extend base content helper to support null content (#173)

src/StardewModdingAPI/Framework/Content/ContentEventData.cs

@@ -6,7 +6,7 @@ namespace StardewModdingAPI.Framework.Content
 {
     /// <summary>Base implementation for a content helper which encapsulates access and changes to content being read from a data file.</summary>
     /// <typeparam name="TValue">The interface value type.</typeparam>
-    internal class ContentEventBaseHelper<TValue> : EventArgs, IContentEventData<TValue>
+    internal class ContentEventData<TValue> : EventArgs, IContentEventData<TValue>
     {
         /*********
         ** Properties
@@ -27,6 +27,9 @@ namespace StardewModdingAPI.Framework.Content
         /// <summary>The content data being read.</summary>
         public TValue Data { get; protected set; }
 
+        /// <summary>The content data type.</summary>
+        public Type DataType { get; }
+
 
         /*********
         ** Public methods
@@ -36,11 +39,21 @@ namespace StardewModdingAPI.Framework.Content
         /// <param name="assetName">The normalised asset name being read.</param>
         /// <param name="data">The content data being read.</param>
         /// <param name="getNormalisedPath">Normalises an asset key to match the cache key.</param>
-        public ContentEventBaseHelper(string locale, string assetName, TValue data, Func<string, string> getNormalisedPath)
+        public ContentEventData(string locale, string assetName, TValue data, Func<string, string> getNormalisedPath)
+            : this(locale, assetName, data, data.GetType(), getNormalisedPath) { }
+
+        /// <summary>Construct an instance.</summary>
+        /// <param name="locale">The content's locale code, if the content is localised.</param>
+        /// <param name="assetName">The normalised asset name being read.</param>
+        /// <param name="data">The content data being read.</param>
+        /// <param name="dataType">The content data type being read.</param>
+        /// <param name="getNormalisedPath">Normalises an asset key to match the cache key.</param>
+        public ContentEventData(string locale, string assetName, TValue data, Type dataType, Func<string, string> getNormalisedPath)
         {
             this.Locale = locale;
             this.AssetName = assetName;
             this.Data = data;
+            this.DataType = dataType;
             this.GetNormalisedPath = getNormalisedPath;
         }
 
@@ -60,8 +73,8 @@ namespace StardewModdingAPI.Framework.Content
         {
             if (value == null)
                 throw new ArgumentNullException(nameof(value), "Can't set a loaded asset to a null value.");
-            if (!this.Data.GetType().IsInstanceOfType(value))
+            if (!this.DataType.IsInstanceOfType(value))
-                throw new InvalidCastException($"Can't replace loaded asset of type {this.GetFriendlyTypeName(this.Data.GetType())} with value of type {this.GetFriendlyTypeName(value.GetType())}. The new type must be compatible to prevent game errors.");
+                throw new InvalidCastException($"Can't replace loaded asset of type {this.GetFriendlyTypeName(this.DataType)} with value of type {this.GetFriendlyTypeName(value.GetType())}. The new type must be compatible to prevent game errors.");
 
             this.Data = value;
         }

src/StardewModdingAPI/Framework/Content/ContentEventHelper.cs

@@ -5,7 +5,7 @@ using Microsoft.Xna.Framework.Graphics;
 namespace StardewModdingAPI.Framework.Content
 {
     /// <summary>Encapsulates access and changes to content being read from a data file.</summary>
-    internal class ContentEventHelper : ContentEventBaseHelper<object>, IContentEventHelper
+    internal class ContentEventHelper : ContentEventData<object>, IContentEventHelper
     {
         /*********
         ** Public methods

src/StardewModdingAPI/Framework/Content/ContentEventHelperForDictionary.cs

@@ -5,7 +5,7 @@ using System.Linq;
 namespace StardewModdingAPI.Framework.Content
 {
     /// <summary>Encapsulates access and changes to dictionary content being read from a data file.</summary>
-    internal class ContentEventHelperForDictionary<TKey, TValue> : ContentEventBaseHelper<IDictionary<TKey, TValue>>, IContentEventHelperForDictionary<TKey, TValue>
+    internal class ContentEventHelperForDictionary<TKey, TValue> : ContentEventData<IDictionary<TKey, TValue>>, IContentEventHelperForDictionary<TKey, TValue>
     {
         /*********
         ** Public methods

src/StardewModdingAPI/Framework/Content/ContentEventHelperForImage.cs

@@ -5,7 +5,7 @@ using Microsoft.Xna.Framework.Graphics;
 namespace StardewModdingAPI.Framework.Content
 {
     /// <summary>Encapsulates access and changes to dictionary content being read from a data file.</summary>
-    internal class ContentEventHelperForImage : ContentEventBaseHelper<Texture2D>, IContentEventHelperForImage
+    internal class ContentEventHelperForImage : ContentEventData<Texture2D>, IContentEventHelperForImage
     {
         /*********
         ** Public methods

src/StardewModdingAPI/IContentEventData.cs

@@ -18,6 +18,9 @@ namespace StardewModdingAPI
         /// <summary>The content data being read.</summary>
         TValue Data { get; }
 
+        /// <summary>The content data type.</summary>
+        Type DataType { get; }
+
 
         /*********
         ** Public methods

src/StardewModdingAPI/StardewModdingAPI.csproj

@@ -150,7 +150,7 @@
     <Compile Include="Framework\AssemblyDefinitionResolver.cs" />
     <Compile Include="Framework\AssemblyParseResult.cs" />
     <Compile Include="Framework\CommandManager.cs" />
-    <Compile Include="Framework\Content\ContentEventBaseHelper.cs" />
+    <Compile Include="Framework\Content\ContentEventData.cs" />
     <Compile Include="Framework\Content\ContentEventHelper.cs" />
     <Compile Include="Framework\Content\ContentEventHelperForDictionary.cs" />
     <Compile Include="Framework\Content\ContentEventHelperForImage.cs" />
@@ -165,10 +165,10 @@
     <Compile Include="Framework\Serialisation\SelectiveStringEnumConverter.cs" />
     <Compile Include="Framework\Serialisation\SemanticVersionConverter.cs" />
     <Compile Include="ICommandHelper.cs" />
+    <Compile Include="IContentEventData.cs" />
     <Compile Include="IContentEventHelper.cs" />
     <Compile Include="IContentEventHelperForDictionary.cs" />
     <Compile Include="IContentEventHelperForImage.cs" />
-    <Compile Include="IContentEventData.cs" />
     <Compile Include="IModRegistry.cs" />
     <Compile Include="Events\LocationEvents.cs" />
     <Compile Include="Events\MenuEvents.cs" />