如何在 UIWebView 中保存内容以便在下次启动时更快加载? [英] How to save the content in UIWebView for faster loading on next launch?

问题描述

我知道最近在iphone sdk中引入了一些缓存类，并且还有一个来自three20's library的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 在 UIWebView 中加载网页，所以这些技术并不真正适用.

I know that there are some caching classes introduced in the iphone sdk recently, and there is also a TTURLRequest from three20's library that allows you to cache a request to a URL. However, because I am loading the web page in UIWebView by calling UIWebView's loadRequest, those techniques are not really applicable.

有什么想法可以保存网页，以便在下一次启动应用程序时，我不必再次从网络上获取完整页面?页面本身已经有一些 ajax 机制，可以自动更新自身的某些部分.

Any ideas how I can save a web page so that on next app launch, I don't have to fetch from the web again for the full page? The page itself already have some ajax mechanism that updates parts of itself automatically.

推荐答案

UIWebView 的缓存工作方式有一堆文章，总体感觉是即使有些机制在 MacOS X 下看起来工作正常，同样的方法在 iPhone 下可能会有奇怪的行为.

There are a bunch of articles about the way the cache of the UIWebView works and the global feeling is that even if some mechanisms seems to work OK under MacOS X, the same approaches may have curious behavior under iPhone.

然而， 我正在通过使用任何 NSURLConnection、UIWebView 访问的全局缓存来实现它.就我而言，它有效;)

HOWEVER, I'm doing it by playing with the global cache that is accessed by any NSURLConnection, UIWebView included. And in my case, it works ;).

您需要了解的是全局流程:

What you need to understand is the global flow:

• 你 -> loadRequest 在 UIWebView
• 这会进入 NSURLCache 以询问是否为该请求缓存了某些内容?":

• YOU -> loadRequest on a UIWebView
• This goes into NSURLCache to ask "is there something cached for this request?":

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

从那以后，这是我在磁盘上处理缓存的方法，以加快 UIWebView 的加载速度:

From that, here's what I do to handle the cache on the disk, on my side, to speed up the load of a UIWebView:

• 子类化 NSURLCache 并覆盖对 -(NSCachedURLResponse *)cachedResponseForRequest:(NSURLRequest *)request 选择器的 get 控制
• 以这样的方式重新实现这个选择器，如果这个请求没有在 FS 上写任何东西(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.
• 创建子类的实例并将其设置到系统中，以便您的应用程序使用它

• Subclass the NSURLCache and override the get control over the -(NSCachedURLResponse *)cachedResponseForRequest:(NSURLRequest *)request selector
• Reimplement this selector in such a way that if nothing has been written on the FS for this request (no cache), then do the request on your side and store the content on FS. Otherwise, return what has been previously cached.
• Create an instance of your subclass and set it to the system so that it is used by your application

现在代码:

@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:

And the use of it in your application:

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.我在完成这项工作时遇到了很多麻烦，希望这会有所帮助.

This code deserves a lot of cleanup.. but the main things should be in there. I had a lot of trouble to get this working, hope this helps.

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