The WPF Podcatcher Series - Part 2 (Structural Skinning)

using System;
using System.ComponentModel;
using System.Windows;
using System.Windows.Controls.Primitives;
using System.Windows.Threading;
using Podder.Model;

namespace Podder.DefaultSkin.Controls
{
    /// <summary>
    /// A ToggleButton that knows how to both play and pause.
    /// </summary>
    public partial class PlayButton : ToggleButton
    {
        #region Constructor

        public PlayButton()
        {
            InitializeComponent();

            PodderDataSource.Instance.EpisodePlayerSettings.PropertyChanged += this.OnEpisodePlayerSettingsPropertyChanged;

            this.IsChecked = PodderDataSource.Instance.EpisodePlayerSettings.IsPlaying;
        }

        #endregion // Constructor

        #region State

        private static readonly DependencyPropertyKey StatePropertyKey =
            DependencyProperty.RegisterReadOnly(
                "State",
                typeof(PlayButtonState),
                typeof(PlayButton),
                new UIPropertyMetadata(PlayButtonState.Play));

        public static readonly DependencyProperty StateProperty = StatePropertyKey.DependencyProperty;

        public PlayButtonState State
        {
            get { return (PlayButtonState)GetValue(StateProperty); }
            private set { SetValue(StatePropertyKey, value); }
        }

        #endregion // State

        #region OnEpisodePlayerSettingsPropertyChanged

        void OnEpisodePlayerSettingsPropertyChanged(object sender, PropertyChangedEventArgs e)
        {
            if (e.PropertyName == "IsPlaying")
            {
                // Note: I tried to establish this relationship as a Binding, but in certain
                // situations the property did not update correclty.  If you bind the IsChecked
                // property in XAML like this: IsChecked="{Binding EpisodePlayerSettings.IsPlaying, Mode=OneWay}"
                // it will not update the IsChecked property when you click the Play button, deselect 
                // the selected item in the list of Episodes, and click the Stop button.
                // This is a palatable workaround, in my opinion.
                this.IsChecked = PodderDataSource.Instance.EpisodePlayerSettings.IsPlaying;
            }
        }

        #endregion // OnEpisodePlayerSettingsPropertyChanged        

        #region Base Class Overrides

        protected override void OnChecked(RoutedEventArgs e)
        {
            base.OnChecked(e);

            // Delay a call which sets the State so that it
            // occurs after the Click event.  This allows 
            // the current Command to be effective until 
            // the entire click processing is complete.
            base.Dispatcher.BeginInvoke(
                DispatcherPriority.Background,
                (Action)delegate
                {
                    this.State = PlayButtonState.Pause;
                });
        }
        
        protected override void OnUnchecked(RoutedEventArgs e)
        {
            base.OnUnchecked(e);

            base.Dispatcher.BeginInvoke(
                DispatcherPriority.Background,
                (Action)delegate
                {
                    this.State = PlayButtonState.Play;
                });
        }

        #endregion // Base Class Overrides
    }

    public enum PlayButtonState
    {
        Play,
        Pause
    }
}