[WinRT] Toggle selection of a list item on long press

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As you probably know, the standard way to select or deselect an item in a WinRT list control is to slide it up or down a little. Although I rather like this gesture, it’s not very intuitive for users unfamiliar with Modern UI. And it gets even more confusing, because my previous statement wasn’t perfectly accurate: in fact, you have to slide the item perpendicularly to the panning direction. In a GridView, which (by default) pans horizontally, that means up or down; but in a ListView, which pans vertically, you have to slide the item left or right. If an application uses both kinds of lists, it becomes very confusing for the user.

Sure, in the default style, there is visual hint (a discrete “slide down” animation with a gray tick symbol) when the user presses and holds an item, but it’s not always enough for everyone to understand. Many people (e.g. Android users) are used to do a “long press” gesture (known as “Hold” in Modern UI terminology) to select items. So, in order to make your app easier to use for a larger number of people, you might want to enable selection by long press.

A simple way to do it is to create an attached property which, when set to true, subscribes to the Holding event of an item, and toggles the IsSelected property when the event occurs. Here’s a possible implementation:

using Windows.UI.Input;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Controls.Primitives;
using Windows.UI.Xaml.Input;

namespace TestSelectOnHold
{
    public static class SelectorItemEx
    {
        public static bool GetToggleSelectedOnHold(SelectorItem item)
        {
            return (bool)item.GetValue(ToggleSelectedOnHoldProperty);
        }

        public static void SetToggleSelectedOnHold(SelectorItem item, bool value)
        {
            item.SetValue(ToggleSelectedOnHoldProperty, value);
        }

        public static readonly DependencyProperty ToggleSelectedOnHoldProperty =
            DependencyProperty.RegisterAttached(
              "ToggleSelectedOnHold",
              typeof(bool),
              typeof(SelectorItemEx),
              new PropertyMetadata(
                false,
                ToggleSelectedOnHoldChanged));

        private static void ToggleSelectedOnHoldChanged(DependencyObject o, DependencyPropertyChangedEventArgs e)
        {
            var item = o as SelectorItem;
            if (item == null)
                return;

            var oldValue = (bool)e.OldValue;
            var newValue = (bool)e.NewValue;

            if (oldValue && !newValue)
            {
                item.Holding -= Item_Holding;
            }
            else if (newValue && !oldValue)
            {
                item.Holding += Item_Holding;
            }
        }

        private static void Item_Holding(object sender, HoldingRoutedEventArgs e)
        {
            var item = sender as SelectorItem;
            if (item == null)
                return;

            if (e.HoldingState == HoldingState.Started)
                item.IsSelected = !item.IsSelected;
        }
    }
}

You can then set this property in the ItemContainerStyle of the list control

<GridView.ItemContainerStyle>
    <Style TargetType="GridViewItem">
        ...
        <Setter Property="local:SelectorItemEx.ToggleSelectedOnHold" Value="False" />
    </Style>
</GridView.ItemContainerStyle>

And you’re done : the user can now select items by holding them. The standard gesture still works, of course, so users who know it can still use it.

Note that this feature could also have been implemented as a full-fledged Behavior. There are two reasons why I didn’t choose this approach:

  • Behaviors are not natively supported in WinRT (though they can be added as a Nuget package)
  • Behaviors don’t play well with styles, because Interaction.Behaviors is a collection, and you can’t add items to a collection from a style. A possible workaround would be to create an IsEnabled attached property that would add the behavior to the item when set to true, but then we would end up with a solution almost identical to the one described above, only more complex…

[WPF] Automatically sort a GridView (continued)

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A few months ago, I wrote a post where I explained how to automatically sort a GridView when a column header is clicked. I had mentioned a possible improvement : add a sort glyph in the column header to show which column is sorted. In today’s post, I present a new version of the GridViewSort class, which displays the sort glyph.

GridViewSort sample with sort glyph

GridViewSort sample with sort glyph

To achieve this result, I used an Adorner : this is a component which allows to draw over existing UI elements, on an independant rendering layer.

The new version of the GridViewSort class can be used as before, in that case the grid displays default sort glyphs. These default glyphs are not particularly good-looking, so if you have some artistic skills you can provide you own images, as shown in the code below :

        <ListView ItemsSource="{Binding Persons}"
                  IsSynchronizedWithCurrentItem="True"
                  util:GridViewSort.AutoSort="True"
                  util:GridViewSort.SortGlyphAscending="/Images/up.png"
                  util:GridViewSort.SortGlyphDescending="/Images/down.png">

It is also possible to disable the sort glyphs, by setting the ShowSortGlyph attached property to false :

        <ListView ItemsSource="{Binding Persons}"
                  IsSynchronizedWithCurrentItem="True"
                  util:GridViewSort.AutoSort="True"
                  util:GridViewSort.ShowSortGlyph="False">

Note that in the current version, the sort glyph is only displayed when using the automatic sort mode (AutoSort = true). The case of a custom sort using the Command property is not handled yet.

Here is the complete code of the new version of the class :

using System.ComponentModel;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Documents;

namespace Wpf.Util
{
    public class GridViewSort
    {
        #region Public attached properties

        public static ICommand GetCommand(DependencyObject obj)
        {
            return (ICommand)obj.GetValue(CommandProperty);
        }

        public static void SetCommand(DependencyObject obj, ICommand value)
        {
            obj.SetValue(CommandProperty, value);
        }

        // Using a DependencyProperty as the backing store for Command.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty CommandProperty =
            DependencyProperty.RegisterAttached(
                "Command",
                typeof(ICommand),
                typeof(GridViewSort),
                new UIPropertyMetadata(
                    null,
                    (o, e) =>
                    {
                        ItemsControl listView = o as ItemsControl;
                        if (listView != null)
                        {
                            if (!GetAutoSort(listView)) // Don't change click handler if AutoSort enabled
                            {
                                if (e.OldValue != null && e.NewValue == null)
                                {
                                    listView.RemoveHandler(GridViewColumnHeader.ClickEvent, new RoutedEventHandler(ColumnHeader_Click));
                                }
                                if (e.OldValue == null && e.NewValue != null)
                                {
                                    listView.AddHandler(GridViewColumnHeader.ClickEvent, new RoutedEventHandler(ColumnHeader_Click));
                                }
                            }
                        }
                    }
                )
            );

        public static bool GetAutoSort(DependencyObject obj)
        {
            return (bool)obj.GetValue(AutoSortProperty);
        }

        public static void SetAutoSort(DependencyObject obj, bool value)
        {
            obj.SetValue(AutoSortProperty, value);
        }

        // Using a DependencyProperty as the backing store for AutoSort.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty AutoSortProperty =
            DependencyProperty.RegisterAttached(
                "AutoSort",
                typeof(bool),
                typeof(GridViewSort),
                new UIPropertyMetadata(
                    false,
                    (o, e) =>
                    {
                        ListView listView = o as ListView;
                        if (listView != null)
                        {
                            if (GetCommand(listView) == null) // Don't change click handler if a command is set
                            {
                                bool oldValue = (bool)e.OldValue;
                                bool newValue = (bool)e.NewValue;
                                if (oldValue && !newValue)
                                {
                                    listView.RemoveHandler(GridViewColumnHeader.ClickEvent, new RoutedEventHandler(ColumnHeader_Click));
                                }
                                if (!oldValue && newValue)
                                {
                                    listView.AddHandler(GridViewColumnHeader.ClickEvent, new RoutedEventHandler(ColumnHeader_Click));
                                }
                            }
                        }
                    }
                )
            );

        public static string GetPropertyName(DependencyObject obj)
        {
            return (string)obj.GetValue(PropertyNameProperty);
        }

        public static void SetPropertyName(DependencyObject obj, string value)
        {
            obj.SetValue(PropertyNameProperty, value);
        }

        // Using a DependencyProperty as the backing store for PropertyName.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty PropertyNameProperty =
            DependencyProperty.RegisterAttached(
                "PropertyName",
                typeof(string),
                typeof(GridViewSort),
                new UIPropertyMetadata(null)
            );

        public static bool GetShowSortGlyph(DependencyObject obj)
        {
            return (bool)obj.GetValue(ShowSortGlyphProperty);
        }

        public static void SetShowSortGlyph(DependencyObject obj, bool value)
        {
            obj.SetValue(ShowSortGlyphProperty, value);
        }

        // Using a DependencyProperty as the backing store for ShowSortGlyph.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty ShowSortGlyphProperty =
            DependencyProperty.RegisterAttached("ShowSortGlyph", typeof(bool), typeof(GridViewSort), new UIPropertyMetadata(true));

        public static ImageSource GetSortGlyphAscending(DependencyObject obj)
        {
            return (ImageSource)obj.GetValue(SortGlyphAscendingProperty);
        }

        public static void SetSortGlyphAscending(DependencyObject obj, ImageSource value)
        {
            obj.SetValue(SortGlyphAscendingProperty, value);
        }

        // Using a DependencyProperty as the backing store for SortGlyphAscending.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty SortGlyphAscendingProperty =
            DependencyProperty.RegisterAttached("SortGlyphAscending", typeof(ImageSource), typeof(GridViewSort), new UIPropertyMetadata(null));

        public static ImageSource GetSortGlyphDescending(DependencyObject obj)
        {
            return (ImageSource)obj.GetValue(SortGlyphDescendingProperty);
        }

        public static void SetSortGlyphDescending(DependencyObject obj, ImageSource value)
        {
            obj.SetValue(SortGlyphDescendingProperty, value);
        }

        // Using a DependencyProperty as the backing store for SortGlyphDescending.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty SortGlyphDescendingProperty =
            DependencyProperty.RegisterAttached("SortGlyphDescending", typeof(ImageSource), typeof(GridViewSort), new UIPropertyMetadata(null));

        #endregion

        #region Private attached properties

        private static GridViewColumnHeader GetSortedColumnHeader(DependencyObject obj)
        {
            return (GridViewColumnHeader)obj.GetValue(SortedColumnHeaderProperty);
        }

        private static void SetSortedColumnHeader(DependencyObject obj, GridViewColumnHeader value)
        {
            obj.SetValue(SortedColumnHeaderProperty, value);
        }

        // Using a DependencyProperty as the backing store for SortedColumn.  This enables animation, styling, binding, etc...
        private static readonly DependencyProperty SortedColumnHeaderProperty =
            DependencyProperty.RegisterAttached("SortedColumnHeader", typeof(GridViewColumnHeader), typeof(GridViewSort), new UIPropertyMetadata(null));

        #endregion

        #region Column header click event handler

        private static void ColumnHeader_Click(object sender, RoutedEventArgs e)
        {
            GridViewColumnHeader headerClicked = e.OriginalSource as GridViewColumnHeader;
            if (headerClicked != null && headerClicked.Column != null)
            {
                string propertyName = GetPropertyName(headerClicked.Column);
                if (!string.IsNullOrEmpty(propertyName))
                {
                    ListView listView = GetAncestor<ListView>(headerClicked);
                    if (listView != null)
                    {
                        ICommand command = GetCommand(listView);
                        if (command != null)
                        {
                            if (command.CanExecute(propertyName))
                            {
                                command.Execute(propertyName);
                            }
                        }
                        else if (GetAutoSort(listView))
                        {
                            ApplySort(listView.Items, propertyName, listView, headerClicked);
                        }
                    }
                }
            }
        }

        #endregion

        #region Helper methods

        public static T GetAncestor<T>(DependencyObject reference) where T : DependencyObject
        {
            DependencyObject parent = VisualTreeHelper.GetParent(reference);
            while (!(parent is T))
            {
                parent = VisualTreeHelper.GetParent(parent);
            }
            if (parent != null)
                return (T)parent;
            else
                return null;
        }

        public static void ApplySort(ICollectionView view, string propertyName, ListView listView, GridViewColumnHeader sortedColumnHeader)
        {
            ListSortDirection direction = ListSortDirection.Ascending;
            if (view.SortDescriptions.Count > 0)
            {
                SortDescription currentSort = view.SortDescriptions[0];
                if (currentSort.PropertyName == propertyName)
                {
                    if (currentSort.Direction == ListSortDirection.Ascending)
                        direction = ListSortDirection.Descending;
                    else
                        direction = ListSortDirection.Ascending;
                }
                view.SortDescriptions.Clear();

                GridViewColumnHeader currentSortedColumnHeader = GetSortedColumnHeader(listView);
                if (currentSortedColumnHeader != null)
                {
                    RemoveSortGlyph(currentSortedColumnHeader);
                }
            }
            if (!string.IsNullOrEmpty(propertyName))
            {
                view.SortDescriptions.Add(new SortDescription(propertyName, direction));
                if (GetShowSortGlyph(listView))
                    AddSortGlyph(
                        sortedColumnHeader,
                        direction,
                        direction == ListSortDirection.Ascending ? GetSortGlyphAscending(listView) : GetSortGlyphDescending(listView));
                SetSortedColumnHeader(listView, sortedColumnHeader);
            }
        }

        private static void AddSortGlyph(GridViewColumnHeader columnHeader, ListSortDirection direction, ImageSource sortGlyph)
        {
            AdornerLayer adornerLayer = AdornerLayer.GetAdornerLayer(columnHeader);
            adornerLayer.Add(
                new SortGlyphAdorner(
                    columnHeader,
                    direction,
                    sortGlyph
                    ));
        }

        private static void RemoveSortGlyph(GridViewColumnHeader columnHeader)
        {
            AdornerLayer adornerLayer = AdornerLayer.GetAdornerLayer(columnHeader);
            Adorner[] adorners = adornerLayer.GetAdorners(columnHeader);
            if (adorners != null)
            {
                foreach (Adorner adorner in adorners)
                {
                    if (adorner is SortGlyphAdorner)
                        adornerLayer.Remove(adorner);
                }
            }
        }

        #endregion

        #region SortGlyphAdorner nested class

        private class SortGlyphAdorner : Adorner
        {
            private GridViewColumnHeader _columnHeader;
            private ListSortDirection _direction;
            private ImageSource _sortGlyph;

            public SortGlyphAdorner(GridViewColumnHeader columnHeader, ListSortDirection direction, ImageSource sortGlyph)
                : base(columnHeader)
            {
                _columnHeader = columnHeader;
                _direction = direction;
                _sortGlyph = sortGlyph;
            }

            private Geometry GetDefaultGlyph()
            {
                double x1 = _columnHeader.ActualWidth - 13;
                double x2 = x1 + 10;
                double x3 = x1 + 5;
                double y1 = _columnHeader.ActualHeight / 2 - 3;
                double y2 = y1 + 5;

                if (_direction == ListSortDirection.Ascending)
                {
                    double tmp = y1;
                    y1 = y2;
                    y2 = tmp;
                }

                PathSegmentCollection pathSegmentCollection = new PathSegmentCollection();
                pathSegmentCollection.Add(new LineSegment(new Point(x2, y1), true));
                pathSegmentCollection.Add(new LineSegment(new Point(x3, y2), true));

                PathFigure pathFigure = new PathFigure(
                    new Point(x1, y1),
                    pathSegmentCollection,
                    true);

                PathFigureCollection pathFigureCollection = new PathFigureCollection();
                pathFigureCollection.Add(pathFigure);

                PathGeometry pathGeometry = new PathGeometry(pathFigureCollection);
                return pathGeometry;
            }

            protected override void OnRender(DrawingContext drawingContext)
            {
                base.OnRender(drawingContext);

                if (_sortGlyph != null)
                {
                    double x = _columnHeader.ActualWidth - 13;
                    double y = _columnHeader.ActualHeight / 2 - 5;
                    Rect rect = new Rect(x, y, 10, 10);
                    drawingContext.DrawImage(_sortGlyph, rect);
                }
                else
                {
                    drawingContext.DrawGeometry(Brushes.LightGray, new Pen(Brushes.Gray, 1.0), GetDefaultGlyph());
                }
            }
        }

        #endregion
    }
}

I hope you’ll find that useful :)

Update: uploaded example project to demonstrate how to use the code

[WPF] Automatically sort a GridView when a column header is clicked

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It’s quite simple, in WPF, to present data in a grid, thanks to the GridView class. If you want to sort it, however, it gets a little harder… With the DataGridView in Windows Forms, it was “automagic” : when the user clicked a column header, the grid was automatically sorted. To achieve the same behavior in WPF, you need to get your hands dirty… The method recommended by Microsoft is described in this article ; it is based on the Click event of the GridViewColumnHeader class. In my view, this approach has two major drawbacks :

  • The sorting must be done in code-behind, something we usually want to avoid if the application is designed according to the MVVM pattern. It also makes the code harder to reuse.
  • This method assumes that the text of the column header is also the name of the property to use as the sort criteria, which isn’t always true, far from it… We could use the DisplayMemberBinding of the column, but it’s not always set (for instance if a CellTemplate is defined instead).

After spending a long time trying to find a flexible and elegant approach, I came up with an interesting solution. It consists of a class with a few attached properties that can be set in XAML.

This class can be used as follows :

    <ListView ItemsSource="{Binding Persons}"
          IsSynchronizedWithCurrentItem="True"
          util:GridViewSort.AutoSort="True">
        <ListView.View>
            <GridView>
                <GridView.Columns>
                    <GridViewColumn Header="Name"
                                    DisplayMemberBinding="{Binding Name}"
                                    util:GridViewSort.PropertyName="Name"/>
                    <GridViewColumn Header="First name"
                                    DisplayMemberBinding="{Binding FirstName}"
                                    util:GridViewSort.PropertyName="FirstName"/>
                    <GridViewColumn Header="Date of birth"
                                    DisplayMemberBinding="{Binding DateOfBirth}"
                                    util:GridViewSort.PropertyName="DateOfBirth"/>
                </GridView.Columns>
            </GridView>
        </ListView.View>
    </ListView>

The GridViewSort.AutoSort property enables automatic sorting for the ListView. The GridViewSort.PropertyName property, defined for each column, indicates the property to use as the sort criteria. There is no extra code to write. A click on a column header triggers the sorting on this column ; if the ListView is already sorted on this column, the sort order is reversed.

In case you need to handle the sorting manually, I also added a GridViewSort.Command attached property. When used with the MVVM pattern, this property allows you to bind to a command declared in the ViewModel :

    <ListView ItemsSource="{Binding Persons}"
          IsSynchronizedWithCurrentItem="True"
          util:GridViewSort.Command="{Binding SortCommand}">
    ...

The sort command takes as parameter the name of the property to use as the sort criteria.

Note : if both the Command and AutoSort properties are set, Command has priority. AutoSort is ignored.

Here is the full code of the GridViewSort class :

using System.ComponentModel;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Input;
using System.Windows.Media;

namespace Wpf.Util
{
    public class GridViewSort
    {
        #region Attached properties

        public static ICommand GetCommand(DependencyObject obj)
        {
            return (ICommand)obj.GetValue(CommandProperty);
        }

        public static void SetCommand(DependencyObject obj, ICommand value)
        {
            obj.SetValue(CommandProperty, value);
        }

        // Using a DependencyProperty as the backing store for Command.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty CommandProperty =
            DependencyProperty.RegisterAttached(
                "Command",
                typeof(ICommand),
                typeof(GridViewSort),
                new UIPropertyMetadata(
                    null,
                    (o, e) =>
                    {
                        ItemsControl listView = o as ItemsControl;
                        if (listView != null)
                        {
                            if (!GetAutoSort(listView)) // Don't change click handler if AutoSort enabled
                            {
                                if (e.OldValue != null && e.NewValue == null)
                                {
                                    listView.RemoveHandler(GridViewColumnHeader.ClickEvent, new RoutedEventHandler(ColumnHeader_Click));
                                }
                                if (e.OldValue == null && e.NewValue != null)
                                {
                                    listView.AddHandler(GridViewColumnHeader.ClickEvent, new RoutedEventHandler(ColumnHeader_Click));
                                }
                            }
                        }
                    }
                )
            );

        public static bool GetAutoSort(DependencyObject obj)
        {
            return (bool)obj.GetValue(AutoSortProperty);
        }

        public static void SetAutoSort(DependencyObject obj, bool value)
        {
            obj.SetValue(AutoSortProperty, value);
        }

        // Using a DependencyProperty as the backing store for AutoSort.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty AutoSortProperty =
            DependencyProperty.RegisterAttached(
                "AutoSort",
                typeof(bool),
                typeof(GridViewSort),
                new UIPropertyMetadata(
                    false,
                    (o, e) =>
                    {
                        ListView listView = o as ListView;
                        if (listView != null)
                        {
                            if (GetCommand(listView) == null) // Don't change click handler if a command is set
                            {
                                bool oldValue = (bool)e.OldValue;
                                bool newValue = (bool)e.NewValue;
                                if (oldValue && !newValue)
                                {
                                    listView.RemoveHandler(GridViewColumnHeader.ClickEvent, new RoutedEventHandler(ColumnHeader_Click));
                                }
                                if (!oldValue && newValue)
                                {
                                    listView.AddHandler(GridViewColumnHeader.ClickEvent, new RoutedEventHandler(ColumnHeader_Click));
                                }
                            }
                        }
                    }
                )
            );

        public static string GetPropertyName(DependencyObject obj)
        {
            return (string)obj.GetValue(PropertyNameProperty);
        }

        public static void SetPropertyName(DependencyObject obj, string value)
        {
            obj.SetValue(PropertyNameProperty, value);
        }

        // Using a DependencyProperty as the backing store for PropertyName.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty PropertyNameProperty =
            DependencyProperty.RegisterAttached(
                "PropertyName",
                typeof(string),
                typeof(GridViewSort),
                new UIPropertyMetadata(null)
            );

        #endregion

        #region Column header click event handler

        private static void ColumnHeader_Click(object sender, RoutedEventArgs e)
        {
            GridViewColumnHeader headerClicked = e.OriginalSource as GridViewColumnHeader;
            if (headerClicked != null)
            {
                string propertyName = GetPropertyName(headerClicked.Column);
                if (!string.IsNullOrEmpty(propertyName))
                {
                    ListView listView = GetAncestor<ListView>(headerClicked);
                    if (listView != null)
                    {
                        ICommand command = GetCommand(listView);
                        if (command != null)
                        {
                            if (command.CanExecute(propertyName))
                            {
                                command.Execute(propertyName);
                            }
                        }
                        else if (GetAutoSort(listView))
                        {
                            ApplySort(listView.Items, propertyName);
                        }
                    }
                }
            }
        }

        #endregion

        #region Helper methods

        public static T GetAncestor<T>(DependencyObject reference) where T : DependencyObject
        {
            DependencyObject parent = VisualTreeHelper.GetParent(reference);
            while (!(parent is T))
            {
                parent = VisualTreeHelper.GetParent(parent);
            }
            if (parent != null)
                return (T)parent;
            else
                return null;
        }

        public static void ApplySort(ICollectionView view, string propertyName)
        {
            ListSortDirection direction = ListSortDirection.Ascending;
            if (view.SortDescriptions.Count > 0)
            {
                SortDescription currentSort = view.SortDescriptions[0];
                if (currentSort.PropertyName == propertyName)
                {
                    if (currentSort.Direction == ListSortDirection.Ascending)
                        direction = ListSortDirection.Descending;
                    else
                        direction = ListSortDirection.Ascending;
                }
                view.SortDescriptions.Clear();
            }
            if (!string.IsNullOrEmpty(propertyName))
            {
                view.SortDescriptions.Add(new SortDescription(propertyName, direction));
            }
        }

        #endregion
    }
}

Of course, this class could probably be improved… for instance, we could add an arrow glyph on the sorted column (maybe by using an Adorner). Maybe I’ll do that someday… meanwhile, please feel free to use it ;)

Update : A new version that displays the sort glyph in the sorted column is now available in this blog post.

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