The AutoEventWireup attribute may have a value of true or false.
When an ASP.NET Web Application is created by using Microsoft Visual Studio .NET, the value of the AutoEventWireup attribute is set as false.
We can specify the default value of the AutoEventWireup attribute in the following locations:
The Machine.config file.
The Web.config file.
Individual Web Forms (.aspx files).
Web User Controls (.ascx files)
The value of the AutoEventWireup attribute can be declared in the
If you make these changes in the Machine.config file, the changes affect all ASP.NET Web Forms on the computer. If you make these changes in the Web.config file, the changes affect only the application that the file belongs to. However, to make changes in the individual Web Form Only, we have to add the AutoEventWireup attribute to the @ Page directive, as shown above.
Check out the Code
When we create a new ASP.NET Web Application in Visual Studio .NET, as mentioned earlier, by default, the value of the AutoEventWireup attribute is set to false in the .aspx page and event handlers are automatically created. We can find this in the InitializeComponent method:
this.Load += new System.EventHandler(this.Page_Load);
The best way to see the working of this attribute would be:
Declare a string variable msg as public in WebForm1.aspx.cs.
In the HTML section of WebForm1.aspx, enter the following code in the section: <% Response.Write(msg); %>
In the Page_Load, you could enter a value for the variable msg declared.
msg= "We are in Page_Load()";
On running the application, you will get the message We are in Page_Load() [hereafter referred to as message]. Note: this is in the default case where the attribute is set to false.
Now try commenting the event handler code for the Page_Load in the aspx.cs file; and set the AutoEventWireup attribute to false in the .aspx page. On running the application this time, you will not get the message.
Now with the event handler code for the Page_Load in the aspx.cs file still commented; set the AutoEventWireup attribute to true in the .aspx page. On running the application this time, you will get the message.
Reason: In the case where AutoEventWireup attribute is set to false (by default), event handlers are automatically required for Page_Load or Page_Init. However, when we set the value of the AutoEventWireup attribute to true, the ASP.NET runtime does not require events to specify event handlers like Page_Load or Page_Init.
A thing to be kept in mind is that the AutoEventWireup attribute of the Page directive is set to true by default for the machine (check out the value of this attribute in the machine.config) but set to false by default for a .aspx page). So if it is missing, since by default it is true (i.e., at the machine level), 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.
Performance Issues
We must not set the value of the AutoEventWireup attribute to true if performance is a key consideration. If we set the value of the AutoEventWireup attribute to true, the ASP.NET page framework must make a call to the CreateDelegate method for every Web Form (.aspx page), and instead of relying on the automatic hookup, manually override the events from the page.
Credits
The whole thing was really simple but I just thought of posting it online; hope it helps someone. To give credit to where it is due. Most of the information was garnered from different places on the net. I've just complied them together and added a bit of my own to help folks along their way. I was also able to find an article related to this in MSDN Online (Article ID: 317690) but for VB.NET.
posted by Soumalyade @ 9:17 PM
