Answer Posted / ashutosh tripathi

Unfortunately there is not built in support to change page
themes at runtime. Here is a simple code which can be used
to change page themes at runtime:
At first though we may say we can easily achieve this by
coding it in Page_Preinit Event as shown below.

protected void Page_PreInit(object sender, EventArgs e)
{
Page.Theme = "Black"

}

But problem with this is we cant assign value from dropdown
box because Page_Preinit event is fired much before
dropdown has changed value.

To resolve this issue, just use the following steps:
1-Create one session variable which will hold current theme
value
2-On selection change event of dropdown combo box , assign
value form combo box to session variable.
3-During Page_preInit Event assign this variable value to
Page.Theme property.
4-Stop page loading and reload same page again using
server.transfer method as shown below


protected void Page_PreInit(object sender, EventArgs e)
{
string thm;
thm = (string)Session["themeSelected"];
if (thm != null)
{
Page.Theme = thm;
DropDownList1.Text = thm;
}
else
{
Session["themeSelected"] = DropDownList1.Text;
Page.Theme = "Blue";
}

protected void DropDownList1_SelectedIndexChanged(object
sender, EventArgs e)
{
Session["themeSelected"] = DropDownList1.Text;
Server.Transfer(Request.FilePath);

}

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