Skip to main content

An Event Handler is a subroutine that executes code for a given event.


ASP.NET - Event Handlers

Look at the following code:
<%
lbl1.Text="The date and time is " & now()
%>

<html>
<body>
<form runat="server">
<h3><asp:label id="lbl1" runat="server" /></h3>
</form>
</body>
</html>
When will the code above be executed? The answer is: "You don't know..."

The Page_Load Event

The Page_Load event is one of many events that ASP.NET understands. 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:

Example

<script runat="server">
Sub Page_Load
lbl1.Text="The date and time is " & now()
End Sub
</script>

<html>
<body>
<form runat="server">
<h3><asp:label id="lbl1" runat="server" /></h3>
</form>
</body>
</html>

Show example »
Note: The Page_Load event contains no object references or event arguments!

The Page.IsPostBack Property

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):

Example

<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="Hello World!"
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>

Show example »
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 "Hello World!" to the second label, but the date and time in the first label will not change.

Comments

Post a Comment

Popular posts from this blog

Tip/Trick: Fix Common SEO Problems Using the URL Rewrite Extension

Search engine optimization (SEO) is important for any publically facing web-site.  A large % of traffic to sites now comes directly from search engines, and improving your site’s search relevancy will lead to more users visiting your site from search engine queries.  This can directly or indirectly increase the money you make through your site. This blog post covers how you can use the free Microsoft  URL Rewrite Extension  to fix a bunch of common SEO problems that your site might have.  It takes less than 15 minutes (and no code changes) to apply 4 simple  URL Rewrite  rules to your site, and in doing so cause search engines to drive more visitors and traffic to your site.  The techniques below work equally well with both ASP.NET Web Forms and ASP.NET MVC based sites.  They also works with all versions of ASP.NET (and even work with non-ASP.NET content). [In addition to blogging, I am also now using Twitter for quick updates and to sh...
Post a Comment
Read more

ASP.NET MVC - Set custom IIdentity or IPrincipal

Here's how I do it. I decided to use IPrincipal instead of IIdentity because it means I don't have to implement both IIdentity and IPrincipal. Create the interface interface ICustomPrincipal : IPrincipal { int UserId { get ; set ; } string FirstName { get ; set ; } string LastName { get ; set ; } } CustomPrincipal public class CustomPrincipal : ICustomPrincipal { public IIdentity Identity { get ; private set ; } public bool IsInRole ( string role ) { return false ; } public CustomPrincipal ( string email ) { this . Identity = new GenericIdentity ( email ); } public int UserId { get ; set ; } public string FirstName { get ; set ; } public string LastName { get ; set ; } } CustomPrincipalSerializeModel - for serializing custom information into userdata field in FormsAuthenticationTicket object. public class CustomPrincipalSerializeMode...
8 comments
Read more

linq orderby multiple columns dynamically

So, it's been a while, but I thought I take moment and do my annual blog post ;). I've been playing around with  ASP.NET MVC  and the Linq stuff for  NHibernate  recently. I was in need of an OrderBy extension method that could take a SQL-Like OrderBy string and sort a IQueryable<> or IEnumerable<> collection. I wrote up an implementation that worked, but I just wasn't satisfied with its internals (quite a bit of reflection to get the correct type to construct a LambdaExpression, etc) At any rate, I couldn't leave well enough alone, and, after a bit of Googling, I ran across this  StackOverflow  answer about Dynamic LINQ OrderBy . The extension method wasn't exactly what I was looking for, but that ApplyOrder method is slick, and solved the portion of my implementation that was bothering me. So, I though I would post up my version in case anybody finds it useful. It handles the following inputs: list.OrderBy( "SomeProperty" ); list.Ord...
2 comments
Read more