WinForms Multithreading – How to Update UI from a Different Thread

asynchronousmultithreadingwinforms

I know this question has been asked before, but I feel it wasn't asked correctly.

I have an intensive operation and I'd like the UI to remain responsive. I've read a few posts that say Background worker is the best way to go, however, I think this assumes you have the source code to the intensive task.

I have a library that I have no source code for, the only way I can check on the progress is to attach to events that get fired and get information that way.

The example I saw on the MSDN site assumed one would have the source.

I know how to get progress (which is a percentage value) by attaching to events, but how do I get that value back to the UI?

Best Answer

The following answer is based on my gut feeling and have not actually done it a test with third party libs.

Call your third party lib code as usual you call in a simple background (not BackGroundWorker) thread.
Attach the library components' events to normal event handlers in your code (meant to update UI).

In the event handler code should look like this:

private void EventHandler(object sender, DirtyEventArgs e)
{
    if (myControl.InvokeRequired)
        myControl.Invoke(new MethodInvoker(MethodToUpdateUI), e);
    else
        MethodToUpdateUI(e);
}

private void MethodToUpdateUI(object obj) 
{
    // Update UI
}

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WinForms – Updating UI from Background Thread in Loop

Add a Winforms Project, Drop a Label Control on the Form , Copy-Paste this code and Hit F5

[EDIT]: Updated with the business class comment from the user

NB: My form class is named Form3. You may have to change your Program.cs or vice-versa.

using System.ComponentModel;
using System.Windows.Forms;

namespace WindowsFormsApplication1
{
    public class BusinessClass
    {
        public int MyFunction(int input)
        {
            return input+10;
        }
    }

    public partial class Form3 : Form
    {
        private BackgroundWorker _worker;
        BusinessClass _biz = new BusinessClass();
        public Form3()
        {
            InitializeComponent();
            InitWorker();
        }

        private void InitWorker()
        {
            if (_worker != null)
            {
                _worker.Dispose();
            }

            _worker = new BackgroundWorker
            {
                WorkerReportsProgress = true,
                WorkerSupportsCancellation = true
            };
            _worker.DoWork += DoWork;
            _worker.RunWorkerCompleted += RunWorkerCompleted;
            _worker.ProgressChanged += ProgressChanged;
            _worker.RunWorkerAsync();
        }


        void DoWork(object sender, DoWorkEventArgs e)
        {
            int highestPercentageReached = 0;
            if (_worker.CancellationPending)
            {
                e.Cancel = true;
            }
            else
            {
                double i = 0.0d;
                int junk = 0;
                for (i = 0; i <= 199990000; i++)
                {
                    int result = _biz.MyFunction(junk);
                    junk++;

                    // Report progress as a percentage of the total task.
                    var percentComplete = (int)(i / 199990000 * 100);
                    if (percentComplete > highestPercentageReached)
                    {
                        highestPercentageReached = percentComplete;
                        // note I can pass the business class result also and display the same in the LABEL  
                        _worker.ReportProgress(percentComplete, result);
                        _worker.CancelAsync();
                    }
                }

            }
        }

        void RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
        {
            if (e.Cancelled)
            {
                // Display some message to the user that task has been
                // cancelled
            }
            else if (e.Error != null)
            {
                // Do something with the error
            }
        }

        void ProgressChanged(object sender, ProgressChangedEventArgs e)
        {
            label1.Text =  string.Format("Result {0}: Percent {1}",e.UserState, e.ProgressPercentage);
        }
    }
}

With this you can achieve Cancel functionality also very easily. Observe that during initialisation, I set the WorkerSupportsCancellation = true & then I check for _worker.CancellationPending in the DoWork. So, if you want to cancel the process by a Cancel Button click, then you will write this code in the button handler- _worker.CancelAsync();

Best Answer

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