I need to calculate the current offset from UTC time when a page is loaded. This I can do very simply via a javascript function call as part of the page's body onload event as shown below:
<script type="text/javascript" language="javascript">
function getOffset() {
var curUTCDate = new Date();
var iMins = curUTCDate.getTimezoneOffset();
return iMins;
}
</script>
<body id="bodymain" onload="javascript:document.forms[0]['hdnOffset'].value=getOffset();">
<form id="form1" runat="server">
<input id="hdnOffset" runat="server"/>
<asp:Label ID="lblText" runat="server"></asp:Label>
However when I try to use this value in the code behind as part of Page_LoadComplete on the server side the offset value has not been set as shown below
protected void Page_LoadComplete(object sender, EventArgs e)
{
if (!String.IsNullOrEmpty(hdnOffset.Value))
{
lblText.Text = hdnOffset.Value + " value set";
}
else
{
lblText.Text = " value not set ";
}
}
however the offset does bee available once the Page has fully rendered as its value is now displayed in the input box. So to me this looks as if the javascript called as part of a body onload event only gets called after the Page has pletely loaded.
How is this even possible?
I need to calculate the current offset from UTC time when a page is loaded. This I can do very simply via a javascript function call as part of the page's body onload event as shown below:
<script type="text/javascript" language="javascript">
function getOffset() {
var curUTCDate = new Date();
var iMins = curUTCDate.getTimezoneOffset();
return iMins;
}
</script>
<body id="bodymain" onload="javascript:document.forms[0]['hdnOffset'].value=getOffset();">
<form id="form1" runat="server">
<input id="hdnOffset" runat="server"/>
<asp:Label ID="lblText" runat="server"></asp:Label>
However when I try to use this value in the code behind as part of Page_LoadComplete on the server side the offset value has not been set as shown below
protected void Page_LoadComplete(object sender, EventArgs e)
{
if (!String.IsNullOrEmpty(hdnOffset.Value))
{
lblText.Text = hdnOffset.Value + " value set";
}
else
{
lblText.Text = " value not set ";
}
}
however the offset does bee available once the Page has fully rendered as its value is now displayed in the input box. So to me this looks as if the javascript called as part of a body onload event only gets called after the Page has pletely loaded.
How is this even possible?
Share Improve this question edited Apr 14, 2011 at 16:07 BalusC 1.1m376 gold badges3.7k silver badges3.6k bronze badges asked Apr 14, 2011 at 15:57 Johnv2020Johnv2020 2,1463 gold badges20 silver badges36 bronze badges 1-
Because the body onload event occurs on the client side after the page has been fully rendered from the server. The only event that occurs on the server at this point is
Unload. If you're expecting client-to-server munication without a postback, you'll need to use ajax. – Jim Schubert Commented Apr 14, 2011 at 16:12
3 Answers
Reset to default 8You're confusing two pletely different "load" events here.
First, the server side code (in your case ASP.NET) runs in its entirety. In this cycle, there are a couple of things that happen, and among them are the Load and LoadComplete events.
When the server is done determining what should be rendered, it starts sending stuff (HTML and JavaScript, usually) to the browser. On the browser end, another load event is triggered - that of the <body> element on the page. They're named the same, but they're pletely independent.
To fix this problem, set lblText.Text to "value not set" on the server side, and change it in JavaScript when you change the offset indicator.
Server side:
protected void Page_LoadComplete(object sender, EventArgs e)
{
// Possibly even better to do this in the properties of the control...
lblText.Text = "value not set...";
}
Client side:
<script type="text/javascript" language="javascript">
function setOffset() {
var curUTCDate = new Date();
var iMins = curUTCDate.getTimezoneOffset();
document.forms[0]['hdnOffset'].value = iMins;
document.getElementById('lblText').innerHtml = 'value set';
}
</script>
<body id="bodymain" onload="javascript:setOffset();">
If you're not using ASP.NET 4, where you are given extensive control over the client-side IDs of your controls, you should take a look at jQuery. It's a javascript library that you can use for an endless amount of things, which will in this specific case make it a lot easier to find the label control.
The ASP.Net will have finished processing the page before it returns the HTML to the browser at which point the onload function is called.
Refer to the following link to read about Page life cycle ..
http://msdn.microsoft./en-us/library/ms178472.aspx