Inserting into a C# List of Objects that uses a Property of the Object to Sort

Question

There's a list of objects, each object representing a record from a database. To sort the records there is a property called SortOrder. Here's a sample object:

public class GroupInfo
{
    public int Id { get; set; }
    public string Text { get; set; }
    public int SortOrder { get; set; }

        public GroupInfo()
        {
            Id = 0;
            Text = string.Empty;
            SortOrder = 1;
        }
}

A list object would look like this:

var list = new List<GroupInfo>();

I need to be able to change the SortOrder and update the SortOrder on the other objects in the list. I figured out how to sort up or down by one. I need to know how to change it by more than one and adjust the SortOrder on the other records. Any ideas?

Answer 1

This could be done by first getting the original SortOrder and the updated SortOrder . You would then iterate through your collection and adjust the SortOrder of any other GroupInfo objects that fall inside the range between original and updated . you could put all of this in a "SetSortOrder" function that takes in the containing collection.

public static void SetSortOrder(List<GroupInfo> groupInfos, GroupInfo target, int newSortOrder)
{
    if (newSortOrder == target.SortOrder)
    {
        return; // No change
    }
    // If newSortOrder > SortOrder, shift all GroupInfos in that range down
    // Otherwise, shift them up
    int sortOrderAdjustment = (newSortOrder > target.SortOrder ? -1 : 1);
    // Get the range of SortOrders that must be updated
    int bottom = Math.Min(newSortOrder, target.SortOrder);
    int top = Math.Max(newSortOrder, target.SortOrder);
    // Get the GroupInfos that fall within our range
    var groupInfosToUpdate = from g in groupInfos
                                where g.Id != target.Id
                                && g.SortOrder >= bottom
                                && g.SortOrder <= top
                                select g;
    // Do the updates
    foreach (GroupInfo g in groupInfosToUpdate)
    {
        g.SortOrder += sortOrderAdjustment;
    }

    target.SortOrder = newSortOrder;
    // Uncomment this if you want the list to resort every time you update
    // one of its members (not a good idea if you're doing bulk changes)
    //groupInfos.Sort((info1, info2) => info1.SortOrder.CompareTo(info2.SortOrder));
}

Update: As suggested, I moved the logic into a static helper function.

Answer 2

var sortedList = list.OrderBy(item => item.SortOrder);

Edit: Sorry, I misunderstood. You will need to write yourself a method outside of GroupInfo to handle the updating of that property.