Updating UI from a background thread which is called in a loop in main UI when the thread finishes

Question

I have a WinForms application that is calling a business class method that performs some heavy duty action taking about 5 seconds for each call. The main form calls this method in a loop. This loop can run from 10 times to maybe up to 10 thousand times.

The WinForms application sends a parameter to the business class and has an area to display the time taken for each method call and what the value returned by the method. How do I inform my main window and update a text area in the main winform with what the method has returned for each call?

Currently the data comes all at once after all the threads have finished. Is there a way to update the UI for all the iterations of the loop once the each call is done? I don't mind if it is done sequentially also.

The FORM

    HeavyDutyClass hd;
    public Form1()
    {
        InitializeComponent();
        hd = new HeavyDutyClass();
    }


    //BUTTON CLICK
    private void Start_Click(object sender, EventArgs e)
    {

        int filecount = 5000;  //BAD - opening 5000 threads! Any other approach?
        hd.FileProcessed += new EventHandler(hd_FileProcessed);


        var threads = new Thread[filecount];

        for (int i = 0; i < filecount; i++)
        {
            threads[i] = new Thread(() => { hd.LongRunningMethod(); });
            threads[i].Start();   
        }

    }

    //BUSINESS CLASS EVENT THAT FIRES WHEN BUSINESS METHOD COMPELTES
    void hd_FileProcessed(object sender, EventArgs e)
    {

        if (dgv.InvokeRequired)
        {
            dgv.Invoke((MethodInvoker)delegate { UpdateGrid(); });

        }
    }

    private void UpdateGrid()
    {
        dgv.Rows.Add(1);
        int i = dgv.Rows.Count;
        dgv.Rows [ i-1].Selected = true;
        dgv.FirstDisplayedScrollingRowIndex = i - 1;

    }

The business HeavyDuty class

    public event EventHandler FileProcessed;

    public HeavyDutyClass()
    {
    }

    protected virtual void OnMyEvent(EventArgs e)
    {
        if (FileProcessed != null)
        {
            FileProcessed(this, e);
        }
    }

    public bool LongRunningMethod()
    {
        for (double i = 0; i < 199990000; i++)
        {
            //time consuming loop
        }
        OnMyEvent(EventArgs.Empty);
        return true;
    }

Answer 1

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();