Updating Winforms UI in real time while waiting for a Parallel.ForEach

Question

The below code does not work in 'real time'. The intention is, when the button is clicked, validate a set of data on the background thread. I cannot allow true 'submission' until all of the data is validated, but I do want the textbox to update in real time.

Instead, the textbox gets updated with the odd numbers, all at once.

I imagine what is happening is that the task.Wait is blocking the observable since I am observing on the main thread, but I cannot see a way around this as I need to update on the main thread.

(Obviously this is just a proof of concept)

Somewhat related note - is this code guaranteed to threadsafe? Thanks.

private Subject<int> _subject; 
    public Form1()
    {
        InitializeComponent();
    }

    private int sleep = 2000;
    private int i = 0;
    private void LongRunningValidation(int num)
    {
        if (num % 2 == 0) return;

        Thread.Sleep(sleep * (i++));

        _subject.OnNext(num);
    }


    private ConcurrentBag<int> _bag;
    private void simpleButton1_Click(object sender, EventArgs e)
    {
        _subject = new Subject<int>();
        _subject.SubscribeOn(Scheduler.TaskPool).ObserveOn(SynchronizationContext.Current).Synchronize().Subscribe(UpdateTextBox);

        _bag = new ConcurrentBag<int>() { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };

        if(Validate())
        {
            //submit
        }
    }

    private bool Validate()
    {
        var task = Task.Factory.StartNew(StartValidationAsync);

        task.Wait();

        return true;
    }

    private void StartValidationAsync()
    {
        Parallel.ForEach(_bag, LongRunningValidation);
    }

    private void UpdateTextBox(int i)
    {
        textEdit1.Text = textEdit1.Text + "," + i;

    }
}

Answer 1

Your Validate method not async and as you say block main thread. Try use events:

public delegate void ValidatedHandler(bool validate);
public event ValidatedHandler Validated;

private void Validate()
    {
        var task = Task.Factory.StartNew(StartValidationAsync);

        if (Validated != null)
           Validated(true);
    }

And subscribe on event:

private void simpleButton1_Click(object sender, EventArgs e)
{
    _subject = new Subject<int>();
     _subject.SubscribeOn(Scheduler.TaskPool).ObserveOn(SynchronizationContext.Current).Synchronize().Subscribe(UpdateTextBox);

_bag = new ConcurrentBag<int>() { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };

this.Validated += OnValidated;
}


public void OnValidated(bool validate)
{
        if(validate)
        {
            //submit
        }
}

Answer 2

Windows Forms does not automatically update the UI, even if you are running a background thread. Try calling Update() on whatever you want to update.