Sort NSArray with NSDate object into NSDictionary by month

问题

I am building a UITableView and would like to group by month so that I can have those strings as my section headers, e.g.:

February 2013
- Item 1
- Item 2

January 2013
- Item 1
- Item 2

I have an NSArray which has custom objects that have a pubDate property that is an NSDate.

How can I use that NSDate object to group my custom objects into a NSDictionary by month?

回答1:

Sort array like this

NSArray *sortedArray = [yourArrayOfCustomObjects sortedArrayUsingComparator:^NSComparisonResult(id obj1, id obj2) {
        NSDate *firstDate = [(YourCustomObject*)obj1 pubDate];
        NSDate *secondDate = [(YourCustomObject*)obj2 pubDate];
        return [firstDate compare:secondDate];        

    }];

// Now a simple iteration and you can determine all same month entries.

// Code is not complete just for illustration purpose.

// You have to handle Year change as well.

int curMonth = 0;
int prevMonth = 0;
foreach(CustomObject *obj in sortedArray)
{
   NSDateComponents *components = [[NSCalendar currentCalendar] components:NSDayCalendarUnit | NSMonthCalendarUnit | NSYearCalendarUnit fromDate:obj.pubDate];
   prevMonth = curMonth; 
   curMonth = components.month;
   if(prevMonth != 0 && curMonth != prevMonth)
   {
      //Month Changed
   }
}

回答2:

Take a look at NSDateComponents. If you convert your dates to date components:

[[NSCalendar currentCalendar] components:(NSMonthCalendarUnit | NSYearCalendarUnit) fromDate:date]

then you'll have objects you can very easily compare for equality.

回答3:

I think, this question was missing answer from Ole Begemann, however this is a link (and I'm not able to post a comment < repo) I'm giving an answer to this question,

If someone still looking for some elegant solution, check this out,

http://oleb.net/blog/2011/12/tutorial-how-to-sort-and-group-uitableview-by-date/

来源：https://stackoverflow.com/questions/14987147/sort-nsarray-with-nsdate-object-into-nsdictionary-by-month