using wpf datagridcomboboxcolumn's IsSynchronizedWithCurrentItem - wpf

Question

(see below for my own answer that I came up with after letting this percolate for days & days)
I am trying to achieve the following scenario in WPF.
I have a datagrid that is displaying rows of data for viewing and additional data entry. It is a new app but there is legacy data.
One particular field in the past has had data randomly entered into it. Now we want to limit that field's values to a particular list. So I'm using a DataGridComboBoxColumn. FWIW I have alternatively tried this with a DataGridTemplateColumn containing a ComboBox.
At runtime, if the existing value is not on the list, I want it to display anyway. I just cannot seem to get that to happen. While I have attempted a vast array of solutions (all failures) here is the one that is most logical as a starting point.
The list of values for the drop down are defined in a windows resource called "months".
<DataGridComboBoxColumn x:Name="frequencyCombo" MinWidth="100" Header="Frequency"
ItemsSource="{Binding Source={StaticResource months}}"
SelectedValueBinding="{Binding Path=Frequency,UpdateSourceTrigger=PropertyChanged}">
<DataGridComboBoxColumn.ElementStyle>
<Style TargetType="ComboBox">
<Setter Property="IsSynchronizedWithCurrentItem" Value="False" />
</Style>
</DataGridComboBoxColumn.ElementStyle>
</DataGridComboBoxColumn>
What is happening is that if a value is not on the list then the display is blank. I have verified at runtime that the IsSynchronizedWithCurrentItem element is indeed False. It is just not doing what I am expecting.
Perhaps I am just going down the wrong path here. Maybe I need to use a textbox in combination with the combobox. Maybe I need to write some code, not just XAML. I have spent hours trying different things and would be really appreciative of a solution. I have had a few suggestions to use this class or that control but without explanation of how to use it.
Thanks a bunch!

Answer 1

I have finally solved this.
The trick is to get rid of the comboboxcolumn and use a template that has a textbox for display and a combobox for editing. However, I still spent hours with a new problem...when making a selection in the combobox, it would modify any other rows where I had also used the combobox in the grid. Guess what solved the problem! The IsSynchronizedWithCurrentItem property that I was trying to use before. :)
<DataGridTemplateColumn x:Name="frequencyCombo" Header="Frequency">
<DataGridTemplateColumn.CellTemplate>
<DataTemplate>
<TextBlock Text="{Binding Path=Frequency}" />
</DataTemplate>
</DataGridTemplateColumn.CellTemplate>
<DataGridTemplateColumn.CellEditingTemplate>
<DataTemplate>
<ComboBox
ItemsSource="{Binding Source={StaticResource frequencyViewSource},
TargetNullValue=''}"
SelectedItem="{Binding Path=Frequency}" IsSynchronizedWithCurrentItem="False"
/>
</DataTemplate>
</DataGridTemplateColumn.CellEditingTemplate>
</DataGridTemplateColumn>
No ugly hacks. No non-usable choices hanging around at the bottom of the dropdown. No code to add those extra values and then clean them up.
I am not going to take away the "Answer" on Mark's suggestion since it enabled me to get the app into my client's hands, but this is the solution I was looking for. I found it buried in a "connect" item after hours of web searching.
Thanks for everyones help!

Answer 2

Could you please clarify what's happening here? It's unclear what the "existing value" is at runtime - if this is the field where data is being randomly entered, by limiting it does this mean you're running some sort of validation logic although you still want it to display?
Also, I'm more on the Silverlight side of things...does WPF also default to one way binding?

Answer 3

Rather than mixing the static resource and the view model property as a source for items on the list, have you tried using an ObservableCollection or CollectionViewSource in the view model? Then you could insert and remove the non-standard items at will and make them selected (or not) whenever you want. So the "normal" list would have the normal months, but when an odd one comes along, add that to the list and make it selected. Seems like it would be easier to control exclusively in the view model.

Answer 4

Why not just do something like:
//create collection
PagedCollectionView view = new PagedCollectionView(e.Result);
view.SortDescriptions.Add(
new SortDescription("Months", ListSortDirection.Ascending));
gridProducts.ItemsSource = view;
//filter collection by category
PagedCollectionView view = new PagedCollectionView(e.Result);
view.Filter = delegate(object filterObject)
{
Product product = (Product)filterObject;
return (product.CategoryName == "Legacy");
};
gridProducts.ItemsSource = view;
//create categories through grouping
PagedCollectionView view = new PagedCollectionView(e.Result);
view.GroupDescriptions.Add(new PropertyGroupDescription("Legacy"));
view.GroupDescriptions.Add(new PropertyGroupDescription("etc..."));
gridProducts.ItemsSource = view;

Answer 5

Try this:
<DataGridTemplateColumn>
<DataGridTemplateColumn.CellTemplate>
<DataTemplate>
<ComboBox ItemsSource="{Binding Months}"
Text="{Binding Value}"
IsEditable="True" />
</DataTemplate>
</DataGridTemplateColumn.CellTemplate>
</DataGridTemplateColumn>