Module 4: Writing XML

To teach this module, you need the following materials: Microsoft® PowerPoint® file 2663A_04.ppt Code samples file 2663A_04_Code.htm To prepare to effectively teach this module: Re

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Lesson: Generating XML with Namespaces 25

Lesson: Controlling XML Format and

Review 41

Module 4: Writing XML

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Instructor Notes

After completing this module, students will be able to:

Use the XmlTextWriter class to write well-formed XML

Generate namespaces for elements and attributes

Control indentation and other code format characteristics when generating XML

Write XML that preserves characters that are normally represented by using escape characters

To teach this module, you need the following materials:

Microsoft® PowerPoint® file 2663A_04.ppt

Code samples file 2663A_04_Code.htm

To prepare to effectively teach this module:

Read the following Microsoft Visual Studio® Help topics:

• Writing XML with the XmlWriter

• XmlWriter Class

• Namespace Features within the XmlTextWriter

• XmlConvert Class

Read the entire module

Complete the practices and the lab

Practice delivering the demonstrations

In this module, some of the PowerPoint slides provide hyperlinks that open a code samples page in the Web browser The code samples page provides a way

to show and discuss code samples when there is not enough space for the code

on the PowerPoint slide It also allows students to copy code samples directly from the browser window and paste them into a development environment All

of the linked code samples for this module are in a single htm file

To open a code sample, click the appropriate hyperlink on the slide To navigate between code samples in a particular language, use the table of contents

provided at the top of the code page Each hyperlink opens a separate instance

the Web browser, so it is a good practice to click Back in Microsoft

Internet Explorer after you view a code sample This will close the browser window and return you to the PowerPoint presentation

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How to Teach This Module

This section contains information that will help you to teach this module

Lesson: Overview of Generating XML Documents

This section describes the instructional methods for teaching each topic in this lesson

Briefly discuss why an application might need to generate data in general and why it might be advantageous to generate that data in XML

Briefly describe how XmlTextWriter is a descendent of XmlWriter

The slide for the topic is a process illustration Here is one way to talk about this illustration:

1 First, describe how data might be made available to an application by means

of a connection to an OLE DB source or a file, such as a comma-separated value (CSV) file If the data originates from an OLE DB source, it will likely be processed by using Microsoft ADO.NET classes If the data originates from a file format, the application will likely use a stream object

as an intermediary

2 Next, you might discover that the XML that is being sent to your application contains XML that is not well-formed For example, a database application might send XML elements that contain spaces, because the table names upon which the XML is based also contain spaces In such cases, you can

use the XmlConvert() method to process known problems in incoming

Show the code that creates an XmlTextWriter

Show the code that writes the XML document root

Show the code that writes elements

Show the code that writes attributes

Show the code that writes processing instructions, comments, and CDATA sections

How to Write Elements

How to Write Attributes

How to Write Processing

Instructions, Comments,

and CDATA

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Use the debugging environment to show how the code modifies several objects

This practice allows students to write the XML parts described in the preceding topics Provide learners with plenty of time to complete this practice Offer plenty of guidance, because the skills practiced here are fundamental

Lesson: Generating XML With Namespaces

Briefly summarize the main benefits of using XML namespaces and the technical problems they are used to solve Learners should already know this information, so this topic is a review

Show the code that generates elements with namespaces

Show the code that generates attributes with namespaces

Lesson: Controlling XML Format and Converting XML

Show the code that sets XML formatting, such as how to indent the XML and whether a single or a double quotation character is used

Show the code that controls aspects of generated XML, such as white space and the use of escape characters in element names

Show the code that invokes XmlConvert The main use for this class is to

programmatically fix errors in XML names You can also use it to convert strongly typed data into a string type that is suitable for generating XML content

Use the custom add-in and watch expressions to show how code converts an OLE DB data table source to XML

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Customization Information

This section identifies the lab setup requirements for a module and the configuration changes that occur on student computers during the labs This information is provided to assist you in replicating or customizing Training and Certification courseware

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Overview

Overview of Generating XML Documents

Writing XML

Generating XML with Namespaces

Controlling XML Format and Converting XML

***************************** ILLEGAL FOR NON - TRAINER USE ******************************

Writing Extensible Markup Language (XML) is a task that is central to developing XML-based applications In this chapter, you will learn about the Microsoft® NET Framework classes that you use to generate XML You will also learn how to incorporate namespaces as the XML is generated Finally, you will learn how to control many format characteristics of generated XML After completing this module, you will be able to:

Use the XmlTextWriter class to write well-formed XML

Generate namespaces for elements and attributes

Control indentation and other code format characteristics when generating XML

Write XML that preserves characters that are normally represented by using escape characters

Introduction

Objectives

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Lesson: Overview of Generating XML Documents

Why Generate XML?

What Is the XmlTextWriter Class?

The Process of Writing XML

The XmlTextWriter class is an implementation of the XmlWriter class that

provides the application programming interface (API) that writes XML to a file,

stream, or TextWriter

Typically, you use the XmlTextWriter class to write XML as raw data

Although you can accomplish this task by using the Document Object Model

(DOM), XmlTextWriter is often preferred because it is more efficient

After completing this lesson, you will be able to:

Identify development tasks requiring XML writing functionality

Identify the places in the process of writing XML that can be handled by

using the XmlTextWriter class

Introduction

Lesson objectives

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Why Generate XML?

To translate data formats into XML

SQL Server database tables

OLE DB data sources

Electronic Data Interchange (EDI)

The main reason to generate XML is to encode data in a format that can be easily decoded, transformed, and shared

Often the reason to generate XML is to translate data that is formatted in a language or system other than XML to prepare the data for use in an application that can use XML Data formats that might serve as sources for the data from which you generate XML include:

Microsoft SQL Server™ database tables

OLE DB data sources

Electronic data interchange (EDI) Another reason to generate XML is to encode application data, such as the data for storing session state and user preferences For example, if you search a computer running Microsoft Windows® XP or Microsoft Office XP for XML files, you will build a list of files used for data storage by applications

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What Is the XmlTextWriter Class?

Writes XML rapidly

Forward-only

XmlTextWriterderived from XmlWriter

XmlWriter is an abstract base class that defines an interface for writing XML The XmlWriter class provides a forward-only, read-only, non-cached way of

generating XML streams This helps you to build XML documents that conform to the World Wide Web Consortium (W3C) XML 1.0 (Second Edition) recommendation, located at

http://www.w3.org/TR/2000/REC-xml-20001006.html, and the W3C Namespaces in XML recommendation, located at

http://www.w3.org/TR/REC-xml-names/

XmlTextWriter class is derived from XmlWriter In your application you will use the XmlTextWriter to implement the functionality of XmlWriter

The XmlTextWriter class has methods and properties that are defined to:

Specify whether to support namespaces

Write well-formed XML

Encode binary bytes as base64 and as BinHex, and write out the resulting text

Manage the output, including methods to determine the progress of the

output, by using the WriteState property

Write multiple documents to one output stream

Flush or close the output

Write valid names, qualified names, and name tokens

Introduction

What the XmlTextWriter

can do

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The Process of Writing XML

tea infuser

7.99 11234

coffee mug

Price

S K U Product Name

Applications that write XML often get their data from sources that are external

to the application Although the data source for such an application might attempt to provide the data in well-formed XML, errors can still occur and be sent along to the application The application must have a way, prior to writing any XML of its own, to ensure that any XML it consumes is well-formed For example, the data that is written by an application in XML format might begin as a database table or a string of comma separated value (CSV) text A database table might be translated into XML by an application that uses ADO.NET functionality Sometimes database tables have spaces in the names These spaces might be converted directly into an XML element name, creating XML that is not well-formed

Since the XmlTextWriter class simply writes XML without performing any

checks to determine whether the XML being generated is well-formed, any errors in the XML that the text writer receives will simply be written

Therefore, if your code instructs XmlTextWriter to generate XML, there is no

internal check to prevent:

Errors that can result from the use of illegal characters in element and

attribute names The XmlWriter class cannot write an element whose name

contains a space character, for example

Unicode characters that do not fit the specified encoding If the Unicode

characters do not fit the specified encoding, the XmlWriter class does not

process the Unicode characters into escape characters

The existence of duplicate attributes

To prevent XML errors from propagating through the writing process, you

would use XmlConvert to fix XML error prior to writing by using XmlTextWriter

Introduction

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Lesson: Writing XML

Demonstration: Writing XML

How to Create an XmlTextWriter Object

How to Write the XML Document Root

How to Write Processing Instructions, Comments, and CDATA

Code Examination: Writing XML from a Text File

Practice: Writing XML Content and Nodes

In this lesson, you will learn how to use the XmlTextWriter class to generate

well-formed XML

After completing this lesson, you will be able to:

Create an instance of an XmlTextWriter object

Write an XML document root

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This demonstration introduces the XML writing functionality of the XML Tools add-in The add-in should already be installed and loaded If not, see

Appendix A for instructions

To convert a sample text file into XML

1 In Microsoft Visual Studio® NET, open the file names.csv

2 On the XML Tools toolbar, click Text to XML

3 In the Write XML from Text File dialog box, click OK The resulting

XML file appears in the Output window Notice that the columns are stored

as attributes and are named Column01, Column02, and so on

Introduction

Demonstration

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If the active window is not the Text Editor window or the internal Web browser, a dialog box appears that allows the user to select the file

from which to read Select the file names.csv, and then click OK

5 In the Write XML from Text File dialog box, under Store columns as, click Elements, and then click OK The resulting XML file appears in the

Output window Notice that the columns are stored as elements and are named Column01, Column02, and so on

6 In the Text Editor, add a new first row to specify the column names for each field Avoid space characters For example:

FirstName,LastName,Age

8 In the Text to XML dialog box, select the First Row Contains Field Names check box, and then click OK The resulting XML file appears in

the Output window Notice that the columns now have names other than Column01, Column02, and so on

To convert a sample database table into XML by using attributes

1 On the XML Tools toolbar, click OLE DB to XML

2 In the Write XML from Database dialog box, in the Command Text box, change the table name from Employees to Employee

Note

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3 Click Test What happens?

A message box opens, stating that the input table Employee cannot be found

4 Fix the error, and then click Test What happens? Why?

A message box opens, stating “9 row(s) affected” because the Employees table contains nine records

5 Click OK The resulting XML file appears in the Output window

To convert a sample database table into XML by using elements

1 On the XML Tools toolbar, click OLE DB to XML

2 In the Write XML from Database dialog box, in the Command Text box, change Employees to Suppliers

3 In the Command Type list, click Table

4 Under Store columns as, click Elements

5 Click Test What happens?

A message box opens, stating “29 row(s) affected” because the Suppliers table contains 29 records

6 Click OK The resulting XML file appears in the Output window

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How to Create an XmlTextWriter Object

To use the XmlTextWriter constructor set the following:

Parameter to a TextWriter, Stream, or String

Encoding property to ASCII, UTF-7, UTF-8 or Unicode

Formatting property to Indented

' Visual Basic Dim BookWriter As New XmlTextWriter( _

"\catalog\books.xml", Encoding.UTF7) BookWriter.Formatting = Formatting.Indented // Visual C#

XmlTextWriter BookWriter = new XmlTextWriter(

@"\catalog\books.xml", Encoding.UTF7);

BookWriter.Formatting = Formatting.Indented;

' Visual Basic Dim BookWriter As New XmlTextWriter( _

"\catalog\books.xml", Encoding.UTF7) BookWriter.Formatting = Formatting.Indented // Visual C#

@"\catalog\books.xml", Encoding.UTF7);

BookWriter.Formatting = Formatting.Indented;

The XmlTextWriter class is a versatile XML writer You can use it to write

XML to a file, console, stream, or other output type

The XmlTextWriter constructor creates an instance of the XmlTextWriter, which takes a file name, stream, or TextWriter There is an overloaded method

that takes an additional parameter that defines the encoding type

The XmlTextWriter class gives you the following encoding options:

ASCII

UTF-7

UTF-8 (this is the default)

Unicode

If you want the output XML file to be automatically indented and new line

characters to be inserted as white space, set the Formatting property to Indented

Introduction

Constructor

Encoding options

Formatting options

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The following example instantiates a new XmlTextWriter by using a string

containing a file name, and specifies UTF-7 encoding Formatting is set to

Indented, which also preserves automatic white space; for example, new lines

for parent elements

' Visual Basic Dim BookWriter As New XmlTextWriter( _ "\catalog\books.xml", Encoding.UTF7) BookWriter.Formatting = Formatting.Indented // C#

with escaped entities, depending on what it finds

WriteString() XmlTextWriter encodes special characters with escaped

entities, replacing them with & < > and numeric

character entities when required

WriteBase64() XmlTextWriter encodes the base64 bytes, which can then

be read by using the ReadBinary() method of the XmlReader

Close() Close() checks to see if the XML is an invalid XML

document and throws an InvalidOperationException

if it is

The XmlTextWriter performs the following additional tasks to ensure

well-formed XML:

Ensures that the XML elements are written in the correct order For

example, the XmlTextWriter does not let you write an attribute outside of

an element, write a CDATA block inside an attribute, or write multiple root elements In addition, it ensures that the <?xml declaration comes first and that the <!DOCTYPE node comes before the root element

Ensures that the value and format of the xml:space attribute are correct, and

that its value is acceptable according to the WC3 XML 1.0 (Second Edition) recommendation, located at

http://www.w3.org/XML/Group/2000/07/REC-xml-2e-review#sec-white-space Valid values for the xml:space attribute are "default" and "preserve"

If the argument is not one of these values, an ArgumentException class is

thrown

Checks when a string is used as a parameter (for example, Null==String.Empty and String.Empty) and whether it follows the W3C rules

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How to Write the XML Document Root

A well-formed XML document must have a declaration and a root element

Use the WriteStartDocument() method and the WriteEndDocument() method to create the declaration, also known as the document root

Use the WriteStartElement() method and the WriteEndElement() method to create the root element

Visual Basic Example C# Example

The WriteStartDocument() method starts a new document and writes the XML declaration with version attribute set to "1.0" The WriteEndDocument()

method closes that document

When you call the next WriteStartDocument() to start writing the next

document, you can modify the formatting, indentation, and other properties of

the document The WriteStartDocument() method programmatically

recognizes that an XML document is being written, and applies root-level rules

If this method is not used, an XML fragment is created and verifies whether the document is well-formed Root-level rules are not applied

Introduction

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Because a well-formed XML document must have a root element, you normally

combine a WriteStartDocument() method call with a WriteStartElement()

BookWriter.WriteStartElement("books") ' write other elements

BookWriter.WriteEndElement() BookWriter.WriteEndDocument() BookWriter.Close()

document and to allow the creation of complex elements or attributes

Root element

Example

Method pairs

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To write elements that has no children or attributes, use the WriteElementString() method

To write elements with children or attributes, use the WriteStartElement() and WriteEndElement() methods

You can write an element by using either a single method call or multiple method calls, depending on whether the element has any child elements or attributes

The following code shows how to write an element that has no child elements

or attributes:

' Visual Basic BookWriter.WriteElementString("price", "19.95") // C#

Single method call

Multiple method calls

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To write attributes in a single step, use WriteAttributeString()

To write attributes in multiple steps, use WriteStartAttribute() and WriteEndAttribute()

Visual Basic Example C# Example

You can use the WriteAttributeString() method in two different ways: to

write attributes and associate them with a user-defined namespace prefix, and to generate namespace declarations If you write attributes and the localname

parameter is xmlns, the WriteAttributeString() method is considered to be a

namespace declaration You will learn how to handle namespaces in the next lesson

In the following code example, the WriteAttributeString() method writes

attributes inside an element:

' Visual Basic BookWriter.WriteStartElement("book") BookWriter.WriteAttributeString("price", "19.95") BookWriter.WriteEndElement()

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The WriteStartAttribute() and WriteEndAttribute() methods are similar to

other start and end methods, but deal specifically with the start and end of

attributes You use the WriteStartAttribute() method to write the start of the attribute, the WriteString() method to write the attribute value, and the WriteEndAttribute() method to end the attribute tag The following code example shows how to use the WriteStartAttribute(), WriteString(), and WriteEndAttribute() methods:

' Visual Basic BookWriter.WriteStartElement("book") BookWriter.WriteStartAttribute("price", "") BookWriter.WriteString("19.95")

BookWriter.WriteEndAttribute() BookWriter.WriteEndElement() // C#

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How to Write Processing Instructions, Comments, and CDATA

Writing a processing instruction

"xml-stylesheet", "type='text/xsl' href='style.xsl'");

BookWriter.WriteCData("Prices < $100 are 15% Off!"); BookWriter.WriteComment("This is a comment");

Some common methods of the XmlWriter class are listed in this topic For a complete list of XmlWriter class members, see the XmlWriter Members

topic in the MSDN® online documentation

The WriteProcessingInstruction() method writes a processing instruction with

a space between the name and text, as follows:

' Visual Basic BookWriter.WriteProcessingInstruction("xml-stylesheet", _ "type='text/xsl' href='books.xsl'")

// C#

BookWriter.WriteProcessingInstruction("xml-stylesheet", "type='text/xsl' href='books.xsl'");

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The WriteComment() method writes a comment containing the specified text,

as follows:

' Visual Basic BookWriter.WriteComment("This is the comment") // C#

BookWriter.WriteComment("This is the comment");

<! XML Output >

<! This is the comment >

The WriteCData() method writes out a <![CDATA[ ]]> block containing the

specified text The only parameter is the text that you want to place inside the CDATA block, as follows:

' Visual Basic BookWriter.WriteCData("Prices < $100 are 15% Off!") // C#

BookWriter.WriteCData("Prices < $100 are 15% Off!");

<! XML Output >

<![CDATA[Prices < $100 are 15% Off!]]>

How to write a comment

How to write a CDATA

section

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Code Examination: Writing XML from a Text File

This code generates XML from a text file

Highlights

.NET Framework String objects have a method named Split() that can break a string into an array of strings

.NET Framework Stream objects have an internal buffer that can be monitored by using the debugging tools

In this code examination, you will see how the Text to XML functionality in the XML Tools add-in works For detailed instructions for debugging an add-in, see Appendix A

Solutions are provided for both C# and Visual Basic languages in the following folders:

install_folder\Democode\Addins\XmlToolsAddinCS\

install_folder\Democode\Addins\XmlToolsAddinVB\

To set breakpoints in the add-in

1 In Microsoft Visual Studio® NET, open one of the solutions for this demonstration

2 In the Solution Explorer, right-click the Connect class, and then click View Code

3 On the View menu, click Shows Tasks, and then click All

4 Double-click each TODO task in the following list and set a breakpoint on the line of code following each comment:

a TODO: Mod04: instantiate a writer using a memory stream

b TODO: Mod04: reset column counter

c TODO: Mod04: write an attribute otherwise write an element

5 On the Debug menu, click Start A second instance of Visual Studio NET

starts

Introduction

Code examination

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To convert a sample text file into XML

1 Open the file names.csv for this demonstration

using the delimiter character

7 Press F5 to continue executing The current line branches depending on if an element or an attribute needs to be written

8 Hover the mouse pointer over the objects named strColumnName and strColumn Notice the values

9 Press F5 to continue executing

10 Hover the mouse pointer over the objects named strColumnName and strColumn Notice the values

11 On the Debug menu, click Clear All Breakpoints

12 Press F5 to allow the code to complete

13 Close both instances of Visual Studio NET

Tiêu đề	Writing xml
Trường học	Microsoft Corporation
Thể loại	module
Năm xuất bản	2002
Thành phố	Redmond

Định dạng
Số trang	52
Dung lượng	0,93 MB