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
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
- 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.
- 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.
- 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.
The disadvantage of the AutoEventWireup attribute is that it requires that the page event handlers have specific, predictable names. This limits your flexibility in how you name your event handlers. Therefore, in Visual Studio, the AutoEventWireup attribute is set to false by default and the designer generates explicit code to bind page events to methods.
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