Comments by hardover (Top 20 by date)

I understand that the binding is triggered when the list is assigned to the property; and that any subsequent changes will not be noticed. In this particular case, however, I am only using the List<> internally in the control. I AM using an ObservableCollection<> for the presentation and updating of the interface.

After going through ComboBox example, I see that you have assumed I needed to be educated on the use of ObservableCollection/INotifyPropertyChanged/…; I do understand these things. While I appreciate your time to offer this information, it is not related to the question I have raised here.
I have solved the problem. See solution posted.

Thank you for looking at my issue. I will certainly study what you have presented here as soon as I can; most likely over the weekend. Your note at the beginning, however, must mean more that it seems. My sample solution proves that List<> binds to a dependency property without issue when the control is used stand-alone. Would you expound on your point there for me when you can? Thank you.

Gerry, I think I see why you might think I don't have properties. Maybe I should have shown a lot more code here even while being encouraged to minimize it. My bad.
If you are still inclined to help, please take a look at my github repo to see all of the code for the solution.

just a classification item (observable)
public int TagID
public string Name
public string Description

I hope what I think is not what your meant. I'll just accept the comment as an eloquent, meaning, idiomatic I was not aware of.

Thank you that appears to be exactly what I needed. Great help!

I implemented your update in your first response code that I had working. It works as advertised. The differences in what you are doing here and what I have are (1) the base class for the control is Label, where mine is UserControl, (2) and used the UserControl partial class structure to have XAML to work with in the UC. Yours works as I had expected mine to work. Do you think these differences contribute to my problem? There are bindings being created in mine, but the lists are empty when used in the DataGrid?

OK. Thanks for input.

@Graeme_Grant: Thank you for you effort here, but what you are doing here misses my problem. As I said
"The UC here is trivial and does nothing meaningful. But eventually I want a UC that does. It will need to take a bound List<t> and use it. That is why this demo tries to bind a List."

I have checked my bindings. I DO want to do this with a usercontrol.

"Notice that the UC works as planned when it is used on the MainWindow but does not when used in the DataGrid."

Can we just focus on why it fails in the DataGridRow?

The solution code can be found at: https://github.com/hardoverton/BindingTest

@salty06: Sorry I don't understand your point. This example is just a proof of concept for using a UC in a DataGridRowColumn. I need to understand why it works on the MainWindow and not in the DataGridTemplateColumn. Any ideas?

Tags is a collection in every row of the DataEntries collection. The tags collection is a list of selected tags from a larger domain of alltags. alltags are handled inside the usercontrol. Tags is used to set the selections for the listview of the UC

Thank you. I see all of your points. So the Tags collection does exist in the viewmodel as a collection object DataEntry in the collection DataEntries. How should I make a reference to that?

Also, the first two TextColumns are using the standard binding reference to properties of DataEntry and working fine.

In most of what I have tried, there is no binding failure noted. I do know that SelectedTags DP is not bound only when the UC is used on the DataGrid. That is why I didn't include the UC code because I felt it would be too much and distracting.

The one thing I keep thinking of is a number of mentions that a DataGridTemplateColumn does not appear in the Visual Tree. I assume this is in reference to using a relative source reference. But I don't know what to do with that info.

Dave K, what is the best way to get a description and the code so you can see it? I have a .RAR file with the VS solution and in is a doc the describes intent and results. I don't see a way to attach a file to the question.

Thank you for your response. I realize more detail is required. I will soon post a simplified example of what I am seeing. I would appreciate our input at that time.

This is a good recommendation. Thank you. It is squarely in the "should have thought of that" category.
I implemented it and it left me with only a one-line call for each event handler in the View code-behind. This allows the move to one instance of the common code which is now in the static class.