NSString去除空格字符-包括两边字符trim()

 NSString *cleanString = [dirtyString stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceAndNewlineCharacterSet]];

还有就是去除多于的空格，如下：

 NSString *theString = @"    Hello      this  is a   long       string!   ";

 NSCharacterSet *whitespaces = [NSCharacterSet whitespaceCharacterSet];
 NSPredicate *noEmptyStrings = [NSPredicate predicateWithFormat:@"SELF != ''"];

 NSArray *parts = [theString componentsSeparatedByCharactersInSet:whitespaces];
 NSArray *filteredArray = [parts filteredArrayUsingPredicate:noEmptyStrings];
 theString = [filteredArray componentsJoinedByString:@" "];