比如限制输入字符为ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789@-_.

 

例子：

 

+( BOOL) isStringInCharacterSet:( NSString*) str  (需要判断的字符串)

{

     static   NSString * s_strEmailChar = @"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789@-_." ;

     NSCharacterSet* charset = [ NSCharacterSet  characterSetWithCharactersInString:s_strEmailChar];

    NSCharacterSet* cs = [charSet invertedSet];

    NSString *filtered = [[str componentsSeparatedByCharactersInSet:cs] componentsJoinedByString:@""];

    return [str isEqualToString:filtered];

}