js加载某盘下html文件位置,APP在加载外部html时选择加载本地的js、css、img等资源文件（下：iOS篇）<转载>...

上篇博客回顾了下安卓开发如何在加载外部html的时候加载本地的js、css、img等资源文件，这篇回顾一下iOS的方法，iOS要实现这个就要用到一个类NSURLProtocol，以下文章转载自一位大神的博客：

NSURLProtocol

它是干什么的呢,是一个挺牛逼的类，它是一个抽象类,不能去实例化它,只能子类化NSURLProtocol，

每次在对一个 URL 进行请求的时候 URL Loading System 都会向 已经注册的 Protocol 询问是否可以处理该请求。这里就看出他的作用来了. 比如: 拦截UIWebView的请求,忽略请求,重定向… …

如何使用NSURLProtocol

创建

#import

@interface FilteredProtocol : NSURLProtocol

@end

在合适的地方注册(demo是在appdelegate类中)

[NSURLProtocol registerClass:[FilteredProtocol class]];

取消注册,一般在加载完成或dealloc方法里面取消

[NSURLProtocol unregisterClass:[FilteredProtocol class]];

重写父类方法

+ (BOOL)canInitWithRequest:(NSURLRequest *)request;

+ (NSURLRequest *)canonicalRequestForRequest:(NSURLRequest *)request;

+ (BOOL)requestIsCacheEquivalent:(NSURLRequest *)a toRequest:(NSURLRequest *)b;

- (void)startLoading;

- (void)stopLoading;

一个个的说

+ (BOOL)canInitWithRequest:(NSURLRequest *)request;

这个方法是决定这个 protocol 是否可以处理传入的 request 的如是返回 true 就代表可以处理,如果返回 false 那么就不处理这个 request 。

+ (NSURLRequest *)canonicalRequestForRequest:(NSURLRequest *)request;

这个方法主要是用来返回格式化好的request，如果自己没有特殊需求的话，直接返回当前的request就好了。如果你想做些其他的，比如地址重定向，或者请求头的重新设置，你可以copy下这个request然后进行设置。

+ (BOOL)requestIsCacheEquivalent:(NSURLRequest *)a toRequest:(NSURLRequest *)b;

该方法主要是判断两个请求是否为同一个请求，如果为同一个请求那么就会使用缓存数据。通常都是调用父类的该方法。

- (void)startLoading;

- (void)stopLoading;

开始处理这个请求和结束处理这个请求

我们处理(拦截)好请求之后,就要开始对他经常处理,这个时候就用到了父类里面的client 对象.

/*! @method client @abstract Returns the NSURLProtocolClient of the receiver. @result The NSURLProtocolClient of the receiver. */

@property (nullable, readonly, retain) id client;

他是一个协议,里面的方法和NSURLConnection 差不多

- (void)URLProtocol:(NSURLProtocol *)protocol wasRedirectedToRequest:(NSURLRequest *)request redirectResponse:(NSURLResponse *)redirectResponse;

- (void)URLProtocol:(NSURLProtocol *)protocol cachedResponseIsValid:(NSCachedURLResponse *)cachedResponse;

- (void)URLProtocol:(NSURLProtocol *)protocol didReceiveResponse:(NSURLResponse *)response cacheStoragePolicy:(NSURLCacheStoragePolicy)policy;

- (void)URLProtocol:(NSURLProtocol *)protocol didLoadData:(NSData *)data;

- (void)URLProtocolDidFinishLoading:(NSURLProtocol *)protocol;

- (void)URLProtocol:(NSURLProtocol *)protocol didReceiveAuthenticationChallenge:(NSURLAuthenticationChallenge *)challenge;

- (void)URLProtocol:(NSURLProtocol *)protocol didCancelAuthenticationChallenge:(NSURLAuthenticationChallenge *)challenge;

实际应用(拿我拦截css为例子)

需求是要去掉下面图片上立刻下载的广告:

我是原图

这是运行后打印的log

运行ing

上图可以看到截获的所有的请求地址,不管是js,css还是png图片都有

这是代码运行后的效果

我是最终效果图

代码如下:

static NSString*const sourUrl = @"http://cdn.web.chelaile.net.cn/ch5/styles/main-1cb999d572.css";

static NSString*const localUrl = @"http://h5apps.scity.cn/hack/cdn.web.chelaile.net.cn/ch5/styles/main-1cb999d572.css";

static NSString*const FilteredCssKey = @"filteredCssKey";

@interface FilteredProtocol ()

@property (nonatomic, strong) NSMutableData *responseData;

@property (nonatomic, strong) NSURLConnection *connection;

@end

@implementation FilteredProtocol

+ (BOOL)canInitWithRequest:(NSURLRequest *)request

{

NSLog(@"request.URL.absoluteString = %@",request.URL.absoluteString);

//只处理http和https请求

NSString *scheme = [[request URL] scheme];

if ( ([scheme caseInsensitiveCompare:@"http"] == NSOrderedSame ||

[scheme caseInsensitiveCompare:@"https"] == NSOrderedSame ))

{

//看看是否已经处理过了，防止无限循环

if ([NSURLProtocol propertyForKey:FilteredCssKey inRequest:request])

return NO;

return YES;

}

return NO;

}

+ (NSURLRequest *)canonicalRequestForRequest:(NSURLRequest *)request

{

NSMutableURLRequest *mutableReqeust = [request mutableCopy];

//截取重定向

if ([request.URL.absoluteString isEqualToString:sourUrl])

{

NSURL* url1 = [NSURL URLWithString:localUrl];

mutableReqeust = [NSMutableURLRequest requestWithURL:url1];

}

return mutableReqeust;

}

+ (BOOL)requestIsCacheEquivalent:(NSURLRequest *)a toRequest:(NSURLRequest *)b

{

return [super requestIsCacheEquivalent:a toRequest:b];

}

- (void)startLoading

{

NSMutableURLRequest *mutableReqeust = [[self request] mutableCopy];

//给我们处理过的请求设置一个标识符, 防止无限循环,

[NSURLProtocol setProperty:@YES forKey:FilteredCssKey inRequest:mutableReqeust];

BOOL enableDebug = NO;

//这里最好加上缓存判断

if (enableDebug)

{

NSString *str = @"写代码是一门艺术";

NSData *data = [str dataUsingEncoding:NSUTF8StringEncoding];

NSURLResponse *response = [[NSURLResponse alloc] initWithURL:mutableReqeust.URL

MIMEType:@"text/plain"

expectedContentLength:data.length

textEncodingName:nil];

[self.client URLProtocol:self

didReceiveResponse:response

cacheStoragePolicy:NSURLCacheStorageNotAllowed];

[self.client URLProtocol:self didLoadData:data];

[self.client URLProtocolDidFinishLoading:self];

}

else

{

self.connection = [NSURLConnection connectionWithRequest:mutableReqeust delegate:self];

}

}

- (void)stopLoading

{

if (self.connection != nil)

{

[self.connection cancel];

self.connection = nil;

}

}

#pragma mark- NSURLConnectionDelegate

- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error {

[self.client URLProtocol:self didFailWithError:error];

}

#pragma mark - NSURLConnectionDataDelegate

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response

{

self.responseData = [[NSMutableData alloc] init];

[self.client URLProtocol:self didReceiveResponse:response cacheStoragePolicy:NSURLCacheStorageNotAllowed];

}

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data {

[self.responseData appendData:data];

[self.client URLProtocol:self didLoadData:data];

}

- (void)connectionDidFinishLoading:(NSURLConnection *)connection {

[self.client URLProtocolDidFinishLoading:self];

}

@end

注意点:

Protocols的遍历是反向的，也就是最后注册的Protocol会被优先判断。就是先注册A再注册B ,优先判断B

一定要注意标记请求，不然你会无限的循环下去。。。因为一旦你需要处理这个请求，那么系统会创建你这个protocol的实例，然后你自己又开启了connection进行请求的话，又会触发URL Loading system的回调。系统给我们提供了+ (void)setProperty:(id)value forKey:(NSString *)key inRequest:(NSMutableURLRequest *)request;和+ (id)propertyForKey:(NSString *)key inRequest:(NSURLRequest *)request;这两个方法进行标记和区分。

后记:

我在开发中发现 http 转 https 的时候 会有错误,有哪位大神指导下改如何去改,多谢.

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