Wednesday, August 1, 2007

Is WinForms DataBinding currently in progress?

I've recently been looking into WinForms DataBinding. We have an in house databinding solution that we use, but it is vary narrow in scope, so I wanted to learn how WinForms does it.

I started with an example where I have a very simple user control with 5 or 6 fields (combo boxes, text boxes). I wanted to bind these fields to data from a .NET class which has properties which exactly match the fields I'm displaying. Using WinForms databinding to accomplish this was startlingly easy. But then I hit a snag.

I've registered the ValueChanged event on all my controls (These are in house controls which implement an interface so they all have a ValueChanged. For the most part, all it does is forward the TextChanged and SelectedValueChanged events) and hooked it up to a single event handler. When this event handler fires I enable a "reset" link. Thus if the user changes any of the values, they can click reset to put the values back as they were.

The snag is that when the data binding initially loads the controls, the value changed events fire and I enable my reset link. But when its the data binding that has caused my value changed event to fire, I don't want to enabled the reset link. In other words, I need to know if the data binding caused the value changed or if a user editing the field caused the value changed.

Ideally, I'd like to be able to write something like this:

void Fields_ValueChanged( object sender, EventArgs e )
if ( !bindingSource.IsUpdatingControls )
resetLink.Enabled = true;

Unfortunately for me, nothing like this seems to exist. And even more infuriating, I can't find anyone else complaining about this on the web...

Now from what I've read I understand that if you're using data binding you're not supposed to depend on the controls. Instead you're supposed to use the object that contains your data. This is for MVC purposes apparently. This means: don't use the control's ValueChanged event. But this doesn't work in my case for 3 reasons: 1) I don't need two way binding here, so my underlying data object shouldn't even get updated. 2) To use two way binding I'd have to change the update mode to OnPropertyChanged instead of OnValidation, which I just don't want to have to do. 3) From an MVC perspective, this is View logic which should remain in the View layer and not be dependent on what update mode the underlying data binding is using.

Am I missing something huge here? Is there any way to do this? Or do I have to abandon WinForms data binding? Seems like such a silly thing to force me to write the binding code manually.

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