Question

I have a task that might take a while to complete.

I have tried a simple demo but it locks up the GUI thread for some reason. I thought the task would be asynchronous and the GUI would update whilst the task is running.

Is this possible with a Task?

    private void button5_Click(object sender, EventArgs e)
    {
        var task = Task.Factory.StartNew(() => DoSomething());
        while (!task.IsCompleted)
        {
            label1.Text += ".";
            if (label1.Text.Length == 5)
                label1.Text = ".";
        }
    }

    private void DoSomething()
    {
        Thread.Sleep(5000);
    }

UPDATE: After Damien’s answer I tried the below but the CPU ramped up

        private void button5_Click(object sender, EventArgs e)
        {
            var task = Task.Factory.StartNew(() => DoSomething());
        }
        public delegate void dgUpdateLabel();

        private void UpdateLabel()
        {
            if (this.InvokeRequired)
            {
                this.BeginInvoke(new dgUpdateLabel(UpdateLabel), new object[] { });
            }
            else
            {
                label1.Text += ".";
                if (label1.Text.Length == 5)
                    label1.Text = ".";
            }
        }

        private void DoSomething()
        {
            var task = Task.Factory.StartNew(() => Sleep());
            while (!task.IsCompleted)
            {
                UpdateLabel();
            }
        }

        private void Sleep()
        {
            Thread.Sleep(5000);
        }

UPDATE2: I think the speed of trying to update the label is too fast for it to handle. If you put a Thread.Sleep(500) after the UpdateLabel method call it works as expected.

Answer 1

Updating according to our chat 🙂 :

private void Form1_Load(object sender, EventArgs e)
{
  CancellationTokenSource cts = new CancellationTokenSource();
  Task worker = new Task(() => DoSomething());
  Task ui_updater = new Task(() => UpdateGui(CancellationToken token));
  worker.Start();
  updater.Start();
  // Worker task completed, cancel GUI updater.
  worker.ContinueWith(task => cts.Cancel());
}
private void DoSomething()
{
 // Do an awful lot of work here.
}
private void UpdateGui(CancellationToken token)
{ 
  while (!token.IsCancellationRequested)
 {      
   UpdateLabel();
   Thread.Sleep(500);
 }
}
private void UpdateLabel()
{
  if (this.InvokeRequired)
  {
   this.BeginInvoke(new Action(() => UpdateLabel()), new object[] { });
  }
    else
    {
        label1.Text += ".";
        if (label1.Text.Length >= 5)
            label1.Text = ".";
    }
}