C＃窗口显示从数据库更新表单GUI时正在加载GIF

Question

Application Description:
Developed a small windows MDI application in C# where multiple users update and scan product bar codes before dispatching. We are using SQL as a database.

Activity:
The supervisors have form named dashboard in the application where they can check multiple count details like scanning done by each user, daily scan count, hourly scan count, product scan count etc.

Done:
I have used multiple list-views and labels to display this details successfully.

Requirement:
The database contains millions of scanning records. I am using multiple stored procedures to update the list view and labels. Loading the same takes time. I want to show an animated GIF in picture box while the loading is being done in the background.

I tried using threading and background worker but updating multiple controls like list view and labels on the master GUI doesn't look feasible [cross-threading]. Is this the only way to achieve this, Please direct me in the right direction.

        string queryString = "select scanby,count(distinct refno),count(1) from SecRec where scan='Y' and convert(varchar(10),ScanTime,111) like '" + comboDate + "' group by scanby order by 3,2 desc";
        lstVUser.Clear();

        lstVUser.Columns.Add("User", 105);
        lstVUser.Columns.Add("Cust", 60);
        lstVUser.Columns.Add("Imp", 60);

        using (SqlConnection conn = new SqlConnection(connectString))
        {
            SqlCommand cmd = new SqlCommand(queryString, conn);
            try
            {
                conn.Open();
                SqlDataAdapter adp = new SqlDataAdapter(queryString, conn);
                DataTable dt = new DataTable();
                adp.Fill(dt);
                for (int i = 0; i < dt.Rows.Count; i++)
                {
                    DataRow dr = dt.Rows[i];
                    ListViewItem listitem = new ListViewItem(dr[0].ToString());
                    listitem.SubItems.Add(dr[1].ToString().PadLeft(3));
                    listitem.SubItems.Add(dr[2].ToString().PadLeft(3));
                    lstVUser.Items.Add(listitem);
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }

Answer 1

It sounds like you're coming from Delphi / FoxPro background. In .NET, grids are not virtual by default, so data binding millions of rows is always a terrible idea.

This requires a bit of thought.

First, figure out how much data you really need to get at a time - maybe loading everything at once (but separately from the data binding) is a good option, maybe you want to read data on-demand.

Second, figure out how to present the data. For a few hundred rows, binding it directly to the grid is fine. For anything more, you really need some way of partitioning the data to avoid always presenting everything. The default winforms DataGridView is in fact designed to deal with this - you just have to enable virtual mode, and write a bit of code. See https://msdn.microsoft.com/en-us/library/system.windows.forms.datagridview.virtualmode(v=vs.110).aspx for more information.

In most cases, you don't really want to work with a grid with millions of rows, virtual or not. You might want to consider adding some filters that align well with the requirements of your customers. It might very well be fine to only show the last hundred rows without filters, for example, and only giving access to the rest with a filter.

Applying those ideas, you should be able to get away with having to use a loading animation at all. If the loading still does take some perceptible amount of time (eg more than 100-200ms), you can add the animation, but make sure you separate the data loading, and the data binding - this allows you to load the data in the background (using asynchronous database requests or a background worker), and only block the GUI while doing the actual binding (unavoidable, but painless when using virtual grids).

EDIT:

Working with your code, you'd want to do something like this:

async Task<DataTable> LoadData()
{
  // Setup the command, connection etc. as usual
  using (var reader = await command.ExecuteReaderAsync())
  {
    var results = new DataTable();
    results.Load(reader);

    return results;
  }
}

async void btnDoStuff_Click(object sender, EventArgs e)
{
  try
  {
    loadingAnimation.Show();

    var dataTable = await LoadData();

    // Use the data table to bind the ListView's data as usual
  }
  finally
  {
    loadingAnimation.Hide();
  }
}

Answer 2

Well, if you want to access a control that is created in another thread then you will always face a [cross-threading] problem. so you will need to use Control.Invoke and the patterns associated with it.

Here is a sample:

private delegate void SetListProperties(DataTable myData);

private void UpdateListView(DataTable myData)
{
    if (lstVUser.InvokeRequired)
    {
        SetListProperties d = new SetListProperties(UpdateListView);
        lstVUser.BeginInvoke(d, myData);
    }
    else
    {
       for (int i = 0; i < dt.Rows.Count; i++)
       {
           DataRow dr = dt.Rows[i];
           ListViewItem listitem = new ListViewItem(dr[0].ToString());
           listitem.SubItems.Add(dr[1].ToString().PadLeft(3));
           listitem.SubItems.Add(dr[2].ToString().PadLeft(3));
           lstVUser.Items.Add(listitem);
       }
    }
}

Concerning the splash screen, you will need to be absolutely sure that all initialization logic happens outside the GUI thread.

Here is a nice solution Splash_Screen_Sample