将javascript变量传递到服务器端C＃逻辑

Question

Is there a way to assign/pass/copy a javascript variable to a server side variable in C#? For the sake of argument, let's say that I was able to parse some JSON for variables that I want to store and assign them on the client (ie. var = FirstName and var = 25 and var = someDateTime, etc) .

Answer 1

Javascript variables exist on the client so in order to get those values into the server you'll need to execute a request from the client. You probably want an approach called AJAX. AJAX involves Javascript making requests to the server in the background of your page. You'll set up a C# web page that expects these background requests. If you use a GET request then then place the variables in the query string of your AJAX request to your new C# page. If you want to use a POST request then you'll set parameters in the data that you post to your page.

Libraries like jQuery make this kind of thing pretty simple.

Answer 2

There's no direct way to access variables in client-side code from your server-side code.

An easy way, without writing handlers, ajax posts, etc., to accomplish this is to simply store the java script variable in a hidden text box and retrieve it on your post. You can also write back to the hidden field and feed your script with the value, eg

Markup

<asp:HiddenField runat="server" Id="JavascriptValue" value="0">

Script

<script>
   var myValue = <%=JavascriptValue.Value%>
</script>

Server-Side

protected void Page_Load(object sender, EventArgs e)
{
string val = JavascriptValue.Value;
}

Answer 3

what I did is save the javaScript variable in a cookie and then read it from C#.

JavaScript Code:

<script>
$(document).ready(function () {
   createCookie("height", $(window).height(), "10");
 });

 function createCookie(name, value, days) {
   var expires;
   if (days) {
     var date = new Date();
     date.setTime(date.getTime() + (days * 24 * 60 * 60 * 1000));
     expires = "; expires=" + date.toGMTString();
   } else {
     expires = "";
   }
   document.cookie = escape(name) + "=" + escape(value) + expires + "; path=/";
  }
</script>  

C# Code:

height of browser:@Request.Cookies["height"].Value;   

Answer 4

Write the value to a control (eg HiddenField ) via JS and read that on the postback.

You can register hidden fields from code-behind on the Page_Load

if (this.Request.Form["myHiddenField"] == null) { 
    ClientScript.RegisterHiddenField("myHiddenField", ""); }

populate it with a script

ClientScript.RegisterOnSubmitStatement(this.GetType(),
     MethodBase.GetCurrentMethod().DeclaringType.Name + "_myHiddenField",
     "var res=document.getElementById('myHiddenField');if(res!=null){res.value='some value';}");

and read it on postbacks (also Page_Load )

var myValue = (!IsPostBack)
    ? null
    : this.Request.Form["myHiddenField"];