Question

Not being experienced in multi-threaded programming or technologies, I would like to ask this question as a way to focus a design to accomplish the following requirements for relatively long running jobs (between 4 and 10 seconds) that are launched in real time by some user action:

1. After the job is initiated and until it completes:
   * Show some indeterminate progress indicator (ie, spinning ball, progress bar)
   * Show a running count of the elapsed number of seconds as part of a status update
2. Use an MVVM design with the status and notion of IsBusy being data bound properties in some INPC view model class
3. Unit testable

I started down the path of trying to use a BackgroundWorker that is either subclassed or otherwise encapsulated, but found myself getting tripped up on how to synchronize the notion of counting the elapsed seconds on a timer thread while another thread is doing the work.

Design ideas that might lead to more focused programming questions much appreciated!

Cheers,
Berryl

Answer 1

Use a DispatcherTimer to update a ElapsedTime property in your view model. This is called from the GUI thread so you can directly bind to the property. Use a BackgroundWorker to perform your thread task.

public class ViewModel : INotifyPropertyChanged  
{
  public DateTime ElapsedTime {get; private set;}
  public bool IsRunning {get; private set;}

  private BackgroundWorker worker = new BackgroundWorker();
  private DateTime startTime;
  private DispatcherTimer t = new DispatcherTimer();

  public ViewModel()
  {
    t.Interval = 500; 
    t.Tick += (ox,ex) => UpdateTime();
    worker.DoWork += YourMethodHere;
    worker.RunWorkerCompleted += (ox,ex)=> {
      IsRunning = false;
      if (PropertyChanged != null)
       PropertyChanged(this, new PropertyChangedEventArgs("IsRunning"));
    };
  }

  public void UpdateTime()
  {
     ElapsedTime=startTime.Subtract(DateTime.Now);
     if (PropertyChanged != null)
       PropertyChanged(this, new PropertyChangedEventArgs("ElapsedTime"));
  }

  public void Start()
  {
    startTime=DateTime.Now;
    worker.RunWorkerAsync();
    IsRunning = true;
    if (PropertyChanged != null)
     PropertyChanged(this, new PropertyChangedEventArgs("IsRunning"));
  }

}

You can bind the progress bar GUI element to a bool property in your view model which is updated when started and finishing your background task (use the RunWorkerComplete event).