Written by Lara Kannan in ,


ASP.NET : Dynamically change a style at Run-Time

A nice feature of CSS is the ability to assign multiple classes to can DOM element via the class attribute. This opens up the possibility to dynamically set a class assignment based on some logic as the page is being rendered.

The example below demonstrates having a common style rule and a rule added at run-time. Of course you are not limited to this methodology, there are many ways to apply styles to an element.
<div class="contentBox bkg1">...</div>
I find the solution from Chris blog, for easiest way to set something like a dynamic style at run-time is to define a public method in the page class to return the desired rule. For my demonstration I will return a style rule name based on a QueryString parameter, but you can use all sorts of criteria. I also chose to apply the rule to the Body tag.

This is a simple method to return a style rule to define the background color of the page. I have three rules defined.
public string GetBackgroundClass()
{
    switch ( Request.QueryString["bkg"])
    {
        case "1":
            return "bkg1";
        case "2":
            return "bkg2";
        case "3":
            return "bkg3";
        default:
            return "bkg1";
    }
}
The style rules just set the color as follows, a nice egg shell (at least that is what I call it), red and blue.
.bkg1
{
    background-color: #FFFFCC;
}

.bkg2
{
    background-color: #C30000;
}

.bkg3
{
    background-color: #0000CC;
}
Finally I just inline the call to the method in the HTML markup:
<body class="<%=GetBackgroundClass() %>">
I hope this ll help you. A 'Thank You' would be nice!

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