copyright © 2008 pearson education, inc. publishing as pearson addison-wesley chapter 12...

Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley

Chapter 12Introduction to

ASP.NET

12-2Copyright © 2008 Pearson Education, Inc. Publishing as Pearson Addison-Wesley

12.1 Overview of the .NET Framework

• .NET is a collection of technologies• Run time environment

• Library

• Programming languages


12.1 Background

• A component is a piece of software that can used by other components

• A component has an interface that specifies how it can be used without necessarily exposing the implementation

• Microsoft’s component system was named COM

• .NET is a framework for developing and deploying software• Software consists of components

• These components can reside on multiple systems

• These components can be programmed in different languages


12.1 .NET Languages

• .NET initially included five languages• Visual Basic .NET

• Managed C++ .NET

• JScript.NET (similar to JavaScript)

• J#.NET (Similar to Java)

• C#.NET (A new language in the C/C++/Java family)

• Other languages have been added• Including COBOL, Eiffel, Fortran, Perl Python


12.1 The Common Language Runtime

• CLR

• Services for processing and executing .NET software no matter what language• Garbage collection

• Type checking

• Debugging

• Exception handling

• Compilers translate a .NET language in Intermediate Language (IL)

• The runtime system compiles IL on the fly to native machine code and executes that code• The IL is not interpreted directly


12.1 The Common Language Infrastructure

• Two components• Common Type System (CTS)

• Common Language Specification (CLS)


12.1 CTS

• CTS defines types supported by .NET languages

• Each type has a specified representation

• Integer types, for example, include Int32, 32-bit, signed integers

• .NET languages map their types into the CTS types

• C# type in maps to Int32

• Two categories of CTS types• Value types

• Reference types (an address of a memory location)


12.1 CLS

• Defines characteristics that languages must have to properly interoperate with other languages in the .NET framework

• Include requirements and restrictions• No operator overloading

• No pointers

• Identifiers not case sensitive

• The C# language violates the listed restrictions

• The Framework Class Library (FCL) is a collections of classes providing resources for software


12.1 Introduction to C#

• C# has many similarities with Java


12.2 Origins of C#

• Designed as part of .NET

• Object-oriented

• Single inheritance, interfaces, garbage collection, no global variables or methods

• Pointers, operator overloading, preprocessor

• Properties

• Delegates

• Indexes, attributes, events


12.1 Primitive Types and Expressions

• Unsigned integer types• byte, ushort, uint, ulong

• Signed integer types• sbyte, short, int, long

• Floating point types• float, double

• bool

• decimal

• char


12.2 Data Structures

• Array, ArrayList, Queue, Stack defined by the .NET FCL

• Array is a class, but syntax is like C/C++/Java• int[] a = new int[100]

• Length property gives number of elements in the array

• Enumeration type• Value type

• Finite set of values defined by the programmer

• Type safe


12.2 Control Statements

• The standard control statements of C/C++/Java are in C# as well

• foreach is added to step through a collection

foreach (type identifier in collection) …

• The switch statement is almost the same except the syntax requires either a break or a goto at the end of each case


12.2 Classes, Methods, Structures

• C# has no methods or variables outside of classes

• Syntax of class definitions, variable declarations and function definitions similar to Java

• Parameters may be passed in any of three modes• Pass by value (in)

• Pass by reference (in-out)

• Pass by result (out)

• A method may take a single formal parameter that is an array notated by the keyword params. This allows the method to be called with a variable number of parameters of the type of the elements of the array

• Overriding methods requires • Marking the overridden method with virtual

• Marking the overriding method with override


12.2 Structs

• A C# struct is a lightweight class• No inheritance

• Can have constructors

• Struct type objects are value types rather than reference types

• C# primitive types are implemented as structs


12.2 Properties

• A property of a class acts as if it were an instance variable

• However, assignment to the property actually invokes a ‘set’ method associated with the property

• Access to the property invokes a ‘get’ method

• Either method may be omitted• If the set method is omitted, assignments to the property are not

allowed

• Methods may perform whatever checks or calculations are needed


12.2 Delegates

• A delegate is a pointer to a method

• Methods may be subscribed to a delegate

• A delegate declaration specifies the protocol, or the signature, of methods that may be subscribed to the delegate

• Methods subscribed to the delegate may be called through the delegate


12.2 Program Structure• The FCL is divided into numerous namespaces• The most important namespace is System

• Input and output• String manipulation• Event handling• Threading• Collections• System.Console is used for input and output to the console

• ReadLine• WriteLine

• The using statement allows reference to members of a namespace without qualifying the references

• The main method of a program is Main• Does not require parameters• May return int or void


12.2 File Storage for Programs

• Multiple classes can be defined in a single source file• Each class may have a Main method

• In that case, running a program must specify which Main is to start

• Source file names do not have to match the class name

• Visual Studio is the usual vehicle for developing .NET programs

• Programs can, however, be developed with any text editor

• The stackClass.cs file defines two classes


12.3 Introduction to ASP.NET


12.3 Basics of ASP.NET

• Active Server Pages

• Building dynamic web documents

• The predecessor, ASP, embedded interpreted scripting languages in XHTML• This approach has performance problems

• It is difficult to divide up the development to different skill sets

• ASP.NET is similar• The embedded languages allowed are the .NET languages

• All code is compiled

• ASP.NET documents extend the System.Web.UI.Page class• Request and Response objects

• HTMLControls, WebControls

• IsPostBack


12.3 Page Members

• The Write method in Response sends output to the response document

• IsPostBack tells whether the current process is the original request for the page or a subsequent request with information from the initial page


12.3 Code-Behind

• Code for ASP may be moved to a code-behind class

• The ASP document itself will extend the code-behind class rather than System.Web.UI.Page


12.3 ASP.NET Documents

• Documents can include• XHTML

• Directives

• Render Blocks Programming code in script elements

• Cannot define subprograms

• Program code in script elements

• Declare variables, define methods

• Server side comments

• <%-- …--%>


12.3 Directives

• Directive names begin with @

• Directives appear in <% … %> but the @ usually is attached to the <%:

• <%@ directive-name attributes %>• @Page is required

• Language attribute required: specifies .NET language used for program code


12.3 Output to XHTML Document

• Use Response.Write method

• Takes a string parameter• Include markup since the target is an XHTML document

• The string.Format method can be used to format output


12.3 Example

• The ex1.aspx example creates an array of random numbers and displays them in the response page

• A on object of class Random is created to generate numbers• Method Next generates the next number

• None or one or two parameters

• Two parameter form used, result is in range n…m-1

• A script element in the header declares three variables and defines a method

• The render block in the body references these definitions and creates the dynamic part of the response

• Static XHTML is sent as part of the response unchanged


12.3 Code-Behind Files

• The example ex2 has two files, ex2.aspx and ex2.aspx.cs

• This partitions the declaration code into a C# file

• The @Page directive includes two new attributes• Inherits: value is the class name in the code-behind file

• Src: value is the name of the code-behind file

• The Src attribute can be omitted if a compiled version of the file is available in a bin subdirectory


12.4 ASP.NET Controls

• XHTML elements associated with program code

• The code is executed on the server

• Two categories• HTML controls

• Web controls


12.4 HTML Controls

• HTML controls are based on elements of XHTML pages

• The appearance and functionality of these elements can be changed as the server executes

• Executable code can be associated with the controls

• Certain controls can raise events• ServerClick: control was clicked• ServerChange: control content was changed

• HTML elements become HTML controls if• They are on the list associated with controls (Table 12.2)

• The runat attribute has the value “server”


12.4 Controls and Code

• Note the runat attribute in the following XHTML:

<form runat=“server”>

<input type=“text” id=“address” runat=“server”/>

</form>

• There is a corresponding instance variable in the code generated from this

protected HtmlInputText address;

• There is no action attribute in the form: the ASP document defines the actions that result from submitting the form


12.4 Control Objects

• Controls are represented as objects in the code generated from ASP

• Control classes inherit from HtmlControl deriving properties and methods• Attributes property provides tag attributes as name/value pairs

• The Href property is defined by the HtmlAnchor class

• An XHTML tag can be designated as an HTML control by simply adding the runat attribute with the value “server”


12.4 Life Cycle of an ASP.NET Document

• An ASP.NET document can describe both a form and the response

• Two kinds of requests to a ASP.NET document• Initial request

• Request with form filled in, called a postback

• The IsPostBack property is true if the request is a postback request

• In a postback, the Value propety of a control provides the data entered into the corresponding widget

• The state of a document is stored in the response after the initial service• A hidden control named ViewState contains a reference to a StateBag

object

• The StateBag object stores data about the state of the document

• This requires extra information to be exchanged between browser and server


10.4 Life Cycle

• A request is received

• A document object is created and initialized ViewState is initialized

• The document is sent

• The client sends a request back

• A document object is created and initialized with form data, including ViewState

• Form data is used to update the state of the document object

• ViewState is updated• The program can directly set name/value pairs in ViewState before this

point

• A response is returned


10.4 Postback Sources

• Clicking a submit button will cause a postback

• If the AutoPostBack property is set to true, a postback will occur when a change is made to a control


12.4 Page Level Events

• Two levels of events raised during processing• Control events (ServerClick, Server Change)

• Page-level events

• Init: after document class instantiated

• Load: after state set from form data

• PreRender: before instance is executed

• Unload: before instance is discarded

• Implementing page-level event handling• Controlled by AutoEventWireup, default true

• Which means use predefined method name by default

• Implement predefined method names (Page_unload, Page_load, …)

• Override the virtual handlers


12.4 Control Events

• Two ways to register event handlers• Assign method names to attributes OnServerClick and/or

OnServerChange

• Use delegates

• Using attributes, the methods have predetermined signatures

• Using delegates• Event handler written with proper signature

• New instance of delegate type created using the event handler

• Delegate subscribed to the event property of a control

• This is often done in the Page_Init handler so it is done one time as the page class is instantiated


12.4 Web Controls

• Web controls are based on the controls from Visual Basic

• Namespace System.Web.UI.WebControls

• Web controls do not match up directly with HTML form widgets

• An example of including a control in a page

<asp:textbox id=“phone” runat=“server”/>


12.4 Some Web Controls• Panel organizes other controls• AdRotator produces different content on different

requests• ListControl has four subclasses

• DropDownList• ListBox• CheckBoxList• RadioButtonList


12.4 Creating Control Elements in Code

• A control can be created with <asp:button…. in the document

• The same control can be created by instantiating the Button class and assigning values to properties of the object• .Text for the button label

• .id for the id attribute

• .OnClick for the handler

• .runat to specify this as a web control

• A asp:placeholder tag can be used to define a place for controls defined in code• Those controls are added to the place holder


12.4 Response Output for Controls

• Response.Write does not place text properly when intermixed with controls

• Using a label is an alternative in order to place text

<asp:label id="output" runat="server"/>

• This can be filled in later in the code

<% string msg = string.Format(

"The result is {0} <br />", result);

output.Text = msg; %>


12.4 Example

• The ex4.aspx example crates a number of controls and creates a response

• File ex4.aspx.cs is the code-behind file


12.4 Validation Controls

• Validation controls validate data entered from other controls• Server side validation is an important component of security

• These controls are placed immediately after the control whose input is being validated

• Four common validation controls• RequiredFieldValidator

• CompareValidator

• RangeValidator

• RegularExpresionValidator

• Example ex5.aspsx illustrates three of these• One field is required

• One field (a phone number) must match a regular expression pattern

• One field must be in a specific range of values


12.5 Web Services

• “A collection of one or more related methods that can be called by remote systems”

• .NET provides support for constructing and advertising web services


12.5 Constructing Web Services

• A document with extension .asmx is created• This may simply have a WebService directive spcifying a codebehind

file

• The web service is implemented as a class that extends System.Web.Services.WebService

• The web service should be place in a developer defined namespace in order to avoid conflicts

• Some methods of the class will be tagged with [WebMethod] to indicate that they are available as part of the web service

• Once a service is published, aspects of it can be viewed using Internet Explorer


12.5 Advertising Web Services

• Two approaches to making a web service known to potential clients• A web services discovery document

• A web services directory written with UDDI

copyright © 2008 pearson education, inc. publishing as pearson addison-wesley chapter 12...

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