Databinding issue with stopwatched elapsed

Question

I am trying to make a class that when it starts it starts a stopwatch and all the time the elapsed time is written to a local variable Elapsed which I have a Listview that databinds to. But when I use this code the Listview just displays 00:00:00.00000001 and never changes. The class' code is:

namespace project23
{
    public class ActiveEmployee
    {
        public int EmpID { get; set; }
        public string EmpName { get; set; }
        private DateTime date;
        private BackgroundWorker worker;
        public Stopwatch sw;

        public ActiveEmployee(int empID, string empName)
        {
            date = DateTime.Now;
            worker = new BackgroundWorker();
            worker.DoWork += BackgroundWork;
            worker.WorkerReportsProgress = true;

            worker.RunWorkerAsync();
        }

        private TimeSpan elapsed;
        public TimeSpan Elapsed
        {
            get { return elapsed; }
            set
            {
                elapsed = value;
                NotifyPropertyChanged("Elapsed");
            }
        }

        private void BackgroundWork(object sender, DoWorkEventArgs args)
        {
            sw = new Stopwatch();
            sw.Start();
            if(true)
            {
                Elapsed = sw.Elapsed;
            }
        }

        public event PropertyChangedEventHandler PropertyChanged;

        private void NotifyPropertyChanged(String info)
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(info));
            }
        }
    }
}

Now it works using Timers instead

using System;
using System.ComponentModel;
using System.Timers;

namespace Eksamen_Januar_2011
{
    public class ActiveEmployee : INotifyPropertyChanged
    {
        public int EmpID { get; set; }
        public string EmpName { get; set; }
        private DateTime startDate;
        private BackgroundWorker worker;
        private Timer timer;

    public ActiveEmployee(int empID, string empName)
    {
        startDate = DateTime.Now;
        worker = new BackgroundWorker();
        worker.DoWork += BackgroundWork;
        timer = new Timer(1000);
        timer.Elapsed += TimerElapsed;
        worker.RunWorkerAsync();
    }

    private TimeSpan elapsed;
    public TimeSpan Elapsed
    {
        get { return elapsed; }
        set
        {
            elapsed = value;
            NotifyPropertyChanged("Elapsed");
        }
    }

    private void BackgroundWork(object sender, DoWorkEventArgs args)
    {
        timer.Start();
    }
    private void TimerElapsed(object sender, ElapsedEventArgs e)
    {
        Elapsed = DateTime.Now - startDate;
    }
    public event PropertyChangedEventHandler PropertyChanged;

    private void NotifyPropertyChanged(String info)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(info));
        }
    }
}

}

Answer 1

You need to implement the INotifyPropertyChanged interface. Modify your class declaration to:

public class Employee : System.ComponentModel.INotifyPropertyChanged

See http://msdn.microsoft.com/en-us/library/system.componentmodel.inotifypropertychanged.aspx.

Answer 2

Data-binding and observing change relies on change-notification events; either *Changed (for property *) or INotifyPropertyChanged typically (although custom implementations are possible).

Stopwatch does not provide such; you may be better off using a Timer instead, to update the UI every so often. Just store the DateTime when you start, and whenever the timer fires calculate the offset from then to now.