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Publisher17.4 Methods Reference
| AddCacheItemDependencies |
Response.AddCacheItemDependencies(ByVal cacheKeys As ArrayList) |
cache item keys upon which the output cache of the current response
depends. If one of the cache items identified by the keys is
modified, the output cache of the current response will be
invalidated and a fresh response will be generated.
Parameter
- cacheKeys
An ArrayList containing one or more cache item key names.
Example
The example shows how you can use the AddCacheItemDependencies method
to set a number of cache keys as dependencies for the output cache of
the current response. If any of the cache items represented by these
keys is modified, the output cache is invalidated and the page is
refreshed by using Response.Redirect.
<%@ Page Language="vb" %>
<%@ OutputCache Duration="300" VaryByParam="None" %>
<html>
<head>
<title>Adding cache dependencies in ASP.NET</title>
<script runat="server">
Sub Page_Load( )
Dim myArrayList As New ArrayList
myArrayList.Add("Key1")
myArrayList.Add("Key2")
Response.AddCacheItemDependencies(myArrayList)
Message.Text = DateTime.Now.ToString( )
End Sub
Sub Button1_Click(sender As Object, e As EventArgs)
Cache("Key1") = "foo" & DateTime.Now.ToString( )
Response.Redirect("AddCacheItemDependencies.aspx")
End Sub
Sub Button2_Click(sender As Object, e As EventArgs)
Cache("Key2") = "bar" & DateTime.Now.ToString( )
Response.Redirect("AddCacheItemDependencies.aspx")
End Sub
</script>
</head>
<body>
<form runat="server">
<asp:label id="Message" runat="server"/>
<asp:button id="Button1" text="Change Key 1"
onClick="Button1_Click" runat="server"/>
<asp:button id="Button2" text="Change Key 2"
onClick="Button2_Click" runat="server"/>
</form>
</body>
</html>
Notes
The AddCacheItemDependencies method is useful when you want to output
cache a page, but the page depends on the value of several items
stored in the ASP.NET cache. Rather than caching the page with a very
short duration to avoid stale data, you can use
AddCacheItemDependencies to automatically invalidate the output cache
when the dependencies change.
| AddCacheItemDependency |
Response.AddCacheItemDependency(ByVal cacheKey As String) |
cache of the current response depends. If the cache item identified
by the key is modified, the output cache of the current response will
be invalidated and a fresh response will be generated.
Parameter
- cacheKey
A String containing the cache item key to add.
Example
The example shows how you can use the AddCacheItemDependency method
to set a cache key as a dependency for the output cache of the
current response. If the cache item represented by this key is
modified, the output cache is invalidated and the page is refreshed
by using Response.Redirect.
<%@ Page Language="vb" %>
<%@ OutputCache Duration="300" VaryByParam="None" %>
<html>
<head>
<title>Adding a cache dependency in ASP.NET</title>
<script runat="server">
Sub Page_Load( )
Response.AddCacheItemDependency("Key1")
Message.Text = DateTime.Now.ToString( )
End Sub
Sub Button1_Click(sender As Object, e As EventArgs)
Cache("Key1") = "foo" & DateTime.Now.ToString( )
Response.Redirect("AddCacheItemDependency.aspx")
End Sub
</script>
</head>
<body>
<form runat="server">
<asp:label id="Message" runat="server"/>
<asp:button id="Button1" text="Change Key 1" onClick="Button1_ Click" runat="server"/>
</form>
</body>
</html>
Notes
The AddCacheItemDependency method provides the same functionality as
the AddCacheItemDependencies method, but for a single cache item
rather than multiple items.
| AddFileDependencies |
Response.AddFileDependencies(ByVal filenames As ArrayList) |
upon which the output cache of the current request depends. If any of
these files is modified, the output cache is invalidated.
Parameter
- filenames
An ArrayList containing one or more path/filenames.
Example
The example shows how you can use the AddFileDependencies method to
set a number of files as dependencies for the output cache of the
current response. If any of these files is modified, the output cache
is invalidated.
<%@ Page Language="vb" %>
<%@ OutputCache Duration="300" VaryByParam="None" %>
<html>
<head>
<title>Adding file dependencies in ASP.NET</title>
<script runat="server">
Sub Page_Load( )
Dim myArrayList As New ArrayList
myArrayList.Add(Server.MapPath("dep.txt"))
myArrayList.Add(Server.MapPath("dep1.txt"))
Response.AddFileDependencies(myArrayList)
Message.Text = DateTime.Now.ToString( )
End Sub
</script>
</head>
<body>
<asp:label id="Message" runat="server"/>
</body>
</html>
Notes
The AddFileDependencies method is useful when you want to output
cache a page, but the page depends on the value of several files on
the web server (which can be accessed by a file path from the web
server). Rather than caching the page with a very short duration to
avoid stale data, you can use AddFileDependencies to automatically
invalidate the output cache when the dependencies change.
| AddFileDependency |
Response.AddFileDependency(ByVal filename As String) |
current request depends. If the named by the filename argument is
modified, the output cache is invalidated.
Parameter
- filename
A String containing the path and filename to add.
Example
The example below shows how you can use the AddFileDependency method
to set a file as a dependency for the output cache of the current
response. If the file is modified, the output cache is invalidated.
<%@ Page Language="vb" %>
<%@ OutputCache Duration="300" VaryByParam="None" %>
<html>
<head>
<title>Adding a file dependency in ASP.NET</title>
<script runat="server">
Sub Page_Load( )
Response.AddFileDependency(Server.MapPath("dep.txt"))
Message.Text = DateTime.Now.ToString( )
End Sub
</script>
</head>
<body>
<asp:label id="Message" runat="server"/>
</body>
</html>
The dep.txt file named in the code above should
reside in the same directory as the page. The contents of the page
can be whatever you choose. If the file content is changed, the cache
will be invalidated.
Notes
The AddFileDependency method provides the same functionality as the
AddFileDependencies method, but for a single file rather than
multiple files.
| AddHeader |
Response.AddHeader(ByVal name As String, ByVal value As String) |
stream.
Parameters
- name
A String argument containing the name for the header.- value
A String argument containing the value for the header.
Notes
The AddHeader property provides for backward compatibility with
classic ASP. This property has been deprecated in favor of the new
AppendHeader method.
| AppendHeader |
Response.AppendHeader(ByVal name As String, _ |
stream. This method can be used to add custom HTTP headers or to
modify the value of standard HTTP headers.
Parameters
- name
A String argument containing the name for the header.- value
A String argument containing the value for the header.
Example
The example sets the HTTP Content-Type header to
"text/xml" and then displays the new value by
setting the Text property of the Message Label control to the value
of the ContentType property. This causes the page output to be
treated as XML.
Sub Page_Load( )
Response.AppendHeader("Content-Type", "text/xml")
Message.Text = Response.ContentType
End Sub
Notes
When using this method with HTTP headers related to caching policy,
if more restrictive settings are applied through the use of the
ASP.NET cache APIs, the more restrictive settings will take priority
over the settings applied using AppendHeader.
| AppendToLog |
Response.AppendToLog(ByVal param As String) |
argument to the IIS log file for the current IIS application.
Parameter
- param
A String argument containing the text to be appended to the IIS log.
Example
The following example writes a message to the IIS log for the
application the page is a part of, and then writes a message to the
ASP.NET Message label control indicating that the message was
written:
Sub Page_Load( )
Response.AppendToLog("Hello from Page_Load!")
Message.Text = "Message written to IIS Log!"
End Sub
The IIS log entry generated by the example above looks similar to the
following:
2001-10-14 00:13:14 127.0.0.1 - 127.0.0.1 80 GET
/ASPdotNET_iaN/Chapter_17/AppendToLog.aspx
Hello+from+Page_Load! 200 BrowserString
Notes
Unlike the AppendToLog method in classic ASP, which had a limit of 80
characters per call, you can write as much text as you wish to the
log by using AppendToLog in ASP.NET. The IIS Log files are located by
default in
%windir%\System32\LogFiles\W3SVCx\exdate.log,
where %windir% is the name of the Windows
directory, x is the number of the Web site for
the log (this is the IIS Metabase name for the desired application),
and date is the creation date of the log file.
| ApplyAppPathModifier |
String = Response.ApplyAppPathModifier(ByVal virtualPath _ |
virtual path containing the SessionID. This new virtual path can be
used to create absolute URLs for use in applications that use
cookieless Sessions.
Parameters
- String
A String argument that will receive the modified virtual path.- virtualPath
A String argument containing the virtual path to be modified.
Example
The following example retrieves a virtual path including the
SessionID and displays the path by using the Text property of the
Message label control:
Sub Page_Load( )
Dim NewPath As String
NewPath = Response.ApplyAppPathModifier(Request.Path)
Message.Text = "Modified virtual path = " & NewPath
End Sub
The web.config file to set the Session state
handler to use cookieless Sessions is shown below:
<configuration>
<system.web>
<sessionState mode="InProc" cookieless="true"/>
</system.web>
</configuration>
Notes
This method is very useful when making use of the cookieless Session
state functionality introduced by ASP.NET. If the cookieless
attribute of the sessionState config section in
web.config is not set to
True, this method will simply return the virtual
path passed in without modification.
| BinaryWrite |
Response.BinaryWrite(ByVal buffer( ) As Byte) |
modification of the output is performed before sending the binary
content to the client.
Parameter
- buffer( )
A Byte array containing the binary data to be written to the output
stream.
Example
Here is an example of BinaryWrite:
Sub Page_Load( )
Dim ImageStream As New FileStream(MapPath("aspnetian.jpg"), _
FileMode.Open, FileAccess.Read)
Dim ImageBytes(ImageStream.Length) As Byte
ImageStream.Read(ImageBytes, 0, ImageStream.Length)
ImageStream.Close( )
Response.ContentType = "image/bmp"
Response.BinaryWrite(ImageBytes)
Response.End( )
End Sub
Notes
This method is especially useful for writing binary content retrieved
from a database to the browser. When writing image or other nontext
data to the browser, you should set the Response.ContentType property
to the appropriate MIME type for the image type being sent (such as
"image/jpg").
| Clear |
Response.Clear( ) |
Parameters
None
Notes
The Clear method clears all currently
buffered output, but does not clear the HTTP response headers. If
buffering of output is disabled by setting the BufferOutput property
to False, this method will not have any effect,
since it only clears buffered content. This behavior is different
from classic ASP, in which calling Clear when buffering is disabled
results in an error.
| ClearContent |
Response.ClearContent( ) |
Parameters
None
Example
The example writes a text message using Response.Write and then
clears the buffered output by calling Response.Clear. If buffering is
on, the text message will never be sent to the browser.
Sub Page_Load( )
Response.Write("This content will not be seen.")
Response.Clear( )
Message.Text = _
"Content written with <i>Response.Write</i> was cleared."
End Sub
Notes
The ClearContent method clears all currently buffered output, but
does not clear the HTTP response headers. HTTP headers can be cleared
by calling the ClearHeaders method. If buffering of output has been
disabled by setting the BufferOutput property to
False, the ClearContent method will not have any
effect, since it only clears buffered content.
| ClearHeaders |
Response.ClearHeaders( ) |
Parameters
None
Example
The example sets the HTTP Content-Type header to
"text/xml", clears the HTTP headers by calling the
ClearHeaders method, and then writes the value of the
Response.ContentType property to the Text property of the Message
ASP.NET Label control. The displayed Content-Type is the default of
"text/html".
Sub Page_Load( )
Response.AppendHeader("Content-Type", "text/xml")
Response.ClearHeaders( )
Message.Text = Response.ContentType
End Sub
Notes
The ClearHeaders method clears only the HTTP response headers, not
the buffered content.
| Close |
Response.Close( ) |
Parameters
None
Example
See the example for the SuppressContent property.
Notes
The Close method can be used to immediately close the network socket
for the current response. This closure will typically result in a
browser error (such as "Cannot find
server") being displayed to the client.
| End |
Response.End( ) |
request and sends all buffered content to the client immediately.
Parameters
None
Example
The example below writes the text "Hello,
World!" to the browser, calls Response.End, and then
attempts to set the Text property of the Message ASP.NET Label
control to "Hello, World!" However,
that code will not be executed, as the End method immediately halts
execution of page processing.
Sub Page_Load( )
Response.Write("Hello, World!")
Response.End( )
Message.Text = "Hello, World!"
End Sub
In fact, the code above will result in only the
"Hello, World!" text being output
to the browser, as even the rendering of the static HTML and controls
in the page will not occur.
Notes
When the End method is called, in addition to sending buffered output
to the client and terminating processing, the Application_EndRequest
event is fired.
| Flush |
Response.Flush( ) |
Parameters
None
Example
See the example for the BufferOutput property. If you comment out the
lines that set BufferOutput to False and then
uncomment the line that calls Response.Flush, you will see that the
Flush method allows you to explicitly send buffered content to the
browser.
Notes
Since buffering is on by default in ASP.NET, the Flush method becomes
especially useful. Rather than turning off buffering, which results
in any content sent from a Response.Write call being sent immediately
to the browser, you can use Response.Flush to send content in
discrete chunks or to ensure that an entire operation completes
before sending the currently buffered content.You can also combine calls to Response.Flush with calls to
Response.Clear to allow you to perform preverification on content
before it is sent to the browser. If a given set of calculations or
output encounters an error, you can call Response.Clear to clear the
problematic output and then replace it with an error message or with
other replacement content. If there are no problems with the output,
you can call Response.Flush to send the buffered output to the
browser and then continue processing.
| Pics |
Response.Pics(ByVal value As String) |
output stream for the current response. The Platform for Internet
Content Selection (PICS) is used to rate Internet content based on
violence, sexual content, language, and nudity.
Parameter
- value
A String argument containing the text for the PICS-Label header.
Example
The following example sets a PICS header that specifies RSAC as the
rating organization, sets the rating effective period from 8/1/2001
to 2/28/2002, and sets the ratings as follows:
- Violence - 1
- Sexual content - 2
- Adult Language - 3
- Nudity - 4
Sub Page_Load( )
Dim PICSLabel As String
PICSLabel &= "(PICS-1.1 <http://www.rsac.org/ratingsv01l> "
PICSLabel &= "labels on " & Chr(34)
PICSLabel &= "2001.08.01T06:00-0000" & Chr(34)
PICSLabel &= " until " & Chr(34)
PICSLabel &= "2002.02.28T23:59-0000" & Chr(34)
PICSLabel &= " ratings (V 1 S 2 L 3 N 4))"
Response.PICS(PICSLabel)
Message.Text = PICSLabel
End Sub
Notes
The PICS-Label header is used for rating the content of a site. Users
can configure their browsers to disallow viewing of sites that send
PICS-Label headers, and whose ratings state that the site contains a
higher level of content in one of the rated categories than the
browser is configured to allow. Additional information on the PICS
standard for content ratings is available at the World Wide Web
Consortium web site at http://www.w3c.org.
| Redirect |
Response.Redirect(ByVal url As String) |
executing page to another page specified by the URL argument,
optionally terminating the processing of the current page.
Parameters
- url
A String argument containing the URL for the page to redirect to.- endResponse
A Boolean argument indicating whether to terminate processing of the
current page. If the argument is omitted, the method call causes
processing of the current page to be discontinued.
Example
The example redirects the current request to
BufferOutput.aspx and directs ASP.NET to
discontinue processing of the current page:
Sub Page_Load( )
Response.Redirect("BufferOutput.aspx", True)
End Sub
Notes
Unless additional processing needs to be done in the page from which
you call Response.Redirect, you should always pass
True as the second argument to Response.Redirect
to prevent server resources from being wasted by continuing to
process the current page. This feature is new for ASP.NET. When
calling Response.Redirect with only the
url argument, processing of the current
page is discontinued automatically.Note that when redirecting to a page such as
BufferOutput.aspx in which buffering is turned
off, or to a page that calls Response.Flush, the redirect will not
complete until the target page has completed processing. This means
that all content on the target page will be seen at once, rather than
as it is rendered or flushed from the buffer.
| Write |
Response.Write(ByVal ch As Char) |
content to the output stream. Content may be character data, an
Object (using the object's ToString( ) method), or
String data.
Parameters
- ch
A Char argument containing a character to write to the output stream.- obj
An Object argument containing an object whose string representation
will be written to the output stream.- s
A String argument containing text to write to the output stream.- buffer( )
A Char array argument containing the characters to write to the
output stream.- index
An Integer argument containing the starting point in the Char array
from which to being writing.- count
An Integer argument containing the number of characters to write.
Example
The example creates an array of Chars, sets the values of the Chars,
and then loops through the array and displays its contents by calling
Response.Write:
Sub Page_Load( )
Dim MyChars(2) As Char
Dim MyChar As Char
MyChars(0) = CChar("A")
MyChars(1) = CChar("B")
MyChars(2) = CChar("C")
For Each MyChar in MyChars
Response.Write(MyChar)
Next
End Sub
Notes
As shown above, the Write method in ASP.NET gains a number of new
overloaded implementations. The above code could also be written by
using another overloaded implementation that accepts an array of
Chars, a starting index, and the count of Chars to write, as follows:
Response.Write(MyChars, 0, 3)
The implementation of the Write method that takes an Object as an
argument takes advantage of the built-in ToString method of the
object class to display the string representation of the object.
ToString is inherited by every .NET class and, by default, returns
the namespace and class name of the object's class.
Classes that wish to send other information about themselves can
override the inherited implementation of ToString to send this
information.
| WriteFile |
Response.WriteFile(ByVal fileName As String) |
of the overloaded arguments to the output stream.
Parameters
- fileName
A string argument containing the path and filename of the file whose
content should be written to the output stream.- includeHeaders
A Boolean argument indicating whether the contents of the file should
be written to a memory block.- fileHandle
An argument of type IntPtr containing a handle to a file. You can get
the handle by creating a new FileStream object from the file and then
querying the FileStream's Handle property.- offset
An argument of type Long containing the byte position in the file
from which writing should start.- size
An argument of type Long containing the number of bytes that should
be written to the output stream.
Example
The example writes the contents of the file
dep.txt to the output stream of the current
response:
Sub Page_Load( )
Response.WriteFile("dep.txt")
End Sub
Notes
The WriteFile method can be used in a variety of ways to output text
content directly from a file. Attempts to write other content types
(such as image data) will fail.
