", nil];
             [dict writeToFile:otherInfoPath atomically:YES];
             [data writeToFile:filePath atomically:YES];

             cachedResponse = [[NSCachedURLResponse alloc] initWithResponse:response data:data];
         }


         }];

        return cachedResponse;
        //NSData *data = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&error];


    }
    return nil;
}


@end

如何改进iOS App的离线使用体验 这篇文章很好的简述了 离线缓存的作用。