转自：http://blog.sina.com.cn/s/blog_5421851501014xif.html

去除 username中的空格，table newline，nextline 
代码如下：（三行代码）

NSCharacterSet *whitespace = [NSCharacterSet  whitespaceAndNewlineCharacterSet];

NSString * username = [mUsernameField  stringValue];

username = [username  stringByTrimmingCharactersInSet: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