Passing parameters to modelbinder on action parameter - asp.net

Question

I wish to use a modelbinder I've made directly on an action method parameter. Such as:
public ActionResult MyAction([ModelBinder(typeof(MyBinder))] string param1)
However, I need to pass a string into the binder itself, so I was wondering if you could do something along the lines of:
public ActionResult MyAction([MyBinder("mystring")] string param1)
Is it possible?

Answer 1

No, you cannot pass parameters via the attribute declaration. If you look at the source code for ModelBinderAttribute, you will see that its constructor takes only a type argument, that it has no other properties, and that it is a sealed class. So this road is a dead end.
The only way to get information into the ModelBinder that I know of is the FormCollection itself.
You could, however, make a parent binder type and subtype it for each param value which you intend to use. It's messy, but it would work in the example you give.

Answer 2

Yes, it's possible. You should a create class drived from System.Web.Mvc.CustomModelBinder, and override the method GetBinder. For example, here implementation that takes in addition to a Type object, also an object array for model binder constructor parameters:
public sealed class MyModelBinderAttribute : CustomModelBinderAttribute
{
/// <summary>
/// Gets or sets the type of the binder.
/// </summary>
/// <returns>The type of the binder.</returns>
public Type BinderType { get; }
/// <summary>
/// Gets or sets the parameters for the model binder constructor.
/// </summary>
public object[] BinderParameters { get; }
/// <summary>
/// Initializes a new instance of the <see cref="T:System.Web.Mvc.ModelBinderAttribute" /> class.
/// </summary>
/// <param name="binderType">The type of the binder.</param>
/// <param name="binderParameters">The parameters for the model binder constructor.</param>
/// <exception cref="T:System.ArgumentNullException">The <paramref name="binderType" /> parameter is null.</exception>
public MyModelBinderAttribute(Type binderType, params object[] binderParameters)
{
if (null == binderType)
{
throw new ArgumentNullException(nameof(binderType));
}
if (!typeof(IModelBinder).IsAssignableFrom(binderType))
{
throw new ArgumentException(string.Format(CultureInfo.CurrentCulture,
"An error occurred when trying to create the IModelBinder '{0}'. Make sure that the binder has a public parameterless constructor.",
binderType.FullName), nameof(binderType));
}
this.BinderType = binderType;
this.BinderParameters = binderParameters ?? throw new ArgumentNullException(nameof(binderParameters));
}
/// <summary>Retrieves an instance of the model binder.</summary>
/// <returns>A reference to an object that implements the <see cref="T:System.Web.Mvc.IModelBinder" /> interface.</returns>
/// <exception cref="T:System.InvalidOperationException">An error occurred while an instance of the model binder was being created.</exception>
public override IModelBinder GetBinder()
{
IModelBinder modelBinder;
try
{
modelBinder = (IModelBinder)Activator.CreateInstance(this.BinderType, this.BinderParameters);
}
catch (Exception ex)
{
throw new InvalidOperationException(string.Format(CultureInfo.CurrentCulture,
"An error occurred when trying to create the IModelBinder '{0}'. Make sure that the binder has a public parameterless constructor.",
this.BinderType.FullName), ex);
}
return modelBinder;
}
}

Answer 3

Just a thought, I am looking at needing a similar requirement and I wanted to pass in a castled service.
I wonder if you could use the ControllerContext passed into the Binder and expose the service/property or whever via a property?
Just a thought, I am going to try this now and I will feed back
Rich