C# - Updating windows forms elements from thread

Question

I am currently creating a program to back up laptops to a USB stick. I have created a class from which I call methods. I then start the actual backup via a separate thread. At the moment I'm trying to change a textbox and a progress bar via this thread. However, it always only shows the first change immediately and the other progress only when the program has run through. I have tried several solutions from the internet but nothing has worked so far. Maybe someone has a solution here.

    backup sales_backup = new backup();

    //Start Backup Button
    private void backup_button_Click(object sender, EventArgs e)
    {
        Thread backupprocess = new Thread(new 
        ThreadStart(sales_backup.backup_start));
        backupprocess.Start();
    }

    //Backup Function
        public void backup_start()
        {
            files_to_copy = 0;
            files_copied = 0;

            var principalForm = System.Windows.Forms.Application.OpenForms.OfType<Form1>().FirstOrDefault();

            if (principalForm.drive_selector.SelectedItem != null)
            {
                //Set Parameters
                principalForm.backup_button.Visible = false;
                error_copy = false;
                error_message = "";
                device_removed = false;

                //Fill variables
                string temp = principalForm.drive_selector.SelectedItem.ToString();
                temp = regex_matching_return_match(temp, @"[A-Z,a-z](:\\)");
                backup_device = temp;

                //Set Backup device size
                for (int i = 0; i < backup_devices_list.Count; i++)
                {
                    if (backup_devices_list[i].backup_device_name == temp)
                    {
                        backup_device_size = backup_devices_list[i].device_size;
                        file_system = backup_devices_list[i].file_system;
                        double temp_free = calculate_GB(backup_devices_list[i].device_free_space.ToString());
                        device_free_space = temp_free;
                        break;
                    }
                }

                //If no device is initialized
                if (backup_device == null || backup_device_size == 0)
                {
                    write_to_textbox(get_create_usb_instance_error(), "red");
                }
                else //If select ist successfull
                {
                    //Get Backup size
                    get_size();
                    if (backup_size < device_free_space)
                    {
                        backup_path_target = backup_device + "\\Backup\\";
                        Directory.CreateDirectory(backup_path_target);

                        //Get file count
                        get_file_count();

                        //Create Copy job
                        for (int i = 0; i < backup_path_source.Length; i++)
                        {
                            string backup_path_s = backup_path_source[i] + "\\";
                            string backup_path_t = backup_path_target + backup_path_target_folders[i] + "\\";
                            copy_function(backup_path_s, backup_path_t);
                            int progress = return_progress();
                            TextBox test = principalForm.textBox2;
                            ProgressBar progress_bar = principalForm.progressBar1;
                            //Delegate Textbox
                            if (test.InvokeRequired)
                            {
                                test.Invoke(new Action(() => test.Text = "Copying: " + backup_path_t));
                            }
                            else
                            {
                                test.Text = "Copying: " + backup_path_t;
                            }
                            //Delegate Progressbar
                            if (progress_bar.InvokeRequired)
                            {
                                test.Invoke(new Action(() => progress_bar.Value = progress));
                            }
                            else
                            {
                                progress_bar.Value = progress;
                            }
                        }

You can't update the UI from a background thread. You *don't* need `Invoke` either, if you use `async/await` and the `Process` class to report progress to other threads — Panagiotis Kanavos, Feb 05 '19 at 10:43
If you use `Task.Run` and `async/await` you won't have to use `Invoke().`. Invoke itself *blocks* if the UI thread is busy. You should separate UI from file processing code too - there's no need to access the main form like this when you can pass drives etc as method parameters — Panagiotis Kanavos, Feb 05 '19 at 11:08

score 0 · Answer 1 · answered Feb 05 '19 at 10:39

0

Make sure you are doing the update from the correct thread. GUI can only be updated from its own thread. More here.

answered Feb 05 '19 at 10:39

Pati K

129
2
11

score 0 · Answer 2 · answered Feb 05 '19 at 11:07

I couldn't test this, but it should at least help you get there:

private void InvokeIfRequired<C>(C control, Action<C> action) where C : Control
{
    if (control.InvokeRequired)
    {
        control.Invoke((Action)(() => action(control)));
    }
    else
    {
        action(control);
    }
}

private void backup_button_Click(object sender, EventArgs e)
{
    var principalForm = System.Windows.Forms.Application.OpenForms.OfType<Form1>().FirstOrDefault();
    if (principalForm.drive_selector.SelectedItem != null)
    {
        principalForm.backup_button.Visible = false;

        string temp = principalForm.drive_selector.SelectedItem.ToString();

        TextBox test = principalForm.textBox2;
        ProgressBar progress_bar = principalForm.progressBar1;

        Action<string> updateTest = t => this.InvokeIfRequired<TextBox>(test, c => c.Text = t);
        Action<int> updateProgress = v => this.InvokeIfRequired<ProgressBar>(progress_bar, c => c.Value = v);

        Thread backupprocess = new Thread(new ThreadStart(() => sales_backup.backup_start(temp, updateTest, updateProgress)));
        backupprocess.Start();
    }
}

//Backup Function
public void backup_start(string temp, Action<string> updateTest, Action<int> updateProgress)
{
    files_to_copy = 0;
    files_copied = 0;

    //Set Parameters

    error_copy = false;
    error_message = "";
    device_removed = false;

    //Fill variables
    temp = regex_matching_return_match(temp, @"[A-Z,a-z](:\\)");
    backup_device = temp;

    //Set Backup device size
    for (int i = 0; i < backup_devices_list.Count; i++)
    {
        if (backup_devices_list[i].backup_device_name == temp)
        {
            backup_device_size = backup_devices_list[i].device_size;
            file_system = backup_devices_list[i].file_system;
            double temp_free = calculate_GB(backup_devices_list[i].device_free_space.ToString());
            device_free_space = temp_free;
            break;
        }
    }

    //If no device is initialized
    if (backup_device == null || backup_device_size == 0)
    {
        write_to_textbox(get_create_usb_instance_error(), "red");
    }
    else //If select ist successfull
    {
        //Get Backup size
        get_size();
        if (backup_size < device_free_space)
        {
            backup_path_target = backup_device + "\\Backup\\";
            Directory.CreateDirectory(backup_path_target);

            //Get file count
            get_file_count();

            //Create Copy job
            for (int i = 0; i < backup_path_source.Length; i++)
            {
                string backup_path_s = backup_path_source[i] + "\\";
                string backup_path_t = backup_path_target + backup_path_target_folders[i] + "\\";
                copy_function(backup_path_s, backup_path_t);
                int progress = return_progress();

                //Delegate Textbox
                updateTest("Copying: " + backup_path_t);

                //Delegate Progressbar
                updateProgress(progress);
            }
        }
    }
}

score -1 · Answer 3 · answered Feb 05 '19 at 10:43

-1

Have you tried using progress_bar.Invoke((MethodInvoker)(() => progress_bar.Value = progress));

answered Feb 05 '19 at 10:43

Carl Kevin Garcia

1
1

This isn't an answer. It should be deleted. Please earn the 50 rep points to post comments. – Enigmativity Feb 05 '19 at 10:46
Changing the delegate type won't change what gets invoked. The code could be `progress_bar.Invoke(() => progress_bar.Value = progress);`. – Panagiotis Kanavos Feb 05 '19 at 10:47

C# - Updating windows forms elements from thread

3 Answers3