List<> OrderBy IComparer？

Question

我有一个List<ListViewItem>，我在VirtualMode的ListView中使用过它

列表中有5000个项目，每当单击ListView的列时，我都会使用LINQ和OrderBy对其进行排序，所以我编写了以下代码：

List<ListViewItem> ListOfItems = new List<ListViewItem>();
ListViewColumnSorter lvwColumnSorter;

void listView1_ColumnClick(object sender, ColumnClickEventArgs e)
{
    try
    {
        // Determine if clicked column is already the column that is being sorted.
        if (e.Column == lvwColumnSorter.SortColumn)
        {
            // Reverse the current sort direction for this column.
            if (lvwColumnSorter.Order == SortOrder.Ascending)
            {
                lvwColumnSorter.Order = SortOrder.Descending;
            }
            else
            {
                lvwColumnSorter.Order = SortOrder.Ascending;
            }
        }
        else
        {
            // Set the column number that is to be sorted; default to ascending.
            lvwColumnSorter.SortColumn = e.Column;
            lvwColumnSorter.Order = SortOrder.Ascending;
        }

        if (lvwColumnSorter.Order == SortOrder.Descending)
            this.ListOfItems.OrderByDescending(a => a, new CompareListItemsClass(e.Column, lvwColumnSorter.Order));
        else
            this.ListOfItems.OrderBy(a => a, new CompareListItemsClass(e.Column, lvwColumnSorter.Order));

        this.listView1.VirtualListSize = ListOfItems.Count;
        this.listView1.Refresh();
    }
    catch { }
}

public class CompareListItemsClass : IComparer<ListViewItem>
{
    private CaseInsensitiveComparer ObjectCompare = new CaseInsensitiveComparer();
    private SortOrder OrderOfSort;
    private int ColumnToSort;

    public CompareListItemsClass(int columnIndex, SortOrder sortOrder)
    {
        ColumnToSort = columnIndex;
        OrderOfSort = sortOrder;
    }

    public int Compare(ListViewItem listviewX, ListViewItem listviewY)
    {
        // Compare the two items
        try
        {
            compareResult = ObjectCompare.Compare(
                int.Parse(listviewX.SubItems[ColumnToSort].Text),
                int.Parse(listviewY.SubItems[ColumnToSort].Text));
        }
        catch
        {
            compareResult = ObjectCompare.Compare(listviewX.SubItems[ColumnToSort].Text,
                listviewY.SubItems[ColumnToSort].Text);
        }


        // Calculate correct return value based on object comparison
        if (OrderOfSort == SortOrder.Ascending)
        {
            // Ascending sort is selected, return normal result of compare operation
            return compareResult;
        }
        else if (OrderOfSort == SortOrder.Descending)
        {
            // Descending sort is selected, return negative result of compare operation
            return (-compareResult);
        }
        else
        {
            // Return '0' to indicate they are equal
            return 0;
        }
    }

    int IComparer<ListViewItem>.Compare(ListViewItem x, ListViewItem y)
    {
        throw new NotImplementedException();
    }
}

但是什么都没发生！我希望至少抛出一个异常！

你能给我带路吗？

谢谢。

Answer 1

LINQ方法不影响集合，它们返回一个新的集合。您可以使用ToList方法将结果转换为列表，并将其分配回列表变量：

this.ListOfItems = this.ListOfItems.OrderBy(a => a, new CompareListItemsClass(e.Column, lvwColumnSorter.Order)).ToList();

Answer 2

OrderBy和OrderByDescending扩展方法不修改集合，它们以指定的顺序返回集合的一系列项。在您的代码中，您只需丢弃这些方法的结果，因此不会发生任何事情……

如果您需要“就地”对集合进行排序(即修改项的实际顺序)，请使用List.Sort方法。

编辑

要实现降序和升序，实际上使用Comparison<T>比使用IComparer<T>更容易，因为您只需要否定结果...下面是一个例子：

Comparison<ListViewItem> temp = (x, y) =>
{
    int xvalue = int.Parse(x.SubItems[e.Column].Text);
    int yvalue = int.Parse(y.SubItems[e.Column].Text);
    return xvalue.CompareTo(yvalue);
};

Comparison<ListViewItem> comparison;
if (lvwColumnSorter.Order == SortOrder.Ascending)
{
    comparison = temp;
}
else
{
    comparison = (x, y) => -temp(x, y);
}

this.ListOfItems.Sort(comparison);