Add FlagsEnumModelBinder

src/MAOToolkit.Web/Utilities/ModelBinders/FlagsEnumModelBinder.cs

@@ -0,0 +1,78 @@
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.AspNetCore.Mvc.ModelBinding;
+
+namespace MAOToolkit.Utilities.ModelBinders
+{
+    public class FlagsEnumModelBinder : IModelBinder
+    {
+        public Task BindModelAsync(ModelBindingContext bindingContext)
+        {
+            if (bindingContext is null)
+            {
+                throw new ArgumentNullException(nameof(bindingContext));
+            }
+
+            // Only accept enum values.
+            if (!bindingContext.ModelMetadata.IsFlagsEnum)
+                return Task.CompletedTask;
+
+            var valueProviderResult = bindingContext.ValueProvider.GetValue(bindingContext.ModelName);
+
+            if (valueProviderResult == ValueProviderResult.None)
+            {
+                return Task.CompletedTask;
+            }
+
+            // Get the real enum type.
+            var enumType = bindingContext.ModelType;
+            enumType = Nullable.GetUnderlyingType(enumType) ?? enumType;
+
+            // Each value self may contains a series of actual values, split it with comma.
+            var strs = valueProviderResult.Values.SelectMany(s => s?.Split(',') ?? Array.Empty<string>());
+
+            // Convert all items into enum items.
+            var actualValues = strs.Select(valueString => Enum.Parse(enumType, valueString));
+
+            // Merge to final result.
+            var result = actualValues.Aggregate(0, (current, value) => current | Convert.ToInt32(value));
+
+            // Convert to Enum object.
+            var realResult = Enum.ToObject(enumType, result);
+
+            // Result
+            bindingContext.Result = ModelBindingResult.Success(realResult);
+            return Task.CompletedTask;
+        }
+    }
+
+    /// <inheritdoc />
+    /// <summary>
+    ///     An <see cref="IModelBinderProvider" /> used to provider <see cref="FlagsEnumModelBinder" /> instances.
+    /// </summary>
+    public class FlagsEnumModelBinderProvider : IModelBinderProvider
+    {
+        /// <inheritdoc />
+        /// <summary>
+        ///     Creates a <see cref="IModelBinder" /> based on <see cref="ModelBinderProviderContext" />.
+        /// </summary>
+        /// <param name="context">The <see cref="ModelBinderProviderContext" />.</param>
+        /// <returns>An <see cref="IModelBinder" />.</returns>
+        public IModelBinder? GetBinder(ModelBinderProviderContext context)
+        {
+            if (context is null)
+            {
+                throw new ArgumentNullException(nameof(context));
+            }
+
+            return context.Metadata.IsFlagsEnum ? new FlagsEnumModelBinder() : null;
+        }
+    }
+
+    public static class FlagsEnumModelBinderExtensions
+    {
+        public static void AddFlagsEnumProvider(this MvcOptions option)
+        {
+            option.ModelBinderProviders.Insert(0, new FlagsEnumModelBinderProvider());
+        }
+    }
+}