Here Mudassar Ahmed Khan has explained with an example, how to avoid (Prevent) Page refresh (reload) after SelectedIndexChanged is fired in ASP.Net DropDownList using C# and VB.Net.

The only possible way is to place the DropDownList inside ASP.Net AJAX UpdatePanel so that, instead of Full PostBack which causes Page refresh (reload), a Partial PostBack will occur.

Here Mudassar Ahmed Khan has explained with an example, how to implement AJAX Call using XML using JavaScript XmlHttpRequest (XHR) in ASP.Net MVC Razor.

The Controller’s Action method will be called using JavaScript XmlHttpRequest (XHR) and JSON from View in ASP.Net MVC Razor.

Here Mudassar Ahmed Khan has explained with an example, how to set Session variable using jQuery in ASP.Net using C# and VB.Net.

jQuery is a JavaScript library and JavaScript is a Client Side language and hence directly it is not possible to set Session variable in jQuery.

Thus, the solution is to make an AJAX call using jQuery AJAX and pass the value of JavaScript variable to a Web Method and inside the Web Method, the value will be set in Session variable in ASP.Net using C# and VB.Net .

Here Mudassar Ahmed Khan has explained with an example, how to set Session variable in JavaScript using jQuery in ASP.Net MVC Razor.

JavaScript is a Client Side language and hence directly it is not possible to set Session variable in JavaScript.

Thus, the solution is to make an AJAX call using jQuery AJAX and pass the value of JavaScript variable to a Controller and inside the Controller the value will be set in Session variable in ASP.Net MVC Razor.