Question

I’d like to use a designer (e.g. Expression Blend) to template the LongListSelector control (from the SL toolkit for WP7), but I can’t figure out how to format the data to fit what this control expects.

Any pointers to a tutorial would be appreciated. Thanks.

Answer 1

Use a specialized collection, like this:

using System;
using System.Linq;
using System.Collections.Generic;
using System.Linq.Expressions;
using System.Collections.ObjectModel;

namespace Stackoverflow.Collections
{
    /// <summary>
    /// Represents a specialized collection to integrate with the 
    /// <see cref="Microsoft.Phone.Controls.LongListSelector"/> control.
    /// </summary>
    /// <typeparam name="T">The type of the values in the collection.</typeparam>
    /// <typeparam name="TKey">The type of the keys in the collection.</typeparam>
    public class LongListCollection<T, TKey> : ObservableCollection<LongListItem<T, TKey>>
        where T : IComparable<T>
        where TKey : IComparable<TKey>
    {
        /// <summary>
        /// The key selector for adding items.
        /// </summary>
        private Func<T, TKey> keySelector;

        /// <summary>
        /// Initializes a new instance of the <see cref="LongListCollection&lt;T, TKey&gt;"/> class.
        /// </summary>
        /// <param name="keySelector">The key selector.</param>
        public LongListCollection(Func<T, TKey> keySelector)
        {
            if (keySelector == null)
                throw new ArgumentNullException("keySelector");

            this.keySelector = keySelector;
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="LongListCollection&lt;T, TKey&gt;"/> class.
        /// </summary>
        /// <param name="keySelector">The key selector.</param>
        /// <param name="items">A initial collection.</param>
        public LongListCollection(Func<T, TKey> keySelector, IEnumerable<T> items)
        {
            if (keySelector == null)
                throw new ArgumentNullException("keySelector");

            if (items == null)
                throw new ArgumentNullException("items");

            this.keySelector = keySelector;

            var groups = new Dictionary<TKey, LongListItem<T, TKey>>();

            foreach (var item in items.OrderBy(x => x))
            {
                var key = keySelector(item);

                if (groups.ContainsKey(key) == false)
                    groups.Add(key, new LongListItem<T, TKey>(key));

                groups[key].Add(item);
            }

            foreach (var value in groups.Values)
                this.Add(value);
        }

        /// <summary>
        /// Adds the specified item to the collection.
        /// </summary>
        /// <param name="item">The item.</param>
        public void Add(T item)
        {
            TKey key = keySelector(item);

            var group = this.FirstOrDefault(x => x.Key.Equals(key));
            if (group != null)
                group.Add(item);                
            else
                this.Add(new LongListItem<T, TKey>(key) { item });
        }

        /// <summary>
        /// Inserts an item into the collection at the specified index.
        /// </summary>
        /// <param name="index">The zero-based index at which item should be inserted.</param>
        /// <param name="item">The object to insert.</param>
        protected override void InsertItem(int index, LongListItem<T, TKey> item)
        {
            for (int i = 0; i < this.Count; i++)
            {
                switch (Math.Sign(this[i].CompareTo(item)))
                {
                    case 0:
                        throw new InvalidOperationException("Cannot insert duplicated items.");
                    case 1:
                        base.InsertItem(i, item);
                        return;
                    case -1:
                        break;
                }
            }

            base.InsertItem(this.Count, item);
        }
    }

    /// <summary>
    /// Represents a specialized data structure to integrate with the 
    /// <see cref="Microsoft.Phone.Controls.LongListSelector"/> control.
    /// </summary>
    /// <typeparam name="T">The type of the values in the structure.</typeparam>
    /// <typeparam name="TKey">The type of the key in the structure.</typeparam>
    public class LongListItem<T, TKey> : ObservableCollection<T>, IComparable<LongListItem<T, TKey>>
        where T : IComparable<T>
        where TKey : IComparable<TKey>
    {
        /// <summary>
        /// Initializes a new instance of the <see cref="LongListItem&lt;T, TKey&gt;"/> class.
        /// </summary>
        public LongListItem()
        {
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="LongListItem&lt;T, TKey&gt;"/> class.
        /// </summary>
        /// <param name="key">The item's key.</param>
        public LongListItem(TKey key)
        {
            this.Key = key;
        }

        /// <summary>
        /// Gets or sets the item key.
        /// </summary>
        /// <value>The item key.</value>
        public TKey Key
        {
            get;
            set;
        }

        /// <summary>
        /// Gets a value indicating whether this instance has any items.
        /// </summary>
        /// <value><c>true</c> if this instance has any items; otherwise, <c>false</c>.</value>
        public bool HasItems
        {
            get
            {
                return Count > 0;
            }
        }

        /// <summary>
        /// Inserts an item into the collection at the specified index.
        /// </summary>
        /// <param name="index">The zero-based index at which item should be inserted.</param>
        /// <param name="item">The object to insert.</param>
        protected override void InsertItem(int index, T item)
        {                              
            for (int i = 0; i < this.Count; i++)
            {
                switch (Math.Sign(this[i].CompareTo(item)))
                {
                    case 0:
                        return;
                    case 1:
                        base.InsertItem(i, item);
                        return;
                    case -1:
                        break;
                }
            }

            base.InsertItem(this.Count, item);
        }

        /// <summary>
        /// Compares to.
        /// </summary>
        /// <param name="other">The other.</param>
        /// <returns></returns>
        public int CompareTo(LongListItem<T, TKey> other)
        {
            if (other == null)
                return 1;

            return this.Key.CompareTo(other.Key);
        }
    }
}