Implementing a custom sort for WinForms ListView

Question

I have a class called Picture and that has a name and size (int) property.

I was going to sort them using size, but not the displayed file name which is the item name in the listview.

I implemented IComparer<Picture> for the Picture type, and then when I write this:

this.PicList.ListViewItemSorter = AllPictures[0];

or

this.PicList.ListViewItemSorter = Picture;

they don't compile.

How do I do this? On MSDN it shows a separate class for the sorter but can I do it built-in with the used type Picture?

Answer 1

you need to give it an actual instance of your Picture class, not the type. Also, your ListViewItemSorter will actually call the Comparer by passing it the ListViewItem not the Picture class, you can add an instance of the Picture class to the Tag property of your ListViewItem.

Something like this, this is a very rough implementation, just to give you an idea. You can implement your own error handling.

Picture test1 = new Picture() { Name = "Picture #1", Size = 54 };
Picture test2 = new Picture() { Name = "Picture #2", Size = 10 };

this.listView1.ListViewItemSorter = test1;

this.listView1.Items.Add(new ListViewItem(test1.Name) { Tag = test1 });
this.listView1.Items.Add(new ListViewItem(test2.Name) { Tag = test2 });

 public class Picture : IComparer
    {
        public string Name { get; set; }
        public int Size { get; set; }

        #region IComparer Members

        public int Compare(object x, object y)
        {
            Picture itemA = ((ListViewItem)x).Tag as Picture;
            Picture itemB = ((ListViewItem)y).Tag as Picture;

            if (itemA.Size < itemB.Size)
                return -1;

            if (itemA.Size > itemB.Size)
                return 1;

            if (itemA.Size == itemB.Size)
                return 0;

            return 0;

        }

The output is:

• Picture #2
• Picture #1

Here is an MSDN Link

Answer 2

Another implementation you can try is to associate each ListViewItem index with your custom class/struct instance stored in a Dictionary<int, Picture> instance. Your custom list view sorter class could be written with that in mind like so:

public partial class Form1 : Form
{
    public Form1()
    {
        ...

        ListView lv = new ListView();
     lv.ListViewItemSorter = new MyCustomSorter(this);
    }

    private Dictionary<int, Picture> _pictures = new Dictionary<int,Picture>();

    private class MyCustomSorter : IComparer
    {
     private Form1 _parent;

     internal MyCustomSorter(Form1 form)
     {
      _parent = form;
     }

     #region IComparer Members

     public int Compare(object x, object y)
     {
      ListViewItem item1 = x as ListViewItem;
      ListViewItem item2 = y as ListViewItem;

      if (x != null)
      {
       if (y != null)
       {
        Picture p1 = _parent._pictures[item1.Index];
        Picture p2 = _parent._pictures[item2.Index];

        return string.Compare(p1.Location, p2.Location);
       }

       // X is deemed "greater than" y
       return 1;
      }
      else if (y != null)
       return -1;  // x is "less than" y

      return 0;
     }

     #endregion
    }
}

public class Picture
{
    private string _location;

    public string Location{
     get { return _location; }
    }
}

Answer 3

Stan's solution will work, but, on behalf of your users, I'd strongly suggest you don't hard code the sorting order. On a ListView, everyone expects to be able to sort by clicking on the header.

ObjectListView (an open source wrapper around .NET WinForms ListView) provides sort-on-click functionality for free. It could even show a thumbnail of your pictures in its own column if you want it to.