The Global.asax File

• Optional

• But likely to be useful, contains

• directives

• event handlers

• object tags

Directives: 

• @ Application directives - can add descriptive information
  <%@ Application Description="My First ASP.NET Application" %>
  or inheritance
  <%@ Application Inherits="MyApp" %>
  For code behind

• @ Import directives
  <%@ Import Namespace="System.Data" %>

• @ Assembly directives
  <%@ Import Namespace="System.DirectoryServices" %>
  <%@ Assembly Name="System.DirectoryServices" %>

Event Handlers

Most common reason for having a global.asax file

• Start and End events (for the application and for the session)

Global.asax can also include handlers for events fired by HttpApplication instances. If present in Global.asax, the following methods are called in every request in response to HttpApplication events. They’re listed in the order in which they’re called.

e.g

<script language="C#" runat="server">
  void Application_PostRequestHandlerExecute (Object sender, EventArgs e)
  {
      HttpApplication app = (HttpApplication) sender;
      app.Context.Response.Write ("<hr><center><i>" +
          "Copyright © 2002 by Me, Myself, and I</i></center>");
  }
</script>

Error Events

<%@ Import Namespace="System.Diagnostics" %> 

<script language="C#" runat="server"> 
  void Application_Error (Object sender, EventArgs e)
  {
      // Formulate a message to write to the event log
      string msg = "Error accessing " + Request.Path + "\n" +
          Server.GetLastError ().ToString ();

      // Write an entry to the event log
      EventLog log = new EventLog ();
      log.Source = "My ASP.NET Application";
      log.WriteEntry (msg, EventLogEntryType.Error);
  }
</script>

Global Object Tags

Global object tags create object instances declaratively. Suppose you want a new instance of ShoppingCart created for each user that visits your site. Rather than do this:

<script>
  void Session_Start ()
  {
      Session["MyShoppingCart"] = new ShoppingCart ();
  }
</script>

you can do this:

<object id="MyShoppingCart" class="ShoppingCart" scope="session"
  runat="server" />

Application State/Cache

Similar but Cache allows expiration dates and is preferred for that reason

• In memory information about the application (cannot be persisted)

Example

HttpApplicationState properties and methods expose the contents of application state. The following statements add three stock prices keyed by stock symbols to application state and work equally in an ASPX file, in Global.asax, or in a code-behind file:

Application["AMZN"] = 10.00m;
Application["INTC"] = 20.00m;
Application["MSFT"] = 30.00m;

You can also add items to application state using HttpApplicationState.Add:

Application.Add ("AMZN", 10.00m);
Application.Add ("INTC", 20.00m);
Application.Add ("MSFT", 30.00m);

However, Add and [] behave slightly differently when adding items to application state. Add adds an item even if an item with the specified key already exists; [] does not. These statements add two separate items to application state:

Application.Add ("AMZN", 10.00m);
Application.Add ("AMZN", 11.00m);

You can retrieve both items by iterating over the contents of application state, but if you simply ask for the item keyed by “AMZN,” you’ll get back 10. The following example, by contrast, adds just one item to application state. The first statement creates the item and assigns it the value 10. The second statement changes the item’s value to 11:

Application["AMZN"] = 10.00m;
Application["AMZN"] = 11.00m;

How do you read values from application state? The following statements retrieve the stock prices inserted earlier:

decimal amzn = (decimal) Application["AMZN"];
decimal intc = (decimal) Application["INTC"];
decimal msft = (decimal) Application["MSFT"];

Locking and Unlocking

Application.Lock ();
Application["ItemsSold"] = (int) Application["ItemsSold"] + 1;
Application["ItemsLeft"] = (int) Application["ItemsLeft"] - 1;
Application.UnLock ();

An Example

<%@ Import NameSpace="System.IO" %>

<script language="C#" runat="server">
  static string _path;

  void Application_Start ()
  {
      StreamReader reader = null;

      try {
          // If Count.txt exists, read the count from it and
          // store the count in application state
          _path = Server.MapPath ("/Count.txt");
          reader = new StreamReader (_path);
          string line = reader.ReadLine ();
          int count = Convert.ToInt32 (line);
          Application["Count"] = count;
      }
      catch (Exception) {
          // If Count.txt does not exist or contains an invalid
          // count, store a 0 in application state
          Application["Count"] = 0;
      }
      finally {
          // Close the StreamReader
          if (reader != null)
              reader.Close ();
      }
  }

  void Application_End ()
  {
      StreamWriter writer = null;

      try {
          // Save the current count in Count.txt
          writer = new StreamWriter (_path, false);
          writer.Write (Application["Count"]);
      }

      finally {
          // Close the StreamWriter
          if (writer != null)
              writer.Close ();
      }
  }
</script

ASPX page

<%@ Page Language="C#" %>

<html>
  <body>
    <%
      // Fetch the count and increment it by 1. Lock application state
      // to prevent the count from changing as it's being updated.
      Application.Lock ();
      int count = (int) Application["Count"] + 1;
      Application["Count"] = count;
      Application.UnLock ();

      // Write the count to the page
      Response.Write ("Pages in this application " +
          "have been requested " + count + " time");
      if (count > 1)
          Response.Write ("s");
      Response.Write (".");
    %>
  </body>
</html>

To test - run this application, close browser and run again.

The Application Cache

Supports

• Expiration dates

• callbacks when item expires (thus could update the value by reinserting)

• discards least recently accessed when space is needed

• Can store any managed type (lie dataSet and HashTable)

Example

<script language="C#" runat="server">
  void Application_Start ()
  {
      Hashtable stocks = new Hashtable ();
      stocks.Add ("AMZN", 10.00m);
      stocks.Add ("INTC", 20.00m);
      stocks.Add ("MSFT", 30.00m);

      Context.Cache.Insert ("Stocks", stocks, null,
          DateTime.Now.AddMinutes (5), Cache.NoSlidingExpiration);
  }
</script>

Can also be conditional on changes to datasource files,e.g

DataSet ds = new DataSet (); ds.ReadXml (Server.MapPath ("Stocks.xml")); Context.Cache.Insert ("Stocks", ds,     new CacheDependency (Server.MapPath ("Stocks.xml")));

Call also set priorities for removing when space is short OR  use NotRemovable

Using a callback

<%@ Import Namespace="System.Data" %>

<script language="C#" runat="server">
  static Cache _cache;
  static string _path;

  void Application_Start ()
  {
      _cache = Context.Cache;
      _path = Context.Server.MapPath ("Stocks.xml");

      DataSet ds = new DataSet ();
      ds.ReadXml (_path);

      _cache.Insert ("Stocks", ds, new CacheDependency (_path),
          Cache.NoAbsoluteExpiration, Cache.NoSlidingExpiration,
          CacheItemPriority.Default,
          new CacheItemRemovedCallback (RefreshDataSet));
  }

  static void RefreshDataSet (String key, Object item,
      CacheItemRemovedReason reason)
  {
      DataSet ds = new DataSet ();
      ds.ReadXml (_path);

      _cache.Insert ("Stocks", ds, new CacheDependency (_path),
          Cache.NoAbsoluteExpiration, Cache.NoSlidingExpiration,
          CacheItemPriority.Default,
          new CacheItemRemovedCallback (RefreshDataSet));
  }
</script>

Cache demonstration

<%@ Import NameSpace="System.IO" %>

<script language="C#" runat="server">

  static Cache _cache = null;
  static string _path = null;

  void Application_Start ()
  {
      _cache = Context.Cache;
      _path = Server.MapPath ("Quotes.txt");

      ArrayList quotes = ReadQuotes ();

      if (quotes != null) {
          _cache.Insert ("Quotes", quotes, new CacheDependency (_path),
              Cache.NoAbsoluteExpiration, Cache.NoSlidingExpiration,
              CacheItemPriority.Default,
              new CacheItemRemovedCallback (RefreshQuotes));
      }
  }

  static void RefreshQuotes (String key, Object item,
      CacheItemRemovedReason reason)
  {
      ArrayList quotes = ReadQuotes ();

      if (quotes != null) {
          _cache.Insert ("Quotes", quotes, new CacheDependency (_path),
              Cache.NoAbsoluteExpiration, Cache.NoSlidingExpiration,
              CacheItemPriority.Default,
              new CacheItemRemovedCallback (RefreshQuotes));
      }
  }

  static ArrayList ReadQuotes ()
  {
      ArrayList quotes = new ArrayList ();
      StreamReader reader = null;

      try {
          reader = new StreamReader (_path);
          for (string line = reader.ReadLine (); line != null;
              line = reader.ReadLine ())
              quotes.Add (line);
      }

      catch (IOException) {
          return null;
      }
      finally {
          if (reader != null)
              reader.Close ();
      }
      return quotes;
  }
</script>

<%@ Import Namespace="System.IO" %>

<html>
  <body>
    <asp:Label ID="Output" RunAt="server" />
  </body>
</html>

<script language="C#" runat="server">
  void Page_Load (Object sender, EventArgs e)
  {
      ArrayList quotes = (ArrayList) Cache["Quotes"];

      if (quotes != null) {
          Random rand = new Random ();
          int index = rand.Next (0, quotes.Count - 1);
          Output.Text = (string) quotes[index];
      }
      else {
          Output.Text = "Server busy";
      }
  }
</script>

Session State

An example

<%@ Page Language="C#" %>
	
<html>
  <body>
    <%
      if (Session.IsNewSession ││ Session["Count"] == null) {
          Session["Count"] = 1;
          Response.Write ("Welcome! Because this is your first " +
              "visit to this site, a new session has been created " +
              "for you. Your session ID is " + Session.SessionID +
              ".");
      }
      else {
          Session["Count"] = (int) Session["Count"] + 1;
          Response.Write ("You have visited this site " +
              Session["Count"] + " times. Your session ID is still " +
              Session.SessionID + ".");
      }
    %>
  </body>
</html>

Session State Process Models

• Serializable

• Session Lifetimes