Change GuiContext from system-wide to a per-element basis (#610)

A new GUI Context object is now instantiated for each MediaElement and is populated with the current dispatcher. This allows MediaElements to be created on non-UI threads and events will be returned on the correct dispatcher

Unosquare.FFME.MediaElement/MediaElement.Events.cs

@@ -252,7 +252,7 @@ public partial class MediaElement
         internal void PostMediaFailedEvent(Exception ex)
         {
             LogEventStart(nameof(MediaFailed));
-            Library.GuiContext.EnqueueInvoke(() =>
+            GuiContext.EnqueueInvoke(() =>
             {
                 MediaFailed?.Invoke(this, new MediaFailedEventArgs(ex));
                 LogEventDone(nameof(MediaFailed));
@@ -267,7 +267,7 @@ internal void PostMediaFailedEvent(Exception ex)
         internal void PostMediaOpenedEvent(MediaInfo mediaInfo)
         {
             LogEventStart(nameof(MediaOpened));
-            Library.GuiContext.EnqueueInvoke(() =>
+            GuiContext.EnqueueInvoke(() =>
             {
                 MediaOpened?.Invoke(this, new MediaOpenedEventArgs(mediaInfo));
                 LogEventDone(nameof(MediaOpened));
@@ -281,7 +281,7 @@ internal void PostMediaOpenedEvent(MediaInfo mediaInfo)
         internal void PostMediaReadyEvent()
         {
             LogEventStart(nameof(MediaReady));
-            Library.GuiContext.EnqueueInvoke(() =>
+            GuiContext.EnqueueInvoke(() =>
             {
                 MediaReady?.Invoke(this, EventArgs.Empty);
                 LogEventDone(nameof(MediaReady));
@@ -295,7 +295,7 @@ internal void PostMediaReadyEvent()
         internal void PostMediaClosedEvent()
         {
             LogEventStart(nameof(MediaClosed));
-            Library.GuiContext.EnqueueInvoke(() =>
+            GuiContext.EnqueueInvoke(() =>
             {
                 MediaClosed?.Invoke(this, EventArgs.Empty);
                 LogEventDone(nameof(MediaClosed));
@@ -310,7 +310,7 @@ internal void PostMediaClosedEvent()
         internal void PostMediaChangedEvent(MediaInfo mediaInfo)
         {
             LogEventStart(nameof(MediaChanged));
-            Library.GuiContext.EnqueueInvoke(() =>
+            GuiContext.EnqueueInvoke(() =>
             {
                 MediaChanged?.Invoke(this, new MediaOpenedEventArgs(mediaInfo));
                 LogEventDone(nameof(MediaChanged));
@@ -326,7 +326,7 @@ internal void PostMediaChangedEvent(MediaInfo mediaInfo)
         internal void PostPositionChangedEvent(TimeSpan oldValue, TimeSpan newValue)
         {
             // Event logging disabled because this happens too often.
-            Library.GuiContext.EnqueueInvoke(() =>
+            GuiContext.EnqueueInvoke(() =>
             {
                 PositionChanged?.Invoke(
                     this, new PositionChangedEventArgs(MediaCore.State, oldValue, newValue));
@@ -342,7 +342,7 @@ internal void PostPositionChangedEvent(TimeSpan oldValue, TimeSpan newValue)
         internal void PostMediaStateChangedEvent(MediaPlaybackState oldValue, MediaPlaybackState newValue)
         {
             LogEventStart(nameof(MediaStateChanged));
-            Library.GuiContext.EnqueueInvoke(() =>
+            GuiContext.EnqueueInvoke(() =>
             {
                 MediaStateChanged?.Invoke(this, new MediaStateChangedEventArgs(oldValue, newValue));
                 LogEventDone(nameof(MediaStateChanged));
@@ -356,7 +356,7 @@ internal void PostMediaStateChangedEvent(MediaPlaybackState oldValue, MediaPlayb
         internal void PostBufferingStartedEvent()
         {
             LogEventStart(nameof(BufferingStarted));
-            Library.GuiContext.EnqueueInvoke(() =>
+            GuiContext.EnqueueInvoke(() =>
             {
                 BufferingStarted?.Invoke(this, EventArgs.Empty);
                 LogEventDone(nameof(BufferingStarted));
@@ -370,7 +370,7 @@ internal void PostBufferingStartedEvent()
         internal void PostBufferingEndedEvent()
         {
             LogEventStart(nameof(BufferingEnded));
-            Library.GuiContext.EnqueueInvoke(() =>
+            GuiContext.EnqueueInvoke(() =>
             {
                 BufferingEnded?.Invoke(this, EventArgs.Empty);
                 LogEventDone(nameof(BufferingEnded));
@@ -384,7 +384,7 @@ internal void PostBufferingEndedEvent()
         internal void PostSeekingStartedEvent()
         {
             LogEventStart(nameof(SeekingStarted));
-            Library.GuiContext.EnqueueInvoke(() =>
+            GuiContext.EnqueueInvoke(() =>
             {
                 SeekingStarted?.Invoke(this, EventArgs.Empty);
                 LogEventDone(nameof(SeekingStarted));
@@ -398,7 +398,7 @@ internal void PostSeekingStartedEvent()
         internal void PostSeekingEndedEvent()
         {
             LogEventStart(nameof(SeekingEnded));
-            Library.GuiContext.EnqueueInvoke(() =>
+            GuiContext.EnqueueInvoke(() =>
             {
                 SeekingEnded?.Invoke(this, EventArgs.Empty);
                 LogEventDone(nameof(SeekingEnded));
@@ -412,7 +412,7 @@ internal void PostSeekingEndedEvent()
         internal void PostMediaEndedEvent()
         {
             LogEventStart(nameof(MediaEnded));
-            Library.GuiContext.EnqueueInvoke(() =>
+            GuiContext.EnqueueInvoke(() =>
             {
                 MediaEnded?.Invoke(this, EventArgs.Empty);
                 LogEventDone(nameof(MediaEnded));

Unosquare.FFME.MediaElement/Platform/IGuiContext.cs

@@ -8,6 +8,11 @@
     /// </summary>
     internal interface IGuiContext
     {
+        /// <summary>
+        /// Gets the type of the context.
+        /// </summary>
+        GuiContextType Type { get; }
+
         /// <summary>
         /// Invokes a task on the GUI thread with the possibility of awaiting it.
         /// </summary>

Unosquare.FFME.MediaElement/Platform/MediaConnector.cs

@@ -40,7 +40,7 @@ public void OnMediaEnded(MediaEngine sender)
         {
             if (Parent == null || sender == null) return;
 
-            Library.GuiContext.EnqueueInvoke(async () =>
+            Parent.GuiContext.EnqueueInvoke(async () =>
             {
                 Parent.PostMediaEndedEvent();
                 var behavior = Parent.LoopingBehavior;
@@ -70,7 +70,7 @@ public void OnMediaOpened(MediaEngine sender, MediaInfo mediaInfo)
         {
             if (Parent == null || sender == null) return;
 
-            Library.GuiContext.EnqueueInvoke(async () =>
+            Parent.GuiContext.EnqueueInvoke(async () =>
             {
                 // Set initial controller properties
                 // Has to be on the GUI thread as we are reading dependency properties

Unosquare.FFME.MediaElement/Unosquare.FFME.MediaElement.projitems

@@ -12,7 +12,6 @@
     <Compile Include="$(MSBuildThisFileDirectory)Common\DataFrameReceivedEventArgs.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Common\ViewModelBase.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Constants.cs" />
-    <Compile Include="$(MSBuildThisFileDirectory)Library.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Common\MediaFailedEventArgs.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Common\FrameDecodedEventArgs.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Common\InputFormatEventArgs.cs" />

Unosquare.FFME.Windows/MediaElement.cs

@@ -1,4 +1,4 @@
-namespace Unosquare.FFME
+namespace Unosquare.FFME
 {
     using Common;
     using Engine;
@@ -63,9 +63,6 @@ static MediaElement()
             MediaEngine.FFmpegMessageLogged += (s, message) =>
                 FFmpegMessageLogged?.Invoke(typeof(MediaElement), new MediaLogMessageEventArgs(message));
 
-            // A GUI context must be registered
-            Library.RegisterGuiContext(GuiContext.Current);
-
             // Content property cannot be changed.
             ContentProperty.OverrideMetadata(typeof(MediaElement), new FrameworkPropertyMetadata(null, OnCoerceContentValue));
 
@@ -86,6 +83,11 @@ public MediaElement()
 
                 if (!Library.IsInDesignMode)
                 {
+                    GuiContext = new GuiContext();
+
+                    VideoView = new ImageHost(GuiContext.Type == GuiContextType.WPF && Library.EnableWpfMultiThreadedVideo)
+                    { Name = nameof(VideoView) };
+
                     // Setup the media engine and property updates timer
                     MediaCore = new MediaEngine(this, new MediaConnector(this));
                     MediaCore.State.PropertyChanged += (s, e) => PropertyUpdates.Add(e.PropertyName);
@@ -139,12 +141,16 @@ public MediaElement()
         /// </summary>
         public RendererOptions RendererOptions { get; } = new RendererOptions();
 
+        /// <summary>
+        /// The GUI context used to create this media element.
+        /// </summary>
+        internal IGuiContext GuiContext { get; private set; }
+
         /// <summary>
         /// This is the image that holds video bitmaps. It is a Hosted Image which means that in a WPF
         /// GUI context, it runs on its own dispatcher (multi-threaded UI).
         /// </summary>
-        internal ImageHost VideoView { get; } = new ImageHost(GuiContext.Current.Type == GuiContextType.WPF && Library.EnableWpfMultiThreadedVideo)
-        { Name = nameof(VideoView) };
+        internal ImageHost VideoView { get; }
 
         /// <summary>
         /// Gets the closed captions view control.

Unosquare.FFME.Windows/Platform/GuiContext.cs

@@ -1,4 +1,4 @@
-namespace Unosquare.FFME.Platform
+namespace Unosquare.FFME.Platform
 {
     using System;
     using System.Diagnostics;
@@ -16,29 +16,21 @@
     internal sealed class GuiContext : IGuiContext
     {
         /// <summary>
-        /// Initializes static members of the <see cref="GuiContext"/> class.
+        /// Initializes a new instance of the <see cref="GuiContext"/> class.
         /// </summary>
-        static GuiContext()
-        {
-            Current = new GuiContext();
-        }
-
-        /// <summary>
-        /// Prevents a default instance of the <see cref="GuiContext"/> class from being created.
-        /// </summary>
-        private GuiContext()
+        public GuiContext()
         {
             Thread = Thread.CurrentThread;
             ThreadContext = SynchronizationContext.Current;
 
-            // Try to extract the dispatcher for the application
-            try { GuiDispatcher = Application.Current.Dispatcher; }
+            // Try to extract the dispatcher from the current thread
+            try { GuiDispatcher = Dispatcher.CurrentDispatcher; }
             catch { /* Ignore error as app might not be available or context is not WPF */ }
 
-            // If the above was unsuccessful, try to extract the dispatcher from the current thread.
+            // If the above was unsuccessful, try to extract the dispatcher for the application
             if (GuiDispatcher == null)
             {
-                try { GuiDispatcher = Dispatcher.CurrentDispatcher; }
+                try { GuiDispatcher = Application.Current.Dispatcher; }
                 catch { /* Ignore error as app might not be available or context is not WPF */ }
             }
 
@@ -49,14 +41,7 @@ private GuiContext()
             IsValid = Type != GuiContextType.None;
         }
 
-        /// <summary>
-        /// Gets the current instance.
-        /// </summary>
-        public static GuiContext Current { get; }
-
-        /// <summary>
-        /// Gets the type of the context.
-        /// </summary>
+        /// <inheritdoc />
         public GuiContextType Type { get; }
 
         /// <summary>

Unosquare.FFME.Windows/Rendering/SubtitleRenderer.cs

@@ -161,7 +161,7 @@ private void SetText(string text)
             }
 
             // We fire-and-forget the update of the text
-            Library.GuiContext.EnqueueInvoke(() =>
+            MediaElement.GuiContext.EnqueueInvoke(() =>
             {
                 lock (SyncLock)
                 {

Unosquare.FFME.Windows/Rendering/VideoRendererBase.cs

@@ -49,7 +49,7 @@ protected VideoRendererBase(MediaEngine mediaCore)
             MediaCore = mediaCore;
 
             // Set the DPI
-            Library.GuiContext.EnqueueInvoke(() =>
+            MediaElement.GuiContext.EnqueueInvoke(() =>
             {
                 var media = MediaElement;
                 if (media != null)