c# - 排序下拉列表？

Question

我很好奇在 C#/ASP.NET 中对 DropDownList 进行排序的最佳路线（更注重简单性，而不是速度或效率） - 我已经查看了一些建议，但它们并不适合我。这个下拉菜单按字母顺序给我列表。但我必须随机整理。

注意：我无法控制数据如何进入 DropDownList - 我无法修改 SQL。

public void populateLocationList()
{
    DataTable dt_locations = (DataTable)daa_addresses.GetDataByEventLocations(int_eventid);

    if (dt_locations != null && dt_locations.Rows.Count > 0)
    {
        // Populate locations dropdown menu
        // Bind locationsList instead of dt_locations
        ddl_locations.DataTextField = "Key";
        ddl_locations.DataValueField = "Value";
        ddl_locations.DataSource = RemoveDuplicateLocations(dt_locations);
        ddl_locations.DataBind();



        string location = "";

        // Set the selection based upon the query string
        if (Request.QueryString["loc"] != null)
        {
            location = Request.QueryString["loc"];
            locationLbl.Text = Request.QueryString["loc"];
            locationID.Value = "-1";
        }

        if (dt_locations.Rows.Count == 1)
        {
            location = ddl_locations.Items[0].Text;
            locationLbl.Text = location;
        }

        // Set location in drop down list
        int int_foundlocation = 0;
        bool foundLocation = false;

        foreach (ListItem lsi_item in ddl_locations.Items)
        {
            if (lsi_item.Text.ToLower().Trim() == location.ToLower().Trim())
            {
                int_foundlocation = ddl_locations.Items.IndexOf(lsi_item);
                foundLocation = true;
                break;
            }
        }

        ddl_locations.SelectedIndex = int_foundlocation;

        if (ddl_locations.Items.Count == 1)
        {
            // Make location label visible.
            locationLbl.Visible = true;
            ddl_locations.Visible = false;
        }
        else
        {
            locationLbl.Visible = false;
            ddl_locations.Visible = true;
        }
        //* defualt location S for short courses *//
        if (!IsPostBack && !foundLocation)
        {
            ListItem s = ddl_locations.Items.FindByText("S");
            int index = 0;

            if (s != null)
            {
                index = ddl_locations.Items.IndexOf(s);
            }

            ddl_locations.SelectedIndex = index;
            ddl_locations.DataBind();
        }
    }
}

Answer 1

我必须随机整理。

您必须改组行，可能使用接近此代码的内容（借自@configurator's answer）：

internal static class Extensions
{
    internal static IEnumerable<T> Shuffle<T>(this IEnumerable<T> source, Random rng)
    {
        T[] elements = source.ToArray();
        // Note i > 0 to avoid final pointless iteration
        for (int i = elements.Length - 1; i > 0; i--)
        {
            // Swap element "i" with a random earlier element it (or itself)
            int swapIndex = rng.Next(i + 1);
            yield return elements[swapIndex];
            elements[swapIndex] = elements[i];
            // we don't actually perform the swap, we can forget about the
            // swapped element because we already returned it.
        }

        // there is one item remaining that was not returned - we return it now
        yield return elements[0]; 
    }
}

假设RemoveDuplicateLocations返回DataTable代码的绑定部分应更改为：

        ddl_locations.DataSource = RemoveDuplicateLocations(dt_locations)
            .AsEnumerable()
            .Shuffle(new Random())
            .CopyToDataTable();