XML Tutorial/ko
소개
확장 가능한 마크업 언어는 W3C가 추천하는 언어로서 다른 시스템간에 정보를 교환하기 위해 만들어 졌다. 텍스트 기반으로 정보를 저장한다. 현대의 XHTML 같은 데이터 교환 언어와 대부분의 웹서비스 기술은 XML에 기초를 두고 있다.
현대 프리 파스칼에서 XML을 위해 지원하는 유닛의 셑이 있다. 이러한 유닛은 "XMLRead", "XMLWrite" 및 "DOM" 이라고 불리며 이들은 프리파스칼 컴파일러상의 프리컴포넌트 라이브러리(FCL)의 일부이다. FCL은 현재(2005년 10월) 문서화 되어있지 않으므로 이 간단한 튜토리얼은 이와같은 유닛을 통해 XML에 접근한다는 것을 소개하고자 함이다.
XML DOM(Document Object Model) 은 표준화된 객체의 집합으로다른 언어와 기종을 사용해서 유사한 인터페이스를 제공해 준다. 표준은 객체의 메써드, 프로퍼티 및 다른 인터페이스 부분만을 명기할 뿐이며, 다른 언어에서 구현하는 것은 자유스럽게 놔둔다. FCL은 현재 XML DOM 1.0 을 모두 지원한다.
예제
Bellow there is a list of XML data manipulation examples with growing complexity.
Reading a text node
For Delphi Programmers: Note that when working with TXMLDocument, the text within a Node is considered a separate TEXT Node. As a result, you must access a node's text value as a separate node. Alternatively, the TextContent property may be used to retrieve content of all text nodes beneath the given one, concatenated together.
The ReadXMLFile procedure always creates a new TXMLDocument, so you don't have to create it beforehand. However, be sure to destroy the document by calling Free when you are done.
For instance, consider the following XML:
<xml>
<?xml version="1.0"?> <request> <request_type>PUT_FILE</request_type> <username>123</username> <password>abc</password> </request>
</xml>
The following code example shows both the correct and the incorrect ways of getting the value of the text node:
<delphi>
var
PassNode: TDOMNode;
Doc: TXMLDocument;
begin
// Read in xml file from disk
ReadXMLFile(Doc, 'c:\xmlfiles\test.xml');
// Retrieve the "password" node
PassNode := Doc.DocumentElement.FindNode('password');
// Write out value of the selected node
WriteLn(PassNode.NodeValue); // will be blank
// The text of the node is actually a separate child node
WriteLn(PassNode.FirstChild.NodeValue); // correctly prints "abc"
// alternatively
WriteLn(PassNode.TextContent);
// finally, free the document
Doc.Free;
end; </delphi>
Printing the names of nodes
A quick note on navigating the DOM tree: When you need to access nodes in sequence, it is best to use FirstChild and NextSibling properties (to iterate forward), or LastChild and PreviousSibling (to iterate backward). For random access it is possible to use ChildNodes or GetElementsByTagName methods, but these will create a TDOMNodeList object which eventually must be freed. This differs from other DOM implementations like MSXML, because FCL implementation is object-based, not interface-based.
The following example shows how to print the names of nodes to a TMemo placed on a form.
Bellow is the XML file called 'C:\Programas\teste.xml':
<xml>
<?xml version="1.0"?> <images directory="mydir"> <imageNode URL="graphic.jpg" title=""> <Peca DestinoX="0" DestinoY="0">Pecacastelo.jpg1.swf</Peca> <Peca DestinoX="0" DestinoY="86">Pecacastelo.jpg2.swf</Peca> </imageNode> </images>
</xml>
And here the Pascal code to execute the task:
<delphi>
var
Documento: TXMLDocument;
Child: TDOMNode;
j: Integer;
begin
ReadXMLFile(Documento, 'C:\Programas\teste.xml');
Memo.Lines.Clear;
// using FirstChild and NextSibling properties
Child := Documento.DocumentElement.FirstChild;
while Assigned(Child) do
begin
Memo.Lines.Add(Child.NodeName + ' ' + Child.Attributes.Item[0].NodeValue);
// using ChildNodes method
with Child.ChildNodes do
try
for j := 0 to (Count - 1) do
Memo.Lines.Add(Item[j].NodeName + ' ' + Item[j].FirstChild.NodeValue);
finally
Free;
end;
Child := Child.NextSibling;
end;
Documento.Free;
end;
</delphi>
This will print:
imageNode graphic.jpg Peca Pecacastelo.jpg1.swf Peca Pecacastelo.jpg1.swf
Populating a TreeView with XML
One common use of XML files is to parse them and show their contents in a tree like format. You can find the TTreeView component on the "Common Controls" tab on Lazarus.
The function below will take a XML document previously loaded from a file or generated on code, and will populate a TreeView with it´s contents. The caption of each node will be the content of the first attribute of each node.
<delphi> procedure TForm1.XML2Tree(tree: TTreeView; XMLDoc: TXMLDocument); var
iNode: TDOMNode;
procedure ProcessNode(Node: TDOMNode; TreeNode: TTreeNode); var cNode: TDOMNode; begin if Node = nil then Exit; // Stops if reached a leaf // Adds a node to the tree TreeNode := tree.Items.AddChild(TreeNode, Node.Attributes[0].NodeValue);
// Goes to the child node cNode := Node.FirstChild;
// Processes all child nodes
while cNode <> nil do
begin
ProcessNode(cNode, TreeNode);
cNode := cNode.NextSibling;
end;
end;
begin
iNode := XMLDoc.DocumentElement.FirstChild; while iNode <> nil do begin ProcessNode(iNode, nil); // Recursive iNode := iNode.NextSibling; end;
end; </delphi>
Modifying a XML document
The first thing to remember is that TDOMDocument is the "handle" to the DOM. You can get an instance of this class by creating one or by loading a XML document.
Nodes on the other hand cannot be created like a normal object. You *must* use the methods provided by TDOMDocument to create them, and latter use other methods to put them on the correct place on the tree. This is because nodes must be "owned" by a specific document on DOM.
Below are some common methods from TDOMDocument:
<delphi>
function CreateElement(const tagName: DOMString): TDOMElement; virtual;
function CreateTextNode(const data: DOMString): TDOMText;
function CreateCDATASection(const data: DOMString): TDOMCDATASection;
virtual;
function CreateAttribute(const name: DOMString): TDOMAttr; virtual;
</delphi>
And here an example method that will locate the selected item on a TTreeView and then insert a child node to the XML document it represents. The TreeView must be previously filled with the contents of a XML file using the XML2Tree function.
<delphi> procedure TForm1.actAddChildNode(Sender: TObject); var
position: Integer; NovoNo: TDomNode;
begin
{*******************************************************************
* Detects the selected element
*******************************************************************}
if TreeView1.Selected = nil then Exit;
if TreeView1.Selected.Level = 0 then begin position := TreeView1.Selected.Index;
NovoNo := XMLDoc.CreateElement('item');
TDOMElement(NovoNo).SetAttribute('nome', 'Item');
TDOMElement(NovoNo).SetAttribute('arquivo', 'Arquivo');
with XMLDoc.DocumentElement.ChildNodes do
begin
Item[position].AppendChild(NovoNo);
Free;
end;
{*******************************************************************
* Updates the TreeView
*******************************************************************}
TreeView1.Items.Clear;
XML2Tree(TreeView1, XMLDoc);
end
else if TreeView1.Selected.Level >= 1 then
begin
{*******************************************************************
* This function only works on the first level of the tree,
* but can easely modifyed to work for any number of levels
*******************************************************************}
end;
end; </delphi>
Create a TXMLDocument from a string
Given al XML file in MyXmlString, the following code will create it's DOM:
<delphi> Var
S : TStringStream; XML : TXMLDocument;
begin
S:= TStringStream.Create(MyXMLString); Try S.Position:=0; XML:=Nil; ReadXMLFile(XML,S); // Complete XML document // Alternatively: ReadXMLFragment(AParentNode,S); // Read only XML fragment. Finally S.Free; end;
end; </delphi>
Validating a document
Since March 2007, DTD validation facility has been added to the FCL XML parser. Validation is checking that logical structure of the document conforms to the predefined rules, called Document Type Definition (DTD).
Here is an example of XML document with a DTD:
<xml>
<?xml version='1.0'?> <!DOCTYPE root [ <!ELEMENT root (child)+ > <!ELEMENT child (#PCDATA)> ]> <root> <child>This is a first child.</child> <child>And this is the second one.</child> </root>
</xml>
This DTD specifies that 'root' element must have one or more 'child' elements, and that 'child' elements may have only character data inside. If parser detects any violations from these rules, it will report them.
Loading such document is slightly more complicated. Let's assume we have XML data in a TStream object:
<delphi> procedure TMyObject.DOMFromStream(AStream: TStream); var
Parser: TDOMParser; Src: TXMLInputSource; TheDoc: TXMLDocument;
begin
// create a parser object Parser := TDOMParser.Create; // and the input source Src := TXMLInputSource.Create(AStream); // we want validation Parser.Options.Validate := True; // assign a error handler which will receive notifications Parser.OnError := @ErrorHandler; // now do the job Parser.Parse(Src, TheDoc); // ...and cleanup Src.Free; Parser.Free;
end;
procedure TMyObject.ErrorHandler(E: EXMLReadError); begin
if E.Severity = esError then // we are interested in validation errors only writeln(E.Message);
end; </delphi>
Generating a XML file
Below is the complete code to write in a XML file. (This was taken from a tutorial in DeveLazarus blog ) Please, remember DOM and XMLWrite libs in uses clause
<delphi> unit Unit1;
{$mode objfpc}{$H+}
interface
uses
Classes, SysUtils, LResources, Forms, Controls, Graphics, Dialogs, StdCtrls, DOM, XMLWrite;
type
{ TForm1 }
TForm1 = class(TForm)
Button1: TButton;
Label1: TLabel;
Label2: TLabel;
procedure Button1Click(Sender: TObject);
private
{ private declarations }
public
{ public declarations }
end;
var
Form1: TForm1;
implementation
{ TForm1 }
procedure TForm1.Button1Click(Sender: TObject); var
xdoc: TXMLDocument; // variable to document RootNode, parentNode, nofilho: TDOMNode; // variable to nodes
begin
//create a document xdoc := TXMLDocument.create;
//create a root node
RootNode := xdoc.CreateElement('register');
Xdoc.Appendchild(RootNode); // save root node
//create a parent node
RootNode:= xdoc.DocumentElement;
parentNode := xdoc.CreateElement('usuario');
TDOMElement(parentNode).SetAttribute('id', '001'); // create atributes to parent node
RootNode.Appendchild(parentNode); // save parent node
//create a child node
parentNode := xdoc.CreateElement('nome'); // create a child node
//TDOMElement(parentNode).SetAttribute('sexo', 'M'); // create atributes
nofilho := xdoc.CreateTextNode('Fernando'); // insert a value to node
parentNode.Appendchild(nofilho); // save node
RootNode.ChildNodes.Item[0].AppendChild(parentNode); // insert child node in respective parent node
//create a child node
parentNode := xdoc.CreateElement('idade'); // create a child node
//TDOMElement(parentNode).SetAttribute('ano', '1976'); // create atributes
nofilho := xdoc.CreateTextNode('32'); // insert a value to node
parentNode.Appendchild(nofilho); // save node
.ChildNodes.Item[0].AppendChild(parentNode); // insert a childnode in respective parent node
writeXMLFile(xDoc,'teste.xml'); // write to XML Xdoc.free; // free memory
end;
initialization
{$I unit1.lrs}
end. </delphi>
The result will be the XML file below: <xml> <?xml version="1.0"?> <register>
<usuario id="001"> <nome>Fernando</nome> <idade>32</idade> </usuario>
</register> </xml>
--Fernandosinesio 22:28, 24 April 2008 (CEST)fernandosinesio@gmail.com
Encoding
Starting from SVN revision 12582, XML reader is able to process data in any encoding by using external decoders. See XML_Decoders for more details.
According to the XML standard, the encoding attribute in the first line of the XML is optional in case the actual encoding is UTF-8 or UTF-16 (which is detected by presence of the BOM). As of version 0.9.26 of Lazarus, there is an encoding property in a TXMLDocument, but it is ignored. writeXMLFile always uses UTF-8 and doesn´t generate an encoding attribute in first line of the XML file.
External Links
- W3Schools Xml Tutorial
- Thomas Zastrow article FPC and XML
