ASP.NET MVC - Custom model binder able to process arrays

Question

I need to implement a functionality to allow users to enter price in any form, i.e. to allow 10 USD, 10$, $10,... as input.

I would like to solve this by implementing a custom model binder for Price class.

 class Price { decimal Value; int ID; }

The form contains an array or Prices as keys

keys:
"Prices[0].Value"
"Prices[0].ID"
"Prices[1].Value"
"Prices[1].ID"
...

The ViewModel contains a Prices property:

public List<Price> Prices { get; set; }

The default model binder works nicely as long as the user enters a decimal-convertible string into the Value input. I would like to allow inputs like "100 USD".

My ModelBinder for Price type so far:

public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
{
    Price res = new Price();
    var form = controllerContext.HttpContext.Request.Form;
    string valueInput = ["Prices[0].Value"]; //how to determine which index I am processing?
    res.Value = ParseInput(valueInput) 

    return res;
}

How do I implement a custom model Binder that handles the arrays correctly?

Do I guess correctly that ID is the user ID and not the ID of the Currency? — AxelEckenberger
– AxelEckenberger, Commented Feb 28, 2010 at 10:01
That is ID of the pricing type, not relevant to this question — Marek
– Marek, Commented Feb 28, 2010 at 10:04
No need for multiple currencies - we are fixed to a single currency but need to allow various kinds of input formats like mentioned in the question — Marek
– Marek, Commented Feb 28, 2010 at 10:05
Look into this also: haacked.com/archive/2008/10/23/model-binding-to-a-list.aspx — Martin
– Martin, Commented Mar 19, 2010 at 13:34

Marek · Accepted Answer · 2010-02-28 10:32:35Z

20

Got it: The point is to not try to bind a single Price instance, but rather implement a ModelBinder for List<Price> type:

    public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
    {
        List<Price> res = new List<Price>();
        var form = controllerContext.HttpContext.Request.Form;
        int i = 0;
        while (!string.IsNullOrEmpty(form["Prices[" + i + "].PricingTypeID"]))
        {
            var p = new Price();
            p.Value = Process(form["Prices[" + i + "].Value"]);
            p.PricingTypeID = int.Parse(form["Prices[" + i + "].PricingTypeID"]);
            res.Add(p);
            i++;
        }

        return res;
    }

//register for List<Price>
ModelBinders.Binders[typeof(List<Price>)] = new PriceModelBinder();

edited Feb 28, 2010 at 10:32

answered Feb 28, 2010 at 10:14

Marek

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