CodeProject的這篇文章確實對我有所啟迪，
http://www.codeproject.com/useritems/SessionWrapper.ASP#xx1208856xx。
誠如作者所說，我們經常在ASP.Net用許多類似於下面的代碼來檢測Session中存儲的對象，來防止Session過期後存儲的變量丟失問題：
Int32 nUserID = -1;
if ( null != Session["userID"] ) {
if ( Session["userID"] is Int32 ) {
if ( 0 < Session["userID"] ) {
nUserID = (Int32) Session["userID"]
}
}
}
if ( -1 == nUserID )
{
throw new ApplicationException ( "Unexpected situation: userID invalid." );
}
this.DOSomething( nUserID );
這樣的代碼會遍布各處。
那麼，利用他的這個封裝方案來做重構，確實讓代碼簡潔干淨了不少！
經過他的封裝，上面的代碼用這麼一句話就行了：
this.DOSomething( CCurrentSession.UserID )
他的類其實也很簡單，如下所示：
using System;
using System.Web;
/**////--------------------------------------------------------------------
/// Developed by M. van Eijkel - aug 2005
/// [e]: [email protected]
/// [w]: www.vaneijkel.com
namespace VanEijkel.Web
{
/**//// <summary>
/// Wrapper class for the session object.
/// It centralizes the logic for retrIEving and validation of session information.
/// By using an approach like this you improve the protection and encapsulation of existing code.
/// It offers a simple, low-risk, easy manageable way to improve existing WebApplication.
/// Therfore, I call it webRefactoring.
/// </summary>
public class CurrentSession
{
Constants#region Constants
private const String sMANDATORY_SESSION_KEY_NOT_FOUND_MSG = "Session variable excepted but does not exist. Key={0}";
private const String sMANDATORY_SESSION_VALUE_INVALID_NULL = "None null session value excepted. Key={0}";
private const Int32 nUSERID_UNKOWN = -1;
private const Int32 nUSERID_MINIMUM = 1;
private const String sUSERID_INVALID = "Invalid UserID:{0}. UserID should be larger than:{1}";
#endregion
UserID#region UserID
/**//// <summary>
/// Returns the userID as a Int32 instead of an object.
/// This way you will get the compiler protection and intelligence support you need.
/// </summary>
public static Int32 UserID
{
get
{
return (Int32) GetValueOrDefault( eKeys.UserID, nUSERID_UNKOWN );
}
set
{
&n
bsp; if ( nUSERID_MINIMUM >= value )
{
throw new ApplicationException ( String.Format(sUSERID_INVALID, value, nUSERID_MINIMUM ));
}
SetValue( eKeys.UserID, value );
}
}
#endregion
private: GetValueOrDefault( eKeys eKey, Object oDefaultValue )#region private: GetValueOrDefault( eKeys eKey, Object oDefaultValue )
/**//// <summary>
/// Gets the value from the session object.
/// </summary>
/// <param name="eKey"> The session key to get the value for.</param>
/// <param name="oDefaultValue">The default value to use if no valid value stored.</param>
/// <returns>When the value is null or the key does not exist,
/// the specifIEd default value is returned.
/// Otherwise, the value is returned</returns>
private static object GetValueOrDefault( eKeys eKey, Object oDefaultValue )
{
//get the value
object oValue = GetValue( eKey );
//value not found or null?
if (null == oValue)
{
//return default value
return oDefaultValue;
}
//everything oke: return session value
return oValue;
}
#endregion
private: GetMandatoryValue( eKeys eKey )#region private: GetMandatoryValue( eKeys eKey )
/**//// <summary>
/// Returns the session value for a session-key that must exist.
/// If the key does not exist an applicationException is thrown.
/// </summary>
/// <param name="eKey"> The session-key to return the session-value for. </param>
/// <returns> A none-null value.</returns>
private static object GetMandatoryValue( eKeys eKey )
{
//get the value
object oValue = GetValue( eKey );
//key not found or value null?
if ( null == oValue )
{
//throw appl
icationException because its application logic error (none CLR)
throw new ApplicationException ( String.Format( sMANDATORY_SESSION_KEY_NOT_FOUND_MSG, eKey.ToString() ));
}
//everything oke: return value
return oValue;
}
#endregion
private: GetValue( eKeys eKey )#region private: GetValue( eKeys eKey )
/**//// <summary>
/// Gets the session value from the specifIEd key.
/// </summary>
/// <param name="eKey">The key to get the value from</param>
/// <returns>The session value for the specifIEd session key.
/// If the key does not exist, null is returned.
/// </returns>
private static object GetValue( eKeys eKey )
{
return HttpContext.Current.Items[ eKey.ToString() ];
}
#endregion
private SetMandatoryValue( eKeys eKey, Object oValue )#region private SetMandatoryValue( eKeys eKey, Object oValue )
private static void SetMandatoryValue( eKeys eKey, Object oValue )
{
if ( null == oValue )
{
throw new ApplicationException( String.Format(sMANDATORY_SESSION_VALUE_INVALID_NULL, eKey.ToString() ) );
}
}
#endregion
private SetValue( eKeys eKey, Object oValue)#region private SetValue( eKeys eKey, Object oValue)
/**//// <summary>
/// Stores the specified session-value to the specifIEd session-key.
/// </summary>
/// <param name="eKey">The key for the value to store in the session.</param>
/// <param name="oValue">The value to store in the session</param>
private static void SetValue ( eKeys eKey, Object oValue)
{
HttpContext.Current.Items[eKey.ToString()] = oValue;
}
#endregion
/**//// <summary>
/// An enum for the
/// </summary>
private enum eKeys
{
UserID
}
}
}
