Data parsing--json & XML

>json

is a lightweight data format ( like the document has a txt format , doc format , JSON is a representation of the data format ), Typically used for data interaction ,

Data returned to the client by the server , usually in JSON format or XML format ( except for file downloads , files )

The format of JSON is much like an array in OC , a dictionary . Standard JSON format :key must be in double quotes , not single quotes

To get the specific data from the JSON , you need to parse the JSON . JSON--->oc

>JSON parsing scheme

• ios Json4
• third-party framework: jsonkitsbjsontouchjson
• Apple native (comes with): Nsjsonserialization ( performance best )
• nsjsonserialization common methods
• json data à oc

+ (ID) jsonobjectwithdata: (NSData *) Data options: (nsjsonreadingoptions) opt error: (NSERROR *) error;

• OC object à JSON data

+ (NSData *) Datawithjsonobject: (ID) obj options: (nsjsonwritingoptions) opt error: (NSERROR *) error;

Xml

• What is XML
• Full name is Extensible Markup Language, translated "Extensible Markup Language"
• like JSON , it's also a common format for interacting data.
• Generally also called XML document (XML documents)
• XML Example

<videos>

<video Name=" Yellow man first " length=" />"

<video Name=" small Yellow Man", " length=" >

<video Name=" small yellow person " length=" />"

</videos>

XML Syntax

• A common XML document typically consists of the following sections
• Document Declaration
• Elements (element)
• Properties (Attribute)
• XML Syntax – Document declaration
• At the very front of the XML document, you must write a document declaration that declares the type of the XML document
• The simplest statement

<?xml version="1.0" ?>

• Use the encoding property to describe the character encoding of a document

<?xml version= "1.0" encoding= "UTF-8"?>

XML Syntax – elements (element)

• An element includes a start tag and an end tag
• own element content:<video> Yellow people </video>
• No element content:<video></video>
• Shorthand for no element content:<video/>
• An element can nest several child elements (no cross-nesting)

<videos>

<video>

<name> Yellow People section of the department </name>

<length></length>

</video>

</videos>

• Canonical XML documents have a maximum of 1 root elements, and other elements are descendants of the root element
• XML Syntax – element's attention
• all spaces and line breaks in XML are treated as concrete content
• The contents of the following two elements are not the same
• The first 1

<video> Small yellow people </video>

• The First 2

<video>

Minions

</video>

XML Syntax – attributes (Attribute)

• An element can have multiple properties

<video Name=" Yellow man first " length=" />"

• The video element has a name and length two properties
• Attribute values must be enclosed in double quotation marks "" or single quotes "
• In fact, the information represented by a property can also be represented by a child element, such as

<video>

<name> Yellow People section of the department </name>

<length></length>

</video>

XML parsing

• To extract useful information from XML, you have to learn to parse the XML
• Extract The contents of the name element

<name> Yellow People section of the department </name>

• Extract The value of the name and length property in the video element

<video Name=" Yellow man first " length=" /> "

• There are 2 ways to parse XML
• DOM: loading an entire XML document into memory at once, which is more suitable for parsing small files
• SAX: Starting from the root element, in order to parse an element down, it is more suitable for parsing large files
• XML parsing in IOS
• In IOS , there are many ways to parse XML
• Apple native
• Nsxmlparser:SAX method parsing, simple to use
• Third-party frameworks
• LIBXML2: pure C language, which is included by default in the iOS SDK while supporting DOM and SAX parsing
• Gdataxml:DOM mode parsing, developed by Google , based on libxml2
• suggestions for choosing XML parsing methods
• Large files:nsxmlparser,libxml2
• Small files:gdataxml
• Nsxmlparser
• Use steps

incoming XML data, creating a parser

Nsxmlparser *parser = [[Nsxmlparser alloc] initwithdata:data];

set up the agent to listen to the parsing process

Parser.delegate = self;

Start parsing

[Parser parse];

• Nsxmlparser take is the SAX parsing, characterized by event-driven, the following situation will notify the agent
• When scanning tothe beginning and end of documents (document)
• When scanning tothe start and end of elements (Element)
• Nsxmlparserdelegate
• Called when scanning to the beginning of a document (parsing is started)

-(void) Parserdidstartdocument: (Nsxmlparser *) parser

• Called when scanning to the end of a document (parsing is complete)

-(void) Parserdidenddocument: (Nsxmlparser *) parser

• Called when scanning to the beginning of an element (attributedict holds the attributes of the element)

-(void) Parser: (Nsxmlparser *) parser didstartelement: (NSString *) elementname NamespaceURI: (NSString *) NamespaceURI QualifiedName: (NSString *) QName attributes: (nsdictionary *) attributedict

• Called when scanning to the end of an element

-(void) Parser: (Nsxmlparser *) parser didendelement: (NSString *) elementname NamespaceURI: (NSString *) NamespaceURI QualifiedName: (NSString *) qName

Gdataxml Use

• classes commonly used in Gdataxml
• Gdataxmldocument: Representing the entire XML document
• Gdataxmlelement
• Represents each element in a document
• Use the attributeforname: method to get the property value

Data parsing--json & XML