Ext.Net MVC - Render partial view with parameter - asp.net-mvc

Question

I have a partial view on my mvc page. The view is rendered by default with no data, but will be updated based on a value selection from a combobox in another section of the page. The partial view takes an id as a parameter which it will use to get the data needed to return the model.
The problem that I am having is that on the initial load, the parameter is null since nothing has been selected and I am getting a null value exception.
Is there a way that I can use an if statement in a direct events call to check the selected item and return 0 is that is null?
See me sample code below for clarification.
Thanks
Here are the relevant parts of my main page (index.cshtml) -
x.ComboBox()
.ID("MyCombo")
.DisplayField("Title")
.ValueField("Number")
.TypeAhead(false)
.Width(500)
.PageSize(10)
.HideBaseTrigger(true)
.MinChars(0)
.TriggerAction(TriggerAction.Query)
.DirectEvents(de =>
{
de.Select.Url = Url.Action("MyPartial");
#* Can I use an if statment here to check the selected item's value? *#
de.Select.ExtraParams.Add(new { id = App.MyCombo.getValue() });
})
.ListConfig(Html.X().BoundList()
.LoadingText("Searching...")
.ItemTpl(Html.X().XTemplate()
.Html(#<text>
<div class="search-item">
<h3><span>{Number}</span>{Title}</h3>
{Description}
</div>
</text>)
)
)
........
#Html.Partial("MyPartial", Model.MyPartialVM)
and here is my controller code -
public ActionResult MyPartial(string id)
{
var vm = new MyPartialViewModel
{
Number = id,
Title = "New Title"
};
ViewData.Model = vm;
var pvr = new Ext.Net.MVC.PartialViewResult
{
ViewData = this.ViewData
};
return pvr;
}
This works if I hardcode a parameter value, but not if I try it as it is now. Here is the error I get -
Message=Cannot perform runtime binding on a null reference
So I was thinking that I can do an if in teh DirectEvents piece to check for a null on the combobox selection, I can inject a 0 when necessary and handle that in the controller. Can this be done?

Answer 1

Try if this works:
x.ComboBox()
.ID("MyCombo")
.DisplayField("Title")
.ValueField("Number")
.TypeAhead(false)
.Width(500)
.PageSize(10)
.HideBaseTrigger(true)
.MinChars(0)
.TriggerAction(TriggerAction.Query)
.DirectEvents(de =>
{
de.Select.Url = Url.Action("MyPartial");
de.Select.ExtraParams.Add(new {
Name = "id",
Value ="App.MyCombo.getValue() == null ? '0' : App.MyCombo.getValue()",
Mode = ParameterMode.Raw
});
})
.ListConfig(Html.X().BoundList()
.LoadingText("Searching...")
.ItemTpl(Html.X().XTemplate()
.Html(#<text>
<div class="search-item">
<h3><span>{Number}</span>{Title}</h3>
{Description}
</div>
</text>)
)
)