Question

I think the title for this question is probably wrong, but I’m not sure quite how to phrase it. I have a C# 4.0 (VS2010) WPF application.

This application consists of a single window with a header including the basics (logos, captions, etc) and a set of navigation buttons (back, retry, next, etc). The rest of the window is comprised of a listbox that is populated with one or more usercontrols based on what mode the app is currently in.

The way the code is currently written when the mode changes the listbox is cleared, all new user controls are added, and the buttons are set to their required state. This is fine for the initial state of each window mode but I’m having trouble deciding a good approach to update the navigation buttons as the contents of the controls change.

For example one screen is a configuration screen and there are three user controls contained within the listbox. These controls are custom classes that inherit from UserControl. Additionally they implement an interface that defines a method ‘bool Validate’ which determines if the control has been completely filled out.

This same scenario could apply to lots of other situations but this is a generic use case that is pretty straightforward to understand. When the screen initially loads the ‘Next’ button, whose visibility is controled by the parent window, is visible but disabled as the child controls can’t possibly yet be valid. At some point as the user fills out arbitrary data within one or more controls each one would return true if its Validate method was called.

At the point where all controls are valid, the next button would then become enabled. Fairly straightforward design.

The problem is each control doesn’t know what screen it is on, and this is by design. I don’t want the controls having to be aware of each other and updating a button status in the parent window. I also don’t want the parent window to run a polling thread to call Validate every second because in some cases the validation could be complex.

I’m thinking that the change event of each control within the UserControl (text boxes, radio buttons, etc) would all call a trigger a private validate event and this would set some public property on the interface or class.

f I can do that is there a way for the parent window to respond in an event-driven manner to the change of that property? I’m not looking to do this in WPF, doing this in C# code is preferable as I don’t want to get into the complexity of WPF quite yet. I’m just not sure, other than constant polling, how to tell when every control’s ‘IsValid’ property will have synchronized all to ‘true’, if that is even a good approach.

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EDIT:

Okay, here is another way to ask the question. I have a List of something (in this case a list of an interface) and want to be able to respond to a public property change on each item in the list so I can take an action when all items are (bool in this case) true. The above explains the use case, but this is a more generic version of the question.

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EDIT:

@Vincent “you might do it in an even simpler way with a custom “ValidatedChanged()” event that you can hook in the same way.”

It turns out that this is really what I was looking for. The property notification approach seems to be more for ease of use with data-bound controls. I read a lot of posts on this site about how to implement that but it really wasn’t what I wanted. I just wanted my objects to notify that an event occured, which happened to be a property change, but that is beside the point. I found documentation on implementing an event in an interface and I have it working now. Thanks for pointing me in the right direction and helping me realize what is really is that I needed.

Answer 1

So you have a ListBox which contains all your controls, and when all controls are validated, the Next button should be enabled ?
If so, when one of your control validates, you might search all sons of the ListBox to check them for validation, using VisualTreeHelper.GetChildren to get them all.
If you don’t want / can’t have a handle on the ListView, you might find it by searching up the visual tree starting from the control that just validated.
Each ‘Validated’ event of each control would be handled by a ‘CheckIfAllValidated’ event handler, and when all are validated, you could raise a ‘AllValidated’ events that would be handled by the button (and maybe some other controls as well) to enable it.

Edit : I understood that you did not want each component to know about their children, but notice that even the quite common PropertyChanged event has a ‘sender’ fields that tells who did raise the event. So any listener of a PropertyChanged on, say, the ‘validated’ property, can go up the visual tree, stop when it encounters a ListView, then search downstairs if all control that have a validated property do have this property set to true…

Edit 2 :
To be more clear about how to do it, either in your window new or on the window loaded event
or maybe on the ContentRendered Event, depending on how your controls are loaded, you
might use once that code to hook a handler to all your controls :

For Each ThisControl In MainListView. 
   Dim ThisControlType = ThisControl.GetType
   Dim ThisControlPropertyChangedEvent = ThisControlType.GetEvent("PropertyChanged")
   ' you might wanna check here if event is not null / nothing
   ThisControlPropertyChangedEvent.AddEventHandler(ThisControl, New PropertyChangedEventHandler(AddressOf APropChanged))
 Next

and you write the APropChanged somehow like that :

Public Sub APropChanged(ByVal sender As Object, ByVal e As PropertyChangedEventArgs)
If e.PropertyName = "Validated" Then
    Dim ValidatedForAll = True
    For Each ThisControl In MainListView.Items
        Dim ThisControlType = ThisControl.GetType
        Dim ThisControlValidatedProperty = ThisControlType.GetProperty("Validated")
        'you might wanna check for non null here
        If Not ThisControlValidatedProperty.GetValue(ThisControl, Nothing) Then
           ValidatedForAll = False
           Exit For
        End If
    Next
    If ValidatedForAll Then
       MessageBox.Show("Yeeppee")    ' you might send an event instead.
    End If
End If
End Sub

Edit 3 : you might do it in an even simpler way with a custom “ValidatedChanged()” event that you can hook in the same way.