asp.net MVC 1.0 and 2.0 currency model binding - asp.net-mvc

Question

I would like to create model binding functionality so a user can enter ',' '.' etc for currency values which bind to a double value of my ViewModel.
I was able to do this in MVC 1.0 by creating a custom model binder, however since upgrading to MVC 2.0 this functionality no longer works.
Does anyone have any ideas or better solutions for performing this functionality? A better solution would be to use some data annotation or custom attribute.
public class MyViewModel
{
public double MyCurrencyValue { get; set; }
}
A preferred solution would be something like this...
public class MyViewModel
{
[CurrencyAttribute]
public double MyCurrencyValue { get; set; }
}
Below is my solution for model binding in MVC 1.0.
public class MyCustomModelBinder : DefaultModelBinder
{
public override object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
{
object result = null;
ValueProviderResult valueResult;
bindingContext.ValueProvider.TryGetValue(bindingContext.ModelName, out valueResult);
bindingContext.ModelState.SetModelValue(bindingContext.ModelName, valueResult);
if (bindingContext.ModelType == typeof(double))
{
string modelName = bindingContext.ModelName;
string attemptedValue = bindingContext.ValueProvider[modelName].AttemptedValue;
string wantedSeperator = NumberFormatInfo.CurrentInfo.NumberDecimalSeparator;
string alternateSeperator = (wantedSeperator == "," ? "." : ",");
try
{
result = double.Parse(attemptedValue, NumberStyles.Any);
}
catch (FormatException e)
{
bindingContext.ModelState.AddModelError(modelName, e);
}
}
else
{
result = base.BindModel(controllerContext, bindingContext);
}
return result;
}
}

Answer 1

You might try something among the lines:
// Just a marker attribute
public class CurrencyAttribute : Attribute
{
}
public class MyViewModel
{
[Currency]
public double MyCurrencyValue { get; set; }
}
public class CurrencyBinder : DefaultModelBinder
{
protected override object GetPropertyValue(
ControllerContext controllerContext,
ModelBindingContext bindingContext,
PropertyDescriptor propertyDescriptor,
IModelBinder propertyBinder)
{
var currencyAttribute = propertyDescriptor.Attributes[typeof(CurrencyAttribute)];
// Check if the property has the marker attribute
if (currencyAttribute != null)
{
// TODO: improve this to handle prefixes:
var attemptedValue = bindingContext.ValueProvider
.GetValue(propertyDescriptor.Name).AttemptedValue;
return SomeMagicMethodThatParsesTheAttemptedValue(attemtedValue);
}
return base.GetPropertyValue(
controllerContext,
bindingContext, propertyDescriptor,
propertyBinder
);
}
}
public class HomeController: Controller
{
[HttpPost]
public ActionResult Index([ModelBinder(typeof(CurrencyBinder))] MyViewModel model)
{
return View();
}
}
UPDATE:
Here's an improvement of the binder (see TODO section in previous code):
if (!string.IsNullOrEmpty(bindingContext.ModelName))
{
var attemptedValue = bindingContext.ValueProvider
.GetValue(bindingContext.ModelName).AttemptedValue;
return SomeMagicMethodThatParsesTheAttemptedValue(attemtedValue);
}
In order to handle collections you will need to register the binder in Application_Start as you will no longer be able to decorate the list with the ModelBinderAttribute:
protected void Application_Start()
{
AreaRegistration.RegisterAllAreas();
RegisterRoutes(RouteTable.Routes);
ModelBinders.Binders.Add(typeof(MyViewModel), new CurrencyBinder());
}
And then your action could look like this:
[HttpPost]
public ActionResult Index(IList<MyViewModel> model)
{
return View();
}
Summarizing the important part:
bindingContext.ValueProvider.GetValue(bindingContext.ModelName)
A further improvement step of this binder would be to handle validation (AddModelError/SetModelValue)