Get information from UI with BackgroundWorker and then update UI

Question

I am filling a DataGridView by running a SQL query with BackgroundWorker. My code works perfectly if I run it directly in a button event handler, but when I put in a DoWork BackgroundWorker it doesn't update the UI. My code is below.

DataTable tab1table = new DataTable();

public Form1()
{
    InitializeComponent();
    Instantiatesearch1Thread();
}

private void Instantiatesearch1Thread()
{
    search1Thread.WorkerReportsProgress = true;
    search1Thread.WorkerSupportsCancellation = true;
    search1Thread.ProgressChanged += search1Thread_ProgressChanged;
    search1Thread.DoWork += search1Thread_Dowrk;
    search1Thread.RunWorkerCompleted += search1Thread_RunWorkerCompleted;
}

    private void sbutton1_Click(object sender, EventArgs e)
{
    search1Thread.RunWorkerAsync();
}
void search1Thread_Dowrk(object sender, DoWorkEventArgs e)
{
    int percentprogress = 0;
    percentprogress++;
    Thread.Sleep(1000);
    // Search1 button event handler
    using (SqlConnection conn = new SqlConnection(connectionstring))
    {

        conn.Open();
        using (SqlDataAdapter cmd = new SqlDataAdapter(comboBox1SQL, conn))
        {
            if (comboBox1.Text.Contains("ID"))
            {
                long para = long.Parse(search1.Text);
                cmd.SelectCommand.Parameters.Add(new SqlParameter
                {
                    ParameterName = "@combo1Par",
                    Value = para,
                    SqlDbType = SqlDbType.BigInt
                });
            }

            else if (comboBox1.Text.Contains("Other Thing") || comboBox1.Text.Contains("Other Stuff"))
            {
                string para = search1.Text;
                cmd.SelectCommand.Parameters.Add(new SqlParameter
                {
                    ParameterName = "@combo1Par",
                    Value = "%" + para + "%",
                    SqlDbType = SqlDbType.NVarChar,
                });
            }
            // Clear datatable if it contains any information and then fill it
            // tab1datatable is a DataGridView
            if (tab1table != null)
                tab1table.Clear();
            cmd.Fill(tab1table);
            //tab1datatable.DataSource = tab1table;

        // A bunch of expensive calculations 
        }
    }
}

void search1Thread_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
    search1Progress.Value = e.ProgressPercentage;
}

void search1Thread_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
    tab1datatable.DataSource = tab1table;
    tab1datatable.Refresh();
    MessageBox.Show("All Done!");
}

By using a MessageBox I discovered that the code is not accessing the if comboBox1.Text.Contains() statements, which I think makes sense, because that information comes from the UI and BackgroundWorker can't directly access the UI. This would also explain why then tab1datatable and tab1table go untouched.

I think I need to use the Invoke method somewhere, but I am not sure how. I took a look at c# - Pass information to BackgroundWorker From UI during execution but it doesn't really answer my question. If Invoke is what I need, how do I implement in this code to allow it to grab information from the UI and subsequently update it with the filled DataGridView?

Why did you commend out datasource? You need to set datasource to null and then back to table to get the paint method to update control : cmd.Fill(tab1table); tab1datatable.DataSource = null; tab1datatable.DataSource = tab1table; — jdweng, Mar 25 '19 at 16:08
Because I updated it in the `search1Thread_RunWorkerCompleted` function, instead. — DrakeMurdoch, Mar 25 '19 at 16:09
Update `DataGridView` in UI thread. `Application.Current.Dispatcher.Invoke(() => // Insert data into grid));` — fhnaseer, Mar 25 '19 at 16:21
@fhnaseer it won't even access the if statements in the background thread, so I can't get to the data to fill the `DataGridView`. Would I put that into `search1Thread_Dowrk`? — DrakeMurdoch, Mar 25 '19 at 16:30
Do this. `ComboBox.CheckForIllegalCrossThreadCalls = false;` And hopefully you will be able to access it from the `BackgroundThread`. — fhnaseer, Mar 25 '19 at 16:41

score 1 · Accepted Answer · answered Mar 27 '19 at 10:58

Here's what you need to do:

    private string search1_Text = "";
    private string comboBox1_Text = "";
    private void Instantiatesearch1Thread()
    {
        search1_Text = search1.Text;
        comboBox1_Text = comboBox1.Text;
        search1Thread.WorkerReportsProgress = true;
        search1Thread.WorkerSupportsCancellation = true;
        search1Thread.ProgressChanged += search1Thread_ProgressChanged;
        search1Thread.DoWork += search1Thread_Dowrk;
        search1Thread.RunWorkerCompleted += search1Thread_RunWorkerCompleted;
    }

You basically take a copy of the data that you need before you run the background worker.

Then you just access the fields in your DoWork code:

    void search1Thread_Dowrk(object sender, DoWorkEventArgs e)
    {
        int percentprogress = 0;
        percentprogress++;
        Thread.Sleep(1000);
        // Search1 button event handler
        using (SqlConnection conn = new SqlConnection(connectionstring))
        {
            conn.Open();
            using (SqlDataAdapter cmd = new SqlDataAdapter(comboBox1SQL, conn))
            {
                if (comboBox1_Text.Contains("ID"))
                {
                    long para = long.Parse(search1_Text);
                    cmd.SelectCommand.Parameters.Add(new SqlParameter
                    {
                        ParameterName = "@combo1Par",
                        Value = para,
                        SqlDbType = SqlDbType.BigInt
                    });
                }

                else if (comboBox1_Text.Contains("Other Thing") || comboBox1_Text.Contains("Other Stuff"))
                {
                    string para = search1_Text;
                    cmd.SelectCommand.Parameters.Add(new SqlParameter
                    {
                        ParameterName = "@combo1Par",
                        Value = "%" + para + "%",
                        SqlDbType = SqlDbType.NVarChar,
                    });
                }
                // Clear datatable if it contains any information and then fill it
                // tab1datatable is a DataGridView
                if (tab1table != null)
                    tab1table.Clear();
                cmd.Fill(tab1table);
                //tab1datatable.DataSource = tab1table;

                // A bunch of expensive calculations 
            }
        }
    }

score -1 · Answer 2 · answered Mar 25 '19 at 16:43

-1

I am not sure if this is a good solution or not but this works. Set CheckForIllegalCrossThreadCalls to false when you initialize the BackgroundWorker.

private void Instantiatesearch1Thread()
{
    // Initialize other stuff
    CheckForIllegalCrossThreadCalls = false;
}

And set it to false once task is completed.

private void search1Thread_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
    // Do your work,
    CheckForIllegalCrossThreadCalls = true;
}

answered Mar 25 '19 at 16:43

fhnaseer

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No idea. I am not a winform person. I do WPF with MVVM. And in MVVM background thread can easily access UI properties. Have a look at this question. There are some details. https://stackoverflow.com/questions/142003/cross-thread-operation-not-valid-control-accessed-from-a-thread-other-than-the?rq=1 – fhnaseer Mar 25 '19 at 16:56
@DrakeMurdoch **Definitely avoid this**. You just need to set the DataSource to null, then reset it with the new DataTable. Or use a BindingSource, which will do this for you. **In the `RunWorkerCompleted` handler.** – Jimi Mar 25 '19 at 16:57
@Jimi if I do `tab1datatable.DataSource = null; tab1datatable.DataSource = tab1table; tab1datatable.Update();` in `search1Thread_RunWorkerCompleted` I get an empty table. – DrakeMurdoch Mar 25 '19 at 16:59
Find out what happens to your DataTable in the meanwhile, then. Your code never calls `ReportProgress`, thus you have somthing that you're not showing here. Do not try to hack the background Thread, you'll have more problems that you bargained for. – Jimi Mar 25 '19 at 17:12

Get information from UI with BackgroundWorker and then update UI

2 Answers2