C# listview reverting sort order by column

Question

I have implemented events to sort listview items by column.But I want to check that if the column is clicked second time if so I would change sorting order from Ascending to Descending. Here my custom implementation is not working.Even I only say that listview1.Sorting=SortOrder.Descending it is always sorting by Ascending order.What is the problem in my code ?

namespace WindowsFormsApplication1
{

public partial class Form_UrunEkrani : Form
{
    VerilerDataContext db;
    private int lastClicked;
    public Form_UrunEkrani()
    {
        InitializeComponent();
        db = new VerilerDataContext();
        var itms = from p in db.Urunlers select p;

        foreach (var item in itms)
        {
            ListViewItem listItem = new ListViewItem();
            listItem.Text = item.Urun_Adi;
            listItem.SubItems.Add(item.Birim_Fiyat.ToString());
            listItem.SubItems.Add(item.Stok_Adeti.ToString());
            listView1.Items.Add(listItem);
        }
    }

    private void listView1_ColumnClick(object sender, ColumnClickEventArgs e)
    {
        this.listView1.ListViewItemSorter = new ListViewItemComparer(e.Column);
        if( e.Column==lastClicked)
        {
            listView1.Sorting = Swap(listView1.Sorting);
        }
        else
        {
            listView1.Sorting = SortOrder.Ascending;
        }
        listView1.Sort();
        lastClicked = e.Column;

    }
    private SortOrder Swap(SortOrder a)
    {
        if (a == SortOrder.Ascending)
            return SortOrder.Descending;
        else if (a == SortOrder.Descending)
            return SortOrder.Ascending;
        else return SortOrder.Ascending;
    }
}
class ListViewItemComparer : IComparer
{
    private int col;
    public ListViewItemComparer()
    {
        col = 0;
    }
    public ListViewItemComparer(int column)
    {
        col = column;
    }
    public int Compare(object x, object y)
    {
        int returnVal = -1;
        returnVal = String.Compare(((ListViewItem)x).SubItems[col].Text,
        ((ListViewItem)y).SubItems[col].Text);
        return returnVal;
    }
}
}

Answer 1

The problem is that its the ListViewItemComparer job to sort but it does not care about the Sorting it always sort ascending.

I made Column public and added Order then changed Compare(...) accordingly.

class ListViewItemComparer : IComparer
{
    public SortOrder Order = SortOrder.Ascending;
    public int Column;

    public ListViewItemComparer()
    {
        Column = 0;
    }
    public ListViewItemComparer(int column)
    {
        Column = column;
    }
    public int Compare(object x, object y)
    {
        int returnVal = String.Compare(((ListViewItem)x).SubItems[Column].Text,
        ((ListViewItem)y).SubItems[Column].Text);

        if (Order == SortOrder.Descending)
            return -returnVal;
        else
            return returnVal;
    }
}

Only add the ListViewItemComparer during initialization

public Form_UrunEkrani()
{
    InitializeComponent();
    this.listView1.ListViewItemSorter = new ListViewItemComparer();
    ...
}

Changed listView1_ColumnClick so it gets the comparer and changes the Order and Column on it

private void listView1_ColumnClick(object sender, ColumnClickEventArgs e)
{
    ListViewItemComparer comparer = (ListViewItemComparer)listView1.ListViewItemSorter;

    if (e.Column == comparer.Column)
    {
        comparer.Order = Swap(comparer.Order);
    }
    else
    {
        comparer.Order = SortOrder.Ascending;
    }

    comparer.Column = e.Column;
    listView1.Sort();
}