外文翻译原文-民宿预定系统的设计与实现

外文翻译原文-民宿预定系统的与实现 ASP.NET2.0 Instant Results ASP.NET is a web application framework developed and marketed by Microsoft to allow programmers to build dynamic web sites, web applications and web services. It was first released in January 2002 with version 1.0 of the .NET Framework, and is the successor to Microsoft's Active Server Pages (ASP) technology. ASP.NET is built on the Common Language Runtime (CLR), allowing programmers to write ASP.NET code using any supported .NET language. Characteristics Pages .NET pages, known officially as "web forms", are the main building block for application development.[8] Web forms are contained in files with an ".aspx" extension; in programming jargon, these files typically contain static (X)HTML markup, as well as markup defining server-side Web Controls and User Controls where the developers place all the required static and dynamic content for the web page. Additionally, dynamic code which runs on the server can be placed in a page within a block <% -- dynamic code -- %> which is similar to other web development technologies such as PHP, JSP, and ASP, but this practice is generally discouraged except for the purposes of data binding since it requires more calls when rendering the page.[citation needed] Note that this sample uses code "inline", as opposed to code behind. <%@ Page Language="C#" %>

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[edit] Code-behind model It is recommended by Microsoft for dealing with dynamic program code to use the code-behind model, which places this code in a separate file or in a specially designated script tag. Code-behind files typically have names like MyPage.aspx.cs or MyPage.aspx.vb based on the ASPX file name (this practice is automatic in Microsoft Visual Studio and other IDEs). When using this style of programming, the developer writes code to respond to different events, like the page being loaded, or a control being clicked, rather than a procedural walk through the document. ASP.NET's code-behind model marks a departure from Classic ASP in that it encourages developers to build applications with separation of presentation and content in mind. In theory, this would allow a web designer, for example, to focus on the design markup with less potential for disturbing the programming code that drives it. This is similar to the separation of the controller from the view in model-view-controller frameworks. [edit] Example <%@ Page Language="C#" CodeFile="SampleCodeBehind.aspx.cs" Inherits="Website.SampleCodeBehind" AutoEventWireup="true" %> The above tag is placed at the beginning of the ASPX file. The CodeFile property of the @ Page directive specifies the file (.cs or .vb) acting as the code-behind while the Inherits property specifies the Class the Page derives from. In this example, the @ Page directive is included in SampleCodeBehind.aspx, then SampleCodeBehind.aspx.cs acts as the code-behind for this page: using System; namespace Website { public partial class SampleCodeBehind : System.Web.UI.Page { protected override void OnLoad(EventArgs e) { base.OnLoad(e); } } } In this case, the Page_Load() method is called every time the ASPX page is requested. The programmer can implement event handlers at several stages of the page execution process to perform processing. [edit] User controls ASP.NET supports creating reusable components through the creation of User Controls. A User Control follows the same structure as a Web Form, except that such controls are derived from the System.Web.UI.UserControl class, and are stored in ASCX files. Like ASPX files, an ASCX file contains static HTML or XHTML markup, as well as markup defining web control and other User Controls. The code-behind model can be used. Programmers can add their own properties, methods,[9] and event handlers.[10] An event bubbling mechanism provides the ability to pass an event fired by a user control up to its containing page. User can also build Custom Controls for Asp.Net application. Where controls are in compiled DLL file. And by using Register directive user can use control from DLL. [edit] Rendering technique ASP.NET uses a visited composites rendering technique. During compilation, the template (.aspx) file is compiled into initialization code which builds a control tree (the composite) representing the original template. Literal text goes into instances of the Literal control class, and server controls are represented by instances of a specific control class. The initialization code is combined with user-written code (usually by the assembly of multiple partial classes) and results in a class specific for the page. The page doubles as the root of the control tree. Actual requests for the page are processed through a number of steps. First, during the initialization steps, an instance of the page class is created and the initialization code is executed. This produces the initial control tree which is now typically manipulated by the methods of the page in the following steps. As each node in the tree is a control represented as an instance of a class, the code may change the tree structure as well as manipulate the properties/methods of the individual nodes. Finally, during the rendering step a visitor is used to visit every node in the tree, asking each node to render itself using the methods of the visitor. The resulting HTML output is sent to the client. After the request has been processed, the instance of the page class is discarded and with it the entire control tree. [edit] State management ASP.NET applications are hosted in a web server and are accessed over the stateless HTTP protocol. As such, if the application uses stateful interaction, it has to implement state management on its own. ASP.NET provides various functionality for state management in ASP.NET applications. [edit] Application state Application state is a collection of user-defined variables that are shared by an ASP.NET application. These are set and initialized when the Application_OnStart event fires on the loading of the first instance of the applications and are available till the last instance exits. Application state variables are accessed using the Applications collection, which provides a wrapper for the application state variables. Application state variables are identified by names.[11] [edit] Session state Session state is a collection of user-defined session variables, which are persisted during a user session. These variables are unique to different instances of a user session, and are accessed using the Session collection. Session variables can be set to be automatically destroyed after a defined time of inactivity, even if the session does not end. At the client end, a user session is identified either by a cookie or by encoding the session ID in the URL itself.[11] ASP.NET supports three modes of persistence for session variables:[11] In Process Mode The session variables are maintained within the ASP.NET process. This is the fastest way, however, in this mode the variables are destroyed when the ASP.NET process is recycled or shut down. Since the application is recycled from time to time this mode is not recommended for critical applications. ASPState Mode In this mode, ASP.NET runs a separate Windows service that maintains the state variables. Because the state management happens outside the ASP.NET process and .NET Remoting must be utilized by the ASP.NET engine to access the data, this mode has a negative impact on performance in comparison to the In Process mode, although this mode allows an ASP.NET application to be load-balanced and scaled across multiple servers. However, since the state management service runs independent of ASP.NET, the session variables can persist across ASP.NET process shutdowns. SqlServer Mode In this mode, the state variables are stored in a database server, accessible using SQL. Session variables can be persisted across ASP.NET process shutdowns in this mode as well. The main advantage of this mode is it would allow the application to balance load on a server cluster while sharing sessions between servers. [edit] View state View state refers to the page-level state management mechanism, which is utilized by the HTML pages emitted by ASP.NET applications to maintain the state of the web form controls and widgets. The state of the controls are encoded and sent to the server at every form submission in a hidden field known as __VIEWSTATE. The server sends back the variable so that when the page is re-rendered, the controls render at their last state. At the server side, the application might change the viewstate, if the processing results in updating the state of any control. The states of individual controls are decoded at the server, and are available for use in ASP.NET pages using the ViewState collection.[12] [13] [edit] Other Other means of state management that are supported by ASP.NET are cookies, caching, and using the query string. [edit] Template engine When first released, ASP.NET lacked a template engine. Because the .NET framework is object-oriented and allows for inheritance, many developers would define a new base class that inherits from "System.Web.UI.Page", write methods here that render HTML, and then make the pages in their application inherit from this new class. While this allows for common elements to be reused across a site, it adds complexity and mixes source code with markup. Furthermore, this method can only be visually tested by running the application - not while designing it. Other developers have used include files and other tricks to avoid having to implement the same navigation and other elements in every page. ASP.NET 2.0 introduced the concept of "master pages", which allow for template-based page development. A web application can have one or more master pages, which begining with ASP.NET 3.5, can be nested.[14] Master templates have place-holder controls, called ContentPlaceHolders to denote where the dynamic content goes, as well as HTML and JavaScript shared across child pages. Child pages use those ContentPlaceHolder controls, which must be mapped to the place-holder of the master page that the content page is populating. The rest of the page is defined by the shared parts of the master page, much like a mail merge in a word processor. All markup and server controls in the content page must be placed within the ContentPlaceHolder control. When a request is made for a content page, ASP.NET merges the output of the content page with the output of the master page, and sends the output to the user. The master page remains fully accessible to the content page. This means that the content page may still manipulate headers, change title, configure caching etc. If the master page exposes public properties or methods (e.g. for setting copyright notices) the content page can use these as well. [edit] Other files Other file extensions associated with different versions of ASP.NET include: Extension Required version Description asax 1.0 Global.asax, used for application-level logic [15] ascx 1.0 Web UserControls: custom controls to be placed onto web pages. ashx 1.0 custom HTTP handlers. asmx 1.0 web service pages. From version 2.0 a Code behind page of an asmx file is placed into the app_code folder. axd 1.0 when enabled in web.config requesting trace.axd outputs application-level tracing. Also used for the special webresource.axd handler which allows control/component developers to package a component/control complete with images, script, css etc. for deployment in a single file (an 'assembly') browser 2.0 browser capabilities files stored in XML format; introduced in version 2.0. ASP.NET 2 includes many of these by default, to support common web browsers. These specify which browsers have which capabilities, so that ASP.NET 2 can automatically customize and optimize its output accordingly. Special .browser files are available for free download to handle, for instance, the W3C Validator, so that it properly shows standards-compliant pages as being standards-compliant. Replaces the harder-to-use BrowserCaps section that was in machine.config and could be overridden in web.config in ASP.NET 1.x. config 1.0 web.config is the only file in a specific Web application to use this extension by default (machine.config similarly affects the entire Web server and all applications on it), however ASP.NET provides facilities to create and consume other config files. These are stored in XML format. cs/vb 1.0 Code files (cs indicates C#, vb indicates Visual Basic). Code behind files (see above) predominantly have the extension ".aspx.cs" or ".aspx.vb" for the two most common languages. Other code files (often containing common "library" classes) can also exist in the web folders with the cs/vb extension. In ASP.NET 2 these should be placed inside the App_Code folder where they are dynamically compiled and available to the whole application. dbml 3.5 LINQ to SQL data classes file master 2.0 master page file resx 1.0 resource files for internationalization and localization. Resource files can be global (e.g. messages) or "local" which means specific for a single aspx or ascx file. sitemap 2.0 sitemap configuration files. Default file name is web.sitemap skin 2.0 theme skin files. svc 3.0 Windows Communication Foundation service file [edit] Directory structure In general, the ASP.NET directory structure can be determined by the developer's preferences. Apart from a few reserved directory names, the site can span any number of directories. The structure is typically reflected directly in the urls. Although ASP.NET provides means for intercepting the request at any point during processing, the developer is not forced to funnel requests through a central application or front controller. The special directory names (from ASP.NET 2.0 on) are [16]: App_Browsers holds site-specific browser definition files. App_Code This is the "raw code" directory. The ASP.NET server automatically compiles files (and subdirectories) in this folder into an assembly which is accessible in the code of every page of the site. App_Code will typically be used for data access abstraction code, model code and business code. Also any site-specific http handlers and modules and web service implementation go in this directory. As an alternative to using App_Code the developer may opt to provide a separate assembly with precompiled code. App_Data default directory for databases, such as Access mdb files and SQL Server mdf files. This directory is usually the only one with write access for the application. App_LocalResources Contains localized resource files for individual pages of the site. E.g. a file called CheckOut.aspx.fr-FR.resx holds localized resources for the french version of the CheckOut.aspx page. When the UI culture is set to french, ASP.NET will automatically find and use this file for localization. App_GlobalResources Holds resx files with localized resources available to every page of the site. This is where the ASP.NET developer will typically store localized messages etc. which are used on more than one page. App_Themes holds alternative themes of the site. App_WebReferences holds discovery files and WSDL files for references to web services to be consumed in the site. Bin Contains compiled code (.dll files) for controls, components, or other code that you want to reference in your application. Any classes represented by code in the Bin folder are automatically referenced in your application. [edit] Performance ASP.NET aims for performance benefits over other script-based technologies (including Classic ASP) by compiling the server-side code to one or more DLL files on the web server.[17] This compilation happens automatically the first time a page is requested (which means the developer need not perform a separate compilation step for pages). This feature provides the ease of development offered by scripting languages with the performance benefits of a compiled binary. However, the compilation might cause a noticeable but short delay to the web user when the newly-edited page is first requested from the web server, but won't again unless the page requested is updated further. The ASPX and other resource files are placed in a virtual host on an Internet Information Services server (or other compatible ASP.NET servers; see Other Implementations, below). The first time a client requests a page, the .NET framework parses and compiles the file(s) into a .NET assembly and sends the response; subsequent requests are served from the DLL files. By default ASP.NET will compile the entire site in batches of 1000 files upon first request. If the compilation delay is causing problems, the batch size or the compilation strategy may be tweaked. Developers can also choose to pre-compile their code before deployment, eliminating the need for just-in-time compilation in a production environment. [edit] Extension Microsoft has released some extension frameworks that plug into ASP.NET and extend its functionality. Some of them are: ASP.NET AJAX An extension with both client-side as well as server-side components for writing ASP.NET pages that incorporate AJAX functionality. ASP.NET MVC Framework An extension to author ASP.NET pages using the MVC architecture. [edit] ASP.NET compared to ASP classic ASP.NET attempts to simplify developers' transition from Windows application development to web development by offering the ability to build pages composed of controls similar to a Windows user interface. A web control, such as a button or label, functions in very much the same way as its Windows counterpart: code can assign its properties and respond to its events. Controls know how to render themselves: whereas Windows controls draw themselves to the screen, web controls produce segments of HTML and JavaScript which form part of the resulting page sent to the end-user's browser. ASP.NET encourages the programmer to develop applications using an event-driven GUI model, rather than in conventional web-scripting environments like ASP and PHP. The framework attempts to combine existing technologies such as JavaScript with internal components like "ViewState" to bring persistent (inter-request) state to the inherently stateless web environment.