.OrderByDescending().ToList() - Where Order by is a Date that might be Null

Question

.OrderByDescending().ToList() - Where Order by is a Date that might be Null

tqeonline (MIS)

(OP)

16 Oct 13 17:25

Hey guys!

I hope all is well. I've been working on my first Windows Phone 8 app in my spare time. It is basically a Task/Todo app that consists of Task Lists that contain multiple Tasks. I can sort the Task Lists off the title and that is no issue, the issue comes when I want to sort the Tasks by Due Date.

The due date it stored at Google (Google Tasks) as: 10/01/2012 00:00:00 and when I pull it into my UI I parse it like:

CODE --> C#

public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            var formatString = value as string;
 
            if (!string.IsNullOrEmpty(formatString))
            {
                return DateTime.Parse(formatString).Date.ToShortDateString();
            }
            return "No Due Date";
        }

And that works great. Here is what the function looks like without sorting:

CODE --> C#

try
                {
                    DateTime dateValue;
                    var o = JObject.Parse(response.Content);
                    var lists = new List<TaskItem>();
                    if (o != null && o["items"] != null)
                    {
                        lists =
                            o["items"].Select(
                                m => new TaskItem((string)m.SelectToken("id"),
                                                  (string)m.SelectToken("kind"),
                                                  ((string)m.SelectToken("title")) ==
                                                  String.Empty
                                                      ? "Empty"
                                                      : (string)
                                                        m.SelectToken("title"),
                                                  (string)m.SelectToken("notes"),
                                                  (string)m.SelectToken("parent"),
                                                  (string)
                                                  m.SelectToken("position"),
                                                  (string)m.SelectToken("update"),
                                                  (string)m.SelectToken("due"),
                                                  (string)m.SelectToken("deleted"),
                                                  (string)m.SelectToken("hidden"),
                                                  (string)m.SelectToken("status"),
                                                  (string)
                                                  m.SelectToken("selfLink"),
                                                  (string)
                                                  m.SelectToken("completed")
                                         )).ToList();
                    }
                    var tasks = new List<TaskItem>();
                    tasks.Clear();
                    tasks.AddRange(lists);

                    var list = obj[1] as Action<List<TaskItem>>;
                    if (list != null) list(tasks);
                }

Below is what is I have now - it returns errors when the x.due is null.

CODE --> C#

)).OrderByDescending(x=>DateTime.Parse(x.due)).ToList();

I have also tried the below and it doesn't like the ??

CODE --> C#

)).OrderByDescending(x=>DateTime.Parse(x.due) ?? DateTime.MinValue)).ToList();

Should I be doing this sort somewhere else or is there a way I can capture the null and return MinValue/MaxValue?

- Matt

"If I must boast, I will boast of the things that show my weakness"

Moregelen (Programmer) · Answer 1 · 2013-10-17 10:17:51

You're problem isn't that DateTime.Parse(null) returns null, its that that doesn't work. You can't parse a null, so you get an exception. You need to check before you try and parse it:

x=> x.due != null ? DateTime.Parse(x.due) : DateTime.MinValue

tqeonline (MIS) · Answer 2 · 2013-10-20 16:56:59

That was it! Thanks Moregelen!

The below is the code for sorting by date where the upcoming items are at the top - and if there is no due date they are put at the top:

CODE

.OrderBy(x=> x.due != null ? DateTime.Parse(x.due) : DateTime.MinValue).ToList();

Change Datetime.MinValue to Datetime.MaxValue and the "Nulls" are pushed to the bottom.

- Matt

"If I must boast, I will boast of the things that show my weakness"

Moregelen (Programmer) · Answer 3 · 2013-10-20 17:07:09

I've not worked with this specific Google API but I'm sure if you look you can actually include a sort option in your request. Most API I've dealt with include things like that, which is pretty convened. Much easier to programmatically change your request string.

Moregelen (Programmer) · Answer 4 · 2013-10-20 17:08:15

Man... iOS autocorrect is making it look like I can't spell...

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.OrderByDescending().ToList() - Where Order by is a Date that might be Null