iOS中XML解析 (二) libxml2（实例：打印xml内容及存储到数组）

关于libxml库的基本使用，在http://xmlsoft.org/网上有文档。

 

准备工作：

1. project=>Edit project setting =>Build=> Searche Paths=>Header Search Paths:把这个拷贝进去${SDKROOT}/usr/include/libxml2，网上有很多都是没给这个的${SDKROOT}。
2. linking => other linker flags =>－lxml2拷贝进去
3. 把dylib包添加导项目中去。
4. 编译 如果还有问题，nclean all targets 确保 两项都打钩 并且 empty xcode 的cache

 

一、使用libxml读XML文件

 

要读xml，需要使用reader，这里介绍两种方式，一种从文件读取，一种从内存读取。其它就是通过libxml库中提供的两个API来建立reader.请看代码：

 

1、从文件建立reader

 xmlTextReaderPtr  reader = xmlNewTextReaderFilename(xmlfile);

 

2、从内存建立reader

 // char* memory, int size
 xmlTextReaderPtr reader = xmlReaderForMemory(memory, size, NULL, "UTF-8", 0);

 

从上述代码来看，建立一个reader是非常容易的。

 

3、从reader中读数据

 

建立了reader之后，我们就可以通过reader的辅助函数来实现xml数据的读取。在这里，我讲述的是如何读一个文本方式的XML，并没有使用XML的专有模型。这种方式最原始，也是最容易理解的。

 

要读一个reader中的数据，使用xmlTextReaderRead来读一个元素，XML中的每一个元素都会经过reader依次读取，我们可以根据需要来检查当前reader位置的元素类型，并取出数据为已所用，当然还要释放由reader分配的数据空间。下面来看一下读的例子：

 ret = xmlTextReaderRead(reader);
 if (ret == 0) return 0;
 if (ret != 1) return -2;
 element = xmlTextReaderName(reader);

 if (element != NULL)
 {
     ntype = xmlTextReaderNodeType(reader);
     if (strcmp((const char*) element, "param-name") == 0)
     {
         xmlFree(element);
         if (XML_READER_TYPE_ELEMENT == ntype)
         {
         /*......*/
         }
     }
 }

 

xmlTextReaderRead需要一个参数，就是我们前面进行的一个文本读取器指针，该函数返回1表示成功读取，0表示到达文件尾。当成功读取时，可能使用xmlTextReaderName读取当前位置的元素数据，并可以通过xmlTextTextReaderNodeType来读取XML元素的类型。

 /**
  * xmlReaderTypes:
  *
  * Predefined constants for the different types of nodes.
  */
 typedef enum {
     XML_READER_TYPE_NONE = 0,
     XML_READER_TYPE_ELEMENT = 1,
     XML_READER_TYPE_ATTRIBUTE = 2,
     XML_READER_TYPE_TEXT = 3,
     XML_READER_TYPE_CDATA = 4,
     XML_READER_TYPE_ENTITY_REFERENCE = 5,
     XML_READER_TYPE_ENTITY = 6,
     XML_READER_TYPE_PROCESSING_INSTRUCTION = 7,
     XML_READER_TYPE_COMMENT = 8,
     XML_READER_TYPE_DOCUMENT = 9,
     XML_READER_TYPE_DOCUMENT_TYPE = 10,
     XML_READER_TYPE_DOCUMENT_FRAGMENT = 11,
     XML_READER_TYPE_NOTATION = 12,
     XML_READER_TYPE_WHITESPACE = 13,
     XML_READER_TYPE_SIGNIFICANT_WHITESPACE = 14,
     XML_READER_TYPE_END_ELEMENT = 15,
     XML_READER_TYPE_END_ENTITY = 16,
     XML_READER_TYPE_XML_DECLARATION = 17
 } xmlReaderTypes;

 

reader支持如上类型，我们可以根据当前类型来读取数据，因为不现的类型，读取数据的方式不同，比如xmlTextReaderReadString只能读元素（XML_READER_TYPE_ELEMENT）的名称或者文件类型（XML_READER_TYPE_TEXT）的数据。注意一点就是reader是按顺序读取每一个元素，在写代码时，应该不要假定后面一定是什么元素或者特定类型，应该去检测，保证软件的稳定性。

 

使用xmlTextReaderReadString返回一个元素（xmlChar*类型）时，该区域是由库分配的内存区域，需要使用xmlFree来释放，不然就有内存泄漏。

 

4、读xml的reader的释放与清理

 xmlTextReaderClose(reader);
 xmlFreeTextReader(reader);
 xmlDictCleanup();
 xmlCleanupParser();
 xmlMemoryDump();
 xmlCleanupCharEncodingHandlers();

 

有一个xmlTextReaderClose函数，当使用该函数时，要注意顺序，一定要在xmlFreeTextReader之前，不然就会出现错误。 

 

二、实例

 

1. 假设xml地址为 http://cdn.domain.com/ipad/settings/config.xml 格式为：

 <?xml version="1.0"?>
 <settings>
 <popupAd>
     <show>1</show>
     <count>3</count>
 </popupAd>
 </settings>

 

读取：

.h

 #import <Foundation/Foundation.h>
 #include <libxml/xmlreader.h>

 @interface NewsFeedParser : NSObject {

 }

 @end

 

.m

 -(void)readXml
 {
     NSURLResponse  *response;
     NSError        *error;
     NSURLRequest   *request     = [NSURLRequest requestWithURL:[NSURL URLWithString:@"http://cdn.domain.com/ipad/settings/config.xml"]];
     NSData         *settingData = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&error];

     xmlTextReaderPtr reader = xmlReaderForMemory([settingData bytes], [settingData length], nil, nil, (XML_PARSE_NOENT|XML_PARSE_NOBLANKS | XML_PARSE_NOCDATA | XML_PARSE_NOERROR | XML_PARSE_NOWARNING));

     if(!reader) NSLog(@"Failed to load setting config xml !");
     else
     {
         char *temp;
         NSString *currentTagName = nil;
         NSString *currentTagValue = nil;
         NSMutableDictionary *config = [NSMutableDictionary dictionary];

         while (TRUE)
         {
             if(!xmlTextReaderRead(reader)) break;

             //NSLog(@"========> %s",xmlTextReaderName(reader));

             if(xmlTextReaderNodeType(reader) == XML_READER_TYPE_ELEMENT)
             {
                 temp = (char *)xmlTextReaderConstName(reader);
                 currentTagName = [NSString stringWithCString:temp encoding:NSUTF8StringEncoding];

                 if([currentTagName isEqualToString:@"show"] || [currentTagName isEqualToString:@"count"])
                 {
                     temp = (char *)xmlTextReaderReadString(reader);
                     currentTagValue = [NSString stringWithCString:temp encoding:NSUTF8StringEncoding];

                     //NSLog(@"===> TagName: %@",currentTagName);
                     //NSLog(@"===> TagValue: %@",currentTagValue);

                     [config setObject:currentTagValue forKey:currentTagName];
                     currentTagValue = nil;
                 }
             }
         }

         NSLog(@"======> %@",[config objectForKey:@"show"]);
         NSLog(@"======> %@",[config objectForKey:@"count"]);
     }
 }

 

2. 假设xml地址为 http://www.domain.com/feed/ipad/marketchart/main.rss 格式为：

 <?xml version="1.0" encoding="UTF-8"?><rss version="2.0" xmlns:atom="http://www.w3.org/2005/Atom" xmlns:media="http://search.yahoo.com/mrss/">
 <channel>
 <atom:link href="http://www.domain.com/feed/ipad/marketchart/main.rss" rel="self" type="application/rss+xml" />
 <title><![CDATA[domain.com : Market data]]></title>
 <description><![CDATA[Market data RSS Feed ]]></description>
 <link>http://www.domain.com/feed/ipad/marketchart/main.rss</link>
 <copyright>All articles are copyrighted by IBTimes.com</copyright>
  <image>
     <url>http://img.domain.com/www/site/2010/main/images/heading_editores_pick_logo.png</url>
     <title><![CDATA[domain.com : Market data]]></title>
     <link>http://www.domain.com/feed/ipad/marketchart/main.rss</link>
  </image>
   <item>
   <title><![CDATA[DOW]]></title>
   <last>13085.53</last>
   <symbol>^DJI</symbol>
   <change>-114.02</change>
   <description><![CDATA[ description ]]></description>
   <pubDate>Wed, 04 Apr 2012 14:51:00 EDT</pubDate>
   </item>
   <item>
   <title><![CDATA[NYSE]]></title>
   <last>8151.97</last>
   <symbol>$NYA</symbol>
   <change>0</change>
   <description><![CDATA[ description ]]></description>
   <pubDate>Fri, 24 Feb 2012 17:05:00 EST</pubDate>
   </item>
   <item>
   <title><![CDATA[NASDAQ]]></title>
   <last>3063.63</last>
   <symbol>$COMP</symbol>
   <change>-49.94</change>
   <description><![CDATA[ description ]]></description>
   <pubDate>Wed, 04 Apr 2012 14:45:00 EDT</pubDate>
   </item>
   <item>
   <title><![CDATA[S&P 500]]></title>
   <last>1399.64</last>
   <symbol>$SPX</symbol>
   <change>-13.74</change>
   <description><![CDATA[ description ]]></description>
   <pubDate>Wed, 04 Apr 2012 14:45:00 EDT</pubDate>
   </item>
 </channel>
 </rss>

 

以item为单位的循环

 

NewsFeedParser.h

 #import <Foundation/Foundation.h>
 #include <libxml/xmlreader.h>

 @interface NewsFeedParser : NSObject {

 }

 +(NSMutableArray*) parseFeedFromUrl:(NSString *) url;

 @end

 

NewsFeedParser.m

 #import "NewsFeedParser.h"

 @implementation NewsFeedParser

 +(NSMutableArray*) parseFeedFromUrl:(NSString *) url
 {
     NSMutableArray *itemsArray = [NSMutableArray array];

     //NSLog(@"NewsFeedParser:%@ begin\n", url);

     NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:url]];
     NSURLResponse *response;
     NSError *error;

     NSData *xmlData = [NSURLConnection sendSynchronousRequest:request returningResponse:&response
                                                         error:&error];
     xmlTextReaderPtr reader = xmlReaderForMemory([xmlData bytes],
                                                  [xmlData length],
                                                  nil, nil,
                                                  (XML_PARSE_NOENT|XML_PARSE_NOBLANKS | XML_PARSE_NOCDATA | XML_PARSE_NOERROR | XML_PARSE_NOWARNING));

         if (!reader) {
         NSLog(@"Failed to load xmlreader");
         return itemsArray;
     }
     NSString *currentTagName = nil;

     NSDictionary *currentItem = nil;


     NSString *currentTagValue = nil;
     bool itemStarted = false;
     bool authorStarted = false;
     bool categoryStarted = false;
     char* temp;

     while (true) {
         if (!xmlTextReaderRead(reader))
             break;
         int type = xmlTextReaderNodeType(reader);
         switch (type) {
             case XML_READER_TYPE_END_ELEMENT:

                 temp =  (char*)xmlTextReaderConstName(reader);
                 currentTagName = [NSString stringWithCString:temp
                                                     encoding:NSUTF8StringEncoding];

                 if ([currentTagName isEqualToString:@"item"]) {
                     itemStarted = false;
                 }
                 continue;

             case XML_READER_TYPE_ELEMENT:
                 //We are starting an element
                 temp =  (char*)xmlTextReaderConstName(reader);
                 currentTagName = [NSString stringWithCString:temp
                                                     encoding:NSUTF8StringEncoding];


                 if ([currentTagName isEqualToString:@"item"]) {
                     //NSLog(@"Item begin\n");
                     currentItem = [NSMutableDictionary dictionary];
                     [itemsArray addObject:currentItem];
                     itemStarted = true;
                     authorStarted = false;
                     categoryStarted = false;
                 }

                 if([currentTagName isEqualToString:@"author"]){
                     authorStarted = true;
                     categoryStarted = false;
                 }

                 if([currentTagName isEqualToString:@"category"]){
                     categoryStarted = true;
                     authorStarted = false;
                 }

                 if(itemStarted == true && [currentTagName isEqualToString:@"media:content"])
                 {
                     temp = (char*)xmlTextReaderGetAttribute(reader,"url");

                     currentTagValue = [NSString stringWithCString:temp
                                                          encoding:NSUTF8StringEncoding];

                     [currentItem setValue:currentTagValue forKey:currentTagName];
                     //NSLog(@"%@ - %@\n", currentTagName, currentTagValue);

                     currentTagValue = nil;

                 }

                 continue;

             case XML_READER_TYPE_TEXT:
                 //The current tag has a text value, stick it into the current person
                 if(itemStarted == false)
                     continue;

                 temp = (char*)xmlTextReaderConstValue(reader);
                 currentTagValue = [NSString stringWithCString:temp
                                                      encoding:NSUTF8StringEncoding];

                 //NSLog(@"%@ - %@\n", currentTagName, currentTagValue);

                 if([currentTagName isEqualToString:@"name"]){

                     if(authorStarted)
                         [currentItem setValue:currentTagValue forKey:@"author"];

                     if(categoryStarted)
                         [currentItem setValue:currentTagValue forKey:@"category"];

                 }
                 else{
                     [currentItem setValue:currentTagValue forKey:currentTagName];
                 }


                 currentTagValue = nil;
                 currentTagName = nil;
                 continue;

             case XML_READER_TYPE_ATTRIBUTE:
                 //temp = (char*)xmlTextReaderConstValue(reader);
                 //NSLog(@"%s\n", temp);
             default:
                 continue;
         }
     }

     //NSLog(@"NewsFeedParser:%@ done\n", url);

     return itemsArray;

 }

 @end

 

ViewController.m

 #import "NewsFeedParser.h"

 -(void) loadMarketData{

     dispatch_async(dispatch_get_global_queue(0, 0), ^{

         NSMutableArray *items = [NewsFeedParser parseFeedFromUrl:@"http://www.domain.com/feed/ipad/marketchart/main.rss"];

         if([items count] == 0)
             return;

         NSLog(@"Title => %@", [[items objectAtIndex:0] objectForKey:@"title"]);
         NSLog(@"Last=> %@", [[items objectAtIndex:0] objectForKey:@"last"]);
         NSLog(@"Change=> %@", [[items objectAtIndex:0] objectForKey:@"change"]);


     });
 }

 

其他一些方法：

 

 

libxml库提供了一些.net风格的函数,以流的形式来读取并分析xml文件.

 

 <libxml/xmlreader.h>

 xmlTextReader xmlTextReaderPtr //XmlReader的结构体及其指针

 xmlTextReaderPtr xmlReaderForFile (const char * filename, const char * encoding, int options) //打开一个xml文件并返回xmlreader对象,准备开始分析.

 int xmlTextReaderRead (xmlTextReaderPtr reader) //读取下一个节点(注意,是下一个,不是下一个同层节点)

 int xmlTextReaderNext (xmlTextReaderPtr reader) //读取下一个同层节点

 int xmlTextReaderNodeType (xmlTextReaderPtr reader) //判断当前节点的类型

 xmlChar *xmlTextReaderGetAttribute (xmlTextReaderPtr reader, const xmlChar * name) //获取当前节点的指定属性

 xmlChar *xmlTextReaderReadString (xmlTextReaderPtr reader) //读取当前节点下的text

 xmlNodePtr xmlTextReaderExpand (xmlTextReaderPtr reader) //将当前节点展开成一个节点对象(慎用)

 int xmlTextReaderHasValue (xmlTextReaderPtr reader) //判断当前节点是否有text值

 int xmlTextReaderHasAttributes (xmlTextReaderPtr reader) //判断当前节点是否包含属性

 int xmlTextReaderMoveToAttribute (xmlTextReaderPtr reader, const xmlChar * name) //移动指针到当前节点的指定属性名的属性

 int xmlTextReaderMoveToAttributeNo (xmlTextReaderPtr reader, int no) //移动指针到当前节点指定属性编号的属性

 int xmlTextReaderMoveToElement (xmlTextReaderPtr reader) //将指针移会当前节点

 int xmlTextReaderMoveToFirstAttribute (xmlTextReaderPtr reader) //将指针移动到当前节点的第一个属性

 int xmlTextReaderMoveToNextAttribute (xmlTextReaderPtr reader) //将指针移动到当前节点的下一个属性

 xmlChar *xmlTextReaderName (xmlTextReaderPtr reader) //返回当前节点的名字

 

libxml自定义了一个字符类型xmlChar,其本质是 unsigned char.

另外,libxml提供了一个宏来将char*转换成xmlChar*, 名字很有趣,叫 BAD_CAST 它的本质其实是 unsigned char*.

为了方便对xmlChar类型字符串的操作,libxml提供了自己的函数,它们的定义于标准c函数库中的字符串函数很像.

 xmlChar* xmlStrcat (xmlChar *cur, const xmlChar * add)

 const xmlChar *xmlStrchr(const xmlChar * str, xmlChar val)

 int xmlStrcmp (const xmlChar * str1, const xmlChar * str2)

 int xmlStrlen (const xmlChar * str)

 xmlChar *xmlStrncat (xmlChar * cur, const xmlChar * add, int len)

 int xmlStrncmp (const xmlChar * str1, const xmlChar * str2, int len)

 const xmlChar *xmlStrstr (const xmlChar * str, const xmlChar * val)

 

更多函数大家可以参考

http://xmlsoft.org/html/libxml-xmlstring.html