WPF Binding DataGridComboBoxColumn to SelectedItem of a ComboBox

Question

I am building an app in WPF (MVVM). The user is to make a selection in a ComboBox, and the choice is supposed to filter the results available in a DataGridComboBoxColumn (DGCBC) in a DataGrid.

But I am at a loss at how to bind the ComboBox SelectedItem to the DGCBC. I did manage to have the ComboBox filter the results of a second ComboBox, but that logic does not seem to transfer well to the DGCBC.

What I have tried:

My ComboBox:

<ComboBox
    DisplayMemberPath="PropertyName1"
    ItemsSource="{Binding Collection1}"
    Loaded="{s:Action NameOfMethodToPopulateComboBox}"
    SelectedItem="{Binding PropertyHolder, UpdateSourceTrigger=PropertyChanged}"/>

The PropertyHolder is ran when an item is selected in the ComboBox, and if it's not null, it runs the method that adds to the ObservableCollection which is bound to the DGCBC. It looks like this:

private ClassName _currentSelectedItem;
public ClassName CurrentSelectedItem {
    get { return this,._selectedItem; }
    set { SetAndNotify(ref this._selectedItem, value);
        if (value != null) {
           FillDataGridComboBoxColumn();
        }
    }
}

The method, FillDataGridComboBoxColumn() looks like this (abbreviated):

DataSet ds = new();
    // Code to run stored procedure
    // CurrentSelectedItem is given as parameter value

DataTable dt = new();
dt = ds.Tables[0];

MyObservableCollection.Clear();

for (int i = 0; i < dt.Rows.Count; i++) {

    DataRow dr = dt.NewRow();
    dr = dt.Rows[i];
    HolderClass holderClass = new(); // this is the class that is bound to the observablecollection
    holderClass.PropertyName = dr["PropertyName2"].ToString();
    MyObservableCollection.Add(holderClass);

This is the XAML for the DataGrid and the DataGridComboBoxColumn:

<DataGrid
    AutoGenerateColumns="False"
    ItemsSource="{Binding MyObservableCollection}">

        <DataGridComboBoxColumn
            SelectedValueBinding="{Binding PropertyName2, UpdateSourceTrigger=PropertyChanged}"
            SelectedValuePath="PropertyName2"
            DisplayMemberPath="PropertyName2"
            ItemsSource="{Binding MyObservableCollection}">
/>

</DataGrid>

When I debug, the DataGridComboBoxColumn is able to get the correct number of rows - but they're just empty placeholders; blanks. If I put a break-point in the code, I see that the collection is indeed loaded with the correct values, but they're just not showing.

I am guessing I am doing something wrong with the binding for the DGCBC.

Thank you.

Answer 1

The DataGridComboBoxColumn ItemSource had to be set as a Static Resource:

<Window.Resources>
    <CollectionViewSource x:Key="MyObservableCollection" Source="{Binding MyObservableCollection}"/>
</Window.Resources>

And then, in the XAML for the DataGridComboBoxColumn:

<DataGridComboBoxColumn
    ItemsSource="{Binding Source={StaticResource MyObservableCollection}}"
    DisplayMemberPath="Property2">
</DataGridComboBoxColumn>