Question

I am using a Dispatch timer set to fire every 20 seconds in which I need to update a databound textblock via it’s propery in my view model. This is the timer code in the viewmodel:

public TestViewModel()
  {
     _dispatcherTimer = new DispatcherTimer();
     _dispatcherTimer.Interval = new TimeSpan(0, 0, 20);
     _dispatcherTimer.Tick += new EventHandler(_dispatcherTimer_Tick);
     _dispatcherTimer.Start();    
  }

void _dispatcherTimer_Tick(object sender, EventArgs e)
    {
        if(blah == blah)
        {
        _dispatcher.BeginInvoke(() => 
                      {
                           // DoneEnabled is a boolean property that my 
                           // textblock's IsEnabled property is bound to   
                           DoneEnabled = true;  
                      });
         }
    }

private bool _doneEnabled;    

    /// <summary>
    /// Gets or sets a value indicating whether [done enabled].
    /// </summary>
    /// <value>
    ///   <c>true</c> if [done enabled]; otherwise, <c>false</c>.
    /// </value>
    public bool DoneEnabled
    {
        get { return _doneEnabled; }
        set
        {
            _doneEnabled = value;
            RaisePropertyChanged("DoneEnabled");
        }
    }

The button gets enabled everywhere else when I try and do so in my viewmodel by updating this property EXCEPT in the timer’s event handler. Any idea if I’m missing something here?

Thanks.

UPDATE:

Edited the _dispatcherTimer_Tick method to the following

void _dispatcherTimer_Tick(object sender, EventArgs e)
    {
        if(blah == blah)
        {           
          // DoneEnabled is a boolean property that my 
          // textblock's IsEnabled property is bound to   
             DoneEnabled = true;  

         }
    }

Works like a charm!

Answer 1

Since you are using a DispatchTimer the method _dispatcherTimer_Tick already runs on the UI/Dispatcher thread (this is built in for convenience of use) – just do:

void _dispatcherTimer_Tick(object sender, EventArgs e)
{
    if(blah == blah)
    {
        DoneEnabled = true;  
    }
}

From MSDN:

Reasons for using a DispatcherTimer opposed to a System.Timers.Timer
are that the DispatcherTimer runs on the same thread as the Dispatcher
and a DispatcherPriority can be set on the DispatcherTimer.