ios：自定义NSURLProtocol不稳定

Question

我有一个使用自定义NSURLProtocol的应用程序想要拦截http请求和响应与本地数据。但它只能在某些时候起作用。 这是两个重要的功能：

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

    NSString *flag=[NSURLProtocol propertyForKey:CachingURLHeaderKey inRequest:request];

    if (flag==nil ) {

       return YES;
    }

    return NO;
}

- (void)startLoading
{

    NSMutableURLRequest *proxyRequest = [self.request mutableCopy];

    [NSURLProtocol setProperty:@"done" forKey:CachingURLHeaderKey inRequest:proxyRequest];

    NSString *resourcePath = [[NSBundle mainBundle] resourcePath];

    NSString *ResourceCacheDir = [resourcePath stringByAppendingPathComponent:[@"cache/" stringByAppendingString:MyFileKey]];

    NSData *ReturnData=[NSData dataWithContentsOfFile:ResourceCacheDir];

    if (ReturnData!=nil) {

        headers = [NSMutableDictionary dictionary];

        NSString *contentType=[self MimeTypeOf:self.request.URL.pathExtension];

        NSString *contentLength=[NSString stringWithFormat:@"%lu", (unsigned long)data.length];

        headers[@"Content-Type"]=contentType;
        headers[@"Content-Length"]=contentLength;

        NSHTTPURLResponse* response = [[NSHTTPURLResponse alloc]
                                       initWithURL:self.request.URL
                                       statusCode:200
                                       HTTPVersion:@"HTTP/1.1"
                                       headerFields:headers];

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


    } else {
        self.connection = [NSURLConnection connectionWithRequest:proxyRequest delegate:self];
    }
}