Deserialize Unknown Enum Values

Author: GuyWhoKnowsTheGuy

src/MudBlazorPages/AppSettings.cs

@@ -2,11 +2,27 @@
 
 namespace MudBlazorPages;
 
+public enum ExampleEnum
+{
+    None = 0,
+    FirstValue = 1,
+}
+
 public class AppSettings
 {
     [JsonPropertyName("stringValue")]
     public string? StringValue { get; set; }
 
     [JsonPropertyName("intValue")]
     public int IntValue { get; set; }
+
+    [JsonPropertyName("enumValue")]
+    public ExampleEnum EnumValue { get; set; }
+
+    /// <summary>
+    ///     This property simply demonstrates that non-existent enum values will not cause an exception during deserialization.
+    ///     See <see cref="Util.UnknownEnumConverter"/>
+    /// </summary>
+    [JsonPropertyName("nonexistentEnumValue")]
+    public ExampleEnum NonexistentEnumValue { get; set; }
 }

src/MudBlazorPages/Program.cs

@@ -3,8 +3,8 @@
 using Microsoft.AspNetCore.Components.Web;
 using Microsoft.AspNetCore.Components.WebAssembly.Hosting;
 using MudBlazor.Services;
-using System.Text.Json.Serialization;
 using MudBlazorPages;
+using MudBlazorPages.Util;
 
 var builder = WebAssemblyHostBuilder.CreateDefault(args);
 builder.RootComponents.Add<App>("#app");
@@ -13,7 +13,7 @@
 var http = new HttpClient { BaseAddress = new Uri(builder.HostEnvironment.BaseAddress) };
 builder.Services.AddScoped(sp => http);
 
-var appSettings = await http.GetFromJsonAsync<AppSettings>("appsettings.json", new System.Text.Json.JsonSerializerOptions() { Converters = { new JsonStringEnumConverter() } });
+var appSettings = await http.GetFromJsonAsync<AppSettings>("appsettings.json", new System.Text.Json.JsonSerializerOptions() { Converters = { new UnknownEnumConverter() } });
 builder.Services.AddSingleton(appSettings ?? new());
 
 builder.Services.AddMudServices();

src/MudBlazorPages/Util/Generic/UnknownEnumConverter.cs

@@ -0,0 +1,40 @@
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace MudBlazorPages.Util.Generic;
+
+/// <summary>
+///     Copied from https://gaevoy.com/2023/09/26/dotnet-serialization-unknown-enums-handling-api.html
+/// </summary>
+/// <typeparam name="T">An <see cref="Enum"/> type</typeparam>
+public class UnknownEnumConverter<T> : JsonConverter<T> where T : struct, Enum
+{
+    private readonly JsonConverter<T> _underlying;
+
+    public UnknownEnumConverter(JsonConverter<T> underlying)
+        => _underlying = underlying;
+
+    public override T Read(ref Utf8JsonReader reader, Type enumType, JsonSerializerOptions options)
+    {
+        try
+        {
+            return _underlying.Read(ref reader, enumType, options);
+        }
+        catch (JsonException) when (enumType.IsEnum)
+        {
+            return default;
+        }
+    }
+
+    public override bool CanConvert(Type typeToConvert)
+        => _underlying.CanConvert(typeToConvert);
+
+    public override void Write(Utf8JsonWriter writer, T value, JsonSerializerOptions options)
+        => _underlying.Write(writer, value, options);
+
+    public override T ReadAsPropertyName(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+        => _underlying.ReadAsPropertyName(ref reader, typeToConvert, options);
+
+    public override void WriteAsPropertyName(Utf8JsonWriter writer, T value, JsonSerializerOptions options)
+        => _underlying.WriteAsPropertyName(writer, value, options);
+}

src/MudBlazorPages/Util/UnknownEnumConverter.cs

@@ -0,0 +1,23 @@
+using System.Text.Json;
+using System.Text.Json.Serialization;
+using MudBlazorPages.Util.Generic;
+
+namespace MudBlazorPages.Util;
+
+/// <summary>
+///     Copied from https://gaevoy.com/2023/09/26/dotnet-serialization-unknown-enums-handling-api.html
+/// </summary>
+public class UnknownEnumConverter : JsonConverterFactory
+{
+    private readonly JsonStringEnumConverter _underlying = new();
+
+    public sealed override bool CanConvert(Type enumType)
+        => _underlying.CanConvert(enumType);
+
+    public sealed override JsonConverter CreateConverter(Type enumType, JsonSerializerOptions options)
+    {
+        var underlyingConverter = _underlying.CreateConverter(enumType, options);
+        var converterType = typeof(UnknownEnumConverter<>).MakeGenericType(enumType);
+        return (JsonConverter)Activator.CreateInstance(converterType, underlyingConverter);
+    }
+}

src/MudBlazorPages/wwwroot/appsettings.json

@@ -1,4 +1,6 @@
 {
   "stringValue": "Example String Value",
-  "intValue":  4
+  "intValue": 4,
+  "enumValue": "FirstValue",
+  "nonexistentEnumValue": "TheNonexistentEnumValue"
 }