AutoEventWireup Attribute

Question

Hi What is use of the AutoEventWireup attribute in the Page directive ?

Satyapriya Nayak · Answer

Hi Arun AutoEventWireup is an attribute of the @ Page directive. The AutoEventWireup attribute may have a value of true or false . The value is set to false when you create a new ASP.NET Web Application. This article describes how to set and to change the default values of the AutoEventWireup attribute. This article also describes some of the options of this attribute by using examples of the ASP.NET Web Forms code that is written in Microsoft Visual C# .NET. You may use the AutoEventWireup attribute to code ASP.NET Web Forms and Web User Controls. When you set the value of the AutoEventWireup attribute to true  the code in ASP.NET Web Forms and in Web User Controls is simple. However when you use the false value in certain circumstances you may receive better performance. You can specify a default value of the AutoEventWireup attribute in several places: The Machine.config file The Web.config file Individual ASP.NET Web Forms (.aspx files) Web User Controls (.ascx files) When you set the value of the AutoEventWireup attribute to true  the ASP.NET runtime does not require events to specify event handlers like the Page_Load event or the Page_Init event. This means that in Visual C# .NET you do not have to initialize and to create the delegate structures. When you use Microsoft Visual Studio .NET the value of the AutoEventWireup attribute is set to false and the designer automatically generates event handlers. This article describes the default settings of the AutoEventWireup attribute and shows you some helpful code. Back to the top Requirements loadTOCNode(2 'summary'); This article assumes that you are familiar with the following topics: Programming in ASP.NET Programming with Microsoft Visual C# .NET The following list outlines the recommended hardware software network infrastructure and service packs that you need: Microsoft Visual Studio .NET 2002 or Microsoft Visual Studio .NET 2003 Back to the top Configuration of the AutoEventWireup attribute default values loadTOCNode(2 'summary'); The AutoEventWireup attribute can be declared in the section in the Machine.config file or the Web.config file. In either of these XML-based files use the following syntax: 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 it belongs to. To change the value of the AutoEventWireup attribute in the individual ASP.NET Web Form add the AutoEventWireup attribute to the @ Page directive as follows: Back to the top When the value of the AutoEventWireup attribute is false loadTOCNode(2 'summary'); If you want to manually hook up events to an event handler set the value of the AutoEventWireup attribute to false . The following sample shows the code that you can use to handle the Load event of the Page object in an ASP.NET Web Form: Start Microsoft Visual Studio .NET. On the File menu point to New  and then click Project . In the New Project dialog box under Project Types  click Visual C# Projects . Under Templates  click ASP.NET Web Application . In the Location box type the project name as http:// ServerName /MyWebApp . Note Replace ServerName with the name of a server. MyWebApp is the name of a sample ASP.NET Web Application. In Solution Explorer right-click the WebForm1.aspx file click Rename  and then type EventWireUpFalse.aspx . Replace the existing code in the EventWireUpFalse.aspx file with the following code: Visual C# .NET WIRE-UP FALSE Replace the existing code in the EventWireUpFalse.aspx.cs file with the following code: using System; namespace MyWebApp { public class EventWireUpFalse : System.Web.UI.Page { public string message; private void Page_Load(object sender System.EventArgs e) { message=The Page_Load Event Fired with AutoEventWireup False; } // Visual C# .NET requires that you override the OnInit function // adding a new delegate for the Page_Load event. override protected void OnInit(EventArgs e) { this.Load += new System.EventHandler(this.Page_Load); } } } On the Debug menu click Start to build and to run the ASP.NET Web application. In this example you receive a message when the ASP.NET page framework raises the Page_Load event handler. If the value of the AutoEventWireup attribute is set to false  you must override the OnInit function and then you must add a new delegate for the Page_Load event handler. Back to the top When the value of the AutoEventWireup attribute is true loadTOCNode(2 'summary'); When you set the value of the AutoEventWireup attribute to false  you must manually hook up events to event handlers. When you set the value of the AutoEventWireup attribute to true  the ASP.NET page framework can automatically raise events. The following sample describes how to code a Page_Load event handler in an ASP.NET Web Form when the value of the AutoEventWireup attribute is true . Start Microsoft Visual Studio .NET. On the File menu point to New  and then click Project . In the New Project dialog box under Project Types  click Visual C# Projects . Under Templates  click ASP.NET Web Application . In the Location box type the project name as http:// ServerName /MyWebApp . Note Replace ServerName with the name of a server. MyWebApp is the name of a sample ASP.NET Web Application. In Solution Explorer right-click the WebForm1.aspx file click Rename  and then type EventWireUpTrue.aspx . Replace the existing code in the EventWireUpTrue.aspx file with the following code: Visual C# .NET WIRE-UP TRUE Replace the existing code in the EventWireUpTrue.aspx.cs file with the following code: using System; namespace MyWebApp { public class EventWireUpTrue : System.Web.UI.Page { public string message; private void Page_Load(object sender System.EventArgs e) { message=The Page_Load Event fired with AutoEventWireup True; } } } On the Debug menu click Start to build and run the project. In this example you receive a message when the ASP.NET page framework raises the Page_Load event handler. If the value of the AutoEventWireup attribute is true  you do not have to override the OnInit function and you do not have to add a new delegate for the Page_Load event handler. Please refer the below links http://support.microsoft.com/kb/324151 http://www.c-sharpcorner.com/uploadfile/puranindia/what-is-the-autoeventwireup-attribute-in-Asp-Net/default.aspx http://www.codeproject.com/Articles/9429/AutoEventWireup-attribute-in-Microsoft-ASP-NET-Web Thanks

Senthilkumar · Answer

Hi Arun Gets or sets a value indicating whether events for ASP.NET pages are automatically connected to event-handling functions. When AutoEventWireup is true ASP.NET does not require that you explicitly bind event handlers to a page event such as Load. When AutoEventWireup is false you must explicitly bind the event to a method. For example if you have a Page_Load method in the code for a page the method will be called in response to the Load event only if you write code like that in the following example (notice the Handles statement in Visual Basic and the event handler code in C#) When AutoEventWireup is true handlers are automatically bound to events at run time based on their name and signature. For each event ASP.NET searches for a method that is named according to the pattern Page_eventname such asPage_Load or Page_Init. ASP.NET checks first for an overload that has the typical event-handler signature (that is it specifies Object and EventArgs parameters). If an event handler with this signature is not found ASP.NET checks for an overload that has no parameters. When AutoEventWireup is false you must explicitly bind event handlers to events as shown in the preceding example. In that case the method names do not have to follow a pattern. The default value is true if AutoEventWireup is not specified in the @ Page directive. Visual Studio automatically includes the attribute when it creates code-behind files. For ASP.NET pages written in C# Visual Studio sets the value to true. For Visual Basic Visual Studio sets the value to false because handlers are bound to events by using the Handles keyword which is inserted automatically by Visual Studio when it generates an event handler. If you set AutoEventWireup to true you can omit (or remove) the Handles keyword. Do not set AutoEventWireup to true if performance is a key consideration. When automatic event wireup is enabled ASP.NET must make between 15 and 30 tries to match events with methods. Note the following about binding event handlers to events: If you set AutoEventWireup to true make sure that you do not also manually attach page event handlers to events. If you do handlers might be called more than one time. Automatic binding is performed only for page events not for events for controls on the page. As an alternative to binding events to handlers you can override the Oneventname methods of the page or of controls. For more info: http://msdn.microsoft.com/en-us/library/system.web.configuration.pagessection.autoeventwireup.aspx http://odetocode.com/Blogs/scott/archive/2006/02/17/inside-autoeventwireup.aspx

Kunal Vaishya · Answer

AutoEventWireUp property when True automatically wires up some of these built-in events in the Page life cycle to their handlers. This means that you do not need to explicitly attach these events (using the Handles keyword for instance in VB). Examples of these built-in events would be Page_Init and Page_Load . If you set AutoEventWireUp to True and provide explicit wiring up of the EventHandlers you will find them being executed twice! This is one reason why Visual Studio keeps this attribute set to false by default.