Suspend Databinding of Controls

Question

I have a series of controls that are databound to values that change every second or so. From time to time, I need to "pause" the controls, so that they do not update their databindings (in either direction). I then later need to "unpause" the controls, so that they can update the datasource with their values, and receive future updates from the source as normal. How do I accomplish this?

Sample Binding:

<TextBox Text="{Binding UpdateSourceTrigger=LostFocus, Mode=TwoWay, Path=myData}">

Answer 1

You don't necessarily have to suspend binding. Another, and possibly simpler, way to do this is to suspend change notification in the view model. For instance:

private HashSet<string> _ChangedProperties = new HashSet<string>();

private void OnPropertyChanged(string propertyName)
{
   if (_Suspended)
   {
      _ChangedProperties.Add(propertyName);
   }
   else
   {
      PropertyChangedEventHandler h = PropertyChanged;
      if (h != null)
      {
         h(this, new PropertyChangedEventArgs(propertyName));
      }
   }
}

private bool _Suspended;

public bool Suspended
{
   get { return _Suspended; }
   set
   {
      if (_Suspended == value)
      {
         return;
      }
      _Suspended = value;
      if (!_Suspended)
      {
         foreach (string propertyName in _ChangedProperties)
         {
            OnPropertyChanged(propertyName);
         }
         _ChangedProperties.Clear();
      }
   }
}

This will (if it's debugged and tested, which I haven't done) stop raising PropertyChanged events when Suspended is set to true, and when Suspended is set to false again it will raise the event for every property that changed while it was suspended.

This won't stop changes to bound controls from updating the view model. I submit to you that if you're letting the user edit properties on the screen at the same time that you're changing them in the background, there's something you need to take a closer look at, and it's not binding.

Answer 2

To deal with the source set the UpdateSourceTrigger to be Explicit.

<TextBox Name="myTextBox" Text="{Binding UpdateSourceTrigger=Explicit, Mode=TwoWay, Path=myData}">

Then in code behind reference a service which can deal with the actual updating as defined by your conditions.

BindingExpression be = myTextBox.GetBindingExpression(TextBox.TextProperty);
be.UpdateSource();

This will allow you to specify at which point the data goes back to the source from the target.

The target can be addressed by making a call to the same referenced service which has the knowledge on when to call the INotifyPropertyChanged.PropertyChanged event within your ViewModel.

    class Data : INotifyPropertyChanged
    {
        Manager _manager;

        public Data(Manager manager)
        {
            _manager = manager;
        }

        public event PropertyChangedEventHandler PropertyChanged;

        String _info = "Top Secret";
        public String Information
        {
            get { return _info; }
            set 
            {
                _info = value;

                if (!_manager.Paused)
                {
                    PropertyChangedEventHandler handler = PropertyChanged;
                    if (handler != null)
                        handler(this, new PropertyChangedEventArgs("Information"));
                }
            }
        }
    }