Returning JSON and Partial HTML from ASP.NET MVC Controller Actions

In this tutorial, we will explore how to create ASP.NET MVC controller actions that can return either JSON or partial HTML depending on the request. This is particularly useful when building web applications that require asynchronous updates or when working with AJAX requests.

Introduction to ASP.NET MVC Controller Actions

ASP.NET MVC controller actions are methods that handle HTTP requests and return a response to the client. The response can be in various formats, including JSON, HTML, XML, and more. To return JSON or partial HTML from a controller action, we need to use specific return types and helper methods provided by ASP.NET MVC.

Returning JSON

To return JSON from a controller action, we can use the Json method provided by the Controller class. This method takes an object as a parameter and serializes it into a JSON string.

public ActionResult SomeActionMethod() 
{ 
    return Json(new { foo = "bar", baz = "Blech" });
}

We can also use the JsonRequestBehavior.AllowGet property to allow GET requests to return JSON. This is necessary because, by default, ASP.NET MVC only allows POST requests to return JSON.

[HttpGet]
public ActionResult MyMethod(int keyid, int newval)
{
    // ...
    return Json(new { success = true, oldval = oldval },
                JsonRequestBehavior.AllowGet);
}

Returning Partial HTML

To return partial HTML from a controller action, we can use the PartialView method provided by the Controller class. This method takes a view name as a parameter and returns a partial view result.

public ActionResult SomeActionMethod() 
{ 
    return PartialView("viewname");
}

We can also pass a model to the partial view using the PartialView overload that takes an object as a parameter.

public ActionResult SomeActionMethod() 
{ 
    var model = new MyModel();
    return PartialView("viewname", model);
}

Determining the Response Type

To determine whether to return JSON or partial HTML, we can use various techniques such as checking the request headers, query string parameters, or route values. One common approach is to check the Accept header of the request.

public ActionResult SomeActionMethod() 
{ 
    if (Request.AcceptTypes.Contains("application/json"))
    {
        return Json(new { foo = "bar", baz = "Blech" });
    }
    else
    {
        return PartialView("viewname");
    }
}

We can also use jQuery to make AJAX requests and specify the response type using the dataType property.

$.ajax({
  type: 'get',
  dataType: 'json',
  url: '/MyController/MyMethod',
  success: function (response, textStatus, jqXHR) {
    // ...
  }
});

Best Practices

When returning JSON or partial HTML from ASP.NET MVC controller actions, it’s essential to follow best practices such as:

• Using the JsonRequestBehavior.AllowGet property to allow GET requests to return JSON
• Checking the request headers and query string parameters to determine the response type
• Using jQuery to make AJAX requests and specify the response type
• Returning partial views with a model to ensure data is properly bound

By following these best practices and using the techniques outlined in this tutorial, you can create robust and scalable ASP.NET MVC applications that return JSON and partial HTML from controller actions.