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：

原博客链接：http://www.jianshu.com/p/2ed92d399b4b/comments/4668793

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 <Foundation/Foundation.h>@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 <NSURLProtocolClient> 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.

相关链接:

我看这里学会的,上文大部分都是这里出来的,尊重原作者
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