Threading in C# winform to show a splash screen ERROR

Question

1.00/5 (1 vote)

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Hi guys ,
im trying to show splash screen but the following error is shown:

Cross-thread operation not valid: Control 'cmbEnviroment' accessed from a thread other than the thread it was created on

this is my code for the threading :

private void LoadInstitutions()
      {
          //Thread.Sleep(3000);

          // OperationClass oc = new OperationClass();
          // oc.loading();
          string selectedValue = cmbEnviroment.SelectedItem.ToString().Trim();
          ConnectionClass connectionClass = new ConnectionClass();
          connectionClass.Connection(selectedValue);

          DataTable table4 = new DataTable();

          string sql4 = "A query to gather data";

          try
          {

              OleDbDataAdapter da4 = new OleDbDataAdapter(sql4, connectionClass.Connection(selectedValue));
              da4.Fill(table4);
              DataRow dr4 = table4.NewRow();
              DataRow dr5 = table4.NewRow();
              dr4["hello1"] = "";
              table4.Rows.InsertAt(dr4, 0);

              cmbInstitution.DataSource = table4;
              cmbInstitution.DisplayMember = "hello1";
              cmbInstitution.ValueMember = "hello1";
          }
          catch (Exception ex)
          {
              MessageBox.Show(ex.ToString());
          }





      }

      private async void cmbEnviroment_SelectedIndexChanged(object sender, EventArgs e)
      {

          //using (new PleaseWait(this.Location))
          //{
              ComboBox senderComboBox = (ComboBox)sender;
              if (senderComboBox.SelectedIndex > 0)
              {
                  LoadingScreen ls = new LoadingScreen();
                  ls.TopMost = true;
                  ls.Show();

                  await Task.Run(() => LoadInstitutions());

                  ls.Close();
               }
          //}

      }

What I have tried:

im have tried different methods to show the splash screen while i'm gathering data from database but im stuck .

Posted 26-Jun-18 21:25pm

Joe Doe234

Updated 27-Jun-18 4:50am

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2 solutions

Solution 1

You cannot access any control from any thread other than the UI thread - when you try, you get a "cross thread exception" as you are seeing.

Two ways to fix this:
1) Invoke the control instead of accessing it directly: Control.Invoke Method (Delegate) (System.Windows.Forms)[^]
2) Move your long running code into a background thread using the BackgroundWorker class which is designed to provide progress information to the UI thread for updates.

Posted 26-Jun-18 21:40pm

OriginalGriff

Comments

Joe Doe234 27-Jun-18 3:45am

hi original , thanks for answer my question :). small question
i did this to my long running code :

this.Invoke((MethodInvoker)delegate ()
{ ...

this is working perferctly but the animated gif is not working. it will just appear.

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Richard Deeming · Accepted Answer · 2018-06-27T04:51:00

Refactor your code to move the long-running part to a background thread, and keep the parts that access the UI on the UI thread:

C#

private static DataTable LoadInstitutions(string selectedValue)
{
    ConnectionClass connectionClass = new ConnectionClass();
    const string sql = "A query to gather data";
    
    DataTable result = new DataTable();
    OleDbDataAdapter da = new OleDbDataAdapter(sql, connectionClass.Connection(selectedValue));
    da.Fill(result);
    
    DataRow dr = result.NewRow();
    dr["hello1"] = "";
    result.Rows.InsertAt(dr, 0);
    
    return result;
}

private async Task LoadInstitutions()
{
    try
    {
        string selectedValue = cmbEnviroment.SelectedItem.ToString().Trim();
        DataTable table = await Task.Run(() => LoadInstitutions(selectedValue));
        cmbInstitution.DataSource = table4;
        cmbInstitution.DisplayMember = "hello1";
        cmbInstitution.ValueMember = "hello1";
    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.ToString());
    }
}

private async void cmbEnviroment_SelectedIndexChanged(object sender, EventArgs e)
{
    ComboBox senderComboBox = (ComboBox)sender;
    if (senderComboBox.SelectedIndex > 0)
    {
        LoadingScreen ls = new LoadingScreen();
        ls.TopMost = true;
        ls.Show();
        try
        {
            await LoadInstitutions();
        }
        finally
        {
            ls.Close();
        }
    }
}