iOS Regular expression authentication username password

-(BOOL) checkusername{    nsstring * regex = @ "^[a-za-z0-9]{1,15}$";
    Regular expression    nspredicate *pred = [Nspredicate predicatewithformat:@ "Self MATCHES%@", regex];
    The nspredicate in the cocoa Framework is used for querying, both in principle and in usage similar to where in SQL, which acts as a filter of the database to take    BOOL isMatch = [pred evaluatewithobject: Usernamefield.text];
    To see if the values of the Usernamefield match.

return isMatch; }

-(BOOL) checkpassword{    NSLog (@ "passsowrd:%@", passwordfield.text);    if (PasswordField.text.length > 0) {        return YES;    }    return NO;}

iOS Regular expression authentication username password