Reusable function for raising events (MonoGame#5713)

* Reusable function for raising events

Before raising an event, you must first check the handler to see if it is null in order to check that an object is subscribed to handle the event.  This is best done if the event handler is stored in a local variable just in case the last subscriber unsubscribes in a different thread between the time the event handler is checked and the handler is actually invoked.  This reusable function makes it easy to raise events by storing a local copy of the handler and checking for null before invoking it.  Many classes already had a helper function for this.  This change refactors those into a single function.

There are some instances where more complex logic was being done after the event handler was checked.  In those scenarios, the code was mostly left alone except for the introduction of a local handler variable.

* Safely raising events through common function

- Updated events being raised throughout the framework with the new EventHelpers.Raise function
- Updated the name of EventHelper to be plural in case more helper methods are needed in the future.

Build/Projects/2MGFX.definition

@@ -54,6 +54,9 @@
     </Compile>
     <Compile Include="..\..\MonoGame.Framework\ContainmentType.cs">
       <Link>MonoGame.Framework\ContainmentType.cs</Link>
+    </Compile>
+	<Compile Include="..\..\MonoGame.Framework\EventHelpers.cs">
+      <Link>MonoGame.Framework\EventHelpers.cs</Link>
     </Compile>
     <Compile Include="..\..\MonoGame.Framework\Graphics\ColorWriteChannels.cs">
       <Link>MonoGame.Framework\ColorWriteChannels.cs</Link>

Build/Projects/MonoGame.Framework.definition

@@ -278,6 +278,7 @@
     <Compile Include="CurveTangent.cs" />
     <Compile Include="DisplayOrientation.cs" />
     <Compile Include="DrawableGameComponent.cs" />
+	<Compile Include="EventHelpers.cs" />
     <Compile Include="FrameworkDispatcher.cs" />
 	<Compile Include="FrameworkResources.cs" />
     <Compile Include="GameComponentCollection.cs" />

MonoGame.Framework/Android/AndroidGameActivity.cs

@@ -57,8 +57,7 @@ public override void OnConfigurationChanged (Android.Content.Res.Configuration n
         protected override void OnPause()
         {
             base.OnPause();
-            if (Paused != null)
-                Paused(this, EventArgs.Empty);
+            EventHelpers.Raise(this, Paused, EventArgs.Empty);
 
             if (_orientationListener.CanDetectOrientation())
                 _orientationListener.Disable();
@@ -68,8 +67,7 @@ protected override void OnPause()
         protected override void OnResume()
         {
             base.OnResume();
-            if (Resumed != null)
-                Resumed(this, EventArgs.Empty);
+            EventHelpers.Raise(this, Resumed, EventArgs.Empty);
 
             if (Game != null)
             {

MonoGame.Framework/Android/GamerServices/SignedInGamer.cs

@@ -306,22 +306,14 @@ public GamerPrivileges Privileges
 
 
 		protected virtual void OnSignedIn(SignedInEventArgs e)
-		{
-			 if (SignedIn != null) 
-			 {
-			    // Invokes the delegates. 
-			    SignedIn(this, e);
-			 }
+		{
+            EventHelpers.Raise(this, SignedIn, e);
 		}
 
 		protected virtual void OnSignedOut(SignedOutEventArgs e)
-		{
-			 if (SignedOut != null) 
-			 {
-			    // Invokes the delegates. 
-			    SignedOut(this, e);
-			 }
-		}
+		{
+            EventHelpers.Raise(this, SignedOut, e);
+        }
 
 
 		#region Events

MonoGame.Framework/Audio/DynamicSoundEffectInstance.cs

@@ -289,12 +289,14 @@ internal void UpdateQueue()
             PlatformUpdateQueue();
 
             // Raise the event
-            if (BufferNeeded != null)
+            var bufferNeededHandler = BufferNeeded;
+
+            if (bufferNeededHandler != null)
             {
                 var eventCount = (_buffersNeeded < 3) ? _buffersNeeded : 3;
                 for (var i = 0; i < eventCount; i++)
                 {
-                    BufferNeeded(this, EventArgs.Empty);
+                    bufferNeededHandler(this, EventArgs.Empty);
                 }
             }
 

MonoGame.Framework/Audio/Xact/AudioEngine.cs

@@ -383,8 +383,8 @@ private void Dispose(bool disposing)
             // TODO: Should we be forcing any active
             // audio cues to stop here?
 
-            if (disposing && Disposing != null)
-                Disposing(this, EventArgs.Empty);
+            if (disposing)
+                EventHelpers.Raise(this, Disposing, EventArgs.Empty);
         }
     }
 }

MonoGame.Framework/Audio/Xact/Cue.cs

@@ -352,9 +352,7 @@ private void Dispose(bool disposing)
             {
                 IsCreated = false;
                 IsPrepared = false;
-
-                if (Disposing != null)
-                    Disposing(this, EventArgs.Empty);
+                EventHelpers.Raise(this, Disposing, EventArgs.Empty);
             }
         }
     }

MonoGame.Framework/Audio/Xact/SoundBank.cs

@@ -347,9 +347,7 @@ private void Dispose(bool disposing)
             if (disposing)
             {
                 IsInUse = false;
-
-                if (Disposing != null)
-                    Disposing(this, EventArgs.Empty);
+                EventHelpers.Raise(this, Disposing, EventArgs.Empty);
             }
         }
     }

MonoGame.Framework/Audio/Xact/WaveBank.cs

@@ -431,9 +431,7 @@ private void Dispose(bool disposing)
 
                 IsPrepared = false;
                 IsInUse = false;
-
-                if (Disposing != null)
-                    Disposing(this, EventArgs.Empty);
+                EventHelpers.Raise(this, Disposing, EventArgs.Empty);
             }
         }
     }

MonoGame.Framework/DesktopGL/GamerServices/SignedInGamer.cs

@@ -292,20 +292,12 @@ public GamerPrivileges Privileges
 
 		protected virtual void OnSignedIn(SignedInEventArgs e)
 		{
-			 if (SignedIn != null) 
-			 {
-			    // Invokes the delegates. 
-			    SignedIn(this, e);
-			 }
-		}
+            EventHelpers.Raise(this, SignedIn, e);
+        }
 
 		protected virtual void OnSignedOut(SignedOutEventArgs e)
 		{
-			 if (SignedOut != null) 
-			 {
-			    // Invokes the delegates. 
-			    SignedOut(this, e);
-			 }
+            EventHelpers.Raise(this, SignedOut, e);
 		}
 
 

MonoGame.Framework/DrawableGameComponent.cs

@@ -25,9 +25,7 @@ public int DrawOrder
                 if (_drawOrder != value)
                 {
                     _drawOrder = value;
-                    if (DrawOrderChanged != null)
-                        DrawOrderChanged(this, null);
-                    OnDrawOrderChanged(this, null);
+                    OnDrawOrderChanged(this, EventArgs.Empty);
                 }
             }
         }
@@ -40,8 +38,6 @@ public bool Visible
                 if (_visible != value)
                 {
                     _visible = value;
-                    if (VisibleChanged != null)
-                        VisibleChanged(this, EventArgs.Empty);
                     OnVisibleChanged(this, EventArgs.Empty);
                 }
             }
@@ -70,8 +66,14 @@ protected virtual void UnloadContent () { }
 
         public virtual void Draw(GameTime gameTime) { }
 
-        protected virtual void OnVisibleChanged(object sender, EventArgs args) { }
+        protected virtual void OnVisibleChanged(object sender, EventArgs args)
+        {
+            EventHelpers.Raise(this, VisibleChanged, args);
+        }
 
-        protected virtual void OnDrawOrderChanged(object sender, EventArgs args) { }
+        protected virtual void OnDrawOrderChanged(object sender, EventArgs args)
+        {
+            EventHelpers.Raise(this, DrawOrderChanged, args);
+        }
     }
 }

MonoGame.Framework/EventHelpers.cs

@@ -0,0 +1,45 @@
+// MonoGame - Copyright (C) The MonoGame Team
+// This file is subject to the terms and conditions defined in
+// file 'LICENSE.txt', which is part of this source code package.
+
+using System;
+
+namespace Microsoft.Xna.Framework
+{
+    /// <summary>
+    /// Provides helper methods to make it easier
+    /// to safely raise events.
+    /// </summary>
+    internal static class EventHelpers
+    {
+        /// <summary>
+        /// Safely raises an event by storing a copy of the event's delegate
+        /// in the <paramref name="handler"/> parameter and checking it for
+        /// null before invoking it.
+        /// </summary>
+        /// <typeparam name="TEventArgs"></typeparam>
+        /// <param name="sender">The object raising the event.</param>
+        /// <param name="handler"><see cref="EventHandler{TEventArgs}"/> to be invoked</param>
+        /// <param name="e">The <typeparamref name="TEventArgs"/> passed to <see cref="EventHandler{TEventArgs}"/></param>
+        internal static void Raise<TEventArgs>(object sender, EventHandler<TEventArgs> handler, TEventArgs e)
+            where TEventArgs : EventArgs
+        {
+            if (handler != null)
+                handler(sender, e);
+        }
+
+        /// <summary>
+        /// Safely raises an event by storing a copy of the event's delegate
+        /// in the <paramref name="handler"/> parameter and checking it for
+        /// null before invoking it.
+        /// </summary>
+        /// <param name="sender">The object raising the event.</param>
+        /// <param name="handler"><see cref="EventHandler"/> to be invoked</param>
+        /// <param name="e">The <see cref="EventArgs"/> passed to <see cref="EventHandler"/></param>
+        internal static void Raise(object sender, EventHandler handler, EventArgs e)
+        {
+            if (handler != null)
+                handler(sender, e);
+        }
+    }
+}

MonoGame.Framework/Game.cs

@@ -96,7 +96,7 @@ public void Dispose()
         {
             Dispose(true);
             GC.SuppressFinalize(this);
-            Raise(Disposed, EventArgs.Empty);
+            EventHelpers.Raise(this, Disposed, EventArgs.Empty);
         }
 
         protected virtual void Dispose(bool disposing)
@@ -570,19 +570,19 @@ protected virtual void Update(GameTime gameTime)
 
         protected virtual void OnExiting(object sender, EventArgs args)
         {
-            Raise(Exiting, args);
+            EventHelpers.Raise(this, Exiting, args);
         }
 
 		protected virtual void OnActivated (object sender, EventArgs args)
 		{
-			AssertNotDisposed();
-			Raise(Activated, args);
+			AssertNotDisposed();
+            EventHelpers.Raise(this, Activated, args);
 		}
 
 		protected virtual void OnDeactivated (object sender, EventArgs args)
 		{
-			AssertNotDisposed();
-			Raise(Deactivated, args);
+			AssertNotDisposed();
+            EventHelpers.Raise(this, Deactivated, args);
 		}
 
         #endregion Protected Methods
@@ -618,7 +618,7 @@ private void Platform_AsyncRunLoopEnded(object sender, EventArgs e)
         private void Platform_ApplicationViewChanged(object sender, ViewStateChangedEventArgs e)
         {
             AssertNotDisposed();
-            Raise(ApplicationViewChanged, e);
+            EventHelpers.Raise(this, ApplicationViewChanged, e);
         }
 #endif
 
@@ -760,13 +760,6 @@ private void DecategorizeComponent(IGameComponent component)
                 _drawables.Remove((IDrawable)component);
         }
 
-        private void Raise<TEventArgs>(EventHandler<TEventArgs> handler, TEventArgs e)
-            where TEventArgs : EventArgs
-        {
-            if (handler != null)
-                handler(this, e);
-        }
-
         /// <summary>
         /// The SortingFilteringCollection class provides efficient, reusable
         /// sorting and filtering based on a configurable sort comparer, filter

MonoGame.Framework/GameComponent.cs

@@ -21,9 +21,7 @@ public bool Enabled
                 if (_enabled != value)
                 {
                     _enabled = value;
-                    if (this.EnabledChanged != null)
-                        this.EnabledChanged(this, EventArgs.Empty);
-                    OnEnabledChanged(this, null);
+                    OnEnabledChanged(this, EventArgs.Empty);
                 }
             }
         }
@@ -36,9 +34,7 @@ public int UpdateOrder
                 if (_updateOrder != value)
                 {
                     _updateOrder = value;
-                    if (this.UpdateOrderChanged != null)
-                        this.UpdateOrderChanged(this, EventArgs.Empty);
-                    OnUpdateOrderChanged(this, null);
+                    OnUpdateOrderChanged(this, EventArgs.Empty);
                 }
             }
         }
@@ -60,9 +56,15 @@ public virtual void Initialize() { }
 
         public virtual void Update(GameTime gameTime) { }
 
-        protected virtual void OnUpdateOrderChanged(object sender, EventArgs args) { }
+        protected virtual void OnUpdateOrderChanged(object sender, EventArgs args)
+        {
+            EventHelpers.Raise(this, UpdateOrderChanged, args);
+        }
 
-        protected virtual void OnEnabledChanged(object sender, EventArgs args) { }
+        protected virtual void OnEnabledChanged(object sender, EventArgs args)
+        {
+            EventHelpers.Raise(this, EnabledChanged, args);
+        }
 
         /// <summary>
         /// Shuts down the component.

MonoGame.Framework/GameComponentCollection.cs

@@ -49,18 +49,12 @@ protected override void InsertItem(int index, IGameComponent item)
 
         private void OnComponentAdded(GameComponentCollectionEventArgs eventArgs)
         {
-            if (this.ComponentAdded != null)
-            {
-                this.ComponentAdded(this, eventArgs);
-            }
+            EventHelpers.Raise(this, ComponentAdded, eventArgs);
         }
 
         private void OnComponentRemoved(GameComponentCollectionEventArgs eventArgs)
         {
-            if (this.ComponentRemoved != null)
-            {
-                this.ComponentRemoved(this, eventArgs);
-            }
+            EventHelpers.Raise(this, ComponentRemoved, eventArgs);
         }
 
         protected override void RemoveItem(int index)

MonoGame.Framework/GamePlatform.Desktop.cs

@@ -39,7 +39,7 @@ public ApplicationViewState ViewState
                 if (_viewState == value)
                     return;
 
-                Raise(ViewStateChanged, new ViewStateChangedEventArgs(value));
+                EventHelpers.Raise(this, ViewStateChanged, new ViewStateChangedEventArgs(value));
 
                 _viewState = value;
             }

MonoGame.Framework/GamePlatform.cs

@@ -62,7 +62,7 @@ internal set
                 if (_isActive != value)
                 {
                     _isActive = value;
-                    Raise(_isActive ? Activated : Deactivated, EventArgs.Empty);
+                    EventHelpers.Raise(this, _isActive ? Activated : Deactivated, EventArgs.Empty);
                 }
             }
         }
@@ -107,21 +107,14 @@ protected set
         public event EventHandler<EventArgs> Activated;
         public event EventHandler<EventArgs> Deactivated;
 
-        private void Raise<TEventArgs>(EventHandler<TEventArgs> handler, TEventArgs e)
-            where TEventArgs : EventArgs
-        {
-            if (handler != null)
-                handler(this, e);
-        }
-
         /// <summary>
         /// Raises the AsyncRunLoopEnded event.  This method must be called by
         /// derived classes when the asynchronous run loop they start has
         /// stopped running.
         /// </summary>
         protected void RaiseAsyncRunLoopEnded()
         {
-            Raise(AsyncRunLoopEnded, EventArgs.Empty);
+            EventHelpers.Raise(this, AsyncRunLoopEnded, EventArgs.Empty);
         }
 
         #endregion Events