Using XML in the Delphi environment. Using XML in the Delphi environment Creating xml in delphi

XML is increasingly used to store information and exchange it between applications and Web sites. Many applications use this language as a base language for storing data, while others use it for exporting and importing XML data. This means it's time for developers to think about how they can use XML data in their own applications.

In this article we will look at the XML Document Object Model (DOM) and its implementation by Microsoft - Microsoft XML DOM.

The XML DOM is an object model that provides the developer with objects for loading and processing XML files. The object model consists of the following main objects: XMLDOMDocument, XMLDOMNodeList, XMLDOMNode, XMLDOMNamedNodeMap, and XMLDOMParseError. Each of these objects (except XMLDOMParseError) contains properties and methods that allow you to obtain information about the object, manipulate the object's values ​​and structure, and navigate through the structure of the XML document.

Let's look at the main XML DOM objects and give some examples of their use in Borland Delphi.

Using XML DOM in Borland Delphi

In order to use the Microsoft XML DOM in Delphi applications, you need to connect the appropriate type library to the project. To do this, we execute the command Project | Import Type Library and in the Import Type Library dialog box, select the Microsoft XML version 2.0 library (Version 2.0), which is usually located in the file Windows\System\MSXML.DLL

After clicking the Create Unit button, the MSXML_TLB interface module will be created, which will allow us to use XML DOM objects: DOMDocument, XMLDocument, XMLHTTPRequest and a number of others implemented in the MSXML.DLL library. A reference to the MSXML_TLB module must be listed in the Uses list.

XML DOM device

The Document Object Model represents an XML document as a tree structure consisting of branches. XML DOM programming interfaces allow applications to navigate the document tree and manipulate its branches. Each branch can have a specific type (DOMNodeType), according to which the parent and child branches are determined. In most XML documents you will find branches like element, attribute and text. Attributes are a special kind of branch and are not child branches. Attributes are manipulated using special methods provided by XML DOM objects.

In addition to implementing World Wide Web Consortium (W3C) recommended interfaces, the Microsoft XML DOM contains methods that support XSL, XSL Patterns, Namespaces, and data types. For example, the SelectNodes method allows you to use XSL Pattern Syntax to find branches within a specific context, and the TransformNode method supports the use of XSL to perform transformations.

Test XML document

As an example of an XML document, let's take a directory of music CD-ROMs, which has the following structure:

Bob Dylan USA Columbia 10.90 1985 Bonnie Tylor UK CBS Records 9.90 1988 ... Joe Cocker USA EMI 8.20 1987

Now we're ready to start looking at the XML DOM object model, which we'll start with the XMLDOMDocument object.

XML document - XMLDOMDocument object

Working with an XML document begins with loading it. To do this, we use the Load method, which has only one parameter indicating the URL of the document to be loaded. When loading files from a local disk, only the full file name is specified (the file:/// protocol can be omitted in this case). If the XML document is stored as a string, you should use the LoadXML method to load the document.

To control how the document is loaded (synchronous or asynchronous), use the Async property. By default, this property is set to True, indicating that the document is loaded asynchronously and control is returned to the application before the document is fully loaded. Otherwise, the document is loaded synchronously, and then you have to check the value of the ReadyState property to find out whether the document has loaded or not. You can also create an OnReadyStateChange event handler that will receive control when the value of the ReadyState property changes.

The following shows how to load an XML document using the Load method:

Uses ... MSXML_TLB ... procedure TForm1.Button1Click(Sender: TObject); var XMLDoc: IXMLDOMDocument; begin XMLDoc:= CoDOMDocument.Create; XMLDoc.Async:= False; XMLDoc.Load('C:\DATA\DATA.xml'); // // Here is the code that manipulates // the XML document and its branches // XMLDoc:= Nil; end;

Once the document is loaded, we can access its properties. Thus, the NodeName property will contain the value #document, the NodeTypeString property will contain the value document, and the URL property will contain the value file:///C:/DATA/DATA.xml.

Error handling

Of particular interest are the properties associated with the processing of the document when it is loaded. Thus, the ParseError property returns an XMLDOMParseError object containing information about an error that occurred during document processing.

To write an error handler, you can add the following code:

Var XMLError: IXMLDOMParseError; ... XMLDoc.Load('C:\DATA\DATA.xml'); XMLError:= XMLDoc.ParseError; If XMLError.ErrorCode<>0 Then // // Here we handle the error // Else Memo1.Lines.Add(XMLDoc.XML); ... XMLDoc:= Nil;

To see what information is returned in case of an error, let's change the following directory entry:

Bob Dylan USA Columbia 10.90 1985

removing the closing element .

Now let's add a new branch. Below is the code showing how to add a new music CD-ROM entry:

Var NewNode: IXMLDOMNode; Child: IXMLDOMNode; ... // Create a new branch - NewNode:= XMLDoc.CreateNode(1, 'CD', ''); // Add an element