畢業論文_基于web的學生作業管理系統設計與實現(編輯修改稿)

　

【文章內容簡介】 I A namespace is a logical grouping of classes. For example, all the classes that relate to working with the file system are gathered together into the namespace. The namespaces are anized into a hierarchy (a logical tree). At the root of the tree is the System namespace. This namespace contains all the classes for the base data types, such as strings and arrays. It also contains classes for working with random numbers and dates and times. You can uniquely identify any class in the .NET framework by using the full namespace of the class. For example, to uniquely refer to the class that represents a file system file (the File class), you would use the following: refers to the namespace, and File refers to the particular class. NOTE You can view all the namespaces of the standard classes in the .NET Framework Class Library by viewing the Reference Documentation for the .NET Framework. Standard Namespaces The classes contained in a select number of namespaces are available in your pages by default. (You must explicitly import other namespaces.) These default namespaces contain classes that you use most often in your applications: System— Contains all the base data types and other useful classes such as those related to generating random numbers and working with dates and times. — Contains classes for working with standard collection types such as hash tables, and array lists. — Contains classes that represent specialized collections such as linked lists and string collections. — Contains classes for working with configuration files ( files). — Contains classes for encoding, decoding, and manipulating the contents of strings. XII — Contains classes for performing regular expression match and replace operations. — Contains the basic classes for working with the World Wide Web, including classes for representing browser requests and server responses. — Contains classes used for caching the content of pages and classes for performing custom caching operations. — Contains classes for implementing authentication and authorization such as Forms and Passport authentication. — Contains classes for implementing session state. — Contains the basic classes used in building the user interface of pages. — Contains the classes for the HTML controls. — Contains the classes for the Web controls. .NET FrameworkCompatible Languages For purposes of this book, you will write the application logic for your pages using Visual Basic as your programming language. It is the default language for pages. Although you stick to Visual Basic in this book, you also need to understand that you can create pages by using any language that supports the .NET Common Language Runtime. Out of the box, this includes C, , and the Managed Extensions to C++. NOTE The CD included with this book contains C versions of all the code samples. Dozens of other languages created by panies other than Microsoft have been developed to work with the .NET framework. Some examples of these other languages include Python, SmallTalk, Eiffel, and COBOL. This means that you could, if you really wanted to, write pages using COBOL. Regardless of the language that you use to develop your pages, you need to understand that pages are piled before they are executed. This means that pages can execute very quickly. XIII The first time you request an page, the page is piled into a .NET class, and the resulting class file is saved beneath a special directory on your server named Temporary Files. For each and every page, a corresponding class file appears in the Temporary Files directory. Whenever you request the same page in the future, the corresponding class file is executed. When an page is piled, it is not piled directly into machine code. Instead, it is piled into an intermediatelevel language called Microsoft Intermediate Language (MSIL). All .NETpatible languages are piled into this intermediate language. An page isn39。t piled into native machine code until it is actually requested by a browser. At that point, the class file contained in the Temporary Files directory is piled with the .NET framework Just in Time (JIT) piler and executed. The magical aspect of this whole process is that it happens automatically in the background. All you have to do is create a text file with the source code for your page, and the .NET framework handles all the hard work of converting it into piled code for you. ASP CLASSIC NOTE What about VBScript? Before , VBScript was the most popular language for developing Active Server Pages. does not support VBScript, and this is good news. Visual Basic is a superset of VBScript, which means that Visual Basic has all the functionality of VBScript and more. So, you have a richer set of functions and statements with Visual Basic. Furthermore, unlike VBScript, Visual Basic is a piled language. This means that if you use Visual Basic to rewrite the same code that you wrote with VBScript, you can get better performance. If you have worked only with VBScript and not Visual Basic in the past, don39。t worry. Since VBScript is so closely related to Visual Basic, you39。ll find it easy to make the transition between the two languages. XIV NOTE Microsoft includes an interesting tool named the IL Disassembler (ILDASM) with the .NET framework. You can use this tool to view the disassembled code for any of the classes in the Temporary Files directory. It lists all the methods and properties of the class and enables you to view the intermediatelevel code. This tool also works with all the controls discussed in this chapter. For example, you can use the IL Disassembler to view the intermediatelevel code for the TextBox control (located in a file named ). Introducing Controls controls pro