WPF MVVM: how to bind GridViewColumn to ViewModel-

Question

In my View I got a ListView bound to a CollectionView in my ViewModel, for example like this:

<ListView ItemsSource="{Binding MyCollection}" IsSynchronizedWithCurrentItem="true">
  <ListView.View>
    <GridView>
      <GridViewColumn Header="Title" DisplayMemberBinding="{Binding Path=Title}"/>
      <GridViewColumn Header="Name" DisplayMemberBinding="{Binding Path=Name}"/>
      <GridViewColumn Header="Phone" DisplayMemberBinding="{Binding Path=Phone}"/>
      <GridViewColumn Header="E-mail" DisplayMemberBinding="{Binding Path=EMail}"/>
    </GridView>
  </ListView.View>
</ListView>

Right now these GridViewColumns are fixed, but I'd like to be able to change them from the ViewModel. I'd guess I'll have to bind the GridViewColumn-collection to something in the ViewModel, but what, and how?
The ViewModel does know nothing of WPF, so I got no clue how to achieve this in MVVM.

any help here?

Answer 1

I took Thomas Levesque's excellent solution and modified it to remove the static collection of GridViews and also add the ability to set a column width and string format, so thought I'd share my code.

Modified attached property class:

public static class GridViewColumnCollection
{
    public static readonly DependencyProperty ColumnCollectionBehaviourProperty =
        DependencyProperty.RegisterAttached("ColumnCollectionBehaviour", typeof(GridViewColumnCollectionBehaviour), typeof(GridViewColumnCollection), new UIPropertyMetadata(null));

    public static readonly DependencyProperty ColumnsSourceProperty =
        DependencyProperty.RegisterAttached("ColumnsSource", typeof(object), typeof(GridViewColumnCollection), new UIPropertyMetadata(null, GridViewColumnCollection.ColumnsSourceChanged));

    public static readonly DependencyProperty DisplayMemberFormatMemberProperty =
        DependencyProperty.RegisterAttached("DisplayMemberFormatMember", typeof(string), typeof(GridViewColumnCollection), new UIPropertyMetadata(null, GridViewColumnCollection.DisplayMemberFormatMemberChanged));

    public static readonly DependencyProperty DisplayMemberMemberProperty =
        DependencyProperty.RegisterAttached("DisplayMemberMember", typeof(string), typeof(GridViewColumnCollection), new UIPropertyMetadata(null, GridViewColumnCollection.DisplayMemberMemberChanged));

    public static readonly DependencyProperty HeaderTextMemberProperty =
        DependencyProperty.RegisterAttached("HeaderTextMember", typeof(string), typeof(GridViewColumnCollection), new UIPropertyMetadata(null, GridViewColumnCollection.HeaderTextMemberChanged));

    public static readonly DependencyProperty WidthMemberProperty =
        DependencyProperty.RegisterAttached("WidthMember", typeof(string), typeof(GridViewColumnCollection), new UIPropertyMetadata(null, GridViewColumnCollection.WidthMemberChanged));

    [AttachedPropertyBrowsableForType(typeof(GridView))]
    public static GridViewColumnCollectionBehaviour GetColumnCollectionBehaviour(DependencyObject obj)
    {
        return (GridViewColumnCollectionBehaviour)obj.GetValue(ColumnCollectionBehaviourProperty);
    }

    public static void SetColumnCollectionBehaviour(DependencyObject obj, GridViewColumnCollectionBehaviour value)
    {
        obj.SetValue(ColumnCollectionBehaviourProperty, value);
    }

    [AttachedPropertyBrowsableForType(typeof(GridView))]
    public static object GetColumnsSource(DependencyObject obj)
    {
        return (object)obj.GetValue(ColumnsSourceProperty);
    }

    public static void SetColumnsSource(DependencyObject obj, object value)
    {
        obj.SetValue(ColumnsSourceProperty, value);
    }

    [AttachedPropertyBrowsableForType(typeof(GridView))]
    public static string GetDisplayMemberFormatMember(DependencyObject obj)
    {
        return (string)obj.GetValue(DisplayMemberFormatMemberProperty);
    }

    public static void SetDisplayMemberFormatMember(DependencyObject obj, string value)
    {
        obj.SetValue(DisplayMemberFormatMemberProperty, value);
    }

    [AttachedPropertyBrowsableForType(typeof(GridView))]
    public static string GetDisplayMemberMember(DependencyObject obj)
    {
        return (string)obj.GetValue(DisplayMemberMemberProperty);
    }

    public static void SetDisplayMemberMember(DependencyObject obj, string value)
    {
        obj.SetValue(DisplayMemberMemberProperty, value);
    }

    [AttachedPropertyBrowsableForType(typeof(GridView))]
    public static string GetHeaderTextMember(DependencyObject obj)
    {
        return (string)obj.GetValue(HeaderTextMemberProperty);
    }

    public static void SetHeaderTextMember(DependencyObject obj, string value)
    {
        obj.SetValue(HeaderTextMemberProperty, value);
    }

    [AttachedPropertyBrowsableForType(typeof(GridView))]
    public static string GetWidthMember(DependencyObject obj)
    {
        return (string)obj.GetValue(WidthMemberProperty);
    }

    public static void SetWidthMember(DependencyObject obj, string value)
    {
        obj.SetValue(WidthMemberProperty, value);
    }

    private static void ColumnsSourceChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
    {
        GridViewColumnCollection.GetOrCreateColumnCollectionBehaviour(sender).ColumnsSource = e.NewValue;
    }

    private static void DisplayMemberFormatMemberChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
    {
        GridViewColumnCollection.GetOrCreateColumnCollectionBehaviour(sender).DisplayMemberFormatMember = e.NewValue as string;
    }

    private static void DisplayMemberMemberChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
    {
        GridViewColumnCollection.GetOrCreateColumnCollectionBehaviour(sender).DisplayMemberMember = e.NewValue as string;
    }

    private static void HeaderTextMemberChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
    {
        GridViewColumnCollection.GetOrCreateColumnCollectionBehaviour(sender).HeaderTextMember = e.NewValue as string;
    }

    private static void WidthMemberChanged(DependencyObject sender, DependencyPropertyChangedEventArgs e)
    {
        GridViewColumnCollection.GetOrCreateColumnCollectionBehaviour(sender).WidthMember = e.NewValue as string;
    }

    private static GridViewColumnCollectionBehaviour GetOrCreateColumnCollectionBehaviour(DependencyObject source)
    {
        GridViewColumnCollectionBehaviour behaviour = GetColumnCollectionBehaviour(source);

        if (behaviour == null)
        {
            GridView typedSource = source as GridView;

            if (typedSource == null)
            {
                throw new Exception("This property can only be set on controls deriving GridView");
            }

            behaviour = new GridViewColumnCollectionBehaviour(typedSource);

            SetColumnCollectionBehaviour(typedSource, behaviour);
        }

        return behaviour;
    }
}

Behaviour (this is stored against each GridView and obviates the need to store the collection-GridView mappings centrally):

public class GridViewColumnCollectionBehaviour
{
    private object columnsSource;
    private GridView gridView;

    public GridViewColumnCollectionBehaviour(GridView gridView)
    {
        this.gridView = gridView;
    }

    public object ColumnsSource
    {
        get { return this.columnsSource; }
        set
        {
            object oldValue = this.columnsSource;
            this.columnsSource = value;
            this.ColumnsSourceChanged(oldValue, this.columnsSource);
        }
    }

    public string DisplayMemberFormatMember { get; set; }

    public string DisplayMemberMember { get; set; }

    public string HeaderTextMember { get; set; }

    public string WidthMember { get; set; }

    private void AddHandlers(ICollectionView collectionView)
    {
        collectionView.CollectionChanged += this.ColumnsSource_CollectionChanged;
    }

    private void ColumnsSource_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
    {
        ICollectionView view = sender as ICollectionView;

        if (this.gridView == null)
        {
            return;
        }

        switch (e.Action)
        {
            case NotifyCollectionChangedAction.Add:
                for (int i = 0; i < e.NewItems.Count; i++)
                {
                    GridViewColumn column = CreateColumn(e.NewItems[i]);
                    gridView.Columns.Insert(e.NewStartingIndex + i, column);
                }
                break;
            case NotifyCollectionChangedAction.Move:
                List<GridViewColumn> columns = new List<GridViewColumn>();

                for (int i = 0; i < e.OldItems.Count; i++)
                {
                    GridViewColumn column = gridView.Columns[e.OldStartingIndex + i];
                    columns.Add(column);
                }

                for (int i = 0; i < e.NewItems.Count; i++)
                {
                    GridViewColumn column = columns[i];
                    gridView.Columns.Insert(e.NewStartingIndex + i, column);
                }
                break;
            case NotifyCollectionChangedAction.Remove:
                for (int i = 0; i < e.OldItems.Count; i++)
                {
                    gridView.Columns.RemoveAt(e.OldStartingIndex);
                }
                break;
            case NotifyCollectionChangedAction.Replace:
                for (int i = 0; i < e.NewItems.Count; i++)
                {
                    GridViewColumn column = CreateColumn(e.NewItems[i]);

                    gridView.Columns[e.NewStartingIndex + i] = column;
                }
                break;
            case NotifyCollectionChangedAction.Reset:
                gridView.Columns.Clear();
                CreateColumns(sender as ICollectionView);
                break;
            default:
                break;
        }
    }

    private void ColumnsSourceChanged(object oldValue, object newValue)
    {
        if (this.gridView != null)
        {
            gridView.Columns.Clear();

            if (oldValue != null)
            {
                ICollectionView view = CollectionViewSource.GetDefaultView(oldValue);

                if (view != null)
                {
                    this.RemoveHandlers(view);
                }
            }

            if (newValue != null)
            {
                ICollectionView view = CollectionViewSource.GetDefaultView(newValue);

                if (view != null)
                {
                    this.AddHandlers(view);

                    this.CreateColumns(view);
                }
            }
        }
    }

    private GridViewColumn CreateColumn(object columnSource)
    {
        GridViewColumn column = new GridViewColumn();

        if (!string.IsNullOrEmpty(this.HeaderTextMember))
        {
            column.Header = GetPropertyValue(columnSource, this.HeaderTextMember);
        }

        if (!string.IsNullOrEmpty(this.DisplayMemberMember))
        {
            string propertyName = GetPropertyValue(columnSource, this.DisplayMemberMember) as string;

            string format = null;

            if (!string.IsNullOrEmpty(this.DisplayMemberFormatMember))
            {
                format = GetPropertyValue(columnSource, this.DisplayMemberFormatMember) as string;
            }

            if (string.IsNullOrEmpty(format))
            {
                format = "{0}";
            }

            column.DisplayMemberBinding = new Binding(propertyName) { StringFormat = format };
        }

        if (!string.IsNullOrEmpty(this.WidthMember))
        {
            double width = (double)GetPropertyValue(columnSource, this.WidthMember);
            column.Width = width;
        }

        return column;
    }

    private void CreateColumns(ICollectionView collectionView)
    {
        foreach (object item in collectionView)
        {
            GridViewColumn column = this.CreateColumn(item);

            this.gridView.Columns.Add(column);
        }
    }

    private object GetPropertyValue(object obj, string propertyName)
    {
        object returnVal = null;

        if (obj != null)
        {
            PropertyInfo prop = obj.GetType().GetProperty(propertyName);

            if (prop != null)
            {
                returnVal = prop.GetValue(obj, null);
            }
        }

        return returnVal;
    }

    private void RemoveHandlers(ICollectionView collectionView)
    {
        collectionView.CollectionChanged -= this.ColumnsSource_CollectionChanged;
    }
}

Answer 2

I think this code would cause some memory leak issues; As your class GridViewColumns described, you've defined a static dictionary "_gridViewsByColumnsSource" in which contains the gridviews and their columns source references; so this is a strong reference to the added gridviews and columns source; Because this dictionary is static, it seems that there's a static reference "point" to the gridviews and columns source data all the time, if the screen in which the gridview defined closed, the gridview cannot be collected by GC if GC is started; As more and more similar screens opened, more and more gridviews and its columns source data cannot be collected, there'll be memory leak at the end.

Answer 3

The Columns property is not a dependency property, so you can't bind it. However, it might be possible to create an attached property that you could bind to a collection in your ViewModel. This attached property would then create the columns for you.

---

UPDATE

OK, here's a basic implementation...

Attached properties

using System.Collections.Generic;
using System.Collections.Specialized;
using System.ComponentModel;
using System.Reflection;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;

namespace TestPadWPF
{
    public static class GridViewColumns
    {
        [AttachedPropertyBrowsableForType(typeof(GridView))]
        public static object GetColumnsSource(DependencyObject obj)
        {
            return (object)obj.GetValue(ColumnsSourceProperty);
        }

        public static void SetColumnsSource(DependencyObject obj, object value)
        {
            obj.SetValue(ColumnsSourceProperty, value);
        }

        // Using a DependencyProperty as the backing store for ColumnsSource.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty ColumnsSourceProperty =
            DependencyProperty.RegisterAttached(
                "ColumnsSource",
                typeof(object),
                typeof(GridViewColumns),
                new UIPropertyMetadata(
                    null,
                    ColumnsSourceChanged));


        [AttachedPropertyBrowsableForType(typeof(GridView))]
        public static string GetHeaderTextMember(DependencyObject obj)
        {
            return (string)obj.GetValue(HeaderTextMemberProperty);
        }

        public static void SetHeaderTextMember(DependencyObject obj, string value)
        {
            obj.SetValue(HeaderTextMemberProperty, value);
        }

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


        [AttachedPropertyBrowsableForType(typeof(GridView))]
        public static string GetDisplayMemberMember(DependencyObject obj)
        {
            return (string)obj.GetValue(DisplayMemberMemberProperty);
        }

        public static void SetDisplayMemberMember(DependencyObject obj, string value)
        {
            obj.SetValue(DisplayMemberMemberProperty, value);
        }

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


        private static void ColumnsSourceChanged(DependencyObject obj, DependencyPropertyChangedEventArgs e)
        {
            GridView gridView = obj as GridView;
            if (gridView != null)
            {
                gridView.Columns.Clear();

                if (e.OldValue != null)
                {
                    ICollectionView view = CollectionViewSource.GetDefaultView(e.OldValue);
                    if (view != null)
                        RemoveHandlers(gridView, view);
                }

                if (e.NewValue != null)
                {
                    ICollectionView view = CollectionViewSource.GetDefaultView(e.NewValue);
                    if (view != null)
                    {
                        AddHandlers(gridView, view);
                        CreateColumns(gridView, view);
                    }
                }
            }
        }

        private static IDictionary<ICollectionView, List<GridView>> _gridViewsByColumnsSource =
            new Dictionary<ICollectionView, List<GridView>>();

        private static List<GridView> GetGridViewsForColumnSource(ICollectionView columnSource)
        {
            List<GridView> gridViews;
            if (!_gridViewsByColumnsSource.TryGetValue(columnSource, out gridViews))
            {
                gridViews = new List<GridView>();
                _gridViewsByColumnsSource.Add(columnSource, gridViews);
            }
            return gridViews;
        }

        private static void AddHandlers(GridView gridView, ICollectionView view)
        {
            GetGridViewsForColumnSource(view).Add(gridView);
            view.CollectionChanged += ColumnsSource_CollectionChanged;
        }

        private static void CreateColumns(GridView gridView, ICollectionView view)
        {
            foreach (var item in view)
            {
                GridViewColumn column = CreateColumn(gridView, item);
                gridView.Columns.Add(column);
            }
        }

        private static void RemoveHandlers(GridView gridView, ICollectionView view)
        {
            view.CollectionChanged -= ColumnsSource_CollectionChanged;
            GetGridViewsForColumnSource(view).Remove(gridView);
        }

        private static void ColumnsSource_CollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
        {
            ICollectionView view = sender as ICollectionView;
            var gridViews = GetGridViewsForColumnSource(view);
            if (gridViews == null || gridViews.Count == 0)
                return;

            switch (e.Action)
            {
                case NotifyCollectionChangedAction.Add:
                    foreach (var gridView in gridViews)
                    {
                        for (int i = 0; i < e.NewItems.Count; i++)
                        {
                            GridViewColumn column = CreateColumn(gridView, e.NewItems[i]);
                            gridView.Columns.Insert(e.NewStartingIndex + i, column);
                        }
                    }
                    break;
                case NotifyCollectionChangedAction.Move:
                    foreach (var gridView in gridViews)
                    {
                        List<GridViewColumn> columns = new List<GridViewColumn>();
                        for (int i = 0; i < e.OldItems.Count; i++)
                        {
                            GridViewColumn column = gridView.Columns[e.OldStartingIndex + i];
                            columns.Add(column);
                        }
                        for (int i = 0; i < e.NewItems.Count; i++)
                        {
                            GridViewColumn column = columns[i];
                            gridView.Columns.Insert(e.NewStartingIndex + i, column);
                        }
                    }
                    break;
                case NotifyCollectionChangedAction.Remove:
                    foreach (var gridView in gridViews)
                    {
                        for (int i = 0; i < e.OldItems.Count; i++)
                        {
                            gridView.Columns.RemoveAt(e.OldStartingIndex);
                        }
                    }
                    break;
                case NotifyCollectionChangedAction.Replace:
                    foreach (var gridView in gridViews)
                    {
                        for (int i = 0; i < e.NewItems.Count; i++)
                        {
                            GridViewColumn column = CreateColumn(gridView, e.NewItems[i]);
                            gridView.Columns[e.NewStartingIndex + i] = column;
                        }
                    }
                    break;
                case NotifyCollectionChangedAction.Reset:
                    foreach (var gridView in gridViews)
                    {
                        gridView.Columns.Clear();
                        CreateColumns(gridView, sender as ICollectionView);
                    }
                    break;
                default:
                    break;
            }
        }

        private static GridViewColumn CreateColumn(GridView gridView, object columnSource)
        {
            GridViewColumn column = new GridViewColumn();
            string headerTextMember = GetHeaderTextMember(gridView);
            string displayMemberMember = GetDisplayMemberMember(gridView);
            if (!string.IsNullOrEmpty(headerTextMember))
            {
                column.Header = GetPropertyValue(columnSource, headerTextMember);
            }
            if (!string.IsNullOrEmpty(displayMemberMember))
            {
                string propertyName = GetPropertyValue(columnSource, displayMemberMember) as string;
                column.DisplayMemberBinding = new Binding(propertyName);
            }
            return column;
        }

        private static object GetPropertyValue(object obj, string propertyName)
        {
            if (obj != null)
            {
                PropertyInfo prop = obj.GetType().GetProperty(propertyName);
                if (prop != null)
                    return prop.GetValue(obj, null);
            }
            return null;
        }
    }
}

ViewModel

class PersonsViewModel
{
    public PersonsViewModel()
    {
        this.Persons = new ObservableCollection<Person>
        {
            new Person
            {
                Name = "Doe",
                FirstName = "John",
                DateOfBirth = new DateTime(1981, 9, 12)
            },
            new Person
            {
                Name = "Black",
                FirstName = "Jack",
                DateOfBirth = new DateTime(1950, 1, 15)
            },
            new Person
            {
                Name = "Smith",
                FirstName = "Jane",
                DateOfBirth = new DateTime(1987, 7, 23)
            }
        };

        this.Columns = new ObservableCollection<ColumnDescriptor>
        {
            new ColumnDescriptor { HeaderText = "Last name", DisplayMember = "Name" },
            new ColumnDescriptor { HeaderText = "First name", DisplayMember = "FirstName" },
            new ColumnDescriptor { HeaderText = "Date of birth", DisplayMember = "DateOfBirth" }
        };
    }

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

    public ObservableCollection<ColumnDescriptor> Columns { get; private set; }

    private ICommand _addColumnCommand;
    public ICommand AddColumnCommand
    {
        get
        {
            if (_addColumnCommand == null)
            {
                _addColumnCommand = new DelegateCommand<string>(
                    s =>
                    {
                        this.Columns.Add(new ColumnDescriptor { HeaderText = s, DisplayMember = s });
                    });
            }
            return _addColumnCommand;
        }
    }

    private ICommand _removeColumnCommand;
    public ICommand RemoveColumnCommand
    {
        get
        {
            if (_removeColumnCommand == null)
            {
                _removeColumnCommand = new DelegateCommand<string>(
                    s =>
                    {
                        this.Columns.Remove(this.Columns.FirstOrDefault(d => d.DisplayMember == s));
                    });
            }
            return _removeColumnCommand;
        }
    }
}

XAML :

    <ListView ItemsSource="{Binding Persons}" Grid.Row="0">
        <ListView.View>
            <GridView local:GridViewColumns.HeaderTextMember="HeaderText"
                      local:GridViewColumns.DisplayMemberMember="DisplayMember"
                      local:GridViewColumns.ColumnsSource="{Binding Columns}"/>
        </ListView.View>
    </ListView>

Note that the ColumnDescriptor class is not actually needed, I only added it for clarity, but any type will do (including an anonymous type). You just need to specify which properties hold the header text and display member name.

Also, keep in mind that it's not fully tested yet, so there might be a few problems to fix...