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Publisher12.5 Events Reference
| Error |
Sub Page_Error(Sender As Object, e As Event Args) |
fired when an unhandled exception occurs on the page. If no event
handler is defined for this event, the Application_Error event is
fired. If the exception is still not handled, control is passed to
the page (or pages) defined in the
<customErrors> element in
web.config .
Parameters
- Sender
An argument containing information about the object that raised the
event.- e
An object of type EventArgs containing additional information about
the event.
Example
The following code example deliberately causes an overflow exception
and then handles that exception in the Page_Error handler, displaying
the text of the exception and then clearing it:
Sub Page_Load( )
Dim x, y, overflow As Integer
x = 1
y = 0
overflow = x / y
End Sub
Sub Page_Error( )
Response.Write(Server.GetLastError.ToString( ))
Server.ClearError
End Sub
Notes
The current exception is obtained using the GetLastError method of
the Server class. Once you've
finished with your error handling, you can either clear the exception
by calling Server.ClearError, as shown in the example, or allow the
exception to bubble up to the next level of error handling.Note that the Sender and
e arguments are optional for this event,
as shown in the example.When the AutoEventWireup attribute of the
@ Page directive is set to
True (the default), ASP.NET will automatically
call the event handler for this event, as long as it has the correct
Page_Error signature.
| Init |
Sub Page_Init(Sender As Object, e As EventArgs) |
Parameters
- Sender
An argument containing information about
the object that raised the event.- e
An object of type EventArgs containing additional information about
the event.
Example
The code example initializes a variable for setting the ForeColor
property of a label in Page_Init, and then modifies that value to set
the ForeColor property of another label in Page_Load:
<%@ Page Language="vb" %>
<html>
<head>
<title>Init event example</title>
<script runat="server">
Dim TheColor As System.Drawing.Color
Sub Page_Init( )
TheColor = System.Drawing.Color.Red
End Sub
Sub Page_Load( )
Message.ForeColor = TheColor
Message.Text = "The color of the text was set in Page_Init."
TheColor = System.Drawing.Color.Blue
Message2.ForeColor = TheColor
Message2.Text = "The color of the text was set in Page_Load."
End Sub
</script>
</head>
<body>
<asp:label id="Message" runat="server"/>
<br/>
<asp:label id="Message2" runat="server"/>
</body>
</html>
Notes
The Sender and
e arguments are optional for this event,
as shown in the example.When the AutoEventWireup attribute of the
@ Page directive is set to
True (the default), ASP.NET will automatically
call the event handler for this event, as long as it has the
signature Page_Init.
| Load |
Sub Page_Load(Sender As Object, e As EventArgs) |
page request, we can add any initialization code that needs to be
executed at the page level, including the initialization of the
page's child controls. When the Load event fires,
the page's view state information is also
accessible.The Load event is passed the following arguments by ASP.NET:
- Sender
An argument containing information about the object that raised the
event.- e
An object of type EventArgs containing additional information about
the event.
Example
See the example for Init.
Notes
Note that the Sender and
e arguments are optional for this event,
as shown in the example.When the AutoEventWireup attribute of the
@ Page directive is set to
True (the default), ASP.NET will automatically
call the event handler for this event, as long as it has the correct
Page_Load event signature.
| Unload |
Sub Page_Unload(Sender As Object, e As EventArgs) |
Since this event is fired before the page is unloaded, we can perform
cleanup operations, such as closing open files and database
connections.The Unload event is passed the following arguments by ASP.NET:
- Sender
An argument containing information about the object that raised the
event.- e
An object of type EventArgs containing additional information about
the event.
Example
The example demonstrates the Unload event by closing a file that was
opened for display in the Page_Load event handler:
Dim TheFile As System.IO.StreamReader
Sub Page_Load( )
TheFile = System.IO.File.OpenText(MapPath("Init.aspx"))
Message.Text = "<pre>" & _
Server.HtmlEncode(TheFile.ReadToEnd( )) & "</pre>"
End Sub
Sub Page_Unload( )
TheFile.Close( )
End Sub
Notes
While the Unload event is useful for performing page-level cleanup
tasks, for resources such as databases, for which it is possible that
an exception will interrupt the normal flow of page processing, it
may be better to place the cleanup code for that resource in the
Finally block of a Try...Catch...Finally
statement, which will ensure that the cleanup code is always
executed. For more information on
Try...Catch...Finally, see Chapter 10.Note that the Sender and
e arguments are optional for this event,
as shown in the example.When the AutoEventWireup attribute of the
@ Page directive is set to
True (the default), ASP.NET will automatically
call the event handler for this event, as long as it has the
signature
Page_Unload.
