stringByTrimmingCharactersInSet在苹果官方文档中的description:
Returns a new string made by removing from both ends of the receiver characters contained in a given character set.
Use whitespaceCharacterSet or whitespaceAndNewlineCharacterSet to remove whitespace around strings.
A character set containing the characters to remove from the receiver. de style="line-height: normal;" >setde> must not be de style="line-height: normal;" >nilde>.
A new string made by removing from both ends of the receiver characters contained in de style="line-height: normal;" >setde>. If the receiver is composed entirely of characters from de style="line-height: normal;" >setde>, the empty string is returned

stringByTrimmingCharactersInSet在苹果官方文档中的description:
Returns a new string made by removing from both ends of the receiver characters contained in a given character set.
Use whitespaceCharacterSet or whitespaceAndNewlineCharacterSet to remove whitespace around strings.
A character set containing the characters to remove from the receiver. de style="line-height: normal;" >setde> must not be de style="line-height: normal;" >nilde>.
A new string made by removing from both ends of the receiver characters contained in de style="line-height: normal;" >setde>. If the receiver is composed entirely of characters from de style="line-height: normal;" >setde>, the empty string is returned