iOS url出现特殊字符处理

stringByAddingPercentEscapesUsingEncoding(只对 `#%^{}[]|"<> 加空格共14个字符编码，不包括”&?”等符号), ios9将淘汰，建议用 stringByAddingPercentEncodingWithAllowedCharacters 方法

stringByAddingPercentEncodingWithAllowedCharacters 需要传一个 ****NSCharacterSet 对象（关于 NSCharacterSet 这篇 文章说的很好）

如[NSCharacterSet URLQueryAllowedCharacterSet]

URLFragmentAllowedCharacterSet  "#%<>[\]^`{|}

URLHostAllowedCharacterSet      "#%/<>?@\^`{|}

URLPasswordAllowedCharacterSet  "#%/:<>?@[\]^`{|}

URLPathAllowedCharacterSet      "#%;<>?[\]^`{|}

URLQueryAllowedCharacterSet    "#%<>[\]^`{|}

URLUserAllowedCharacterSet      "#%/:<>?@[\]^`

（2）网络访问请求：中文空格字符解码

stringByRemovingPercentEncoding ---- xcode7可能会提示要将stringByAddingPercentEscapesUsingEncoding替换成此方法，要根据是否是解码来区分

代替 stringByAddingPercentEscapesUsingEncoding

 let customAllowedSet =  NSCharacterSet(charactersInString:"`#%^{}\"[]|\\<> ").invertedSet

NSString *urlStr = [urlStr stringByAddingPercentEncodingWithAllowedCharacters:[[NSCharacterSet characterSetWithCharactersInString:@"?!@#$^&%*+,:;='\"`<>()[]{}/\\| "] invertedSet]];