Is there a way to use AJAX on a DropDownList changed event to dynamically modify a partial view on a page? - ajax

Question

Is there a way to use AJAX on a DropDownList changed event to dynamically modify a partial view on a page?
My main page has a DropDownList (DropDownListFor) and a partial view which ONLY contains a list of "items". The items shown in this partial view are dependent upon the item selected in the DropDownList. There's a 1 to many relationship between the DropDownList item and the items in the partial view. So, when the user changes the value of the DropDownList, the content in the partial view will dynamically change to reflect the item selected in the DropDownList.
Here's my DropDownList:
<div data-role="fieldcontain">
Choose Capsule:<br />
#Html.DropDownListFor(x => x.CapsuleFK, new SelectList(Model.Capsules, "pk", "name", "pk"), new { id = "ddlCapsules" })
<br />
</div>
Here's my Partial View declaration on the same page:
<div data-role="fieldcontain">
#Html.Partial("_FillerPartial", Model.Fillers)
</div>
I'm not very familiar with Ajax, but looking at other examples, here's what I have for my Ajax:
$(document).ready(function () {
$('#ddlCapsules').change(function () {
// make ajax call to modify the filler list partial view
var selection = $('#ddlCapsules').val();
var dataToSend = { cappk: selection };
$.ajax({
url: 'Process/GetFillersByCapsule',
data: { cappk: dataToSend },
success: function (data) {
alert("server returned: " + data);
}
});
});
});
And finally, here's a screenshot of what's going on. By changing the "Choose Capsule" drop down list, I want the Filler list to update dynamically:

Answer 1

You can load the drop down list as a partial view from the controller using ajax.
The controller code:
[HttpGet]
public virtual ActionResult GetFillersByCapsule(string cappk)
{
var model = //Method to get capsules by pk, this returns a ViewModel that is used to render the filtered list.
return PartialView("PartialViewName", model);
}
The main view html:
<div id="filteredList">
</div >
The partial view
#model IEnumerable<MyCapsuleModel>
foreach (var x in Model)
{
//Render the appropriate filtered list html.
}
And you can load the filtered list using ajax:
$('#ddlCapsules').change(function () {
// make ajax call to modify the filler list partial view
var selection = $('#ddlCapsules').val();
var dataToSend = { cappk: selection };
$.ajax({
url: 'Process/GetFillersByCapsule',
data: { cappk: dataToSend },
success: function (data) {
$("#filteredList").empty();
$("#filteredList").html(data);
}
});
});
Hope this helps.

Answer 2

You can't update the partial, per se, because the partial will never be rendered again without a page reload. Once you receive the HTML, ASP is done, you're on your own at that point.
What you can do, of course, is switch out the content of a particular div or whatever using JavaScript. Your example in particular screams Knockout, so that's what I would recommend using.
Change your HTML to add a data-bind to your containing div:
<div data-role="fieldcontain" data-bind="foreach: filler">
<button data-bind="text: name"></button>
</div>
And your DropDownList:
#Html.DropDownListFor(x => x.CapsuleFK, new SelectList(Model.Capsules, "pk", "name", "pk"), new { id = "ddlCapsules", data_bind = "event: { change: updateFillers }" })
Then, some JavaScript:
var FillersViewModel = function () {
var self = this;
self.fillers = ko.observableArray([]);
self.updateFillers = function () {
var selection = $('#ddlCapsules').val();
var dataToSend = { cappk: selection };
$.ajax({
url: 'Process/GetFillersByCapsule',
data: { cappk: dataToSend },
success: function (data) {
self.fillers(data.fillers) // where `fillers` is an array
}
});
}
}
var viewModel = new FillersViewModel();
ko.applyBindings(viewModel);
This is a very simplistic example, and you'll need to do some more work to make it do everything you need it to do in your scenario, but the general idea is that every time the dropdown list is changed, Knockout will call your updateFillers method, which will execute the AJAX and put new data into the fillers observable array. Knockout automatically tracks changes to this array (hence the "observable" part), so an update is automatically triggered to any part of your page that relies on it. In this scenario, that's your div containing the buttons. The foreach binding will repeat the HTML inside for each member of the array. I've used a simple button element here just to illustrate, but you would include the full HTML required to create your particular button like interface. The text binding will drop the content of name in between the opening and closing tag. Refer to: http://knockoutjs.com/documentation/introduction.html for all the binding options you have.
There's much more you could do with this. You could implement templates instead of hard-coding your HTML to be repeated in the foreach. And, you can use your partial view to control the HTML for this template. The important part is that Knockout takes the pain out of generating all this repeating HTML for you, which is why I recommend using it.
Hope that's enough to get you started.