NSDateFormatter *dateFormat = [[NSDateFormatter alloc] init];
  //cccc 星期全名 MMMM月全名
  [dateFormat setDateFormat:@"cccc MMMM dd, yyyy hh:mm a"];
  NSString *prettyVersion = [dateFormat stringFromDate:[NSDate date]];

还有疑问看这个表格
http://www.unicode.org/reports/tr35/tr35-25.html#Date_Format_Patterns

NSDate *myDate = datePicker.date;

NSDateFormatter *dateFormat = [[NSDateFormatter alloc] init];
[dateFormat setDateFormat:@"cccc, MMM d, hh:mm aa"];
NSString *prettyVersion = [dateFormat stringFromDate:myDate];