XML parsing in IOS: DOM and SAX, iosxmldomsax

XML parsing in IOS: DOM and SAX, iosxmldomsax

I. Introduction

Dom is a set of standards specified by w3c. The core is to process data in a tree structure. The dom parser reads xml files and creates a tree with the same structure in the memory ", each section of the tree corresponds to each xml tag, and the "Tree" is manipulated to process files in the xml. When the xml file is large, the created "Tree" will also be large, so it will occupy a lot of memory.
The core of the sax Parser is the event processing mechanism. For example, when a parser discovers a starting tag, it encapsulates the detected data into a tag start event and reports the event to the event processor. The event processor then calls the method (startElement) process the discovered data. Next we will try to parse the SAX and DOM:

The XML format is as follows:

Ii. SAX:

1. We use Apple's NSXMLParser for parsing with SAX. First, initialize a parser and set the proxy to start parsing. The Code is as follows:

// Initialization path NSString * path = [[NSBundle mainBundle] pathForResource: @ "Test. xml "ofType: nil]; NSData * data = [NSData dataWithContentsOfFile: path]; // initialize the parser NSXMLParser * parser = [[NSXMLParser alloc] initWithData: data]; // sets the proxy parser. delegate = self; // start parsing [parser parse];

2. Start parsing through the proxy method. Because the sax method is event-driven, parsing is performed in order. To obtain tag data, we need to monitor the parsing status of each step, therefore, the system provides a proxy method. The following are common proxy methods:

// Start to load the document-(void) parserDidStartDocument :( NSXMLParser *) parser {} // end to load the document-(void) parserDidEndDocument :( NSXMLParser *) parser {} // start parsing the tag-(void) parser :( NSXMLParser *) parser didStartElement :( NSString *) elementName namespaceURI :( NSString *) namespaceURI qualifiedName :( NSString *) qName attributes :( NSDictionary *) attributeDict {} // tag resolution end-(void) parser :( NSXMLParser *) parser didEndElement :( NSString *) elementName namespaceURI :( NSString *) namespaceURI qualifiedName :( NSString *) qName {} // read the text between tags-(void) parser :( NSXMLParser *) parser foundCharacters :( NSString *) string {content = string ;}

3. XM has two storage methods: attribute and text between tags. If you want to obtain attributes, you must obtain them in the proxy method,

 

The proxy method is required to obtain the text between tags.

 

Conclusion: by combining the given proxy method, we can easily obtain XML content.

3. DOM

1. We use a third-party framework GDataXMLNode for DOM parsing, which is a dynamic library. We need to introduce the following:

Third-party support frameworks must also be introduced:

DOM Parsing is a little simpler than SAX. DOM first puts the entire file into the memory. Then obtain the element content in the memory in the form of a binary tree.

　　Main categories involved:

GDataXMLDocument // the entire document
GDataXMLElement // Node object
GDataXMLNode // attribute Node object

You can use the following method to parse data:

// Initialize // Add the file to the memory GDataXMLDocument * document = [[GDataXMLDocument alloc] initWithData: data options: 0 error: nil]; // obtain the root element GDataXMLElement * root = document. rootElement; // obtain all the subnodes of the name-(NSArray *) elementsForName :( NSString *) name; // obtain the attribute value based on the name-(GDataXMLNode *) attributeForName :( NSString *) name;

In this way, we can easily parse and obtain XMl values,

 

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Author: Jerry Education
Source: http://www.cnblogs.com/jerehedu/
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