One collection – many views

By Mirek on (tags: CollectionView, WPF, categories: code)

Let’s imagine we have a huge collection of some objects (may be our data objects) and we need to filter this collection and display only a part of its elements in different places in our WPF application. Instead of creating many different instances of sub collection we can use the benefits of collection views.

CollectionView is a wrapper around a collection that allows filtering, sorting and grouping elements without modifying the source collection. Additionally collection view provide a functionality of navigating the current item of a collection.
Ok, lets see this in practice.

We have a collection People of objects of following class (just for the purpose of this example)

   1: public class Person
   2: {
   3:     public string Name { get; set; }
   5:     public bool IsAuthor { get; set; }
   7:     public bool IsCustomer { get; set; }
   9:     public bool IsExpert { get; set; }
  10: }

filled with some dummy data. Now we want to display the original collection in one data grid, all authors, customers and experts in other separate data grids. So we put four DataGrids in main window

   2: <DataGrid x:Name="lvAll"
   3:          Grid.Row="2"
   4:          Grid.Column="0" />
   6: <DataGrid x:Name="lvAuthors"
   7:          Grid.Row="2"
   8:          Grid.Column="1"
   9:          AutoGenerateColumns="False">
  10:    <DataGrid.Columns>
  11:        <DataGridTextColumn Width="*"
  12:                            Binding="{Binding Name}"
  13:                            Header="Name"
  14:                            SortMemberPath="{Binding Name}" />
  15:    </DataGrid.Columns>
  16: </DataGrid>
  17: <DataGrid x:Name="lvCustomers"
  18:          Grid.Row="2"
  19:          Grid.Column="2"
  20:          AutoGenerateColumns="False">
  21:    <DataGrid.Columns>
  22:        <DataGridTextColumn Width="*"
  23:                            Binding="{Binding Name}"
  24:                            Header="Name"
  25:                            SortMemberPath="{Binding Name}" />
  26:    </DataGrid.Columns>
  27: </DataGrid>
  28: <DataGrid x:Name="lvExperts"
  29:          Grid.Row="2"
  30:          Grid.Column="3"
  31:          AutoGenerateColumns="False">
  32:    <DataGrid.Columns>
  33:        <DataGridTextColumn Width="*"
  34:                            Binding="{Binding Name}"
  35:                            Header="Name"
  36:                            SortMemberPath="{Binding Name}" />
  37:    </DataGrid.Columns>
  38: </DataGrid>
and now the crucial point. For the first data grid we assign (line 10) our original collection as ItemsSource (or rather its default collection view), since we want do display all not filtered elements of our collection in it. Then for each of our filtered data grids we need to create a separate collection view
   1: AuthorsView = new ListCollectionView(People);
   2: AuthorsView.Filter = (p) => { return (p as Person).IsAuthor; };
   4: CustomersView = new ListCollectionView(People);
   5: CustomersView.Filter = (p) => { return (p as Person).IsCustomer; };
   7: ExpertsView = new ListCollectionView(People);
   8: ExpertsView.Filter = (p) => { return (p as Person).IsExpert; };
  10: lvAll.ItemsSource = CollectionViewSource.GetDefaultView(People);
  11: lvAuthors.ItemsSource = AuthorsView;
  12: lvCustomers.ItemsSource = CustomersView;
  13: lvExperts.ItemsSource = ExpertsView;
For each kind of person (customer, expert and author) we create a separate ListCollectionView (derived from CollectionView) class and apply a proper filter on it. Then we assign those views as items sources to our data grids. Having that in place we can have our data grids independently sorted and filtered
Additionally, since we can edit, add and remove items in the most left data grid, we may want to update our views when we change anything. For that we have a refresh button which triggers refreshing on each view
   1: private void Button_Click(object sender, RoutedEventArgs e)
   2: {
   3:     CustomersView.Refresh();
   4:     ExpertsView.Refresh();
   5:     AuthorsView.Refresh();
   6: }
That’s it. We have four different views of the same collection without modifying the collection. Moreover when the source collection changes we only need to refresh appropriate views instead of recreating them.
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