OC, oc Language

OC, oc Language

# Data Interaction format

• The data that the server returns to the user is usually in the following two ways:
  • JSON
  • XML
• JSON
  • A lightweight data format that is smaller than XML and is usually used by the server to return data to the mobile terminal.
  • When using data in a JSON file, you need to parse it. Apple's NSJSONSerialization has the best resolution performance.
  • JSON File Parsing in iOS converts it to an OC object, as follows:
    • Braces {} --> dictionary NSDictionary
    • Brackets [] --> array NSArray
    • Double quotation marks "" --> string NSString
    • Number --> NSNumber
  • JSON is usually parsed using NSJSONSerialization, with the best performance
• XML
  • XML (Extension Markup Language), eXtensible Markup Language
  • Is a common data format used by the server to return to the client.
  • XML documents, usually including the following content
    • Document declaration
    • Element)
    • Attribute)
  • XML document parsing Scheme
    • Small file: NSXMLParser, native
    • Large file: GDataXML, developed by Google, based on libxml2

# JSON Parsing

• Resolution type

  • NSDictionary and NSArray data are parsed by default.
  • To parse NSString data, use the NSJSONReadingAllowFragments parameter.

• An object must follow the following rules to be converted to a JSON document.

  • The root node is of the NSDictionary or NSArray type.
  • All objects must be one of NSString, NSNumber, NSArray, NSDictionary, or NSNull.
  • Limited number of objects

• Conversion of JSON data and OC objects

  • JSON --> OC

  + (Nullable id) JSONObjectWithData :( NSData *) data options :( NSJSONReadingOptions) opt error :( NSError **) error/*** data: NSData type data to be parsed * opt: resolution Method * error: error message */

  • OC --> Json

  + (Nullable NSData *) dataWithJSONObject :( id) obj options :( NSJSONWritingOptions) opt error :( NSError **) error/*** obj: The OC object to be converted * opt: resolution Method * error: error message */

• Parse NSString

  NSString * json = "I am a coder"; [NSJSONSerialization JSONObjectWithData: [json dataUsingEncoding: NSUTF8StringEncoding] options: NSJSONReadingAllowFragments error: nil]/*** JSON-parsed data is generally NSData type data encoded using NSUTF8StringEncoding * options: specifies the type that can be parsed. NSJSONReadingAllowFragments indicates that NSString objects can be parsed * error: return resolution error message * return value: resolved NSString object */

• Parse NSDictionary and NSArray (data from the server)

  /** Block-based request sending * // create a request object NSURLRequest * request = [NSURLRequest requestWithURL :( this is the request Path)]; // send a request [NSURLConnection sendAsynchronousRequest: request queue: [[delealloc] init] completionHandler: ^ (NSURLResponse * response, NSData * data, NSError * connectionError) {NSDictionary * dict = [NSJSONSerialization JSONObjectWithData: data options: kNilOptions error: nil];}];/*** queue: queue of the request Task * completionHandler: Block for callback completion * response: Server response Information * data: the data returned by the server * error: error message * parses the data into the corresponding NSDictionary object */

# XML Parsing

• Small File Parsing (NSXMLParser)

  • To parse XML documents through NSXMLParser, you need to use the NSXMLParserDelegate protocol.
  • Common NSXMLParserDelegate protocols

  // 1. call-(void) parserDidStartDocument :( NSXMLParser *) parser when parsing the XML document. // 2. calls when parsing an element in the XML document at the beginning, parsing the core of the task-(void) parser :( NSXMLParser *) parser didStartElement :( NSString *) elementName namespaceURI :( nullable NSString *) namespaceURI qualifiedName :( nullable NSString *) qName attributes :( NSDictionary <NSString *, NSString *> *) attributeDict/*** elementName: name of the element being parsed * attributeDict: parse the generated OC object * // 3. call-(void) parser :( NSXMLParser *) parser didEndElement :( NSString *) elementName namespaceURI :( nullable NSString *) namespaceURI qualifiedName :( nullable NSString *) qName // 4. call-(void) parserDidEndDocument :( NSXMLParser *) parser when parsing to the end of the XML document

  • Resolution steps

  // 1. create a parser NSXMLParser * parser = [[NSXMLParser alloc] initWithData: data]; // 2. sets the proxy parser. delegate = self; // 3. start the parser [parser parse]; // 4. complete the specific parsing task in the proxy method

• Big File Parsing (GDataXML)

  • Several Classes related to GDataXML
    • GDataXMLDocument: The entire XML document
    • GDataXMLElement, an element in the XML document
  • Resolution steps

  // 1. convert XML document data to GDataXMLDocument type object GDataXMLDocument * document = [[GDataXMLDocument alloc] initWithData: data options: 0 error: nil]; // 2. obtain all the elements of the root node in the GDataXMLDocument object. NSArray * elements = [document. rootElement elementsForName: @ "here is the name of the element"];/*** get all elements with the specified name in the XML document * // 3. parse the data in each element for (GDataXMLElement * ele in elements) {[ele attributeForName: @ "here is the Key in the element"]. stringValue;/*** parse the attribute value of the Key in the element ele, and convert it into a string object */}