CODEWITHSUNDEEP
c#winformsmultithreading
rememberthecant
rememberthecant

Reputation: 153

Multithreading in C# - Update Labels

So I have 3 labels and have to update all three of them at the same time using a random number until the user clicks a button that stops it.

This is what I have on my start button

private void start_Click(object sender, EventArgs e)
{
        t1 = new Thread(new ThreadStart(FirstNumber));
        t2 = new Thread(new ThreadStart(SecondNumber));
        t3 = new Thread(new ThreadStart(ThirdNumber));

        t1.Start();
        t2.Start();
        t3.Start();
}

This is what the methods that generate the random numbers look like

public void FirstNumber()
{
        int j = r.Next(0, 50);
        int k = r.Next(50, 100);
        for (int i = j; i <= k; i++)
        {
            number1.Text = i.ToString();
            Thread.Sleep(200);
        }
}

When I debug I get the following error:

Cross-thread operation not valid: Control 'number2' accessed from a thread other than the thread it was created on.

I don't understand how I am meant to create controls for each thread, so any help is appreciated.

One more thing, will the user be able to click the stop button while the labels are being updated? Or do I need to add another thread that waits for the user input?

Thanks a lot!

Upvotes: 1

Views: 1677

Answers (4)

sergeyxzc
sergeyxzc

Reputation: 615

For synchronous communication between threads in .NET is SynchronizationContext

// gui thread
var syncContext = System.Threading.SynchronizationContext.Current;

public void FirstNumber()
{
        int j = r.Next(0, 50);
        int k = r.Next(50, 100);
        for (int i = j; i <= k; i++)
        {
            // Post or Send mth
            syncContext.Post((o) => 
            {
             number1.Text = i.ToString();
            });

            Thread.Sleep(200);
        }
}

Upvotes: 0

adityaswami89
adityaswami89

Reputation: 583

What you want is parallel activity. MS gives Parallel libraries , please go through below links

http://www.codeproject.com/Articles/152765/Task-Parallel-Library-1-of-n

http://www.codeproject.com/Articles/362996/Multi-core-programming-using-Task-Parallel-Library

Upvotes: 0

cuongle
cuongle

Reputation: 75306

You need set TextBox value only on UI Thread, not other threads, so you can use Control.Invoke or Control.BeginInvoke to execute delegate on UI Thread:

 number1.BeginInvoke(new Action(() => { number1.Text = i.ToString(); }));

Upvotes: 6

Erti-Chris Eelmaa
Erti-Chris Eelmaa

Reputation: 26268

You can access UI only on UI thread. You can post things to UI thread through Dispatcher.BeginInvoke() method.

Upvotes: 1

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