UIwebView实现html的离线缓存

1、html的缓存主要采取ASIHTTPRequest的缓存策略
（1）、设置缓存策略

    //设置缓存
    ASIDownloadCache *cache=[[ASIDownloadCache alloc] init];
    self.myCache=cache;
    //设置缓存路径
    NSArray *paths =NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,NSUserDomainMask, YES);
    NSString *documentDirectory = [paths objectAtIndex:0];
    //设置缓存存放路径
    [self.myCache setStoragePath:[documentDirectory stringByAppendingPathComponent:@"resource"]];
    //ASIAskServerIfModifiedCachePolicy 与默认缓存大致一样，区别仅是每次请求都会 去服务器判断是否有更新
    //ASIOnlyLoadIfNotCachedCachePolicy 如果有缓存在本地，不管其过期与否，总会拿来使用
    //ASIFallbackToCacheIfLoadFailsCachePolicy  这个选项经常被用来与其它选项组合使用。请求失败时，如果有缓存当网络则返回本地缓存信息
    [self.myCache setDefaultCachePolicy:ASIFallbackToCacheIfLoadFailsCachePolicy];      //设置缓存策略

（2）、设置异步缓存

   NSURL *Requesturl=[NSURL URLWithString:url];
    ASIHTTPRequest *request=[ASIHTTPRequest requestWithURL:Requesturl];
    //    //获取全局变量
    AppDelegate *appDelegate = [[UIApplication sharedApplication] delegate];
    //    //设置缓存方式
    [request setDownloadCache:appDelegate.myCache];
    //    //设置缓存数据存储策略，这里采取的是如果无更新或无法联网就读取缓存数据
    [request setCacheStoragePolicy:ASICachePermanentlyCacheStoragePolicy];
    [request setDelegate:self];
     [request startAsynchronous];

html缓存完成。如想查看详细 请点击 ： IOS开发网络篇之──ASIHTTPRequest详解

2、html中的图片缓存
（1）、通过正则获取html代码中的所有图片url

  NSString *urlPattern = @"<img[^>]+?src=[\"‘]?([^>‘\"]+)[\"‘]?";
    NSError *error = [NSError new];

    NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:urlPattern options:NSRegularExpressionCaseInsensitive error:&error ];

    //match 这块内容非常强大
    NSUInteger counts =[regex numberOfMatchesInString:content options:NSRegularExpressionCaseInsensitive range:NSMakeRange(0, [content length])];//匹配到的次数
    if(counts > 0){
        NSArray* matches = [regex matchesInString:content options:NSMatchingReportCompletion range:NSMakeRange(0, [content length])];

        for (NSTextCheckingResult *match in matches) {
            NSInteger count = [match numberOfRanges];//匹配项
            for(NSInteger index = 0;index < count;index++){
                NSRange halfRange = [match rangeAtIndex:index];
                if (index == 1) {
                    //[listImage addObject:[content substringWithRange:halfRange]];
                    NSLog(@"转换出来的字符串＝＝＝%@",[content substringWithRange:halfRange]);
                    [listImage addObject:[content substringWithRange:halfRange]];
                }
            }
        }//遍历后可以看到三个range，1、为整体。2、为([\\w-]+\\.)匹配到的内容。3、([\\w.%&=-]*)匹配到的内容
    }

（2）、SDwebImage下载图片 、JS交互替换

 dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0ul);
    dispatch_group_t group = dispatch_group_create();
    for (int i = 0; i < listImage.count; i++)
    {
        NSString *imageUrl = [imageUrlArray objectAtIndex:i];
        NSString *key=[self getMd5_32Bit_String:imageUrl];
        UIImage *cachedImage=[[SDImageCache sharedImageCache] imageFromDiskCacheForKey:key];
        NSString *index = [NSString stringWithFormat:@"%d", i];

        if (cachedImage) {

            [tchWebView stringByEvaluatingJavaScriptFromString:[self createSetImageUrlJavaScript:index
                                                                                          imgUrl:key]];
        }else{

            dispatch_group_async(group, queue, ^{
                //异步下载图片
                [SDWebImageDownloader.sharedDownloader downloadImageWithURL:[NSURL URLWithString:imageUrl]
                                                                    options:0
                                                                   progress:^(NSInteger receivedSize, NSInteger expectedSize)
                 {
                     // progression tracking code
                 }
                                                                  completed:^(UIImage *image, NSData *data, NSError *error, BOOL finished)
                 {
                     if (image && finished)
                     {
                         [[SDImageCache sharedImageCache] storeImage:image forKey:key];
                         dispatch_sync(dispatch_get_main_queue(), ^{
                             [tchWebView stringByEvaluatingJavaScriptFromString:[self createSetImageUrlJavaScript:index
                                                                                                               imgUrl:key]];
                         });
                     }
                 }];

            });
        }
    }
    dispatch_release(group);

//设置下载完成的图片到web img
- (NSString *)createSetImageUrlJavaScript:(NSString *) index imgUrl:(NSString *) url{
    UIImage *myCachaImage=[[SDImageCache sharedImageCache] imageFromDiskCacheForKey:url];
    NSData *imageData = UIImageJPEGRepresentation(myCachaImage,1.0);
    NSString *imageSource = [NSString stringWithFormat:@"data:image/jpg;base64,%@",[imageData base64Encoding]];

    NSString *js = [NSString stringWithFormat:@"var imgArray = document.getElementsByTagName(‘img‘); imgArray[%@].src=\"%@\"; " , index, imageSource];
    return js;
}

//32位MD5加密方式
- (NSString *)getMd5_32Bit_String:(NSString *)srcString{
    const char *cStr = [srcString UTF8String];
    unsigned char digest[CC_MD5_DIGEST_LENGTH];
    CC_MD5( cStr, strlen(cStr), digest );
    NSMutableString *result = [NSMutableString stringWithCapacity:CC_MD5_DIGEST_LENGTH * 2];
    for(int i = 0; i < CC_MD5_DIGEST_LENGTH; i++)
        [result appendFormat:@"%02x", digest[i]];

    return result;
}

参考：http://bbs.csdn.net/topics/390831054