如何：按日期降序对NSArray进行排序，结果集顶部还保留nil日期

Question

I have the following method where self.orderHeader.meetings is a core data NSManagedObject with meetings being a list of metting. The method sorts the meetings by date (meetingDate):

- (NSArray *)sortMeetingList {
    return [[self.orderHeader.meetings allObjects] sortedArrayUsingDescriptors: [NSArray arrayWithObject: [NSSortDescriptor sortDescriptorWithKey:@"meetingDate" ascending:NO]]];
}

It returns what I want except for meeting objects that do not have a meetingDate set. These are left at the bottom of the list, but (given the descending order) I would like to have them shown on top of the list:

So for example: [nil, 2014-12-29, 2014-12-24] instead of [2014-12-29, 2014-12-24, nil]

Is there an easy way to do this ??

Answer 1

Try something like this:

NSArray *sortedMeetings = [unsortedMeetings sortedArrayUsingComparator:^NSComparisonResult(MeetingObjectClass *obj1, MeetingObjectClass *obj2) {
    if (!obj1.meetingDate)
        return NSOrderedAscending;
    if (!obj2.meetingDate)
        return NSOrderedDescending;
    return [obj2.meetingDate compare:obj1.meetingDate];
}];

Answer 2

您可以用[NSDate distantFuture]替换零日期

Answer 3

使用不同的排序方法，以便您可以明确指定如何处理每个比较，例如使用sortedArrayUsingFunction:context: