QT notes - qtxml

The header file ：#include <QtXml>

understand Xml:
1. The document declaration must be <?xml start , With ?> end ;
2. The document declaration must be from the 0 That's ok 0 Column position starts :
3. Document declaration has only attributes :
a) versioin: Appoint XML Document version . Must attribute , Because we won't choose 1.1, Only select 1.0;
b) encoding: Specifies the encoding of the current document . Optional attribute , The default value is .utf-8:

l Elements element
1. The element is XML The most important part of the document ,
2. The structure of a common element begins with a label 、 Element body 、 The end tag consists of . for example : Hello everyone
3. Element body : An element body can be an element , It can also be text , for example : Hello
4. Empty elements : Empty elements have only start tags , And there's no end tag , But the element must close itself , for example :
5. Element naming :
a) Case sensitive
b) You can't use spaces , You can't use colons :
c) It is not recommended to use XML, xml, Xml start
6. Well formatted XML file , There must be only one root element .

l attribute
1. Attributes are part of an element , It must appear in the start tag of the element
2. Property definition format : Property name = Property value , Where the property value must use single or double reference
3. An element can have O ~ N Attributes , But the attribute with the same name cannot appear in an element
4. Property names cannot use spaces 、 Special characters like colons , And it has to start with a letter

pro Add... To the file QT+=xml

1. open Xml file
2. analysis Xml file
3. Read Xml The contents of the document
increase Xml The contents of the document
Delete Xml The contents of the document
remove Xml The contents of the document
modify Xml The contents of the document
4. Save content to Xml In file

1. open Xml file

QFile file("test.xml");
if (!file.open(QIODevice::ReadOnly))
	return;

2. analysis Xml File and determine whether there is any wrong content

QString errorStr;
int errorLine;
int errorCol;
// analysis XML
QDomDocument doc;
if (!doc.setContent(&file,true, &errorStr, &errorLine, &errorCol))
{
    
	qDebug() << QStringLiteral(" Error string :%1, Wrong number of lines :%2, Number of wrong Columns :%3").arg(errorStr).arg(errorLine).arg(errorCol);
	file.close();
	return;
}
file.close();

3. establish Xml The contents of the document

// Open or create a file 
QFile file("test.xml"); // Relative paths 、 Absolute path 、 Resource paths are OK 
if (!file.open(QFile::WriteOnly | QFile::Truncate)) //Truncate It means to empty the original content 
	return;

QDomDocument doc;
// Add processing command 
QDomProcessingInstruction instruction; 
instruction=doc.createProcessingInstruction("xml","version=\"1.0\" encoding=\"UTF-8\"");
doc.appendChild(instruction);

// establish dom The elements of 
QDomElement root = doc.createElement("library");
doc.appendChild(root);

// Add a child node under the element 
QDomElement book = doc.createElement("book");
// Add the content of the sub node title  

// Method 1 ;  Create element attributes   The values of key value pairs can be various types 
book.setAttribute("id", 1);

// Method 2 ： Create element attributes   The value must be a string 
QDomAttr time = doc.createAttribute("time");
time.setValue("2013/6/13");
book.setAttributeNode(time);

QDomElement title = doc.createElement("title");
// Add the content of the element 
QDomText text = doc.createTextNode("C++ primer");
title.appendChild(text);

// Add it to your parent node 
book.appendChild(title);
root.appendChild(book);

// write file 
QTextStream stream(&file);
doc.save(stream, 4);
file.close();

Read XML The contents of the document

// Return root node 
QDomElement root = doc.documentElement();
qDebug() << root.nodeName(); //  Convert elements to root nodes QString name 

// Get the first child node 
QDomNode node = root.firstChild();
qDebug() << QStringLiteral(" The first child node element name is ：") << node.toElement().tagName();
qDebug() << QStringLiteral(" The node element name of the first child node is ：") << node.firstChildElement().nodeName();

// Get the attribute of an element  
QDomElement e = node.toElement();
//tagName  and  nodeName  almost 
qDebug() << e.tagName() << " " << e.attribute("id") << " "<<e.attribute("time");

// Get all child nodes of a node 
QDomNodeList list=e.childNodes();
// The content of an element , Now turn the node into an element , Get content again 
qDebug()<<n.toElement().text();

QDomNode node = node.nextSibling();			 // Get brother nodes 
QDomElement node = node.nextSiblingElement();// Get sibling elements 

Delete XML Content

QDomElement root=doc.documentElement();
QDomNodeList list=doc.elementsByTagName("book"); // Find all lists with the same tag name 
// Remove the node 
root.removeChild(list.at(i));

modify XML Content

QDomNode oldnode=node.firstChild(); // The content between the tags appears as a child node of the node , Now it's Pride and Projudice
node.firstChild().setNodeValue("Emma");
QDomNode newnode=node.firstChild();
node.replaceChild(newnode,oldnode);

Reference blog ：
https://www.cnblogs.com/gaowc/p/10700348.html
https://blog.csdn.net/hpu11/article/details/80227093