Question

I’ve got a simple little winforms app that performs a long running process on another thread via a TPL Task. During this long running process I’d like to update the UI (the progress bar or something). Is there a way to do this without being required to .ContinueWith()?

public partial class Form1 : Form
{
    private Task _childTask;

    public Form1()
    {
        InitializeComponent();

        Task.Factory.StartNew(() =>
        {
            // Do some work
            Thread.Sleep(1000);

            // Update the UI
            _childTask.Start();

            // Do more work
            Thread.Sleep(1000);
        });

        _childTask = new Task((antecedent) =>
        {
            Thread.Sleep(2000);
            textBox1.Text = "From child task";
        }, TaskScheduler.FromCurrentSynchronizationContext());


    }
}

Executing this code I get the ubiquitous exception:

Cross-thread operation not valid: Control ‘textBox1’ accessed from a thread other than the thread it was created on.

Answer 1

Yes, you can explicitly call BeginInvoke on the Window/Control that you want to communicate with. In your case this would look like this:

this.textBox.BeginInvoke(new Action(() =>
{
   this.textBox.Text = "From child task.";
}));