יום שלישי, 10 בפברואר 2009

What is the difference between const and static readonly?

set to a compile time constant. 

In the static readonly case, the containing class is allowed to modify it only
in the variable declaration (through a variable initializer)
in the static constructor (instance constructors, if it's not static) 

static readonly is typically used if the type of the field is not allowed in a const declaration, or when the value is not known at compile time. 

Instance readonly fields are also allowed.  

Remember that for reference types, in both cases (static and instance) the readonly modifier only prevents you from assigning a new reference to the field. It specifically does not make immutable the object pointed to by the reference.

  class Program

  {

  public static readonly Test test = new Test();

 

  static void Main(string[] args)

  {

  test.Name = "Program";

 

  test = new Test(); // Error: A static readonly field cannot be assigned to (except in a static constructor or a variable initializer)  

 

  }

  }

 

  class Test

  {

  public string Name;

  }

 

On the other hand, if Test were a value type, then assignment to test.Name would be an error.


מהם ה“דורות“ של ה-Garbage collector?

ה-Garbage collector מבוסס על העקרון הבא: כל אובייקט חדש שנוצר מתווסף למה שנקרא “דור 0“. מספר הדור אומר כמה “איסופים“ של ה-Garbage collector הוא “שרד“. “איסוף“ מתייחס לכאשר ה-garbage collector מחליט שצריך לפנות זכרון ובודק אילו אובייקטים יש להשאיר ואיזה אפשר לזרוק. אם ה-garbage collector קובע שהאובייקט צריך להישאר הוא יעביר אותו ל“דור 1“ ובאיסוף הבא ל“דור 2“. אין דורות מעבר לדור 2.

מהי הרשאת internal?

בדומה להרשאות גישה של public/private קיימת הרשאה בשם internal. הראשת internal קובעת כי המשאב הזה יהיה זמין רק בתוך ה-assembly שבה נכתבה המחלקה. למשל, אם יצרנו שכבה אחת במערכת שרצינו להגביל לה גישה למתודה\מחלקה\Property מסויימת לשימוש פנימי בתוך אותה assembly נשתמש בהרשאת הגישה internal.

מה קורה כאשר שרת ה IIS מקבל בקשה חדשה


1. מגיע בקשה לקבלת דף אינטרנט מהשרת מדפדפן הלקוח.

2. ה IIS ממפה את הסיומת של הקובץ אותו הלקוח ביקש (1.aspx)  אל ה ASPNET_ISAPI.DLL  שרות המספוק על ידי ה asp.net

3. ה ASPNET_ISAPI.DLL מעביר את הבקשה לתהליך של ה ASP.NET  - מופיע כ (ASPNET_WP.EXE or W3P.EXE).

4. המשך יבוא......

ASP.NET IIS Registration Tool.

How to and when to use ASP.NET IIS Registration Tool. 

If .NET framework is installed before IIS then we get this problem "Server application unavailable" when we run any application on IIS.
 
For this we need to register ASP.NET with IIS.
 
Go to command promt and go to .NET directory (C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727).
Then run this command aspnet_regiis -i for registering ASP.NET runtime with IIS. and aspnet_regiis -c for installing client side scripts.
 
The tool can also be used to determine which version of the common language runtime (CLR) is used for the application and also to display the status of all installed versions of ASP. NET, register the ASP.NET version that is coupled with the tool, create client-script directories, and perform other configuration operations.
 
Below are the options that we get with this tool.
 
Option Description 
-c
 Installs the client-side scripts for ASP.NET, such as client-side validation scripts, to the aspnet_client subdirectory of each Internet Information Services (IIS) site directory.

Only the client-side scripts for the ASP.NET version that is associated with Aspnet_regiis.exe are installed.
 
-disable
 Disables ASP.NET in the IIS Security Console.

This option can be combined only with the -i, -ir, or -r options. It is not available with IIS versions earlier than IIS 6.0.
 
-e
 Removes the client-side scripts for ASP.NET from the aspnet_client subdirectory of each IIS site directory.

Only the client-side scripts for the ASP.NET version associated with Aspnet_regiis.exe are removed.
 
-ea
 Removes the client-side scripts for all versions of ASP.NET from the aspnet_client subdirectory of each IIS site directory.
 
-enable
 Enables ASP.NET in the IIS Security Console.

This option can be combined only with the -i, -ir, or -r options. It is not available with IIS versions earlier than IIS 6.0 or with ASP.NET versions earlier than ASP.NET version 2.0.
 
-ga user
 Grants the specified user or group access to the IIS metabase and other directories that are used by ASP.NET.

This option is not available with ASP.NET versions earlier than ASP.NET 2.0.
 
-i
 Installs the version of ASP.NET that is associated with Aspnet_regiis.exe and updates the script maps at the IIS metabase root and below.

Only the script maps for applications that use an earlier version of ASP.NET are updated. Applications that use a later version are not affected.
 
-ir
 Installs the version of ASP.NET that is associated with Aspnet_regiis.exe and only registers ASP.NET in IIS.

This option does not update the script maps. To install ASP.NET and update the script maps, use the -i option.
 
-k path
 Removes the script maps to all versions of ASP.NET from all ASP.NET applications at the specified application root path and its subdirectories.
 
-kn path
 Removes the script maps to all versions of ASP.NET from the ASP.NET application only at the specified application root path.

This option does not affect applications in subdirectories of the specified path.
 
-lk
 Lists the path and version of all IIS metabase keys where ASP.NET is mapped.

The keys that inherit ASP.NET script maps from a parent key are not displayed.
 
-lv
 Lists the status and installation path of all versions of ASP.NET that are installed on the computer.
 
-norestart
 Inhibits the restart of the World Wide Web Publishing Service after installing or updating ASP.NET script maps. If you do not use this option, all application pools are recycled.

Use this option with the -i or -r options when the IIS worker process will be restarted manually.
 
-r
 Updates all of the script maps in the IIS metabase and below to point to the ASP.NET ISAPI version that is associated with Aspnet_regiis.exe.

All existing script maps are updated to point to the ASP.NET ISAPI version that is associated with the ASP.NET IIS Registration tool, regardless of the current version.
 
-s path
 Installs the script map that points to the ASP.NET ISAPI version associated with Aspnet_regiis.exe to all ASP.NET applications at the specified application root path and its subdirectories. All existing script maps in the specified path and below that use an earlier version of the ASP.NET ISAPI are updated.
 
-sn path
 Installs the script map that points to the ASP.NET ISAPI version associated with the tool to the ASP.NET application at the specified application root path. All existing script maps in the specified path that use an earlier version of the ASP.NET ISAPI are updated.

This option does not affect applications in subdirectories of path.
 
-u
 Uninstalls the version of ASP.NET that is associated with the ASP.NET IIS Registration tool from the computer. Existing script maps to this version of the ASP.NET ISAPI are automatically remapped to the most recent remaining ASP.NET ISAPI version installed.
 
-ua
 Uninstalls all versions of ASP.NET from the computer.
 
-?
 Displays the command syntax and options for the ASP.NET IIS Registration tool.
 

Configuration Options
Option Description 
-config+
 Enables remote access to ASP.NET configuration on the computer.
 
-config-
 Disables remote access to ASP.NET configuration on the computer.
 
-pa container account
 Grants permission for the specified user or group account to access the specified key container. This argument takes the following optional modifiers:

-pku Substitutes a user-specified container for the default machine container.

-csp provider Specifies the container provider to use.

-full Specifies that full access should be added, rather than the default read-only access.
 
-pc container
 Creates an RSA public/private key pair in the specified container. This argument takes the following optional modifiers:

-size keySize Specifies the key size. The default is 1024 bytes.

-pku Substitutes a user-specified container for the default key container on the computer.

-exp Specifies that private keys must be able to be exported.

-csp provider Specifies the container provider to use.
 
-pd section
 Decrypts the configuration section. This argument takes the following optional parameters:

-app virtualPath Specifies that decryption should occur at the level of the included path.

-location subPath Specifies the subdirectory to decrypt.

-pkm Specifies that the Machine.config file should be decrypted instead of the Web.config file.
 
-pdf section webApplicationDirectory
 Decrypts the specified configuration section of the Web.config file in the specified physical (not virtual) directory.
 
-pe section
 Encrypts the specified configuration section. This argument takes the following optional modifiers:

-prov provider Specifies the encryption provider to use.

-app virtualPath Specifies that encryption should occur at the level of the included path.

-location subPath Specifies the subdirectory to encrypt.

-pkm Specifies that the Machine.config file should be encrypted instead of the Web.config file.
 
-pef section webApplicationDirectory
 Encrypts the specified configuration section of the Web.config file in the specified physical (not virtual) directory.
 
-pi container file
 Imports an RSA public/private key pair to the specified container from the specified XML file. This argument takes the following optional modifiers:

-pku Substitutes a user-specified container for the default machine container.

-exp Specifies that private keys can be exported.

-csp provider Specifies the container provider to use.
 
-pr container account
 Removes permission for the specified user or group account to access the specified key container. This argument takes the following optional modifiers:

-pku Substitutes a user-specified container for the default machine container.

-csp provider Specifies the container provider to use.
 
-px container file
 Exports an RSA public/private key pair from the specified container to the specified XML file. This argument takes the following optional modifiers:

-pku Substitutes a user-specified container for the default machine container.

-csp provider Specifies the container provider to use.
 
-pz container
 Deletes the specified key container. This argument takes the following optional modifier:

-pku Substitutes a user-specified container for the default machine container.
 


מה ההבדל בין Dataset.clone and Dataset.copy

clone:
מעתיק רק מבנה ולא מעתיק מידע
 copy:
מעתיק גם מבנה וגם DATA