Cross Threading Exception - Using Invoke

Question

After recieving the cross thread exception error, I looked it up on the MSDN.

I tried implementing some of the code there but can't get the Callback to work.

addItemCallback d = new addItemCallback(addItem);

this is located in the addItem() method below.

I am trying to have a list of items add themselves to a listbox, eventually updating the form everytime one value is found, rather than all of them being added once the backgrounder has finished work.

private void startWork()
{        
    progressBar1.Value = 0;

    progressBar1.Maximum = 901242;

    backgroundWorker1.RunWorkerAsync();    
}

private void getList()
{
    if (pathFound)
    {
        for (int i = 0; i < numberOfPaths; i++)
        {
            Microsoft.Win32.RegistryKey mainPath = secondaryPath.OpenSubKey("application " + Convert.ToString(i));

            if (mainPath != null)
            {
                    this.addItem((string)mainPath.GetValue("Name"));
            }

            backgroundWorker1.ReportProgress(i);
        }
    }

    pathListBox.Sorted = true;
}

private void addItem(string item)
{
    if (this.pathListBox.InvokeRequired)
    {

        //addItemCallback d = new addItemCallback(addItem); 

        //not sure what this callBack is, can't get it to work, Callback isnt found.

        this.Invoke(d, new object[] { item });
    }

    else 
    {
        this.pathListBox.Items.Add(item);
    }
}

private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
    getList();
}

private void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e)
{
    progressBar1.Value = e.ProgressPercentage;
}

private void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
{
    this.progressBar1.Visible = false;
}

WORK SO FAR

Code 1. When I use the background_doWork and call a method from it, the progressbar hangs in random spots and stops responding, on closing the form i get an object exception as I've closed the form while it is still trying to do work.

Code 2. When I place all the code in the background_doWork rather than call a method from it, the progress bar will work sometimes, every second or every 3rd attempt at running the program it finishes.

What would be causing this?

-----CODE 1-----------

    public Form1()
    {
        InitializeComponent();

        start();
    }

    int number = 900000;

    public void start()
    {
        progressBar1.Value = 0;

        progressBar1.Maximum = number;

        backgroundWorker1.RunWorkerAsync();
    }

    private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
    {
        getList();
    }

    private void getList()
    {
        Microsoft.Win32.RegistryKey mainPath = Microsoft.Win32.Registry.LocalMachine.OpenSubKey(@"SOFTWARE\Wow6432Node");

        for (int i = 0; i < number; i++)
        {
            Microsoft.Win32.RegistryKey mainPath = secondaryPath.OpenSubKey("application " + Convert.ToString(i));

            if (mainPath != null)
            {
                this.addItem((string)mainPath.GetValue("Name"));
            }

            backgroundWorker1.ReportProgress(i);
        }
    }

    private void addItem(string item)
    {
        try
        {

            if (this.listBox1.InvokeRequired)
            {
                this.Invoke(new Action<string>(addItem), item);
            }

            else
            {
                this.listBox1.Items.Add(item);
            }
        }

        catch
        {
            MessageBox.Show("Error - Closed Object before it finished working.");
        }

        //this.steamGamesListBox.Sorted = true;
    }

    private void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e)
    {
        progressBar1.Value = e.ProgressPercentage;
    }

    private void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
    {
        this.progressBar1.Visible = false;
    }

------CODE 2 --------

    public Form1()
    {
        InitializeComponent();

        start();
    }

    int number = 900000;

    public void start()
    {
        progressBar1.Value = 0;

        progressBar1.Maximum = number;

        backgroundWorker1.RunWorkerAsync();
    }

    private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
    {
        Microsoft.Win32.RegistryKey steamApps64 = Microsoft.Win32.Registry.LocalMachine.OpenSubKey(@"SOFTWARE\Wow6432Node\Microsoft\Windows\CurrentVersion\Uninstall");

        for (int i = 0; i < number; i++)
        {
            Microsoft.Win32.RegistryKey steamApps = steamApps64.OpenSubKey("Steam App " + Convert.ToString(i));

            if (steamApps != null)
            {
                this.addItem((string)steamApps.GetValue("DisplayName"));
            }

            backgroundWorker1.ReportProgress(i);
        }
    }

    private void addItem(string item)
    {
        try
        {

            if (this.listBox1.InvokeRequired)
            {
                this.Invoke(new Action<string>(addItem), item);
            }

            else
            {
                this.listBox1.Items.Add(item);
            }
        }

        catch
        {
            MessageBox.Show("Error - Closed Object before it finished working.");
        }

        //this.steamGamesListBox.Sorted = true;
    }

    private void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e)
    {
        progressBar1.Value = e.ProgressPercentage;
    }

    private void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
    {
        this.progressBar1.Visible = false;
    }

Answer 1

You either need to define a custom delegate type (your addItemCallback), or simply use a generic Action delegate:

private void addItem(string item)
{
    if (this.InvokeRequired)
    {
        this.BeginInvoke(new Action<string>(addItem), item);
        return;
    }

    this.pathListBox.Items.Add(item);
}

This is usually the simplest way to do it, since you don't need to introduce additional delegate types.

Note that the object[] parameter is defined with the params keyword, so you don't need to instantiate a new object array, but rather simply pass your arguments to the method.

Answer 2

add delegate void addItemCallback(string item);