ASP.NET.in.a.Nutshell.Second.Edition [Electronic resources] نسخه متنی

14.4 Methods Reference

Context.AddError(ByVal ErrorInfo As Exception)

Adds an Exception object to the
array of exceptions returned by the AllErrors property.

Parameter

ErrorInfo

An Exception object to be added to the array.

Example

The example shows how you can use AddError to add an error to the
current request context. The exception is created within a
Try block. In the Finally
block, the ToString method is used to display the error and the
ClearError method is used to clear the error so that the page will
display properly.

Sub Page_Load( )
Try
Context.AddError(New Exception("Test"))
Finally
Message.Text = "Context.Error.ToString( ) is " & _
Context.Error.ToString( )
Context.ClearError( )
End Try
End Sub

Notes

Adding an exception by using AddError should not be confused with
throwing an exception. Using AddError only adds the exception to the
array returned by the AllErrors property and does not invoke any of
the error handling mechanisms in the application.

Context.ClearError( )

Clears
all errors for the current request. Note that even though ClearError
is singular, it clears all errors for the current request.

Parameters

None.

Example

The example checks whether there are any errors and then clears them.
Finally, it reports if it has cleared any errors.

Sub Page_Load( )
If Not Context.AllErrors Is Nothing Then
Context.ClearError( )
Message.Text = "Errors cleared."
Else
Message.Text = "No Errors to clear."
End If
End Sub

Object = HttpContext.GetAppConfig(ByVal name As String)

Returns the collection of key/value
pairs that are contained in the configuration specified by the
name argument.

Parameters

Object

An object containing the keys and values in the configuration
sections specified by name. This object is
often of a type derived from NameValueCollection.

name

The name of the section to retrieve.

Example

The example shows how you can use the GetAppConfig method to retrieve
all items in a configuration by setting from the

web.config or

machine.config XML configuration file. While
GetAppConfig returns an Object, you must cast the returned object to
the NameValueCollection-derived type defined in the configuration
section to actually access the information. This method is static, so
an instance of the HttpContext class is not
required.

Sub Page_Load( )
Dim i As Integer
Dim nv As NameValueCollection
nv = CType(HttpContext.GetAppConfig("appSettings"), _
NameValueCollection)
For i = 0 To nv.Count - 1
Response.Write(nv.GetKey(i) & " = " & nv(i) & "<br/>")
Next         
End Sub

Notes

Generally you will not use GetAppConfig to get the
appSettings section from the configuration file.
It is much easier and safer to use ConfigurationSettings.AppSettings
to get at these values. This method, however, can be used to get
information from custom configuration sections.

Object = Context.GetConfig(ByVal name As String)

Returns the collection of key/value
pairs that are contained in the configuration specified by the
name argument.

Parameters

Object

An object containing the keys and values in the configuration
sections specified by name. This object is
often of a type derived from NameValueCollection.

name

The name of the section to retrieve.

Example

The example shows how you can use the GetConfig method to retrieve
all items in a configuration setting from the

web.config or

machine.config XML configuration file. While
GetAppConfig returns an object, you must cast the returned object to
the NameValueCollection-derived type defined in the configuration
section to actually access the information.

Sub Page_Load( )
Dim i As Integer
Dim nv As NameValueCollection
nv = CType(Context.GetConfig("appSettings"), _
NameValueCollection)
For i = 0 To nv.Count - 1
Response.Write(nv.GetKey(i) & " = " & nv(i) & "<br/>")
Next         
End Sub

Notes

Generally, you will not use GetConfig to get the
appSettings section from the configuration file.
It is much easier and safer to use ConfigurationSettings.AppSettings
to get these values. This method, however, can be used to get
information from custom configuration sections.

Context.RewritePath(ByVal newURL As String)

Assigns an internal rewrite path.

Parameter

newURL

A String containing a local path to redirect the user silently.

Example

The example below shows how to change the path in a way that is
completely transparent to the user. The URL shown in the address bar
remains the original URL, and the redirection to the new page does
not require a round trip to and from the server. RewritePath is
almost always called from

global.asax rather
than an actual page. That is what this example shows.

Sub Application_BeginRequest(ByVal sender As Object, _ 
ByVal e As EventArgs)
' No matter the URL, redirect to this URL...
Context.RewritePath("/aspnetian/ShowGetConfig.aspx")
End Sub

Notes

This method seems to be redundant when compared with methods like
Server.Transfer, which allow the developer to change the page being
displayed. In fact, RewritePath serves a very unique purpose.

Perhaps you have seen or registered at Web sites that give registered
users a unique URL. For instance, you might be given a URL like this:

http://www.SomeDomain.com/YourName/default.aspx

Implementing such a system that gives a virtual directory to each
user is not practical unless you have very few registered users.
Using RewritePath, the developer can essentially remove a level of
directory hierarchy. This removal occurs without a redirect that
would require a round trip to the server, and without changing the
URL as it appears in the browser. Some information will be extracted
and saved in the Context Items collection for use by pages that will
be displayed while translating from the URL entered by the user to
the URL used for RewritePath.

In the example above, RewritePath might be sent a URL like this:

http://www.SomeDomain.com/default.aspx

The "YourName" folder name was
removed from the URL, and the application can then be
customized for the user identified as
"YourName."