html - 如何将内容保存在 UIWebView 中以便在下次启动时更快地加载？

Question

我知道最近iphone sdk中引入了一些缓存类，three20的库中还有一个TTURLRequest可以让你缓存一个请求到一个URL。但是，因为我是通过调用UIWebView的loadRequest来加载UIWebView中的网页，所以那些技术并不是很适用。

有什么想法可以保存网页，以便在下次应用启动时，我不必再次从网络上获取整个页面吗？页面本身已经有一些自动更新自身部分的 ajax 机制。

Answer 1

有很多关于 UIWebView 缓存工作方式的文章，全局的感觉是，即使某些机制在 MacOS X 下似乎工作正常，但相同的方法在 iPhone 下可能会有奇怪的行为。

---

但是， 我正在通过使用任何 NSURLConnection、UIWebView 访问的全局缓存来实现这一点。 在我的例子中，它有效 ;)。

你需要了解的是全局流:

• 您 -> UIWebView 上的 loadRequest
• 这会进入 NSURLCache 询问“是否有为此请求缓存的内容？”:

- (NSCachedURLResponse *)cachedResponseForRequest:(NSURLRequest *)request

由此，在我这边，这是我处理磁盘缓存以加速 UIWebView 加载的方法:

• 子类化 NSURLCache 并覆盖对 -(NSCachedURLResponse *)cachedResponseForRequest:(NSURLRequest *)request 选择器的控制
• 以这样的方式重新实现这个选择器，如果没有为这个请求在 FS 上写入任何内容(没有缓存)，那么在你这边执行请求并将内容存储在 FS 上。否则，返回之前缓存的内容。
• 创建您的子类的实例并将其设置到系统，以便您的应用程序使用它

---

现在的代码:

MyCache.h

@interface MyCache : NSURLCache {
}
@end

MyCache.m

@implementation MyCache

-(NSCachedURLResponse *)cachedResponseForRequest:(NSURLRequest *)request {
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSLog(@"CACHE REQUEST S%@", request);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    NSArray* tokens = [request.URL.relativePath componentsSeparatedByString:@"/"];
    if (tokens==nil) {
        NSLog(@"ignoring cache for %@", request);
        return nil;
    }
    NSString* pathWithoutRessourceName=@"";
    for (int i=0; i<[tokens count]-1; i++) {
        pathWithoutRessourceName = [pathWithoutRessourceName stringByAppendingString:[NSString stringWithFormat:@"%@%@", [tokens objectAtIndex:i], @"/"]];
    }
    NSString* absolutePath = [NSString stringWithFormat:@"%@%@", documentsDirectory, pathWithoutRessourceName];
    NSString* absolutePathWithRessourceName = [NSString stringWithFormat:@"%@%@", documentsDirectory, request.URL.relativePath];
    NSString* ressourceName = [absolutePathWithRessourceName stringByReplacingOccurrencesOfString:absolutePath withString:@""];
    NSCachedURLResponse* cacheResponse  = nil;
    //we're only caching .png, .js, .cgz, .jgz
    if (
        [ressourceName rangeOfString:@".png"].location!=NSNotFound || 
        [ressourceName rangeOfString:@".js"].location!=NSNotFound ||
        [ressourceName rangeOfString:@".cgz"].location!=NSNotFound || 
        [ressourceName rangeOfString:@".jgz"].location!=NSNotFound) {
        NSString* storagePath = [NSString stringWithFormat:@"%@/myCache%@", documentsDirectory, request.URL.relativePath];
        //this ressource is candidate for cache.
        NSData* content;
        NSError* error = nil;
        //is it already cached ? 
        if ([[NSFileManager defaultManager] fileExistsAtPath:storagePath]) {
            //NSLog(@"CACHE FOUND for %@", request.URL.relativePath);
            content = [[NSData dataWithContentsOfFile:storagePath] retain];
            NSURLResponse* response = [[NSURLResponse alloc] initWithURL:request.URL MIMEType:@"" expectedContentLength:[content length] textEncodingName:nil];
            cacheResponse = [[NSCachedURLResponse alloc] initWithResponse:response data:content];
        } else {
            //trick here : if no cache, populate it asynchronously and return nil
            [NSThread detachNewThreadSelector:@selector(populateCacheFor:) toTarget:self withObject:request];
        }
    } else {
        NSLog(@"ignoring cache for %@", request);
    }
    return cacheResponse;
}

-(void)populateCacheFor:(NSURLRequest*)request {
    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    //NSLog(@"PATH S%@", paths);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    NSArray* tokens = [request.URL.relativePath componentsSeparatedByString:@"/"];
    NSString* pathWithoutRessourceName=@"";
    for (int i=0; i<[tokens count]-1; i++) {
        pathWithoutRessourceName = [pathWithoutRessourceName stringByAppendingString:[NSString     stringWithFormat:@"%@%@", [tokens objectAtIndex:i], @"/"]];
    }
    NSString* absolutePath = [NSString stringWithFormat:@"%@/myCache%@", documentsDirectory, pathWithoutRessourceName];
    //NSString* absolutePathWithRessourceName = [NSString stringWithFormat:@"%@%@", documentsDirectory, request.URL.relativePath];
    //NSString* ressourceName = [absolutePathWithRessourceName stringByReplacingOccurrencesOfString:absolutePath withString:@""];
    NSString* storagePath = [NSString stringWithFormat:@"%@/myCache%@", documentsDirectory, request.URL.relativePath];
    NSData* content;
    NSError* error = nil;
    NSCachedURLResponse* cacheResponse  = nil;
    NSLog(@"NO CACHE FOUND for %@", request.URL);
    //NSLog(@"retrieving content (timeout=%f) for %@ ...", [request timeoutInterval], request.URL);
    content = [NSData dataWithContentsOfURL:request.URL options:1 error:&error];
    //NSLog(@"content retrieved for %@  / error:%@", request.URL, error);
    if (error!=nil) {
        NSLog(@"ERROR %@ info:%@", error, error.userInfo);
        NSLog(@"Cache not populated for %@", request.URL);
    } else {
        NSURLResponse* response = [[NSURLResponse alloc] initWithURL:request.URL MIMEType:@"" expectedContentLength:[content length] textEncodingName:nil];
        cacheResponse = [[NSCachedURLResponse alloc] initWithResponse:response data:content];
        //the store is invoked automatically.
        [[NSFileManager defaultManager] createDirectoryAtPath:absolutePath withIntermediateDirectories:YES attributes:nil error:&error];
        BOOL ok;// = [[NSFileManager defaultManager] createDirectoryAtPath:absolutePath withIntermediateDirectories:YES attributes:nil error:&error];
        ok = [content writeToFile:storagePath atomically:YES];
        NSLog(@"Caching %@ : %@", storagePath , ok?@"OK":@"KO");
    }
    [pool release];
}
@end

以及在您的应用程序中使用它:

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString* documentsDirectory = [paths objectAtIndex:0];
NSString* diskCachePath = [NSString stringWithFormat:@"%@/%@", documentsDirectory, @"myCache"];
NSError* error; 
[[NSFileManager defaultManager] createDirectoryAtPath:diskCachePath withIntermediateDirectories:YES attributes:nil error:&error];
MyCache* cacheMngr = [[MyCache alloc] initWithMemoryCapacity:10000 diskCapacity:100000000 diskPath:diskCachePath];
[NSURLCache setSharedURLCache:cacheMngr];

这段代码值得大量清理..但主要的东西应该在那里。我遇到了很多麻烦才能使它正常工作，希望这对您有所帮助。