/cinch/V1 (VS2008 WPF Only)/cinch/MVVM.Demo/UserControls/TabControlEx.cs

using System;

using System.Collections.Specialized;

using System.Windows;

using System.Windows.Controls;

using System.Windows.Controls.Primitives;



namespace MVVM.Demo

{

    /// <summary>

    /// The standard WPF TabControl is quite bad in the fact that it only

    /// even contains the current TabItem in the VisualTree, so if you

    /// have complex views it takes a while to re-create the view each tab

    /// selection change.Which makes the standard TabControl very sticky to

    /// work with. This class along with its associated ControlTemplate

    /// allow all TabItems to remain in the VisualTree without it being Sticky.

    /// It does this by keeping all TabItem content in the VisualTree but

    /// hides all inactive TabItem content, and only keeps the active TabItem

    /// content shown.

    /// </summary>

    [TemplatePart(Name = "PART_ItemsHolder", Type = typeof(Panel))]

    public class TabControlEx : TabControl

    {

        #region Data

        private Panel itemsHolder = null;

        #endregion



        #region Ctor

        public TabControlEx()

            : base()

        {

            // this is necessary so that we get the initial databound selected item

            this.ItemContainerGenerator.StatusChanged += ItemContainerGenerator_StatusChanged;

            this.Loaded += TabControlEx_Loaded;

        }

        #endregion



        #region Public/Protected Methods

        /// <summary>

        /// get the ItemsHolder and generate any children

        /// </summary>

        public override void OnApplyTemplate()

        {

            base.OnApplyTemplate();

            itemsHolder = GetTemplateChild("PART_ItemsHolder") as Panel;

            UpdateSelectedItem();

        }



        /// <summary>

        /// when the items change we remove any generated panel children and add any new ones as necessary

        /// </summary>

        /// <param name="e"></param>

        protected override void OnItemsChanged(NotifyCollectionChangedEventArgs e)

        {

            base.OnItemsChanged(e);



            if (itemsHolder == null)

            {

                return;

            }



            switch (e.Action)

            {

                case NotifyCollectionChangedAction.Reset:

                    itemsHolder.Children.Clear();

                    break;



                case NotifyCollectionChangedAction.Add:

                case NotifyCollectionChangedAction.Remove:

                    if (e.OldItems != null)

                    {

                        foreach (var item in e.OldItems)

                        {

                            ContentPresenter cp = FindChildContentPresenter(item);

                            if (cp != null)

                            {

                                itemsHolder.Children.Remove(cp);

                            }

                        }

                    }



                    // don't do anything with new items because we don't want to

                    // create visuals that aren't being shown



                    UpdateSelectedItem();

                    break;



                case NotifyCollectionChangedAction.Replace:

                    throw new NotImplementedException("Replace not implemented yet");

            }

        }



        /// <summary>

        /// update the visible child in the ItemsHolder

        /// </summary>

        /// <param name="e"></param>

        protected override void OnSelectionChanged(SelectionChangedEventArgs e)

        {

            base.OnSelectionChanged(e);

            UpdateSelectedItem();

        }



        /// <summary>

        /// copied from TabControl; wish it were protected in that class instead of private

        /// </summary>

        /// <returns></returns>

        protected TabItem GetSelectedTabItem()

        {

            object selectedItem = base.SelectedItem;

            if (selectedItem == null)

            {

                return null;

            }

            TabItem item = selectedItem as TabItem;

            if (item == null)

            {

                item = base.ItemContainerGenerator.ContainerFromIndex(base.SelectedIndex) as TabItem;

            }

            return item;

        }

        #endregion



        #region Private Methods



        /// <summary>

        /// in some scenarios we need to update when loaded in case the 

        /// ApplyTemplate happens before the databind.

        /// </summary>

        /// <param name="sender"></param>

        /// <param name="e"></param>

        private void TabControlEx_Loaded(object sender, RoutedEventArgs e)

        {

            UpdateSelectedItem();

        }



        /// <summary>

        /// if containers are done, generate the selected item

        /// </summary>

        /// <param name="sender"></param>

        /// <param name="e"></param>

        private void ItemContainerGenerator_StatusChanged(object sender, EventArgs e)

        {

            if (this.ItemContainerGenerator.Status == GeneratorStatus.ContainersGenerated)

            {

                this.ItemContainerGenerator.StatusChanged -= ItemContainerGenerator_StatusChanged;

                UpdateSelectedItem();

            }

        }



        /// <summary>

        /// generate a ContentPresenter for the selected item

        /// </summary>

        private void UpdateSelectedItem()

        {

            if (itemsHolder == null)

            {

                return;

            }



            // generate a ContentPresenter if necessary

            TabItem item = GetSelectedTabItem();

            if (item != null)

            {

                CreateChildContentPresenter(item);

            }



            // show the right child

            foreach (ContentPresenter child in itemsHolder.Children)

            {

                child.Visibility = ((child.Tag as TabItem).IsSelected) ? Visibility.Visible : Visibility.Collapsed;

            }

        }



        /// <summary>

        /// create the child ContentPresenter for the given item (could be data or a TabItem)

        /// </summary>

        /// <param name="item"></param>

        /// <returns></returns>

        private ContentPresenter CreateChildContentPresenter(object item)

        {

            if (item == null)

            {

                return null;

            }



            ContentPresenter cp = FindChildContentPresenter(item);



            if (cp != null)

            {

                return cp;

            }



            // the actual child to be added.  cp.Tag is a reference to the TabItem

            cp = new ContentPresenter();

            cp.Content = (item is TabItem) ? (item as TabItem).Content : item;

            cp.ContentTemplate = this.SelectedContentTemplate;

            cp.ContentTemplateSelector = this.SelectedContentTemplateSelector;

            cp.ContentStringFormat = this.SelectedContentStringFormat;

            cp.Visibility = Visibility.Collapsed;

            cp.Tag = (item is TabItem) ? item : (this.ItemContainerGenerator.ContainerFromItem(item));

            itemsHolder.Children.Add(cp);

            return cp;

        }



        /// <summary>

        /// Find the CP for the given object.  data could be a TabItem or a piece of data

        /// </summary>

        /// <param name="data"></param>

        /// <returns></returns>

        private ContentPresenter FindChildContentPresenter(object data)

        {

            if (data is TabItem)

            {

                data = (data as TabItem).Content;

            }



            if (data == null)

            {

                return null;

            }



            if (itemsHolder == null)

            {

                return null;

            }



            foreach (ContentPresenter cp in itemsHolder.Children)

            {

                if (cp.Content == data)

                {

                    return cp;

                }

            }



            return null;

        }

        #endregion

    }

}