string代替

    NSString * t = @"EMMS_Files\Business\WORRF\TXT\20170403\5379774001.pdf";

    

    NSString * a = [t stringByReplacingOccurrencesOfString:@".pdf" withString:@".jpg"];

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 *url = [NSString stringWithFormat:@"whatsapp://send?text=%@", [msg stringByAddingPercentEncodingWithAllowedCharacters:[NSCharacterSet URLHostAllowedCharacterSet]]];

    NSURL *whatsappURL = [NSURL URLWithString: url];