Responsive Filtering

gistfile1.cs

namespace GateGuru.Pages.Search
{
    using System.Collections.Generic;
    using System.Collections.ObjectModel;
    using System.ComponentModel;
    using System.Linq;
    using PixelLab.Common;

    /// <summary>
    /// Provides the view model for the <see cref="Search"/> page.
    /// </summary>
    public class SearchViewModel : PropertyChangeBase
    {
        private readonly BackgroundWorker worker;
        private IOrderedEnumerable<Data> allSorted;
        private List<Data> current;
        private string query = string.Empty;

        /// <summary>
        /// Initializes a new instance of the <see cref="SearchViewModel"/> class.
        /// </summary>
        public SearchViewModel()
        {
            this.Results = new ObservableCollection<Data.Airport>();
            this.worker = new BackgroundWorker
            {
                WorkerSupportsCancellation = true
            };
            this.worker.DoWork += this.Filter;
            this.worker.RunWorkerCompleted += this.Filter_Complete;
        }

        /// <summary>
        /// Gets or sets the search query.
        /// </summary>
        /// <value>The search query.</value>
        public string Query
        {
            get { return this.query; }
            set 
            {
                if (this.UpdateProperty("Query", ref this.query, value))
                {
                    this.StartFilter(value.ToLowerInvariant());
                }
            }
        }

        /// <summary>
        /// Gets the results.
        /// </summary>
        /// <value>The results.</value>
        public ObservableCollection<Data> Results { get; private set; }

        /// <summary>
        /// Loads the data.
        /// </summary>
        public void LoadData()
        {
            // TODO: Initialize this.allSorted
            this.current = this.allSorted.ToList();
            this.current.ForEach(a => this.Results.Add(a));
        }

        private void Filter(object sender, DoWorkEventArgs e)
        {
            var query = (string)e.Argument;
            if (string.IsNullOrWhiteSpace(query))
            {
                e.Result = this.allSorted;
            }
            else
            {
                e.Result = from a in this.current
                           where a.Name.ToLowerInvariant().Contains(query)
                           select a;
            }
        }

        private void Filter_Complete(object sender, RunWorkerCompletedEventArgs e)
        {
            if (!e.Cancelled)
            {
                var filtered = (IEnumerable<Data>)e.Result;
                this.Results.Clear();
                filtered.ForEach(a => this.Results.Add(a));
            }
        }

        private void RefilterOnCompletion(object sender, RunWorkerCompletedEventArgs e)
        {
            this.worker.RunWorkerCompleted -= this.RefilterOnCompletion;
            this.worker.RunWorkerAsync(this.Query.ToLowerInvariant());
        }

        private void StartFilter(string query)
        {
            if (this.worker.IsBusy)
            {
                if (!this.worker.CancellationPending)
                {
                    this.worker.RunWorkerCompleted += this.RefilterOnCompletion;
                    this.worker.CancelAsync();
                }
            }
            else
            {
                this.worker.RunWorkerAsync(query.ToLowerInvariant());
            }
        }
    }
}