Asynchronous WPF Commands

Answer 1

As I answered in your other question, you probably still want to bind to this synchronously and then launch the commands asynchronously. That way you avoid the problems you're having now.

Answer 2

I've been able to refine the original sample down and have some advice for anyone else running into similar situations.

First, consider if BackgroundWorker will meet the needs. I still use AsyncCommand often to get the automatic disable function, but if many things could be done with BackgroundWorker.

But by wrapping BackgroundWorker, AsyncCommand provides command like functionality with asynchronous behavior (I also have a blog entry on this topic)

public abstract class AsyncCommand : ICommand
{
 public event EventHandler CanExecuteChanged;
 public event EventHandler RunWorkerStarting;
 public event RunWorkerCompletedEventHandler RunWorkerCompleted;

 public abstract string Text { get; }
 private bool _isExecuting;
 public bool IsExecuting
 {
  get { return _isExecuting; }
  private set
  {
   _isExecuting = value;
   if (CanExecuteChanged != null)
    CanExecuteChanged(this, EventArgs.Empty);
  }
 }

 protected abstract void OnExecute(object parameter);

 public void Execute(object parameter)
 { 
  try
  { 
   onRunWorkerStarting();

   var worker = new BackgroundWorker();
   worker.DoWork += ((sender, e) => OnExecute(e.Argument));
   worker.RunWorkerCompleted += ((sender, e) => onRunWorkerCompleted(e));
   worker.RunWorkerAsync(parameter);
  }
  catch (Exception ex)
  {
   onRunWorkerCompleted(new RunWorkerCompletedEventArgs(null, ex, true));
  }
 }

 private void onRunWorkerStarting()
 {
  IsExecuting = true;
  if (RunWorkerStarting != null)
   RunWorkerStarting(this, EventArgs.Empty);
 }

 private void onRunWorkerCompleted(RunWorkerCompletedEventArgs e)
 {
  IsExecuting = false;
  if (RunWorkerCompleted != null)
   RunWorkerCompleted(this, e);
 }

 public virtual bool CanExecute(object parameter)
 {
  return !IsExecuting;
 }
}