您也可以检查MIME类型更长的旅程：

You can check the MIME type too, for a slightly longer journey:

@property (nonatomic, strong) NSString *mime;

- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response 
{
   mime = [response MIMEType];
}

- (BOOL)isDisplayingPDF {
    NSString *extension = [[mime substringFromIndex:([mime length] - 3)] lowercaseString];

    return ([[[self.webView.request.URL pathExtension] lowercaseString] isEqualToString:@"pdf"] || [extension isEqualToString:@"pdf"]);
}