Question

Possible Duplicate:
How to update the GUI from another thread in C#?

How can I update my UI from a threaded class? Unable to access update form Controls from threads. I’d like to update my UI on the progress of each specific thread.

class MyClass
    {
        public delegate void CountChangedEventHandler(int vCount, int vIndex);
        public event CountChangedEventHandler CountChanged;

        private int count;
        private int index;

        public MyClass(int index)
        {
            this.index = index;
        }

        public int Count
        {
            get { return this.count; }
            set
            {
                this.count = value;
                if (this.CountChanged != null)
                    this.CountChanged(value, this.index);
            }
        }

        public void DoWork(object o)
        {
            for (int i = 0; i < 10000; i++)
            {
                this.Count = i;
            }
        }
    }

    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            for (int i = 0; i < 3; i++)
            {
                MyClass myCount = new MyClass(i);
                myCount.CountChanged += new MyClass.CountChangedEventHandler(UpdateUI);

                ListViewItem lvi = new ListViewItem();
                lvi.Text = "Thread #" + i.ToString();
                lvi.SubItems.Add("");
                listView1.Items.Add(lvi);

                ThreadPool.QueueUserWorkItem(new WaitCallback(myCount.DoWork));

            }
        }

        private void UpdateUI (int index, int count)
        {
            listView1.Items[index].SubItems[0].Text = count.ToString();
        }
    }

Answer 1

You need to use Invoke or BeginInvoke to marshal the UI access back to the UI thread.

I recommend using Invoke in this instance as this will stop your loop getting too far ahead of itself:

private void UpdateUI (int index, int count)
{
  Invoke( ( MethodInvoker ) (
    () => listView1.Items[index].SubItems[0].Text = count.ToString()
  ) );
}