Question

I am writing a very simple asynchronous helper class to go along with my project. The purpose of the class is that it allows a method to be run on a background thread. Here is the code;

    internal class AsyncHelper
    {
        private readonly Stopwatch timer = new Stopwatch();
        internal event DownloadCompleteHandler OnOperationComplete;

        internal void Start(Func func, T arg)
        {
            timer.Start();
            func.BeginInvoke(Done, func);
        }

        private void Done(IAsyncResult cookie)
        {
            timer.Stop();
            var target = (Func) cookie.AsyncState;
            InvokeCompleteEventArgs(target.EndInvoke(cookie));
        }

        private void InvokeCompleteEventArgs(T result)
        {
            var args = new EventArgs(result, null, AsyncMethod.GetEventByClass, timer.Elapsed);
            if (OnOperationComplete != null) OnOperationComplete(null, args);
        }

        #region Nested type: DownloadCompleteHandler

        internal delegate void DownloadCompleteHandler(object sender, EventArgs e);

        #endregion
    }

The result of the task is then returned through the OnOperationComplete event. The problem is that when the event is raised, its still on the background thread. I.e. if I try to run this code (below) I get a cross threading error;

txtOutput.AppendText(e.Result + Environment.NewLine);

Please advise any thoughts.

Answer 1

Use BackgroundWorker class. It essentially does the same you want.

        private BackgroundWorker _worker;

    public Form1()
    {
        InitializeComponent();
        _worker = new BackgroundWorker();
        _worker.DoWork += Worker_DoWork;
        _worker.RunWorkerCompleted += Work_Completed;
    }

    private void Work_Completed(object sender, RunWorkerCompletedEventArgs e)
    {
        txtOutput.Text = e.Result.ToString();
    }

    private void Worker_DoWork(object sender, DoWorkEventArgs e)
    {
        e.Result = "Text received from long runing operation";
    }