Calling a javascript library from ASP.NET

Question

This is a fairly newbie question I'm sure. I'm looking at replacing our server side charting library with the open source javascript library 'flot'. I can use ASP in the javascript used to call the library as per the following example

<div id="placeholder" style="width: 600px; height: 300px;">
</div>
<script type="text/javascript">
    $(function () {
        var d = [<%
        for (var i = 0; i < 10; i++) {
            if(i > 1)  
                Response.Write(",");  

            Response.Write("[" + i + "," + Math.Sin(i) + "]");
        }%>];

        $.plot($("#placeholder"), [d]);
    });
</script>

This works a charm but what I really need to do is display data from a method in my code behind file (and ultimately a database). A quick Google suggests that I need to use AJAX to accomplish this but I would like to do it on page load.

It strikes me as something that should be simple to do but then I am relatively new to web development (I'm a windows forms developer by trade and an MS Certified one at that so I know my way around C#).

Any help or pointers would be greatly appreciated.

Cheers,

Neil.

Ralph Lavelle · Accepted Answer · 2011-12-14 10:03:34Z

1

Very broadly, what you might consider is this - using jQuery AJAX to call a 'code-behind' page to generate your 'd' variable, and then when that returns from the server, using it in your $.plot($("#placeholder"), [d]); statement.

You can create a handler class, say 'GenerateData.ashx' which gets stuff from the database, and Response.Write()s it all out as your list of i and Sin(i) values, then

$(function () {
    $.ajax({
        url: "GenerateData.ashx",
        success: function(data){
            $.plot($("#placeholder"), data);
        }
    })
};

Something along those lines...

answered Dec 14, 2011 at 10:03

Ralph Lavelle

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2 Comments

mister_b Over a year ago

I think I can see what you're getting at, I'm starting to think the best way is to get my data from a webservice anyway. It still strikes me as bit odd though to load the page and then use AJAX to go and get my data and build my graph. Could this not all be done on my page load somehow?

Ralph Lavelle Over a year ago

Well, the AJAX-y part assumes an asynchronous loading. There might be a delay in loading the data from the database, and it could be useful to have shown the user the rest of the page before that. That also allows them to change the view of the data, which you can fetch without redrawing the rest of the page.

Tom Robinson · Accepted Answer · 2011-12-14 09:27:19Z

0

This isn't necessarily the best practice solution, but you could generate the JavaScript dynamically on the server during page load.

This would be a good starting point: MSDN: ClientScriptManager.RegisterClientScriptBlock Method

answered Dec 14, 2011 at 9:27

Tom Robinson

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Comments

Rupendra · Accepted Answer · 2011-12-14 09:47:20Z

0

You can call some C# function in your Java script code using :

<%# C#_FunctionName(parmVal1,ParamVal2) %>

it will return the return value of the C# function, or execute the C# function.

Thanks

answered Dec 14, 2011 at 9:47

Rupendra

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2 Comments

mister_b Over a year ago

I have placed the following code in my script... var d = [ <%# C#_GetData()%> ]; I get a compilation error when I run this saying 'Preprocessor directives must appear as the first non-whitespace character on a line'. I have tried moving the code around and then I get errors such as 'Preprocessor directive expected'.

Rupendra Over a year ago

Is C#_GetData() name of your function? I added C# only to indicate it as a C# function. If by mistake you added C#_ with the name of your function, Then remove it and try to compile your code.

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