去除username中的空格，table newline，nextline

代码如下：（三行代码）

NSCharacterSet *whitespace = [NSCharacterSetwhitespaceAndNewlineCharacterSet];

NSString *username= [mUsernameFieldstringValue];

username = [usernamestringByTrimmingCharactersInSet:whitespace];

注释：

stringByTrimmingCharactersInSet:

Returns a new string made by removing from both ends of the receiver characters contained in a given character set.

whitespaceAndNewlineCharacterSet

Returns a character set containing only the whitespace characters space (U+0020) and tab (U+0009) and the newline and nextline characters (U+000A–U+000D, U+0085).

另外可以用whitespaceCharacterSet替换whitespaceAndNewlineCharacterSet区别newline nextline

whitespaceCharacterSet

Returns a character set containing only the in-line whitespace characters space (U+0020) and tab (U+0009).

NSString *temptext = [messageTextField.text stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]];

NSString *text = [temptext stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];

第1行是去除2端的空格

第2行是去除回车