将控件的 ItemsSource 作为值传递给依赖项属性

Question

I have a custom ListView Control that takes a list of ModelItems as its ItemsSource:

          <customControls:ListViewEx Name="DocumentListView"
                ItemsSource="{Binding ModelItems, Mode=OneWay}">

I also have a dependency property GridViewColumnHeaderClick.HeaderClick , the property type of which is object :

        public static readonly DependencyProperty HeaderClickProperty = DependencyProperty.RegisterAttached(
        "HeaderClick", 
        typeof(object), 
        typeof(GridViewColumnHeaderClick), 
        new UIPropertyMetadata(null, OnHeaderClickChanged));

I would like ModelItems to be passed as the value to this dependency property, and I've attempted to do as so:

            <GridView.ColumnHeaderContainerStyle>
              <Style BasedOn="{StaticResource {x:Type GridViewColumnHeader}}" TargetType="{x:Type GridViewColumnHeader}">
                <Setter Property = "misc:GridViewColumnHeaderClick.HeaderClick" 
                        Value="{Binding ModelItems}"/>
              </Style>
            </GridView.ColumnHeaderContainerStyle>

and in C#:

            ICollectionView dataView =
            CollectionViewSource.GetDefaultView(HeaderClickProperty);

However, nothing seems to happen when I click the header. I'm not sure if it's because I'm binding it incorrectly in the XAML, or something completely different.

EDIT: apologies for the lack of details, I understand this is a bit messy.

My overall aim is to run a sort function by clicking on header of the GridViewColumn. The GridView is a child of ListViewEx . When the header is clicked, I wish to bind it to the HeaderClick property and set the value as the ItemsSource of the ListView (in this case ItemsSource=ModelItems ) so I can sort it.

When clicked the function OnHeaderClickChanged is run:

        private static void OnHeaderClickChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
    {
        var headerClicked = sender as GridViewColumnHeader;
        headerClicked.MouseUp += (s, me) => HeaderClickedOnMouseUp(s, me, e.NewValue);
    }

This adds the function HeaderClickedOnMouseUp to the MouseUp event. This function is the one carries out the sorting with the ModelItems .

My issue is my lack of understanding when it comes to dependency/attached properties and how to bind it with the view. As correctly mentioned in the comments, the setter is not called at any point when I try debugging it and I'm lost as to why this is the case.

Answer 1

This is a simple sorting example which uses ascending sorting. The Attached Property Sort.IsEnabled should be set on a GridViewColumnHeader . The sorting itself is done by setting the SortDescription of the default CollectionView of the column's parent ListView.ItemsSource .

Recommended read:
Attached Properties Overview
Dependency properties overview

Data model: Person.cs

class Person
{
  public Person(string firstName, string lastName)
  {
    this.FirstName = firstName;
    this.LastName = lastName;
  }

  public string FirstName { get; set; }
  public string LastName { get; set; }
}

ViewModel.cs

class ViewModel : INotifyPropertyChanged
{
  public ViewModel()
  {
    this.Persons = new ObservableCollection<Person>()
    {
      new Person("Derek", "Zoolander"),
      new Person("Tony", "Montana"),
      new Person("The", "Dude")
    };
  }

  public ObservableCollection<Person> Persons { get; set; }
}   

The Attached property Sort : Sort.cs

class Sort : DependencyObject
{
  #region IsEnabled attached property

  public static readonly DependencyProperty IsEnabledProperty = DependencyProperty.RegisterAttached(
    "IsEnabled", typeof(bool), typeof(Sort), new PropertyMetadata(false, Sort.OnIsEnabled));

  public static void SetIsEnabled([NotNull] DependencyObject attachingElement, bool value) => attachingElement.SetValue(Sort.IsEnabledProperty, value);

  public static bool GetIsEnabled([NotNull] DependencyObject attachingElement) => (bool) attachingElement.GetValue(Sort.IsEnabledProperty);

  #endregion

  private static void OnIsEnabled(DependencyObject attachingElement, DependencyPropertyChangedEventArgs e)
  {
    bool isSortingEnabled = (bool) e.NewValue;
    if (isSortingEnabled == (bool) e.OldValue)
    {
      return;
    }

    if (attachingElement is GridViewColumnHeader columnHeader)
    {
      if (isSortingEnabled)
      {
        columnHeader.Click += Sort.SortByColumn;
      }
      else
      {
        columnHeader.Click -= Sort.SortByColumn;
      }  
    }
  }

  private static void SortByColumn(object sender, RoutedEventArgs e)
  {
    var columnHeader = sender as GridViewColumnHeader;
    PropertyPath columnSourceProperty = (columnHeader.Column.DisplayMemberBinding as Binding).Path;

    // Use an extension method to find the parent ListView 
    // by traversing the visual tree
    if (columnHeader.TryFindVisualParentElement(out ListView parentListView))
    {
      var collectionView = (CollectionView)CollectionViewSource.GetDefaultView(parentListView.ItemsSource);
      collectionView.SortDescriptions.Clear();

      // Apply sorting
      collectionView.SortDescriptions.Add(new SortDescription(columnSourceProperty.Path, ListSortDirection.Ascending));
    }
  }
}

Extension helper method to find a visual parent: Extensions.cs

public static class Extensions
{
  /// <summary>
  /// Traverses the visual tree towards the root until an element with a matching element name is found.
  /// </summary>
  /// <typeparam name="TParent">The type the visual parent must match.</typeparam>
  /// <param name="child"></param>
  /// <param name="resultElement"></param>
  /// <returns><c>true</c> when the parent visual was found otherwise <c>false</c></returns>
  public static bool TryFindVisualParentElement<TParent>(this DependencyObject child, out TParent resultElement)
    where TParent : DependencyObject
  {
    resultElement = null;

    DependencyObject parentElement = VisualTreeHelper.GetParent(child);

    if (parentElement is TParent parent)
    {
      resultElement = parent;
      return true;
    }

    return parentElement?.TryFindVisualParentElement(out resultElement) ?? false;
  }
}

Usage: MainWindow.xaml

<Window>
  <Window.DataContext>
    <ViewModel />
  </Window.DataContext>

  <ListView ItemsSource="{Binding Persons}">
    <ListView.View>
      <GridView>
        <GridViewColumn DisplayMemberBinding="{Binding FirstName}">
          <GridViewColumnHeader Sort.IsEnabled="True" Content="First Name" />
        </GridViewColumn>
        <GridViewColumn DisplayMemberBinding="{Binding LastName}">
          <GridViewColumnHeader Sort.IsEnabled="True" Content="Last Name" />
        </GridViewColumn>
      </GridView>
    </ListView.View>
  </ListView>
</Window>