刷新后的'ListView'位置

Question

I am populating a ListView with two data sets from SQL. This happens every 15 seconds. How can I keep the scrolled-to position and still refresh the data? I have seen some questions here with related issues but none really address my specific issue. I have tried the TopMost option with limited success.

Any suggestions on how I can keep the scrolled-to position? Here is a bit of code that I use to populate the data for the ListBox .

private void PopulateData()
{        
    _agent.Stop();
    listView1.Items.Clear();
    listView1.Groups.Clear();
    listView1.BeginUpdate();
    string filter;

    DataTable dt1 = new DataTable();
    DataTable dt2 = new DataTable();

    dt1.Columns.Add("Name", typeof(string));
    dt1.Columns.Add("Status", typeof(string));
    dt1.Columns.Add("Time", typeof(double));
    dt1.Columns.Add("Calls", typeof(double));
    dt1.Columns.Add("InProgress", typeof(double));
    dt1.Columns.Add("Region", typeof(string));

    dt2.Columns.Add("Name", typeof(string));
    dt2.Columns.Add("CChats", typeof(double));
    dt2.Columns.Add("AChats", typeof(double));

    foreach (DataRow dr in _agentStates.Rows)
    {
        DataRow row = dt1.NewRow();
        row["Name"] = dr[0].ToString();
        row["Status"] = dr[1].ToString();
        row["Time"] = Convert.ToDouble(dr[2].ToString());
        row["Calls"] = Convert.ToDouble(dr[3].ToString());
        row["InProgress"] = Convert.ToDouble(dr[4].ToString());
        row["Region"] = dr[5].ToString();
        dt1.Rows.Add(row);
    }

    foreach (DataRow dr in _chatCount.Rows)
    {
        DataRow row = dt2.NewRow();
        row["Name"] = dr[0].ToString();
        row["CChats"] = Convert.ToDouble(dr[1].ToString());
        row["AChats"] = Convert.ToDouble(dr[2].ToString());
        dt2.Rows.Add(row);

    }

    var result = from table1 in dt1.AsEnumerable()
                 join table2 in dt2.AsEnumerable()
                 on (string)table1["Name"] equals (string)table2["Name"]
                 into joinedDt
                 from table2 in joinedDt.DefaultIfEmpty()
                 select new
                 {
                     Name = (string)table1["Name"],
                     Status = (string)table1["Status"],
                     Time = (double)table1["Time"],
                     Calls = (double)table1["Calls"],
                     InProgress = (double)table1["InProgress"],
                     Region = (string)table1["Region"],
                     CChats = (table2 != null ? (double)table2["CChats"] : 0),
                     AChats = (table2 != null ? (double)table2["AChats"] : 0)
                 };

    foreach (var item in result)
    {
        if (item.Status != "NLO" && item.Status !="Webchat Account")
        {
            var calls = item.Calls + item.CChats;
            var lvi = new ListViewItem(item.Name);
            lvi.SubItems.Add(item.Status);
            lvi.SubItems.Add(Conv.Time(item.Time));
            lvi.SubItems.Add(item.Calls.ToString());
            lvi.SubItems.Add(item.CChats.ToString());
            lvi.SubItems.Add((item.AChats + item.InProgress).ToString());
            lvi.SubItems.Add(calls.ToString());
            this.listView1.Items.Add(lvi);
        }
    }

    listView1.EndUpdate();
    _agent.Start();
}

Answer 1

Use the listview in VirtualMode mode and implement the RetrieveVirtualItem event .

It will give you a better control over what is visible, and you don't need to clear all items to get it updated.

If VirtualMode is set to true , you just set the VirtualListSize to the number of items you want to display in the list. The RetrieveVirtualItem event will be fired for each item the listview wants to show to the user. So if your data changes, you can call the Refresh method of the listview and your RetrieveVirtualItem handler will return the new item data.

Consider this example:

public partial class Form1 : Form
{
    private int i = 0;

    public Form1()
    {
        InitializeComponent();
        listView1.View = View.Details;
        listView1.Columns.Add("Col", 250);
        listView1.VirtualMode = true;
        listView1.RetrieveVirtualItem += listView1_RetrieveVirtualItem;
        listView1.VirtualListSize = 25;
        button1.Click += button1_Click;
    }

    private void listView1_RetrieveVirtualItem(object sender, RetrieveVirtualItemEventArgs e)
    {
        e.Item = new ListViewItem((i + e.ItemIndex).ToString());
    }

    private void button1_Click(object sender, EventArgs e)
    {
        // simulate data update
        i += 10;
        //listView1.VirtualListSize += 5; // you can even change the virtual list size while keeping current scroll position
        listView1.Refresh();
    }
}