PagesSection.AutoEventWireup Property

Definition

Gets or sets a value indicating whether events for ASP.NET pages are automatically connected to event-handling functions.

public:
 property bool AutoEventWireup { bool get(); void set(bool value); };
[System.Configuration.ConfigurationProperty("autoEventWireup", DefaultValue=Mono.Cecil.CustomAttributeArgument)]
public bool AutoEventWireup { get; set; }
member this.AutoEventWireup : bool with get, set
Public Property AutoEventWireup As Boolean

Property Value

true if events for ASP.NET pages are automatically connected to event-handling functions; otherwise, false. The default is true.

Attributes

Examples

The following code example shows how to set or read the AutoEventWireup property in code.

// Get the current AutoEventWireup property value.
Console.WriteLine(
    "Current AutoEventWireup value: '{0}'",
    pagesSection.AutoEventWireup);

// Set the AutoEventWireup property to false.
pagesSection.AutoEventWireup = false;
' Get the current AutoEventWireup property value.
Console.WriteLine( _
    "Current AutoEventWireup value: '{0}'", _
    pagesSection.AutoEventWireup)

' Set the AutoEventWireup property to false.
pagesSection.AutoEventWireup = False

The following example shows the two forms of method signatures that are automatically attached to page events when AutoEventWireup is true.

<%@ Page Language="C#" AutoEventWireup="false" CodeFile="Default.aspx.cs" Inherits="_Default" %>
// This method will be automatically bound to the Load event
// when AutoEventWireup is true.
protected void Page_Load(object sender, EventArgs e)
{
    Response.Write("Hello world");

}
// This method will be automatically bound to the Load event 
// when AutoEventWireup is true only if no overload having 
// object and EventArgs parameters is found.
protected void Page_Load()
{
    Response.Write("Hello world");
}
<%@ Page Language="VB" AutoEventWireup="false" CodeFile="Default.aspx.vb" Inherits="_Default" %>
' This method will be automatically bound to the Load event
' when AutoEventWireup is true.
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs)
    Response.Write("Hello world")
End Sub
' This method will be automatically bound to the Load event 
' when AutoEventWireup is true only if no overload having 
' object and EventArgs parameters is found.    
Protected Sub Page_Load()
    Response.Write("Hello world")
End Sub

The following example shows how to explicitly wire up events when AutoEventWireup is false.

// Following are three alternative ways of binding an event
// handler to an event when AutoEventWireup is false.  For
// any given event do this binding only once or the handler
// will be called multiple times.

// You can wire up events in the page's constructor.
public _Default()
{
    Load += new EventHandler(Page_Load);
}

// You can override the OnInit event and wire up events there.
protected override void OnInit(EventArgs e)
{
    base.OnInit(e);
    Load += new EventHandler(Page_Load);
}

// Or you can override the event's OnEventname method and
// call your handler from there.  You can also put the code
// execute when the event fires within the override method itself.
protected override void OnLoad(EventArgs e)
{
    Page_Load(null, null);
    base.OnLoad(e);
}

protected void Page_Load(object sender, EventArgs e)
{
    Response.Write("Hello world");
}
' The Handles keyword binds Page_Load to the Load event.
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
    Response.Write("Hello world")
End Sub

Remarks

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#):

Partial Class AutoEventWireupExample  
    Inherits System.Web.UI.Page  
    Protected Sub Page_Load(ByVal sender As Object, _  
            ByVal e As System.EventArgs) Handles Me.Load  
        Response.Write("Executing Page_Load")  
    End Sub  
End Class  
public partial class AutoEventWireupExample : System.Web.UI.Page  
{   
    protected void Page_Load(object sender, System.EventArgs e)  
    {  
        Response.Write("Executing Page_Load");  
    }  
    override protected void OnInit(EventArgs e)  
    {  
        this.Load += new System.EventHandler(this.Page_Load);  
    }  
}  

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 as Page_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.

Applies to