Pass an array of integers to ASP.NET Web API?

Question

I have an ASP.NET Web API (version 4) REST service where I need to pass an array of integers.

Here is my action method:

Answer 1

ASP.NET Core 2.0 Solution (Swagger Ready)

Input

DELETE /api/items/1,2
DELETE /api/items/1

Code

Write the provider (how MVC knows what binder to use)

public class CustomBinderProvider : IModelBinderProvider
{
    public IModelBinder GetBinder(ModelBinderProviderContext context)
    {
        if (context == null)
        {
            throw new ArgumentNullException(nameof(context));
        }

        if (context.Metadata.ModelType == typeof(int[]) || context.Metadata.ModelType == typeof(List))
        {
            return new BinderTypeModelBinder(typeof(CommaDelimitedArrayParameterBinder));
        }

        return null;
    }
}

Write the actual binder (access all sorts of info about the request, action, models, types, whatever)

public class CommaDelimitedArrayParameterBinder : IModelBinder
{

    public Task BindModelAsync(ModelBindingContext bindingContext)
    {

        var value = bindingContext.ActionContext.RouteData.Values[bindingContext.FieldName] as string;

        // Check if the argument value is null or empty
        if (string.IsNullOrEmpty(value))
        {
            return Task.CompletedTask;
        }

        var ints = value?.Split(',').Select(int.Parse).ToArray();

        bindingContext.Result = ModelBindingResult.Success(ints);

        if(bindingContext.ModelType == typeof(List))
        {
            bindingContext.Result = ModelBindingResult.Success(ints.ToList());
        }

        return Task.CompletedTask;
    }
}

Register it with MVC

services.AddMvc(options =>
{
    // add custom binder to beginning of collection
    options.ModelBinderProviders.Insert(0, new CustomBinderProvider());
});

Sample usage with a well documented controller for Swagger

/// 

/// Deletes a list of items.
/// 
/// The list of unique identifiers for the  items.
/// The deleted item.
/// The item was successfully deleted.
/// The item is invalid.
[HttpDelete("{itemIds}", Name = ItemControllerRoute.DeleteItems)]
[ProducesResponseType(typeof(void), StatusCodes.Status204NoContent)]
[ProducesResponseType(typeof(void), StatusCodes.Status404NotFound)]
public async Task Delete(List itemIds)
=> await _itemAppService.RemoveRangeAsync(itemIds);

EDIT: Microsoft recommends using a TypeConverter for these kids of operations over this approach. So follow the below posters advice and document your custom type with a SchemaFilter.