WPF master-detail input

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C#

WPF

I have a master-detail user interface. Optionally, the user should be able to populate some of the fields with default values.
So I say

void button1_Click(object sender, RoutedEventArgs e)
       {
       textBox1.Text = "6545" // this is fine
           listView1.Items.Add(new { name = "test" , value = "fifty" }); // this throws an exception
       }

Exception is:

Operation is not valid while ItemsSource is in use. Access and modify elements with ItemsControl.ItemsSource instead.


????? Why can't I mimic in code the input of data via the GUI?

============

Relevant portions of the code-behind are:

private void Window_Loaded(object sender, RoutedEventArgs e) {

        this.PostData = db.Posts;

        MasterViewSource = (CollectionViewSource)this.FindResource("MasterView");
            DetailViewSource = (CollectionViewSource)this.FindResource("DetailView");
        MasterView = (BindingListCollectionView)this.MasterViewSource.View;
            MasterView.CurrentChanged += new EventHandler(MasterView_CurrentChanged);
            DetailView = (BindingListCollectionView)this.DetailViewSource.View;
        //.................///

    }

----------

My xaml has


<CollectionViewSource x:Key="MasterView" />
  <CollectionViewSource Source="{Binding Source={StaticResource MasterView}, Path='PostDetails'}" x:Key="DetailView" />

  <!--  .................... -->

 <ListView Name="listView1" IsSynchronizedWithCurrentItem="True" ItemsSource="{Binding Source={StaticResource DetailView}}">
     <!--  ............. -->
    <ListView.View>
        <GridView>
            <!--  .............. -->
            <GridViewColumn>
                            <GridViewColumn.CellTemplate>
                                    <DataTemplate>
                                            <ComboBox ItemsSource="{Binding Source={StaticResource NameLookup}}"SelectedValue="{Binding Path=AccountName}" DisplayMemberPath="name"                                         SelectedValuePath="name" />
                                         </DataTemplate>
                </GridViewColumn.CellTemplate>
                        </GridViewColumn>
                 </GridView>
         </ListView.View>
 </ListView>

-------


Thanks