博客园_Impossible is nothing

断开/开启网络连接命令

2011-03-30T00:35:00Z

断开：ipconfig /release

开启：ipconfig /renew

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FW: Dispose and Finalize

2011-02-21T23:57:00Z

FW from http://www.dotnetspark.com/kb/2694-non-deterministic-destructors-c-sharp.aspx

Introduction

This article provides an introduction to destructors in C# and reveals the non-deterministic destructor problem.

It also analyzes the IDisposable, garbage collection, using statement, etc.

Destructor

The destructor is a special purpose method in a class like a constructor. The constructor is called by the runtime after creating an instance. It is meant for initialization purposes. Like that, a destructor is called by the runtime before destroying an instance. It is meant for finalization operations.

A destructor is declared like a constructor with a prefix tilde(~) in C#. A destructor do not have access modifiers like public, private, etc.

public class Shape
{
    ~Shape() // Destructor
    {
    }
}

In C#, the .NET runtime automatically destroys any class instances that are no longer in reference. It does this during the process of garbage collection.

Using of destructors will make the application slow in performance.

Finalizers

It is important to note that the destructors are also called Finalizers because the compiler converts a C# destructor into a method named Finalize() in the Intermediate Language (IL). The code in the destructor will be wrapped in a try..finally block inside the Finalize() method.

Garbage Collection

This is the process of freeing up of unused memory of objects periodically. The .NET runtime does the process of garbage collection on the following conditions:

When there is shortage of memory
Developer invoked the GC.Collect() method

The garbage collection helps the developer to free up object instances.

But remember, garbage collection only destroys the managed resources, i.e. resources created inside the managed memory.

What is the Need of Destructors?

Since the runtime is managing the destruction of all objects, a question may arise: Why do we need destructors?

Answer: To destroy unmanaged resources.

The unmanaged resources are those created outside the managed environment. They may include file handles, network connections, etc. These resources created should be destroyed by the class itself, because the runtime is not able to destroy them.

Therefore, we use destructors to free up the unmanaged resources. This will ensure that all the unmanaged resources created by the class will be freed in the destructor.

E.g.: Let Channel be a class using unmanaged resources having a constructor and a destructor.

public class Channel
{
    public Channel()
    {
        // Create unmanaged resource
        // Lock("c:\\file.log");
    }

    ~Channel()
    {
        // Destroy unmanaged resource
        // Unlock("c:\\file.log");
    }
}

The Channel class locks a file "c:\file.log" in the constructor and unlocks it in the destructor.

Here arises a problem that we cannot predict when the destructor is called. So the file remains locked until the garbage collection, even if the object instance is out of any reference.

For the above problem, we need some method to free the unmanaged resource. In .NET, there is an interface named IDisposable for the purpose.

IDisposable

The IDisposable interface contains a method Dispose() which should be implemented by the class. So we can move freeing up of unmanaged resources to this Dispose() method.

Again there is a problem, that a typical .NET developer not calling the Dispose() method after the usage of class instance. In that case, we need the call to free unmanaged resources both in the destructor and in the Dispose() method.

We can also use a Close() method instead of implementing the IDisposable interface. But, enabling the IDisposable makes our class usable in the using {}statement of C#.

The using statement will automatically call the Dispose() method after exiting the scope of using. (Please refer to the sample code.)

public class Channel : IDisposable
{
    public Channel()
    {
        // Create unmanaged resource
        Lock("c:\\file.log");
    }
    ~Channel()
    {
        // Destroy unmanaged resource
        Unlock("c:\\file.log");
    }
    void IDisposable.Dispose()
    {
        Unlock("c:\\file.log");
    }
    public void Lock(string file) { }
    public void Unlock(string file) { }
}

At first look, the above code solves all the problems.

But, it creates a new problem due to the non-deterministic destructors of C#.

Non-Deterministic Destructors

In C#, we do not know when the destructor is executed. It is called only during the garbage collection process and we do not know when it actually happens. This state is called non-deterministic destructors or InDeterministic destructors.

The following figure illustrates the problem. Our 'Channel' class is using some unmanaged resources and freeing them in the Dispose() method and also in the destructor.

There are two cases when the Channel class is used:

A developer creates an instance and exits without calling Dispose()
A developer creates an instance and calls Dispose()

Solution using GC.SuppressFinalize(this)

We can instruct the garbage collector not to call the destructor by using the GC.SuppressFinalize(this) method. So, using this in the Dispose() method after freeing up unmanaged resources will solve the non-deterministic destructor problem.

The solution is given below.

Here, the Channel class has freed up code both in the destructor and in the Dispose() method. And if the developer calls the Dispose() method, the unmanaged resources will be freed and the destructor will be disabled by using GC.SuppressFinalize(this);.

If the developer does not call the Dispose() method, the unmanaged resources are freed up in the destructor by the garbage collector. The figure below illustrates the solution:

Note: The Dispose() method is used to free up the unmanaged resources, and calling Dispose() will not free up the instance. It just executes whatever statements are written in it.

Using the Code

The code along with this article demonstrates the case of using/not using Dispose(), and also the initiating of the GarbageCollection process usingGC.Collect(). Please analyze the Channel class to see the details involved.

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Assembly generation failed Referenced assembly ‘xxx’ does not have a strong name

2010-11-29T03:45:00Z

cancel signing in the property of project

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use AjaxControlToolKit Config

2010-11-26T01:21:00Z

options:

.aspx file:

<%@ Register assembly="AjaxControlToolkit" namespace="AjaxControlToolkit" tagprefix="asp" %>

...

<asp:Accordion>...

web.config file:

...

<system.web>

　　　　　　...　　

　　　　　　...

</assemblies>

</compilation>

　　<pages>

...

　　　　</namespaces>

</controls>

</pages>

</system.web>

...

.aspx file:

<asp:Accordion>...

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VFS study

2010-11-24T06:31:00Z

basic configuration:

source control
work items
build

advanced:

automated testing
virtual lab deployment
architectural validation

ways to access TFS

VS (developer)
Test & Lab Manager (tester)
Web/Excel/Project/MOSS (PM)

project templates(need more research on MSDN):

Agile Software Development v5
CMMI Process Improment v5

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Run MVC in older version of IIS

2010-11-23T23:46:00Z

http://www.asp.net/mvc/tutorials/using-asp-net-mvc-with-different-versions-of-iis-cs

IIS 7(integrated mode): no need

IIS 7(classical mode): need

IIS 6: need

two options:

1. modify route table to use file extension if have no right to control web server

modify Global.asax

2. don't want to modify url appearence and could control the web server

modify Global.asax + set up wildcard script map

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MVC study - data validation

2010-11-23T06:20:00Z

Data validation

Sever side:

Required – Indicates that the property is a required field
DisplayName – Defines the text we want used on form fields and validation messages
StringLength – Defines a maximum length for a string field
Range – Gives a maximum and minimum value for a numeric field
Bind – Lists fields to exclude or include when binding parameter or form values to model properties
ScaffoldColumn – Allows hiding fields from editor forms

Client side:

<%@ Import Namespace="MvcMusicStore"%>

<script src="/Scripts/MicrosoftAjax.js" type="text/javascript"></script>

<script src="/Scripts/MicrosoftMvcAjax.js" type="text/javascript"></script>

<script src="/Scripts/MicrosoftMvcValidation.js" type="text/javascript"></script>

<% Html.EnableClientValidation(); %>

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MVC study

2010-11-23T04:38:00Z

default generated folders

Folder	Purpose
/Controllers	Controllers respond to input from the browser, decide what to do with it, and return response to the user.
/Views	Views hold our UI templates
/Models	Models hold and manipulate data
/Content	This folder holds our images, CSS, and any other static content
/Scripts	This folder holds our JavaScript files
/App_Data	This folder holds our database files

based on folder naming convertion, for example, controllers look for views in Views folder

advantages: reduce typing codes and make it easier to understand

controllers

traditional sites: mapping incoming url/ request to files, e.g. /index.aspx

MVC sites: mapping url to methods of classes, these classes are called controllers, these methods are called controller actions

functions:

processing request
handle input
deal with data
determining response - HTML/redirect/download file...

notes:

Default home page naming convertion: HomeController
get parametres from methods' params
HttpUtility.HTMLEncode to prevent users from injecting js into our view

ViewModel

what viewModel to do: encapsulate the data that controllers want to pass to views

build project before view knows new created viewModel class

Views

what views to do: using template files to more easily customize the HTML contents back to browsers

to use view-template, return ActionResult and View();

view's folder location matchs controller's name

view's file name matchs method's name

<% %> "code nuggets"

<%: %> result will be output to the page instead <%= %>

Model Class

manage data and domain logic, unlike viewModel, which was built just for passing data from controller to view

HTML helper

ActionLink create <a> and ensure the URL paths

example:

<%: Html.ActionLink("Go to the Store Index","Index")%>

two params: link text and same controller's method

<%: Html.ActionLink(genreName, "Browse", new { genre = genreName })%>

three params: link text, same controller's method and input

Html.EditorForModel() will first look for the template, otherwise use default template

<%: Html.EditorFor(model => model.Album,

new { Artists = Model.Artists, Genres = Model.Genres}) %>

allows us to specify a specific Editor type

<%: Html.DropDownList("ArtistId", new SelectList(ViewData["Artists"] as IEnumerable,

"ArtistId", "Name", Model.ArtistId))%>

The name of the form field (ArtistId)
The list of values for the dropdown, passed as a SelectList
The Data Value field which should be posted back with the form
The Data Text field which should be displayed in the dropdown list
The Selected Value which is used to set the dropdown list value when the form is displayed

Entity Data Model

Create EDM via Entity Framework, EF - an ORM(object relational mapping) Data API to query and update data stored in DB

ADO.Net Entity data model represents one Database

Editor Template

Must in folder: /Views/Shared/EditorTemplates

Add view as a partial view(.ascx)

Cascade delete

delete one record in table a also delete records in table b connected with table a

set "End1 OnDelete"=Cascade in the relation between table a and table b

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serv-U ftp 550 Permission denied

2009-05-31T03:13:00Z

删除用户，重新建就ok了

安装VS2008提示删除之前的东东-转自Marcel

2009-05-12T02:41:00Z

Upgrading Visual Studio Team System Beta to RTM Upgrading Visual studio Team System Beta to RTM uninstall scripts Today I had to upgrade several machines from the Beta or RC version of VSTS to the RTM...