Wednesday, June 19, 2013

What is AutoEventWireup?

Posted by Rahul Kharde at 9:30 PM

The ASP.NET page framework also supports an automatic way to associate page events and methods. If the AutoEventWireup attribute of the Page directive is set to true (or if it is missing, since by default it is true), 

  • AutoEventWireup is an attribute in Page directive.  
  • AutoEventWireup is a Boolean attribute that indicates whether the ASP.NET pages events are auto-wired. 
  • AutoEventWireup will have a value true or false. By default it is true.

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Default.aspx.cs" Inherits="WebApplication2._Default" %>


the page framework calls page events automatically, specifically the Page_Init and Page_Load methods. In that case, no explicit Handles clause or delegate is needed.

Example 1

With AutoEventWireup="true"

HTML Code

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Default.aspx.cs" Inherits="WebApplication2._Default" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
    <title>Untitled Page</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
   
        <asp:Button ID="Button1" runat="server" onclick="Button1_Click" Text="Button" />
   
    </div>
    </form>
</body>
</html>

Code

protected void Page_Load(object sender, EventArgs e)
{
    Response.Write("IN");
}

protected void Button1_Click(object sender, EventArgs e)
{
    Response.Write("<br>Button Click");
}

When we click Button then both page load and button click event get fired.

OUTPUT

IN
Button Click





Example 2

With  AutoEventWireup="false"

Now set the AutoEventWireup propoerty false

<%@ Page Language="C#" AutoEventWireup="false" CodeBehind="Default.aspx.cs" Inherits="WebApplication2._Default" %>

Again click the Button Event this time only click event get fired.

OUTPUT

Button Click


Why my ASP.NET events fire twice?

A very common question asked. The simple answer to this question is:

If you have AutoEventWireup="true" as well as you also have defined delegates for the event handling in your code, .NET Framework will automatically call methods based on their names and also the methods you defined explicitly.


Disadvantages of AutoEventWireup attribute
  1. AutoEventWireup uses fixed naming convention for the events. Page events handlers have specific predictable names. This limits your flexibility in how you name event handlers.
  2. If you do set AutoEventWireup to true, Visual Studio will generate code to bind the events and the page framework will automatically call events based on their names. This can result in the same event code being called twice when the page runs. As a consequence, you should always leave AutoEventWireup set to false when working in Visual Studio.
  3. Another disadvantage is that performance is adversely affected, because ASP.NET searches for methods at run-time. For a Web site with high traffic volumes, the impact on performance could be significant.



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