<p>My current code looks like the following. How can I pass my array to the controller and what kind of parameters must my controller action accept?</p>

<pre><code>function getplaceholders() {
    var placeholders = $('.ui-sortable');
    var result = new Array();
    placeholders.each(function() {
        var ph = $(this).attr('id');
        var sections = $(this).find('.sort');
        var section;

        sections.each(function(i, item) {
            var sid = $(item).attr('id');

            result.push({ 'SectionId': sid, 'Placeholder': ph, 'Position': i });
        });
    });
    alert(result.toString());
    $.post(
        '/portal/Designer.mvc/SaveOrUpdate',
        result,
        function(data) {
            alert(data.Result);
        }, "json");
};
</code></pre>

<p>My controller action method looks like</p>

<pre><code>public JsonResult SaveOrUpdate(IList&lt;PageDesignWidget&gt; widgets)
</code></pre>

Towards the second half of
Create REST API using ASP.NET MVC that speaks both JSON and plain XML
, to quote:
Now we need to accept JSON and XML payload, delivered via HTTP POST. Sometimes your client might want to upload a collection of objects in one shot for batch processing. So, they can upload objects using either JSON or XML format. There's no native support in ASP.NET MVC to automatically parse posted JSON or XML and automatically map to Action parameters. So, I wrote a filter that does it."
He then implements an action filter that maps the JSON to C# objects with code shown.