My application has many models, many of which contain percentage data. These are represented as decimal
or decimal?
structs in the model. However, not
Bind to a string
in your view model. Then when do the conversion back to the real model.
Instead of representing your percentage properties using decimal primitives (see Primitive Obsession), why don't you create a Percentage type to wrap your desired functionality? You should have much more flexibility doing it that way...
One possibility is to write a custom metadata aware attribute:
public class PercentageAttribute : Attribute, IMetadataAware
{
public void OnMetadataCreated(ModelMetadata metadata)
{
metadata.AdditionalValues["percentage"] = metadata.EditFormatString;
}
}
then decorate your view model properties that represent percentages with it:
public class MyViewModel
{
[DisplayFormat(ApplyFormatInEditMode = true, DataFormatString = "{0:P2}")]
[Percentage]
public decimal? Percentage { get; set; }
}
and inside the custom model binder test for the presence of this value:
public class PercentageModelBinder : DefaultModelBinder
{
public override object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
{
if (bindingContext.ModelMetadata.AdditionalValues.ContainsKey("percentage"))
{
var format = (string)bindingContext.ModelMetadata.AdditionalValues["percentage"];
// TODO: do the custom parsing here
throw new NotImplementedException();
}
else
{
// Let the default parsing occur
return base.BindModel(controllerContext, bindingContext);
}
}
}
Now you can register this model binder to all decimals.