Base Page For Detecting Session Timeout in ASP.Net/C#
In this tutorial we will be going over how to create a base page class to handle your sessions. The number one question I get asked time and time again is how to manage sessions, and how to detect if a session has expired. Back in the days before .Net things were a little more complicated when it came to solving this riddle, but with the advent of the .Net Framework 2.0 a new class was introduced, the HttpSessionState Class, which is a member of the System.Web.SessionState Namespace. The new HttpSessionState Class gives us access to session state items and other lifetime management methods.
One of the items in the HttpSessionState class we will be looking at is the IsNewSession Property. This property lets us know whether the current session was created wtih the current request, or if it was an existing session. This is invaluable as we can use it to determine if the users session had expired or timed out. The IsNewSession Property is more robust and advanced then simply checking if the session is null because it takes into account a session timeout as well.
In this tutorial we will create a base page class that we can inherit all our pages from, and in this class we will check the status of the users session in the Page.OnInit Method. The OnOnit Method fires before the Page Load Event, giving us the ability to check the session before the page is actually rendered. So lets get to some code.
The first thing we will need to do, as with any class you create, is to make sure we have a reference to the appropriate Namespaces. For our class we need but 2 Namespaces, the System.Web.UI Namespace and the System Namespace, so lets add them to our class.
NOTE: All Namespace references need to come before the declaration of your class.
using System; using System.Web.UI;
Now we are going to declare our class, the class in this example is named SessionCheck, and it looks like
public class SessionCheck: System.Web.UI.Page
{
}
You will notice that our base class, which we will be inheriting from, inherits from the System.Web.UI.Page class. Doing this gives us access to all the methods, properties and events of the Page class. In our base class we will have a single property, this will be the property that will hold the URL we want the user to redirect to if there is a problem with their session. We make this property static so we can access it without having to create an instance of the class. We dont want to have to do this because we are inheriting from it. This is our property
/// <summary>
/// property vcariable for the URL Property
/// </summary>
private static string _url;
/// <summary>
/// property to hold the redirect url we will
/// use if the users session is expired or has
/// timed out.
/// </summary>
public static string URL
{
get { return _url; }
set { _url = value; }
}
Now that we have our property out of the way, we will look at the only of our base class, the OnInit which we will override in order to add our ow functionality. In
this method we will also initialize our base class, you do that with line
base.OnInit(e);
In our OnInit Method we will first check to
see if the current session is null. If the session is null we then will
check the IsNewSession Property to see if
this session was created in this request. If we determine the session is
a new session, we will then cal upon the Headers
Property of the HttpRequest
Class, which is located in the System.Web
Namespace.
In our OnInit Method we will first check to
see if the current session is null. If the session is null we then will
check the IsNewSession Property to see if
this session was created in this request. If we determine the session is
a new session, we will then cal upon the Headers
Property of the HttpRequest
Class, which is located in the System.Web
Namespace.
The Header we are retrieving is the Cookie Header. Once we have this, we will first
check to see if it’s null, if it’s not null we will look for the value ASP.Net_SessionId. Now if we make it this far, and
that cookie exists, we know the session has timed out, so we will then
redirect the user to our redirect page, which is set with the URL Property. So lets take a look at our new OnInit Method:
override protected void OnInit(EventArgs e)
{
//initialize our base class (System.Web,UI.Page)
base.OnInit(e);
//check to see if the Session is null (doesnt exist)
if (Context.Session != null)
{
//check the IsNewSession value, this will tell us if the session has been reset.
//IsNewSession will also let us know if the users session has timed out
if (Session.IsNewSession)
{
//now we know it's a new session, so we check to see if a cookie is present
string cookie = Request.Headers["Cookie"];
//now we determine if there is a cookie does it contains what we're looking for
if ((null != cookie) && (cookie.IndexOf("ASP.NET_SessionId") >= 0))
{
//since it's a new session but a ASP.Net cookie exist we know
//the session has expired so we need to redirect them
Response.Redirect("Default.aspx?timeout=yes&success=no");
}
}
}
}
That’s it, we have completed our base class which all our web forms will inherit from, allowing us to keep an eye on the users session. Now that we have the class completed we need to use it. Before it can be affected we need to do 1 of 2 things
- Add EnableSessionState = true to the @Page directive on all pages that will inherit from our base class or
- Add the following line to the <system.web> section of our web.config file:
That’s it, we have completed our base class which all our web forms will inherit from, allowing us to keep an eye on the users session. Now that we have the class completed we need to use it. Before it can be affected we need to do 1 of 2 things
- Add EnableSessionState = true to the @Page directive on all pages that will inherit from our base class or
- Add the following line to the <system.web> section of our web.config file
<pages autoEventWireup="true" enableSessionState="true" enableViewState="true" enableViewStateMac="true" smartNavigation="true" validateRequest="false" />
Number 2 on that list will enable session state on all pages in the web. If you dont access session items in each of your pages, this might be overkill. Next we will need to inherit from our base class. Doing this will give our web form the following declaration
public partial class _Default : SessionCheck
{
}
Then in the Page_Load Event we will set the redirect URL for our base class
protected void Page_Load(object sender, EventArgs e)
{
SessionCheck.URL = "Default.aspx";
}
Now here is the entire base page in its entirety
// A Base Page class for detecting session time outs
//
// Copyright © 2008
// Richard L. McCutchen
// Created: 05MAR08
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program. If not, see <http://www.gnu.org/licenses/>.
//*****************************************************************************************
using System;
using System.Web.UI;
/// <summary>
/// This is a custom "base page" to inherit from which will be used
/// to check the session status. If the session has expired or is a timeout
/// we will redirect the user to the page we specify. In the page you use
/// to inherit this from you need to set EnableSessionState = True
/// </summary>
public class SessionCheck : System.Web.UI.Page
{
/// <summary>
/// property vcariable for the URL Property
/// </summary>
private static string _redirectUrl;
/// <summary>
/// property to hold the redirect url we will
/// use if the users session is expired or has
/// timed out.
/// </summary>
public static string RedirectUrl
{
get { return _redirectUrl; }
set { _redirectUrl = value; }
}
public SessionCheck()
{
_redirectUrl = string.Empty;
}
override protected void OnInit(EventArgs e)
{
//initialize our base class (System.Web,UI.Page)
base.OnInit(e);
//check to see if the Session is null (doesnt exist)
if (Context.Session != null)
{
//check the IsNewSession value, this will tell us if the session has been reset.
//IsNewSession will also let us know if the users session has timed out
if (Session.IsNewSession)
{
//now we know it's a new session, so we check to see if a cookie is present
string cookie = Request.Headers["Cookie"];
//now we determine if there is a cookie does it contains what we're looking for
if ((null != cookie) && (cookie.IndexOf("ASP.NET_SessionId") >= 0))
{
//since it's a new session but a ASP.Net cookie exist we know
//the session has expired so we need to redirect them
Response.Redirect("Default.aspx?timeout=yes&success=no");
}
}
}
}
}
And there you have it, a custom base class that you can use to detect session timeouts. I hope you found this tutorial helpful and useful, and thank you for reading 
Happy Coding!
Reading and Writing XML in C#
In this article, you will see how to read and write XML documents in Microsoft .NET using C# language.
First, I will discuss XML .NET Framework Library namespace and classes. Then, you will see how to read and write XML documents. In the end of this article, I will show you how to take advantage of ADO.NET and XML .NET model to read and write XML documents from relational databases and vice versa.
Introduction to Microsoft .NET XML Namespaces and Classes
Before start working with XML document in .NET Framework, It is important to know about .NET namespace and classes provided by .NET Runtime Library. .NET provides five namespace – System.Xml, System.Xml.Schema, System.Xml.Serialization, System.Xml.XPath, and System.Xml.Xsl to support XML classes.
The System.Xml namespace contains major XML classes. This namespace contains many classes to read and write XML documents. In this article, we are going to concentrate on reader and write class. These reader and writer classes are used to read and write XMl documents. These classes are – XmlReader, XmlTextReader, XmlValidatingReader, XmlNodeReader, XmlWriter, and XmlTextWriter. As you can see there are four reader and two writer classes.
The XmlReader class is an abstract bases classes and contains methods and properties to read a document. The Read method reads a node in the stream. Besides reading functionality, this class also contains methods to navigate through a document nodes. Some of these methods are MoveToAttribute, MoveToFirstAttribute, MoveToContent, MoveToFirstContent, MoveToElement and MoveToNextAttribute. ReadString, ReadInnerXml, ReadOuterXml, and ReadStartElement are more read methods. This class also has a method Skip to skip current node and move to next one. We’ll see these methods in our sample example.
The XmlTextReader, XmlNodeReader and XmlValidatingReader classes are derived from XmlReader class. As their name explains, they are used to read text, node, and schemas.
The XmlWrite class contains functionality to write data to XML documents. This class provides many write method to write XML document items. This class is base class for XmlTextWriter class, which we’ll be using in our sample example.
The XmlNode class plays an important role. Although, this class represents a single node of XML but that could be the root node of an XML document and could represent the entire file. This class is an abstract base class for many useful classes for inserting, removing, and replacing nodes, navigating through the document. It also contains properties to get a parent or child, name, last child, node type and more. Three major classes derived from XmlNode are XmlDocument, XmlDataDocument and XmlDocumentFragment. XmlDocument class represents an XML document and provides methods and properties to load and save a document. It also provides functionality to add XML items such as attributes, comments, spaces, elements, and new nodes. The Load and LoadXml methods can be used to load XML documents and Save method to save a document respectively. XmlDocumentFragment class represents a document fragment, which can be used to add to a document. The XmlDataDocument class provides methods and properties to work with ADO.NET data set objects.
In spite of above discussed classes, System.Xml namespace contains more classes. Few of them are XmlConvert, XmlLinkedNode, and XmlNodeList.
Next namespace in Xml series is System.Xml.Schema. It classes to work with XML schemas such XmlSchema, XmlSchemaAll, XmlSchemaXPath, XmlSchemaType.
The System.Xml.Serialization namespace contains classes that are used to serialize objects into XML format documents or streams.
The System.Xml.XPath Namespce contains XPath related classes to use XPath specifications. This namespace has following classes -XPathDocument, XPathExression, XPathNavigator, and XPathNodeIterator. With the help of XpathDocument, XpathNavigator provides a fast navigation though XML documents. This class contains many Move methods to move through a document.
The System.Xml.Xsl namespace contains classes to work with XSL/T transformations.
Reading XML Documents
In my sample application, I’m using books.xml to read and display its data through XmlTextReader. This file comes with VS.NET samples. You can search this on your machine and change the path of the file in the following line:
XmlTextReader textReader = new XmlTextReader(“C:\\books.xml”);
Or you can use any XML file.
The XmlTextReader, XmlNodeReader and XmlValidatingReader classes are derived from XmlReader class. Besides XmlReader methods and properties, these classes also contain members to read text, node, and schemas respectively. I am using XmlTextReader class to read an XML file. You read a file by passing file name as a parameter in constructor.
XmlTextReader textReader = new XmlTextReader(“C:\\books.xml”);
After creating an instance of XmlTextReader, you call Read method to start reading the document. After read method is called, you can read all information and data stored in a document. XmlReader class has properties such as Name, BaseURI, Depth, LineNumber an so on.
List 1 reads a document and displays a node information using these properties.
About Sample Example 1
In this sample example, I read an XML file using XmlTextReader and call Read method to read its node one by one until end of file and display the contents to the console output.
Sample Example 1.
using System;
using System.Xml;
namespace ReadXml1
{
class Class1
{
static void Main(string[] args)
{
// Create an isntance of XmlTextReader and call Read method to read the file
XmlTextReader textReader = new XmlTextReader("C:\\books.xml");
textReader.Read();
// If the node has value
while (textReader.Read())
{
// Move to fist element
textReader.MoveToElement();
Console.WriteLine("XmlTextReader Properties Test");
Console.WriteLine("===================");
// Read this element's properties and display them on console
Console.WriteLine("Name:" + textReader.Name);
Console.WriteLine("Base URI:" + textReader.BaseURI);
Console.WriteLine("Local Name:" + textReader.LocalName);
Console.WriteLine("Attribute Count:" + textReader.AttributeCount.ToString());
Console.WriteLine("Depth:" + textReader.Depth.ToString());
Console.WriteLine("Line Number:" + textReader.LineNumber.ToString());
Console.WriteLine("Node Type:" + textReader.NodeType.ToString());
Console.WriteLine("Attribute Count:" + textReader.Value.ToString());
}
}
}
}
The NodeType property of XmlTextReader is important when you want to know the content type of a document. The XmlNodeType enumeration has a member for each type of XML item such as Attribute, CDATA, Element, Comment, Document, DocumentType, Entity, ProcessInstruction, WhiteSpace and so on.
List 2 code sample reads an XML document, finds a node type and writes information at the end with how many node types a document has.
About Sample Example 2
In this sample example, I read an XML file using XmlTextReader and call Read method to read its node one by one until end of the file. After reading a node, I check its NodeType property to find the node and write node contents to the console and keep track of number of particular type of nodes. In the end, I display total number of different types of nodes in the document.
Sample Example 2.
using System;
using System.Xml;
namespace ReadingXML2
{
class Class1
{
static void Main(string[] args)
{
int ws = 0;
int pi = 0;
int dc = 0;
int cc = 0;
int ac = 0;
int et = 0;
int el = 0;
int xd = 0;
// Read a document
XmlTextReader textReader = new XmlTextReader("C:\\books.xml");
// Read until end of file
while (textReader.Read())
{
XmlNodeType nType = textReader.NodeType;
// If node type us a declaration
if (nType == XmlNodeType.XmlDeclaration)
{
Console.WriteLine("Declaration:" + textReader.Name.ToString());
xd = xd + 1;
}
// if node type is a comment
if (nType == XmlNodeType.Comment)
{
Console.WriteLine("Comment:" + textReader.Name.ToString());
cc = cc + 1;
}
// if node type us an attribute
if (nType == XmlNodeType.Attribute)
{
Console.WriteLine("Attribute:" + textReader.Name.ToString());
ac = ac + 1;
}
// if node type is an element
if (nType == XmlNodeType.Element)
{
Console.WriteLine("Element:" + textReader.Name.ToString());
el = el + 1;
}
// if node type is an entity\
if (nType == XmlNodeType.Entity)
{
Console.WriteLine("Entity:" + textReader.Name.ToString());
et = et + 1;
}
// if node type is a Process Instruction
if (nType == XmlNodeType.Entity)
{
Console.WriteLine("Entity:" + textReader.Name.ToString());
pi = pi + 1;
}
// if node type a document
if (nType == XmlNodeType.DocumentType)
{
Console.WriteLine("Document:" + textReader.Name.ToString());
dc = dc + 1;
}
// if node type is white space
if (nType == XmlNodeType.Whitespace)
{
Console.WriteLine("WhiteSpace:" + textReader.Name.ToString());
ws = ws + 1;
}
}
// Write the summary
Console.WriteLine("Total Comments:" + cc.ToString());
Console.WriteLine("Total Attributes:" + ac.ToString());
Console.WriteLine("Total Elements:" + el.ToString());
Console.WriteLine("Total Entity:" + et.ToString());
Console.WriteLine("Total Process Instructions:" + pi.ToString());
Console.WriteLine("Total Declaration:" + xd.ToString());
Console.WriteLine("Total DocumentType:" + dc.ToString());
Console.WriteLine("Total WhiteSpaces:" + ws.ToString());
}
}
}
Writing XML Documents
XmlWriter class contains the functionality to write to XML documents. It is an abstract base class used through XmlTextWriter and XmlNodeWriter classes. It contains methods and properties to write to XML documents. This class has several Writexxx method to write every type of item of an XML document. For example, WriteNode, WriteString, WriteAttributes, WriteStartElement, and WriteEndElement are some of them. Some of these methods are used in a start and end pair. For example, to write an element, you need to call WriteStartElement then write a string followed by WriteEndElement.
Besides many methods, this class has three properties. WriteState, XmlLang, and XmlSpace. The WriteState gets and sets the state of the XmlWriter class.
Although, it’s not possible to describe all the Writexxx methods here, let’s see some of them.
First thing we need to do is create an instance of XmlTextWriter using its constructor. XmlTextWriter has three overloaded constructors, which can take a string, stream, or a TextWriter as an argument. We’ll pass a string (file name) as an argument, which we’re going to create in C:\ root.
In my sample example, I create a file myXmlFile.xml in C:\\ root directory.
// Create a new file in C:\\ dir
XmlTextWriter textWriter = new XmlTextWriter(“C:\\myXmFile.xml”, null) ;
After creating an instance, first thing you call us WriterStartDocument. When you’re done writing, you call WriteEndDocument and TextWriter’s Close method.
textWriter.WriteStartDocument();
textWriter.WriteEndDocument();
textWriter.Close();
The WriteStartDocument and WriteEndDocument methods open and close a document for writing. You must have to open a document before start writing to it. WriteComment method writes comment to a document. It takes only one string type of argument. WriteString method writes a string to a document. With the help of WriteString, WriteStartElement and WriteEndElement methods pair can be used to write an element to a document. The WriteStartAttribute and WriteEndAttribute pair writes an attribute.
WriteNode is more write method, which writes an XmlReader to a document as a node of the document. For example, you can use WriteProcessingInstruction and WriteDocType methods to write a ProcessingInstruction and DocType items of a document.
//Write the ProcessingInstruction node
string PI= “type=’text/xsl’ href=’book.xsl’”
textWriter.WriteProcessingInstruction(“xml-stylesheet”, PI);
//’Write the DocumentType node
textWriter.WriteDocType(“book”, Nothing, Nothing, “<!ENTITY h ‘softcover’>”);
The below sample example summarizes all these methods and creates a new xml document with some items in it such as elements, attributes, strings, comments and so on. See Listing 5-14. In this sample example, we create a new xml file c:\xmlWriterText.xml. In this sample example, We create a new xml file c:\xmlWriterTest.xml using XmlTextWriter:
After that, we add comments and elements to the document using Writexxx methods. After that we read our books.xml xml file using XmlTextReader and add its elements to xmlWriterTest.xml using XmlTextWriter.
About Sample Example 3
In this sample example, I create a new file myxmlFile.xml using XmlTextWriter and use its various write methods to write XML items.
Sample Example 3.
using System;
using System.Xml;
namespace ReadingXML2
{
class Class1
{
static void Main(string[] args)
{
// Create a new file in C:\\ dir
XmlTextWriter textWriter = new XmlTextWriter("C:\\myXmFile.xml", null);
// Opens the document
textWriter.WriteStartDocument();
// Write comments
textWriter.WriteComment("First Comment XmlTextWriter Sample Example");
textWriter.WriteComment("myXmlFile.xml in root dir");
// Write first element
textWriter.WriteStartElement("Student");
textWriter.WriteStartElement("r", "RECORD", "urn:record");
// Write next element
textWriter.WriteStartElement("Name", "");
textWriter.WriteString("Student");
textWriter.WriteEndElement();
// Write one more element
textWriter.WriteStartElement("Address", ""); textWriter.WriteString("Colony");
textWriter.WriteEndElement();
// WriteChars
char[] ch = new char[3];
ch[0] = 'a';
ch[1] = 'r';
ch[2] = 'c';
textWriter.WriteStartElement("Char");
textWriter.WriteChars(ch, 0, ch.Length);
textWriter.WriteEndElement();
// Ends the document.
textWriter.WriteEndDocument();
// close writer
textWriter.Close();
}
}
}
Using XmlDocument
The XmlDocument class represents an XML document. This class provides similar methods and properties we’ve discussed earlier in this article.
Load and LoadXml are two useful methods of this class. A Load method loads XML data from a string, stream, TextReader or XmlReader. LoadXml method loads XML document from a specified string. Another useful method of this class is Save. Using Save method you can write XML data to a string, stream, TextWriter or XmlWriter.
About Sample Example 4
This tiny sample example pretty easy to understand. We call LoadXml method of XmlDocument to load an XML fragment and call Save to save the fragment as an XML file.
Sample Example 4.
//Create the XmlDocument.
XmlDocument doc = new XmlDocument();
doc.LoadXml((“<Student type=’regular’ Section=’B'><Name>Tommy
ex</Name></Student>”));
//Save the document to a file.
doc.Save(“C:\\std.xml”);
You can also use Save method to display contents on console if you pass Console.Out as a
arameter. For example:
doc.Save(Console.Out);
About Sample Example 5
Here is one example of how to load an XML document using XmlTextReader. In this sample example, we read books.xml file using XmlTextReader and call its Read method. After that we call XmlDocumetn’s Load method to load XmlTextReader contents to XmlDocument and call Save method to save the document. Passing Console.Out as a Save method argument displays data on the console
Sample Example 5.
XmlDocument doc = new XmlDocument();
//Load the the document with the last book node.
XmlTextReader reader = new XmlTextReader(“c:\\books.xml”);
reader.Read();
// load reader
doc.Load(reader);
// Display contents on the console
doc.Save(Console.Out);
Writing Data from a database
to an XML Document
Using XML and ADO.NET mode, reading a database and writing to an XML document and vice versa is not a big deal. In this section of this article, you will see how to read a database table’s data and write the contents to an XML document.
The DataSet class provides method to read a relational database table and write this table to an XML file. You use WriteXml method to write a dataset data to an XML file.
In this sample example, I have used commonly used Northwind database comes with Office 2000 and later versions. You can use any database you want. Only thing you need to do is just chapter the connection string and SELECT SQ L query.
About Sample Example 6
In this sample, I reate a data adapter object and selects all records of Customers table. After that I can fill method to fill a dataset from the data adapter.
In this sample example, I have used OldDb data provides. You need to add reference to the Syste.Data.OldDb namespace to use OldDb data adapters in your program. As you can see from Sample Example 6, first I create a connection with northwind database using OldDbConnection. After that I create a data adapter object by passing a SELECT SQL query and connection. Once you have a data adapter, you can fill a dataset object using Fill method of the data adapter. Then you can WriteXml method of DataSet, which creates an XML document and write its contents to the XML document. In our sample, we read Customers table records and write DataSet contents to OutputXml.Xml file in C:\ dir.
Sample Example 6.
using System;
using System.Xml;
using System.Data;
using System.Data.OleDb;
namespace ReadingXML2
{
class Class1
{
static void Main(string[] args)
{
// create a connection
OleDbConnection con = new OleDbConnection();
con.ConnectionString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\\Northwind.mdb";
// create a data adapter
OleDbDataAdapter da = new OleDbDataAdapter("Select * from Customers", con);
// create a new dataset
DataSet ds = new DataSet();
// fill dataset
da.Fill(ds, "Customers");
// write dataset contents to an xml file by calling WriteXml method
ds.WriteXml("C:\\OutputXML.xml");
}
}
}
.NET Framework Library provides a good support to work with XML documents. The XmlReader, XmlWriter and their derived classes contains methods and properties to read and write XML documents. With the help of the XmlDocument and XmlDataDocument classes, you can read entire document. The Load and Save method of XmlDocument loads a reader or a file and saves document respectively. ADO.NET provides functionality to read a database and write its contents to the XML document using data providers and a DataSet object.
Main Differences between ASP.NET 3.5 and ASP.NET 4.0
As we all know, ASP.NET 3.5 has introduced with the following main new features
1) AJAX integration
2) LINQ
3) Automatic Properties
4) Lambda expressions
I hope it would be useful for everyone to know about the differences about asp.net 3.5 and its next version asp.net 4.0
Because of space consumption I’ll list only some of them here.
1) Client Data access:
ASP.NET 3.5: There is no direct method to access data from client side. We can go for any of these methods
1) Pagemethods of script manager
2) ICallbackEventHandler interface
3) XMLHttphanlder component
ASP.NET 4.0: In this framework there is an inbuilt feature for this. Following are the methods to implement them.
1) Client data controls
2) Client templates
3) Client data context
i.e we can access the data through client data view & data context objects from client side.
2) Setting Meta keyword and Meta description:
Meta keywords and description are really useful for getting listed in search engine.
ASP.NET 3.5: It has a feature to add meta as following tag
<meta name="keywords" content="These, are, my, keywords" /> <meta name="description" content="This is the description of my page" />
ASP.NET 4.0: Here we can add the keywords and description in Page directives itself as shown below.
< %@ Page Language="C#" CodeFile="Default.aspx.cs" Inherits="_Default" Keywords="Keyword1,Key2,Key3,etc" Description="description" %>
3) Enableviewstage property for each control
ASP.NET 3.5: this property has two values “True” or “false”
ASP.NET 4.0: ViewStateMode property takes an enumeration that has three values: Enabled, Disabled, and Inherit.
Here inherit is the default value for child controls of a control.
4) Setting Client IDs
Some times ClientID property creates head ach for the programmers.
ASP.NET 3.5: We have to use ClientID property to find out the id which is dynamically generated
ASP.NET 4.0: The new ClientIDMode property is introduced to minimize the issues of earlier versions of ASP.NET.
It has following values.
AutoID – Same as ASP.NET 3.5
Static – There won’t be any separate clientid generated at run time
Predictable-These are used particularly in datacontrols. Format is like clientIDrowsuffix with the clientid vlaue
Inherit- This value specifies that a control’s ID generation is the same as its parent.
–
happy programming.
.Net Memory Management & Garbage Collection
Introduction
The Microsoft .NET common language runtime requires that all resources be allocated from the managed heap. Objects are automatically freed when they are no longer needed by the application.
When a process is initialized, the runtime reserves a contiguous region of address space that initially has no storage allocated for it. This address space region is the managed heap. The heap also maintains a pointer. This pointer indicates where the next object is to be allocated within the heap. Initially, the pointer is set to the base address of the reserved address space region.
Garbage collection in the Microsoft .NET common language runtime environment completely absolves the developer from tracking memory usage and knowing when to free memory. However, you’ll want to understand how it works. So let’s do it.
Topics Covered
We will cover the following topics in the article
- Why memory matters
- .Net Memory and garbage collection
- Generational garbage collection
- Temporary Objects
- Large object heap & Fragmentation
- Finalization
- Memory problems
1) Why Memory Matters
Insufficient use of memory can impact
- Performance
- Stability
- Scalability
- Other applications
Hidden problem in code can cause
- Memory leaks
- Excessive memory usage
- Unnecessary performance overhead
2) .Net Memory and garbage collection
.Net manages memory automatically
- Creates objects into memory blocks(heaps)
- Destroy objects no longer in use
Allocates objects onto one of two heaps
- Small object heap(SOH) – objects < 85k
- Large object heap(LOH) – objects >= 85k
You allocate onto the heap whenever you use the “new” keyword in code
Small object heap (SOH)
- Allocation of objects < 85k – Contiguous heap – Objects allocated consecutively
- Next object pointer is maintained – Objects references held on Stack, Globals, Statics and CPU register
- Objects not in use are garbage collected
Figure-1
Next, How GC works in SOH?
GC Collect the objects based on the following rules:
- Reclaims memory from “rootless” objects
- Runs whenever memory usage reaches certain thresholds
- Identifies all objects still “in use”
- Has root reference
- Has an ancestor with a root reference
- Compacts the heap
- Copies “rooted” objects over rootless ones
- Resets the next object pointer
- Freezes all execution threads during GC
- Every GC runs it hit the performance of your app
Figure-2
3) Generational garbage collection
Optimizing Garbage collection
- Newest object usually dies quickly
- Oldest object tend to stay alive
- GC groups objects into Generations
- Short lived – Gen 0
- Medium – Gen 1
- Long Lived – Gen 2
- When an object survives a GC it is promoted to the next generation
- GC compacts Gen 0 objects most often
- The more the GC runs the bigger the impact on performance
Figure-3
Figure-4
Here object C is no longer referenced by any one so when GC runs it get destroyed & Object D will be moved to the Gen 1 (see figure-5). Now Gen 0 has no object, so when next time when GC runs it will collect object from Gen 1.
Figure-5
Figure-6
Here when GC runs it will move the object D & B to Gen 2 because it has been referenced by Global objects & Static objects.
Figure-7
Here when GC runs for Gen 2 it will find out that object A is no longer referenced by anyone so it will destroy it & frees his memory. Now Gen 2 has only object D & B.
Garbage collector runs when
- Gen 0 objects reach ~256k
- Gen 1 objects reach ~2Meg
- Gen 2 objects reach ~10Meg
- System memory is low
Most objects should die in Gen 0.
Impact on performance is very high when Gen 2 run because
- Entire small object heap is compacted
- Large object heap is collected
4) Temporary objects
- Once allocated objects can’t resize on a contiguous heap
- Objects such as strings are Immutable
- Can’t be changed, new versions created instead
- Heap fills with temporary objects
Let us take example to understand this scenario.
Figure – 8
After the GC runs all the temporary objects are destroyed.
Figure–9
5) Large object heap & Fragmentation
Large object heap (LOH)
- Allocation of object >=85k
- Non contiguous heap
- Objects allocated using free space table
- Garbage collected when LOH Threshold Is reached
- Uses free space table to find where to allocate
- Memory can become fragmented
Figure-10
After object B is destroyed free space table will be filled with a memory address which has been available now.
Figure-11
Now when you create new object, GC will check out which memory area is free or available for our new object in LOH. It will check out the Free space table & allocate object where it fit.
Figure-12
6) Object Finalization
- Disk, Network, UI resources need safe cleanup after use by .NET classes
- Object finalization guarantees cleanup code will be called before collection
- Finalizable object survive for at least 1 extra GC & often make it to Gen 2
- Finalizable classes have a
- Finalize method(c# or vb.net)
- C++ style destructor (c#)
Here are the guidelines that help you to decide when to use Finalize method:
- Only implement Finalize on objects that require finalization. There are performance costs associated with Finalize methods.
- If you require a Finalize method, you should consider implementing IDisposable to allow users of your class to avoid the cost of invoking the Finalize method.
- Do not make the Finalize method more visible. It should be protected, not public.
- An object’s Finalize method should free any external resources that the object owns. Moreover, a Finalize method should release only resources that are held onto by the object. The Finalize method should not reference any other objects.
- Do not directly call a Finalize method on an object other than the object’s base class. This is not a valid operation in the C# programming language.
- Call the base.Finalize method from an object’s Finalize method.
Note: The base class’s Finalize method is called automatically with the C# and the Managed Extensions for C++ destructor syntax.
Let see one example to understand how the finalization works.
Each figure itself explain what is going on & you can clearly see how the finalization works when GC run.
Figure-13
Figure-14
Figure-15
Figure-16
Figure-17
For more information on Finalization refer the following links:
http://www.object-arts.com/docs/index.html?howdofinalizationandmourningactuallywork_.htm
http://blogs.msdn.com/cbrumme/archive/2004/02/20/77460.aspx
How to minimize overheads
Object size, number of objects, and object lifetime are all factors that impact your application’s allocation profile. While allocations are quick, the efficiency of garbage collection depends (among other things) on the generation being collected. Collecting small objects from Gen 0 is the most efficient form of garbage collection because Gen 0 is the smallest and typically fits in the CPU cache. In contrast, frequent collection of objects from Gen 2 is expensive. To identify when allocations occur, and which generations they occur in, observe your application’s allocation patterns by using an allocation profiler such as the CLR Profiler.
You can minimize overheads by:
- Avoid Calling GC.Collect
- Consider Using Weak References with Cached Data
- Prevent the Promotion of Short-Lived Objects
- Set Unneeded Member Variables to Null Before Making Long-Running Calls
- Minimize Hidden Allocations
- Avoid or Minimize Complex Object Graphs
- Avoid Preallocating and Chunking Memory
Read more: http://www.guidanceshare.com/wiki/.NET_2.0_Performance_Guidelines_-_Garbage_Collection
Uploading Multiple Files in ASP.NET 2.0
In ASP.NET We can upload more than one file using the following classes:
HttpFileCollection
HttpPostedFile
Request.Files
System.IO.Path
HttpFileCollection:
HttpFileCollection will provide access to the files uploaded by a client.
HttpPostedFile:
HttpPostedFile will provide access to individual files uploaded by a client. Through this class we can access the content and properties of each individual file, and read and save the files.
Request.Files :
The Request.Files will return collection of all files uploaded by user and store them inside the HttpFileCollection.
Follow these steps mentioned below to do so:
Step 1:
Drag and drop multiple (in our case four) FileUpload controls on to the designer.
Step 2:
Drop a Button control and rename it to “Upload”
<asp:Button ID=”btnUpload” runat=”server” Text=”Upload” />
Step 3:
Double click the Upload Button to add an event hander to the code behind.
protected void btnUpload_Click(object sender, EventArgs e)
{
}
Step 4: Import the System.IO namespace.
using System.IO;
Step 5:
Use the ‘HttpFileCollection’ class to retrieve all the files that are uploaded. Files are encoded and transmitted in the content body using multipart MIME format with an HTTP Content-Type header. ASP.NET extracts
this information from the content body into individual members of an HttpFileCollection.
The code would look as follows:
protected void btnUpload_Click(object sender, EventArgs e)
{
try
{
// Get the HttpFileCollection
HttpFileCollection hfc = Request.Files;
for (int i = 0; i < hfc.Count; i++)
{
HttpPostedFile hpf = hfc[i];
if (hpf.ContentLength > 0)
{
hpf.SaveAs(Server.MapPath(”MyFiles”) + “\\” +
Path.GetFileName(hpf.FileName));
}
}
}
catch (Exception ex)
{
// Handle your exception here
}
}
Some important points to consider while uploading
1. To save a file to the server, the account associated with ASP.NET must have sufficient permissions on the folder, where the files are being uploaded. This would usually be the ‘ASPNET’ account for Windows XP or a similar OS. In Windows Server 2003, the account used is ‘NETWORKSERVICE’. So you would be required to explicitly grant write permissions to these accounts on the folder.
2. While uploading the files to a remote server, the default ASPNET user account used by ASP.NET does not have network permissions by default. The solution is to either give the account such permissions or
use impersonation to have it run under a different account that has the permissions.
3. By default, you can upload no more than 4096 KB (4 MB) of data. However there is a workaround for this limitation. You can change the maximum file size by changing the maxRequestLength attribute of the
httpRuntime element in the web.config file. You can also increase the ‘executionTimeout’. By default it is 110 seconds. I would encourage you to experiment with the other attributes of the httpRuntime element.
<configuration>
<system.web>
<httpRuntime
executionTimeout=”200″
maxRequestLength=”8192″
requestLengthDiskThreshold=”256″
useFullyQualifiedRedirectUrl=”false”
minFreeThreads=”8″
minLocalRequestFreeThreads=”4″
appRequestQueueLimit=”5000″
enableKernelOutputCache=”true”
enableVersionHeader=”true”
requireRootedSaveAsPath=”true”
enable=”true”
shutdownTimeout=”90″
delayNotificationTimeout=”5″
waitChangeNotification=”0″
maxWaitChangeNotification=”0″
enableHeaderChecking=”true”
sendCacheControlHeader=”true”
apartmentThreading=”false”/>
</system.web>
</configuration>
References
There are a number of good resources I referred to, for this article. A few of them are:
http://www.wrox.com/WileyCDA/Section/id-292160.html
http://msdn2.microsoft.com/en-US/library/aa479405.aspx
http://msdn2.microsoft.com/en-us/library/system.web.httpfilecollection.aspx
Encryption & Decryption : ASCII encoding
The GetByteCount method determines how many bytes result in encoding a set of Unicode characters, and the GetBytes method performs the actual encoding.
Likewise, the GetCharCount method determines how many characters result in decoding a sequence of bytes, and the GetChars and GetString methods perform the actual decoding.
When selecting the ASCII encoding for your applications, consider the following:
- The ASCII encoding is usually appropriate for protocols that require ASCII.
- If your application requires 8-bit encoding, the UTF-8 encoding is recommended over the ASCII encoding. For the characters 0-7F, the results are identical, but use
of UTF-8 avoids data loss by allowing representation of all Unicode characters that are representable. Note that the ASCII encoding has an 8th bit ambiguity that can allow malicious use, but the UTF-8 encoding removes ambiguity about the 8th bit.
- Previous versions of .NET Framework allowed spoofing by merely ignoring the 8th bit. The current version has been changed so that non-ASCII code points fall back during the decoding of bytes.
——————————————————————
Example of ASCII encoding
——————————————————————
SecurityClass.cs
————————–
public static string EnryptString(string strEncrypted)
{
byte[] b = System.Text.ASCIIEncoding.ASCII.GetBytes(strEncrypted);
string encryptedConnectionString = Convert.ToBase64String(b);
return encryptedConnectionString;
}
public static string DecryptString(string encrString)
{
byte[] b = Convert.FromBase64String(encrString);
string decryptedConnectionString = System.Text.ASCIIEncoding.ASCII.GetString(b);
return decryptedConnectionString;
}
Default.aspx.cs
———————
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
string Password = “SandeepMRamani”;
lblOriginal.Text = Password;
lblEncryption.Text = SecurityClass.EnryptString(Password);
lblDecryption.Text = SecurityClass.DecryptString(lblEncryption.Text);
}
}
Default.aspx
——————
<div align=”center” style=”font-size:xx-large;”>
<h1> Encryption / Decryption Example </h1>
<hr />
Original String :
<asp:Label ID=”lblOriginal” style=”font-weight:bolder;” runat=”server” Text=””></asp:Label>
<br />
Encrypted Text :
<asp:Label ID=”lblEncryption” style=”font-weight:bolder;” runat=”server” Text=””></asp:Label>
<br />
Decrypted Text :
<asp:Label ID=”lblDecryption” style=”font-weight:bolder;” runat=”server” Text=””></asp:Label>
<hr />
</div>
–
Happy programming
Difference between Managed and Unmanaged code.
Managed Code
Managed code is code that is written to target the services of the managed runtime execution environment (like Common Language Runtime in .NET Framework). The managed code is always executed by a managed runtime execution environment rather than the operating system directly. Managed refers to a method of exchanging information between the program and the runtime environment. Because the execution of code is governed by the runtime environment, the environment can guarantee what the code is going to do and provide the necessary security checks before executing any piece of code. Because of the same reason the managed code also gets different services from the runtime environment like Garbage Collection, type checking, exception handling, bounds checking, etc. This way managed code does not have to worry about memory allocations, type safety, etc. Applications written in Java, C#, VB.NET, etc target a runtime environment which manages the execution and the code written using these types of languages is known as Managed Code. Managed code is always compiled into an Intermediate Language (MSIL in case of .NET Framework). The compiler used by .NET framework to compile managed code compiles it into Intermediate Language and generates the necessary metadata, symbolic information that describes all of the entry points and the constructs exposed in the Intermediate Language (e.g., methods, properties) and their characteristics. The Common Language Infrastructure (CLI) Standard describes how the information is to be encoded, and programming languages that target the runtime emit the correct encoding.
In .NET Framework Managed Code runs within the .Net Framework’s CLR and benefits from the services provided by the CLR. When we compile the managed code, the code gets compiled to an intermediate language (MSIL) and an executable is created. When a user runs the executable the Just In Time Compiler of CLR compiles the intermediate language into native code specific to the underlying architecture. Since this translation happens by the managed execution environment (CLR), the managed execution environment can make guarantees about what the code is going to do, because it can actually reason about it. It can insert traps and sort of protection around, if it’s running in a sandboxed environment, it can insert all the appropriate garbage collection hooks, exception handling, type safety, array bounce, index checking and so forth.
Managed code also provides platform independence. As the managed code is first compiled to intermediate language, the CLR’s JIT Compiler takes care of compiling this intermediate language into the architecture specific instructions.
Unmanaged Code
Code that is directly executed by the Operating System is known as un-managed code. Typically applications written in VB 6.0, C++, C, etc are all examples of unmanaged code. Unmanaged code typically targets the processor architecture and is always dependent on the computer architecture. Unmanaged code is always compiled to target a specific architecture and will only run on the intended platform. This means that if you want to run the same code on different architecture then you will have to recompile the code using that particular architecture. Unmanaged code is always compiled to the native code which is architecture specific. When we compile unmanaged code it gets compiled into a binary X86 image. And this image always depends on the platform on which the code was compiled and cannot be executed on the other platforms that are different that the one on which the code was compiled. Unmanaged code does not get any services from the managed execution environment.
In unmanaged code the memory allocation, type safety, security, etc needs to be taken care of by the developer. This makes unmanaged code prone to memory leaks like buffer overruns and pointer overrides and so forth.
Unmanaged executable files are basically a binary image, x86 code, loaded into memory. The program counter gets put there and that’s the last the Operating System knows. There are protections in place around memory management and port I/O and so forth, but the system doesn’t actually know what the application is doing.
Using LINQ to query object hierarchies
I used LINQ to solve the following problem: find all titles of objects at hierarchy level X when you know object ID in hierarchy level Y. I cannot imagine if there is some other solution that is same short and clear as one that LINQ provides. Take a look and decide by yourself.
Here is simple diagram with my entities. Here are my simple rules. Level1 has no parent level and my contain one ore more Level2 entities. Level2 entities have one Level1 parent and one or more Level3 enitities. Level3 entities have one Level2 parent entity and collection of one or more Items. So there is many-to-many relationship between Level3 and Items.
We cannot use composite pattern here because these classes will be very different and there will be no point where we need one common interface for them. That’s why we have one class per level. Also the number of levels is fixed and there is no plan to expand this hierarchy.
By the way, you can model arbitrary class hierarchies on this model and still use this example (as long as it doesn’t hurt performance and you are really sure what you are doing).
Excercise: having Level1 items collection and knowing Level3 item ID find all Items for specified Level3 item and return string of their titles separated by comma. As you don’t have access to source code of data source you must use IList<Level1> and LINQ.
We will use simple class structure given below and we expect that we already got list of Level1 items from some repository or data context.
public class Level1
{
public int Id { get; set; }
public string Title { get; set; }
public IList<Level2> Level2Items { get; set; }
}
public class Level2
{
public int Id { get; set; }
public string Title { get; set; }
public Level1 Parent { get; set; }
public IList<Level3> Level3Items { get; set; }
}
public class Level3
{
public int Id { get; set; }
public string Title { get; set; }
public Level2 Parent { get; set; }
public IList<Item> Items { get; set; }
}
public class Item
{
public int Id { get; set; }
public string Title { get; set; }
}
===
Now it’s time to write some hardcore loops and create a cool code-hell… or maybe it’s time to be elegant and use LINQ as stated before. Using LINQ we can provide the following solution:
public string GetItemsStringForLevel3(IList<Level1> level1Items, int level3Id)
{
var items = from l in level1Items
from l2 in l.Level2Items
from l3 in l2.Level3Items
from p in l3.Items
where l3.Id == level3Id
select p.Title;
return string.Join(“, “, items.ToArray());
}
–
Happy Programming
Statement cannot appear within a method body. End of method assumed
<script language=”vbscript” runat=”server”></script>
–
Happy Programming
What is Maximum Request size for asp.net application?
The default max request size is 4MB (4096).
You can change a setting in your web.config to allow larger requests.
Here is the example:
1: <configuration>
2: <system.web>
3: <httpRuntime maxRequestLength="4096"/>
4: </system.web>
5: </configuration>
This is default setting, we have to change this to the size that you want to allow user to request like 10MB, 20MB…
——
Happy Programming
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