The Page.IsPostBack Property
The Page_Load event is triggered when a page loads, and ASP.NET will automatically call the subroutine Page_Load, and execute the code inside it. The Page_Load subroutine runs EVERY time the page is loaded. If you want to execute the code in the Page_Load subroutine only the FIRST time the page is loaded, you can use the Page.IsPostBack property. If the Page.IsPostBack property is false, the page is loaded for the first time, if it is true, the page is posted back to the server (i.e. from a button click on a form):
<script runat=”server”>
Sub Page_Load
if Not Page.IsPostBack then
lbl1.Text=”The date and time is ” & now()
end if
End Sub
Sub Submit(s As Object, e As EventArgs)
lbl2.Text=”The Page is posted back to the server”
End Sub
</script>
<html>
<body>
<form runat=”server”>
<h3><asp:label id=”lbl1″ runat=”server” /></h3>
<h3><asp:label id=”lbl2″ runat=”server” /></h3>
<asp:button text=”Submit” onclick=”submit” runat=”server” />
</form>
</body>
</html>
The example above will write the “The date and time is….” message only the first time the page is loaded. When a user clicks on the Submit button, the submit subroutine will write “The Page is posted back to the server” to the second label, but the date and time in the first label will not change.
