ASP.NET编程技巧精华

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"本书《ASP.NET：技巧、教程与代码》由多位知名作者共同编写，涵盖了ASP.NET编程中的常见技术，包括使用集合、操作文件系统、正则表达式应用、动态生成图片、发送电子邮件、网络访问、文件上传、进程信息获取、访问Windows事件日志、服务器性能计数器以及信息的加密解密等。这些技术对于ASP.NET开发人员来说至关重要，能帮助他们高效地构建和管理Web应用程序。" 在本章中，我们将深入探讨以下几个关键知识点： 1. 使用集合：集合是编程中用于存储可变数量元素的对象，它们提供了添加和删除元素的便利，而无需关注内存管理细节。在ASP.NET中，你可以使用各种类型的集合，如ArrayList、LinkedList、Dictionary等，来存储不同类型的数据，并实现灵活的数据操作。 2. 工作于文件系统：在ASP.NET中，可以使用System.IO命名空间的类来操作文件和目录，如File、Directory、FileInfo和DirectoryInfo等。这些类允许你读写文件、创建、删除和移动文件及目录，从而实现动态内容生成和数据持久化。 3. 使用正则表达式：正则表达式是一种强大的文本处理工具，用于匹配、查找、替换和验证字符串模式。在ASP.NET中，可以使用Regex类来实现这些功能，以处理用户输入验证、数据清洗或格式化等任务。 4. 动态生成图片：通过GDI+（Graphics Device Interface）库，开发者可以在服务器端生成图片，例如验证码、图表或根据数据生成的图像，然后将其发送到客户端，增强了Web应用程序的交互性和功能。 5. 从ASP.NET页面发送电子邮件：利用System.Net.Mail命名空间的SmtpClient和MailMessage类，开发者可以轻松地在ASP.NET应用中发送邮件，这在通知、确认和客户服务场景中非常有用。 6. 网络访问：通过HttpWebRequest和WebResponse类，可以实现ASP.NET页面对其他Web资源的访问，例如进行HTTP请求、下载数据或集成API。 7. 从浏览器上传文件到Web服务器： ASP.NET提供文件上传功能，通常通过HtmlInputFile控件实现，允许用户选择本地文件并将其上传到服务器，常用于用户提交表单时上传附件。 8. 使用ProcessInfo获取进程信息： Process类允许开发者获取关于系统上运行的进程的信息，如ID、CPU使用率、内存占用等，这对于监控和管理Web应用程序的性能很有价值。 9. 访问Windows事件日志：通过System.Diagnostics.EventLog类，可以读取、写入和管理Windows事件日志，这对于诊断和故障排除非常有帮助。 10. 工作于服务器性能计数器： ASP.NET允许访问性能计数器，通过PerformanceCounter类可以实时监测服务器的硬件和软件性能指标，如CPU使用率、内存使用、磁盘I/O等。 11. 加密和解密信息：为了保护敏感数据，ASP.NET提供了加密和解密的功能。例如，可以使用System.Security.Cryptography命名空间的类如Aes、Rijndael或RSA进行数据加密，确保信息安全。这些ASP.NET代码技术的掌握，将使开发者能够构建更强大、更安全且高效的Web应用程序，同时提高开发效率和用户体验。

Next, each remaining student’s test score is upped by 5%. On lines 31 through 34, each test

score is visited via a For ... Next loop (which is possible because SortedList elements can

be accessed by an index). Because .NET collections are zero-based, notice that we loop from 0

to slTestScores.Count – 1 (line 31). On line 32, the value of each element is accessed via

the GetValueList method, which returns a collection of values; this collection can then be

indexed numerically.

On lines 37 through 40, another For ... Next loop is used to display the curved test results.

On line 38, the GetKeyList method is used to return a collection of keys (which is then

accessed by index); on line 39, the test results are outputted using the Double.Format function.

This format string passed to the Double.Format function (“#.#”) specifies that test results

should only display one decimal place. Finally, on line 42, all the test results are erased with

a single call to the Clear method.

Working with the Queue Class

ArrayLists, Hashtables, and SortedLists all have one thing in common—they allow random

access to their elements. That is, a developer can programmatically read, write, or remove any

element in the collection, regardless of its position. However, the Queue and Stack classes (the

remaining two collections we’ll examine) are unique in that they provide sequential access

only. Specifically, the Queue class can only access and remove elements in the order they were

inserted.

Adding, Removing, and Accessing Elements in a Queue

Queues are often referred to as First In, First Out (FIFO) data structures because the Nth ele-

ment inserted will be the Nth element removed or accessed. It helps to think of the queue data

structure as a line of people. There are two parts to a queue as there are two parts to any line

up: the tail of the queue, where people new to the line start waiting, and the head of the queue,

where the next person in line waits to be served. In a line, the person who is standing in line

first will be first served; the person standing second will be served second, and so on; in a

queue, the element that is added first will be the element that is removed or accessed first,

whereas the second element added will be the second element removed or accessed.

The .NET Framework provides support for the queue data structure with the Queue class. To add

an element to the tail, use the Enqueue method. To retrieve and remove an element from the

head of a queue, use Dequeue. As with the other collection types we’ve examined thus far, the

Queue class contains a Clear method to remove all elements. To simply examine the element at

the head without altering the queue, use the Peek method. As with all the other collections, the

elements of a Queue can be iterated through using an enumerator or a For Each ... Next loop.

Listing 2.4 illustrates some simple queue operations. The output is shown in Figure 2.4.

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property prior to using Dequeue, see lines 28 through 32 in Listing 2.4.) As with all the other

collection types, you can remove all the Queue elements with a single call to the Clear method

(line 36).

There might be times when you want to access the element at the head of the Queue without

removing it from the Queue. This is possible via the Peek method, which returns the element at

the head of the Queue without removing it. As with the Dequeue method, if you try to Peek an

empty Queue, an InvalidOperationException exception will be thrown.

Iterating Through the Elements of a Queue

One way to iterate through the elements of a Queue is to simply use Dequeue to successively

grab each item off the head. This approach can be seen in lines 27 through 32 in Listing 2.4.

The major disadvantage of this approach is that, after iteration is complete, the

Queue is empty!

As with every other collection type, the

Queue can be iterated via a For Each ... Next loop

or through the use of an enumerator. The following code snippet illustrates using the C# fore-

ach statement to iterate through all the elements of a Queue without affecting the structure:

Queue qMyQueue = new Queue(); // Create a Queue

qMyQueue.Enqueue(5);

qMyQueue.Enqueue(62); // Add some elements to the Queue

qMyQueue.Enqueue(-7);

// Iterate through each element of the Queue, displaying it

foreach (int i in qMyQueue)

Response.Write(“Visiting Queue Element with Value: “ + i + “<br>”);

Working with the Stack Class

A stack is a data structure similar to a queue in that is supports only sequential access.

However, a stack does bear one major difference from a queue: rather than storing elements

with a First In, First Out (FIFO) semantic, a stack uses Last In, First Out (LIFO). A crowded

elevator behaves similar to a stack: the first person who enters the crowded elevator is the last

person to leave, whereas the last person to board the elevator is the first out when it reaches its

destination.

Adding, Removing, and Accessing Elements in a Stack

The .NET Framework provides an implementation of the stack data type with the Stack

class. A stack has two basic operations: adding an element to the top of the stack, which is

accomplished with the Push method, and removing an element from the top of the stack,

accomplished via the Pop method. Similar to the Queue class, the Stack class also contains a

Peek method to permit developers to access the top of the stack without removing the element.

Common ASP.NET Code Techniques

HAPTER 2

COMMON ASP .NET

ODE TECHNIQUES

2143-2 ch02 3/19/01 3:43 PM Page 19

Up until this point, the code provided in the previous listings have just given you a feel for the

syntax of the various collections. Listing 2.5, however, contains a handy little piece of reusable

code that can be placed on each page of your Web site to provide a set of navigation history

links for your visitors.

The code in Listing 2.5 uses a session-level Stack class instance that is used to store the links

that a Web visitor has traversed on your site since the start of his session. Each time a user

visits a Web page, the stack is displayed in a history label and the page’s URL is pushed onto

the stack. As the user visits various pages on your Web site, his navigation history stack will

continue to grow and he will be able to quickly jump back to previous pages on your site. This

is, basically, mimicking the functionality of a browser’s Back button. The output is shown in

Figure 2.5.

LISTING 2.5 A Stack Is Ideal for Keeping Track of a User’s Navigation History

1: <script language=”c#” runat=”server”>

3: void Page_Load(Object source, EventArgs e)

4: {

5: // See if we have a stack created or not:

6: if (Session[“History”] == null)

7: {

8: // the history stack has not been created, so create it now.

9: Session[“History”] = new Stack();

10: } else {

11: // we already have a history stack. Display the history:

12: IEnumerator enumHistory =

13: ((Stack) Session[“History”]).GetEnumerator();

14: while (enumHistory.MoveNext())

15: lblStackHistory.Text += “<a href=\”” + enumHistory.Current +

16: “\”>” + enumHistory.Current +

17: “</a><br>”;

18: }

19:

20: // Push current URL onto Stack IF it is not already on the top

21: if (((Stack) Session[“History”]).Count > 0)

22: {

23: if(((Stack) Session[“History”]).Peek().ToString() !=

24: Request.Url.Path.ToString())

25: ((Stack) Session[“History”]).Push(Request.Url.Path);

26: } else

27: ((Stack) Session[“History”]).Push(Request.Url.Path);

28: }

29:

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