How to update UI from async routine without BeginInvoke or Invoke [duplicate]

Question

I saw many code that they use BeginInvoke to update UI from another thread. is it possible to update UI from async function without BeginInvoke ?

private async void button1_Click(object sender, EventArgs e)
        {
            button1.Enabled = false;
            var count = 0;

            await Task.Run(() =>
            {
                for (var i = 0; i <= 500; i++)
                {
                    count = i;
                    BeginInvoke((Action)(() =>
                    {
                        label1.Text = i.ToString();

                    }));
                   Thread.Sleep(100);
                }
            });

            label1.Text = @"Counter " + count;
            button1.Enabled = true;
        }

Edit

see the below code i have got from a link which show that without BeginInvoke we can update UI when using task.run.

private readonly SynchronizationContext synchronizationContext;
private DateTime previousTime = DateTime.Now;

public Form1()
{
    InitializeComponent();
    synchronizationContext = SynchronizationContext.Current;
}

private async void button1_Click(object sender, EventArgs e)
{
    button1.Enabled = false;
    var count = 0;

    await Task.Run(() =>
    {
        for (var i = 0; i <= 5000000; i++)
        {
            UpdateUI(i);
            count = i;
        }
    });

    label1.Text = @"Counter " + count;
    button1.Enabled = true;
}

public void UpdateUI(int value)
{
    var timeNow = DateTime.Now;

    if ((DateTime.Now - previousTime).Milliseconds <= 50) return;

    synchronizationContext.Post(new SendOrPostCallback(o =>
    {
        label1.Text = @"Counter " + (int)o;
    }), value);             

    previousTime = timeNow;
}

So tell me synchronizationContext and BeginInvoke both are same ? which one should use to update UI from different thread ? which one is most efficient ?

please guide me i am new in async/await & Task usage.

create a static webmethod and call it with ajax in timeinterval. — Murat Oğuzhan
– Murat Oğuzhan, Commented Dec 22, 2018 at 19:17
Either asynchronous code with Invoke or synchronous code without Invoke. You cannot modify UI objects from another thread. — Camilo Terevinto
– Camilo Terevinto, Commented Dec 22, 2018 at 19:20
Why do you try to avoid (Begin)Invoke? These methods were designed specially to make easier an interprocess communications. I think, you can take a look on the ConfigureAwait method of the Task class - it deals with execution context and can be helpful for you. — Miamy
– Miamy, Commented Dec 22, 2018 at 19:24
@HenkHolterman You're right, the comment wasn't the best. The OP is explicitly using multi-threading though — Camilo Terevinto
– Camilo Terevinto, Commented Dec 22, 2018 at 20:21

Alexander Petrov · Accepted Answer · 2018-12-22 20:08:15Z

2

Use Progress class.

private async void button1_Click(object sender, EventArgs e)
{
    button1.Enabled = false;
    var count = 0;

    // The Progress<T> constructor captures UI context,
    // so the lambda will be run on the UI thread.
    IProgress<int> progress = new Progress<int>(value =>
    {
        label1.Text = value.ToString();
    });

    await Task.Run(() =>
    {
        for (var i = 0; i <= 500; i++)
        {
            count = i;
            progress.Report(i);
            Thread.Sleep(100);
        }
    });

    label1.Text = @"Counter " + count;
    button1.Enabled = true;
}

answered Dec 22, 2018 at 20:08

Alexander Petrov

14.4k2 gold badges23 silver badges56 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Henk Holterman Over a year ago

You still have a Task.Run to execute Thread.Sleep()

Alexander Petrov Over a year ago

@HenkHolterman - I think the OP does CPU-bound calculations in real code instead of Sleep.

Henk Holterman Over a year ago

Maybe. Maybe not.

Mist Over a year ago

please see my edit part and guide me again for my new sample code.

Henk Holterman · Accepted Answer · 2018-12-22 20:29:47Z

2

The thing to avoid is Task.Run(). And when you manage that, you won't need [Begin]Invoke().

private async void button1_Click(object sender, EventArgs e)
{
    button1.Enabled = false;
    var count = 0;

    for (var i = 0; i <= 500; i++)
    {
        count = i;          
        label1.Text = i.ToString();
        await Task.Delay(100);         // do async I/O or Task.Run() here
    }    
}

edited Dec 22, 2018 at 20:29

answered Dec 22, 2018 at 20:21

Henk Holterman

276k33 gold badges353 silver badges540 bronze badges

1 Comment

Mist Over a year ago

please see my edit part and guide me again for my new sample code.

Fabio · Accepted Answer · 2018-12-22 20:27:53Z

It will depend on what kind of asynchronous method you are using. For example asynchronous method which access external resources (database, webservices, file system etc.) will be executed on the same thread and you don't need to bother with Invoke.

private async Task UpdateDatabase()
{
    using (var connection = new SqlConnection(connectionString))
    using (var command = connection.CreateCommand())
    {
        command.CommandText = "SELECT Id FROM Table";
        await connection.OpenAsync();
        using (var reader = await command.ExecuteReaderAsync())
        {
            var rowsCount = 0;
            // Since execution will happen on same thread 
            // you will be able update UI controls.
            Label1.Text = $"Rows: {rowsCount}";

            while (await reader.ReadAsync())
            {
                rowsCount ++;
                Label1.Text = $"Rows: {rowsCount}";
            }
        }
    }
}

private async void button1_Click(object sender, EventArgs e)
{
    button1.Enabled = false;

    await UpdateDatabase();

    button1.Enabled = true;
}

For methods which are executed on other threads, best practice is to execute those methods without "touching" UI controls, instead return result of the method back to main thread and then update UI.

For your particular case where you want update UI with "progress" information, then you can use BackgroundWorker class or already mentioned Progress class.

please see my edit part and guide me again for my new sample code.

Collectives™ on Stack Overflow

How to update UI from async routine without BeginInvoke or Invoke [duplicate]

Edit

3 Answers 3

4 Comments

1 Comment

1 Comment

Linked

Hot Network Questions

Collectives™ on Stack Overflow

Edit

3 Answers 3

4 Comments

1 Comment

1 Comment

Linked

Related