用stringByAddingPercentEncodingWithAllowedCharacters取代CFURLCreateStringByAddingPercentEscapes

在 iOS 程序访问 HTTP 资源时需要对 URL 进行 Encode，比如像拼出来的 http://unmi.cc?p1=%+&sd
f&p2=中文，其中的中文、特殊符号&％和空格都必须进行转译才能正确访问。现在以"?!@#$^&%*+,:;='\"`<>()[]{}/\\| "字符串为例子，用stringByAddingPercentEncodingWithAllowedCharacters取代CFURLCreateStringByAddingPercentEscapes

原字符串为：

<span style="font-family:SimSun;font-size:14px;">NSString *url = @"ertehtt""p://xxdsdscrg?!@#$^&%*+,:;='\"`<>()[]{}/\\| ";</span>

CFURLCreateStringByAddingPercentEscapes方法为：

<span style="font-family:SimSun;font-size:14px;">    CFStringRef encodedCFString = CFURLCreateStringByAddingPercentEscapes(kCFAllocatorDefault,
(__bridge CFStringRef) url,
nil,
CFSTR("?!@#$^&%*+,:;='\"`<>()[]{}/\\| "),
kCFStringEncodingUTF8);
NSString *encodedString1 = [[NSString alloc] initWithString:(__bridge_transfer NSString*) encodedCFString];</span>

stringByAddingPercentEncodingWithAllowedCharacters方法为：

NSString *charactersToEscape = @"?!@#$^&%*+,:;='\"`<>()[]{}/\\| ";
NSCharacterSet *allowedCharacters = [[NSCharacterSet characterSetWithCharactersInString:charactersToEscape] invertedSet];
NSString *encodedUrl = [url stringByAddingPercentEncodingWithAllowedCharacters:allowedCharacters];
NSLog(@"\n%@\n%@",encodedUrl,encodedString1);
之后获得的字符串为一致的。