Question

I have a datagrid. A column of the datagrid is a simple <DataGridTemplateColumn> with its CellTemplate containing a <DataTemplate> which contains a <ComboBox> such as

<my:DataGrid Name="dataGridMain" AutoGenerateColumns="False">
   <my:DataGrid.Columns>
       <my:DataGridTemplateColumn Header="Food" >
           <my:DataGridTemplateColumn.CellTemplate >
               <DataTemplate>
                  <ComboBox Name="comboDataTemplate" 
                            Text="{Binding Path=Food, 
                                           Mode=TwoWay, 
                                           UpdateSourceTrigger=PropertyChanged}"
                            ItemsSource="{Binding Source={StaticResource resFoodLookups}}"
                            DisplayMemberPath="FoodName" 
                            SelectedValuePath="FoodID" IsEditable="True" />
                </DataTemplate>
           </my:DataGridTemplateColumn.CellTemplate>
       </my:DataGridTemplateColumn>
    </my:DataGrid.Columns>
</my:DataGrid>

All is working fine. Each combobox is bound to a static list due to the ItemsSource="{Binding Source={StaticResource resFoodLookups}}" statement.

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But my requirement is that this list will change from row-to-row.

That is: each time a user types a new entry in the combobox list on one row, I want to have it available in the selection on the next row.

Basically, I want to create a new list for the user each time the user inserts a new word in the combobox on any of the rows. (The combobox is editable).

Now, I can wire up the “ItemsSource=…” at run-time, but I’m only able to do this once thus the <DataTemplate> propagates the ‘same’ list to ‘all’ the comboboxes on ‘all’ the rows.

My thoughts are that I need to change the ItemsSource=… property on an object-by-object basis on each combobox that is created in memory after the DataTemplate has created them – but I have no idea how to do this.

Answer 1

What you need to do is perform 2 way data binding to your the ItemsSource, this way when the ItemSource is updated in one of the combo boxes it will auto update your original collection and therefore your other combo boxes as well.

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What I normally do is use the MVVM pattern. It is worth some research if you are not already using a particular pattern on your application.

Using it to solve your problem i would do the following:

1. Create a ViewModel (Lets call it MyViewModel) which has a collection of values called ‘MyComboBoxItems’ (It is important that you use ObservableCollection for the databinding to work)

2. When I create the Window/Control that contains your table, I also create an instance of MyViewModel and set its the Window.DataContext=myViewModelInstance

3. For your combobox binding use ItemsSource=”{Binding Path=MyComboBoxItems, Mode=TwoWay}