The ASP Page-based tutorials show how you can replace the built-in HttpHandler with custom ASP pages, thereby gaining extra control over the chart rendering mechanism. This method allows you to customize, for example, the behavior of the client and server caches, and IIS logging.
Both tutorials use the following ASP page to replace the HttpHandler mechanism, and differ only in the way they store the chart data. The code below can handle both Session and Cache transfers. It performs the exact same functions as the built-in HttpHandler, and should be useful as a starting point for your custom pages.
Imports System
Imports System.Web
Imports System.Web.SessionState
Namespace AspPageSample
_
Public Class StreamResponse
Inherits System.Web.UI.Page
Private Sub Page_Load(sender As Object, e As System.EventArgs)
' Determine how the image is transferred to this page
Dim ses As String = Request("SessionID") ' non null if session transfer
Dim cac As String = Request("CacheID") ' non null if cache transfer
Dim del As String = Request("Delete") ' non null if delete request
Dim doDelete As Boolean = False
' Check the delete request status
If Not (del Is Nothing) Then
del = del.ToLower()
doDelete = del = "t" Or del = "true"
End If
Dim image As Byte() = Nothing
Dim imgtype As String = String.Empty
Dim img As String = String.Empty
Dim hsh As String = String.Empty
If Not (ses Is Nothing) Then
' extract the image info from the session object
img = ses + "_ImageBytes"
hsh = ses + "_Hash"
image = CType(Session(img), Byte())
imgtype = CStr(Session(hsh))
If doDelete Then
Session.Remove(img)
Session.Remove(hsh)
End If
Else
If Not (cac Is Nothing) Then
' extract the image info from the Application cache
img = cac + "_ImageBytes"
hsh = cac + "_Hash"
image = CType(Cache(img), Byte())
imgtype = CStr(Cache(hsh))
If doDelete Then
Cache.Remove(img)
Cache.Remove(hsh)
End If
End If
End If
If Not (image Is Nothing) And Not (imgtype Is Nothing) Then
' return the binary image to the client
imgtype = "image/" + imgtype.Substring((imgtype.LastIndexOf("."c) + 1))
Response.Clear()
Response.Cache.SetExpires(DateTime.MinValue) ' clear client cache
Response.ContentType = imgtype
Response.BinaryWrite(image)
Response.Flush()
End If
End Sub
End Class
End Namespace
•C#
using System;
using System.Web;
using System.Web.SessionState;
namespace AspPageSample
{
public class StreamResponse : System.Web.UI.Page
{
private void Page_Load(object sender,
System.EventArgs e)
{
// determine how the image is
// transferred to this page
string ses = Request["SessionID"];
// non null if session transfer
string cac = Request["CacheID"];
// non null if cache transfer
string del = Request["Delete"];
// non null if delete request
bool doDelete = false;
// check the delete request status
if(del != null)
{
del = del.ToLower();
doDelete = (del == "t" || del == "true");
}
byte [] image = null;
string imgtype = string.Empty;
string img = string.Empty;
string hsh = string.Empty;
if (ses != null)
{
// get image info from Session object
img = ses + "_ImageBytes";
hsh = ses + "_Hash";
image = (byte[])Session[img];
imgtype = (string)Session[hsh];
if(doDelete)
{
Session.Remove(img);
Session.Remove(hsh);
}
}
else if (cac != null)
{
// get image info from Application cache
img = cac + "_ImageBytes";
hsh = cac + "_Hash";
image = (byte[])Cache[img];
imgtype = (string)Cache[hsh];
if (doDelete)
{
Cache.Remove(img);
Cache.Remove(hsh);
}
}
// return image to the client
if (image != null && imgtype != null)
{
int iext = imgtype.LastIndexOf('.')+1;
imgtype = "image/" +
imgtype.Substring(iext);
Response.Clear();
Response.Cache.SetExpires(DateTime.MinValue);
// clear client cache
Response.ContentType = imgtype;
Response.BinaryWrite(image);
Response.Flush();
}
}
}
}