.NET面试必备：C#与ASP.NET重点问答集锦

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"C# 和 Asp.Net 面试题集锦" 本文主要聚焦于C#和Asp.Net技术领域，提供了一系列面试中可能出现的问题和答案，旨在帮助读者在一个统一的资料中获取全面的.Net、C#、ADO.NET、Web服务和.Net框架相关的学习材料。以下是一些关键知识点的详细解释： 1. ViewState是什么？有何用途？ ViewState是ASP.NET中的一个机制，用于在页面的多个生命周期之间存储页面和控件的状态信息。当用户提交表单时，ViewState数据会自动编码并嵌入到HTML响应中，然后在后续的请求中解码，恢复页面的状态。这使得服务器能够记住用户交互，如文本框的值或控件的可见性，即使在POST回发中也能保持这些状态。 2. 用户控件(UserControls)和自定义控件(CustomControls)有什么区别？ - 自定义控件：自定义控件是用户或第三方开发者编写的，不属于.Net Framework类库的标准控件。它们可以是针对WebForms（ASP.NET页面）的服务器端控件，也可以是用于Windows Forms应用程序的客户端控件。自定义控件允许开发者扩展功能，创建具有特定行为和外观的复杂组件。 - 用户控件：在ASP.NET中，用户控件是由用户创建的服务器端控件，它们可以将多个基础控件组合在一起，形成一个逻辑单元。用户控件提供了一种重用代码的方式，可以在多个页面中复用相同的设计和功能，但它们不具有自定义控件那样的高度可扩展性。 3. ASP.NET中有哪些其他重要的概念和技术？ - 控件事件模型：ASP.NET提供了丰富的事件处理机制，使得开发者可以轻松地处理用户交互，如按钮点击、文本框更改等。 - 页面生命周期：了解页面从加载到呈现的各个阶段对于有效编程至关重要，包括初始化、加载、验证、呈现和卸载等阶段。 - 数据绑定：ASP.NET提供了多种数据绑定机制，如DataBinder、DataSource控件和Linq-to-SQL，方便地将数据展示在网页上。 - MVC（Model-View-Controller）框架：ASP.NET MVC提供了一种分离关注点的开发模式，使开发者可以更好地管理业务逻辑、视图呈现和用户交互。 - WebAPI：用于构建RESTful服务，便于移动应用和Web应用通过HTTP协议进行数据交换。 - SignalR：实现实时双向通信的库，支持服务器推送，常用于聊天应用、协作工具等实时场景。这些知识点构成了C#和Asp.Net开发的核心，理解和掌握它们对于准备面试或提升开发技能都极为重要。通过深入学习和实践，开发者可以更好地应对各种项目需求和挑战。

What is the difference between in-proc and out-of-proc?

An inproc is one which runs in the same process area as that of the client giving tha advantage of speed

but the disadvantage of stability becoz if it crashes it takes the client application also with it.Outproc is

one which works outside the clients memory thus giving stability to the client, but we have to compromise

a bit on speed.

When you’re running a component within ASP.NET, what process is it running within on

Windows XP? Windows 2000? Windows 2003?

On Windows 2003 (IIS 6.0) running in native mode, the component is running within the w3wp.exe

process associated with the application pool which has been configured for the web application containing

the component.

On Windows 2003 in IIS 5.0 emulation mode, 2000, or XP, it's running within the IIS helper process

whose name I do not remember, it being quite a while since I last used IIS 5.0.

What does aspnet_regiis -i do ?

Aspnet_regiis.exe is The ASP.NET IIS Registration tool allows an administrator or installation program to

easily update the script maps for an ASP.NET application to point to the ASP.NET ISAPI version associated

with the tool. The tool can also be used to display the status of all installed versions of ASP. NET, register

the ASP.NET version coupled with the tool, create client-script directories, and perform other configuration

operations.

When multiple versions of the .NET Framework are executing side-by-side on a single computer, the

ASP.NET ISAPI version mapped to an ASP.NET application determines which version of the common

language runtime is used for the application.

The tool can be launched with a set of optional parameters. Option "i" Installs the version of ASP.NET

associated with Aspnet_regiis.exe and updates the script maps at the IIS metabase root and below. Note

that only applications that are currently mapped to an earlier version of ASP.NET are affected

What is a PostBack?

The process in which a Web page sends data back to the same page on the server.

What is ViewState? How is it encoded? Is it encrypted? Who uses ViewState?

ViewState is the mechanism ASP.NET uses to keep track of server control state values that don't

otherwise post back as part of the HTTP form. ViewState Maintains the UI State of a Page

ViewState is base64-encoded.

It is not encrypted but it can be encrypted by setting EnableViewStatMAC="true" & setting the

machineKey validation type to 3DES. If you want to NOT maintain the ViewState, include the directive <

%@ Page EnableViewState="false" % > at the top of an .aspx page or add the attribute

EnableViewState="false" to any control.

What is the < machinekey > element and what two ASP.NET technologies is it used for?

Configures keys to use for encryption and decryption of forms authentication cookie data and view state

data, and for verification of out-of-process session state identification.There fore 2 ASP.Net technique in

which it is used are Encryption/Decryption & Verification

What three Session State providers are available in ASP.NET 1.1? What are the pros and cons of

each?

ASP.NET provides three distinct ways to store session data for your application: in-process session state,

out-of-process session state as a Windows service, and out-of-process session state in a SQL Server

database. Each has it advantages.

1.In-process session-state mode

Limitations:

* When using the in-process session-state mode, session-state data is lost if aspnet_wp.exe or the

application domain restarts.

* If you enable Web garden mode in the < processModel > element of the application's Web.config file,

do not use in-process session-state mode. Otherwise, random data loss can occur.

Advantage:

* in-process session state is by far the fastest solution. If you are storing only small amounts of volatile

data in session state, it is recommended that you use the in-process provider.

2. The State Server simply stores session state in memory when in out-of-proc mode. In this mode the

worker process talks directly to the State Server

3. SQL mode, session states are stored in a SQL Server database and the worker process talks directly to

SQL. The ASP.NET worker processes are then able to take advantage of this simple storage service by

serializing and saving (using .NET serialization services) all objects within a client's Session collection at

the end of each Web request

Both these out-of-process solutions are useful primarily if you scale your application across multiple

processors or multiple computers, or where data cannot be lost if a server or process is restarted.

What is the difference between HTTP-Post and HTTP-Get?

As their names imply, both HTTP GET and HTTP POST use HTTP as their underlying protocol. Both of these

methods encode request parameters as name/value pairs in the HTTP request.

The GET method creates a query string and appends it to the script's URL on the server that handles the

request.

The POST method creates a name/value pairs that are passed in the body of the HTTP request message.

Name and describe some HTTP Status Codes and what they express to the requesting client.

When users try to access content on a server that is running Internet Information Services (IIS) through

HTTP or File Transfer Protocol (FTP), IIS returns a numeric code that indicates the status of the request.

This status code is recorded in the IIS log, and it may also be displayed in the Web browser or FTP client.

The status code can indicate whether a particular request is successful or unsuccessful and can also reveal

the exact reason why a request is unsuccessful. There are 5 groups ranging from 1xx - 5xx of http status

codes exists.

101 - Switching protocols.

200 - OK. The client request has succeeded

302 - Object moved.

400 - Bad request.

500.13 - Web server is too busy.

Explain < @OutputCache% > and the usage of VaryByParam, VaryByHeader.

OutputCache is used to control the caching policies of an ASP.NET page or user control. To cache a page

@OutputCache directive should be defined as follows < %@ OutputCache Duration="100"

VaryByParam="none" % >

VaryByParam: A semicolon-separated list of strings used to vary the output cache. By default, these

strings correspond to a query string value sent with GET method attributes, or a parameter sent using the

POST method. When this attribute is set to multiple parameters, the output cache contains a different

version of the requested document for each specified parameter. Possible values include none, *, and any

valid query string or POST parameter name.

VaryByHeader: A semicolon-separated list of HTTP headers used to vary the output cache. When this

attribute is set to multiple headers, the output cache contains a different version of the requested

document for each specified header.

What is the difference between repeater over datalist and datagrid?

The Repeater class is not derived from the WebControl class, like the DataGrid and DataList. Therefore,

the Repeater lacks the stylistic properties common to both the DataGrid and DataList. What this boils

down to is that if you want to format the data displayed in the Repeater, you must do so in the HTML

markup.

The Repeater control provides the maximum amount of flexibility over the HTML produced. Whereas the

DataGrid wraps the DataSource contents in an HTML < table >, and the DataList wraps the contents in

either an HTML < table > or < span > tags (depending on the DataList's RepeatLayout property), the

Repeater adds absolutely no HTML content other than what you explicitly specify in the templates.

While using Repeater control, If we wanted to display the employee names in a bold font we'd have to

alter the "ItemTemplate" to include an HTML bold tag, Whereas with the DataGrid or DataList, we could

have made the text appear in a bold font by setting the control's ItemStyle-Font-Bold property to True.

The Repeater's lack of stylistic properties can drastically add to the development time metric. For

example, imagine that you decide to use the Repeater to display data that needs to be bold, centered, and

displayed in a particular font-face with a particular background color. While all this can be specified using

a few HTML tags, these tags will quickly clutter the Repeater's templates. Such clutter makes it much

harder to change the look at a later date. Along with its increased development time, the Repeater also

lacks any built-in functionality to assist in supporting paging, editing, or editing of data. Due to this lack of

feature-support, the Repeater scores poorly on the usability scale.

However, The Repeater's performance is slightly better than that of the DataList's, and is more noticeably

better than that of the DataGrid's. Following figure shows the number of requests per second the Repeater

could handle versus the DataGrid and DataList

Can we handle the error and redirect to some pages using web.config?

Yes, we can do this, but to handle errors, we must know the error codes; only then we can take the user

to a proper error message page, else it may confuse the user.

CustomErrors Configuration section in web.config file:

The default configuration is:

< customErrors mode="RemoteOnly" defaultRedirect="Customerror.aspx" >

< error statusCode="404" redirect="Notfound.aspx" / >

< /customErrors >

If mode is set to Off, custom error messages will be disabled. Users will receive detailed exception error

messages.

If mode is set to On, custom error messages will be enabled.

If mode is set to RemoteOnly, then users will receive custom errors, but users accessing the site locally

will receive detailed error messages.

Add an < error > tag for each error you want to handle. The error tag will redirect the user to the

Notfound.aspx page when the site returns the 404 (Page not found) error.

[Example]

There is a page MainForm.aspx

Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles

MyBase.Load

'Put user code to initialize the page here

Dim str As System.Text.StringBuilder

str.Append("hi") ' Error Line as str is not instantiated

Response.Write(str.ToString)

End Sub

[Web.Config]

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