Html.Partial vs Html.RenderPartial & Html.Action vs Html.RenderAction

Question

In ASP.NET MVC, what is the difference between:

• Html.Partial and Html.RenderPartial
• Html.Action and Html.

Answer 1

Think of @Html.Partial as HTML code copied into the parent page. Think of @Html.RenderPartial as an .ascx user control incorporated into the parent page. An .ascx user control has far more overhead.

'@Html.Partial' returns a html encoded string that gets constructed inline with the parent. It accesses the parent's model.

'@Html.RenderPartial' returns the equivalent of a .ascx user control. It gets its own copy of the page's ViewDataDictionary and changes made to the RenderPartial's ViewData do not effect the parent's ViewData.

Using reflection we find:

public static MvcHtmlString Partial(this HtmlHelper htmlHelper, string partialViewName, object model, ViewDataDictionary viewData)
{
    MvcHtmlString mvcHtmlString;
    using (StringWriter stringWriter = new StringWriter(CultureInfo.CurrentCulture))
    {
        htmlHelper.RenderPartialInternal(partialViewName, viewData, model, stringWriter, ViewEngines.Engines);
        mvcHtmlString = MvcHtmlString.Create(stringWriter.ToString());
    }
    return mvcHtmlString;
}

public static void RenderPartial(this HtmlHelper htmlHelper, string partialViewName)
{
    htmlHelper.RenderPartialInternal(partialViewName, htmlHelper.ViewData, null, htmlHelper.ViewContext.Writer, ViewEngines.Engines);
}