IOS 解析XML文档

前段时间想找点事做，就是试着看能不能用豆瓣的API做点什么，于是就碰到了这个问题——XML解析。

　　老师还没讲，只能自己去查。

　　XML文档解析主要有SAX和DOM两种模式，IOS上两种模式都可以用，这里就不做过多介绍，我选择的SAX模式。

IOS解析XML用的是自带的NSXML框架，框架的核心是NSXMLParser类和它的委托协议NSXMLParserDelegate，其主要的解析工作是在NSXMLParserDelegate实现类中完成的。委托中定义了许多回掉方法，在SAX解析器从上到下遍历XML文档的过程中，遇到开始标签、结束标签、文档开始、文档结束和字符串结束是就会触发这些方法。这些方法有很多，下面我们列出5个常用的方法。

在文档开始时触发

 -(void)parserDidStartDocument:(NSXMLParser *)parser      

　　遇到一个新标签是触发，其中namespaceURI是命名空间，qualifiedName是限定名，attributes是字典类型的属性集合。

-(void)parser:(NSXMLParser *)parser didStartElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName attributes:(NSDictionary *)attributeDict 

　　找到字符串时触发

    -(void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string

　　遇到结束标签时触发

    -(void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName 

　　在文档结束时触发

-(void)parserDidEndDocument:(NSXMLParser *)parser         

下面通过一个具体的例子来看整个的调用与解析过程

首先这是我们将要解析的XML文件 "info.xml"

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

    ​    ​    ​<root>  ​    ​

    ​    ​    ​    ​ <person id="1">

    ​    ​    ​    ​    ​ <firstName>Wythe</firstName>
   ​    ​    ​    ​    ​
    ​    ​    ​    ​    ​ <lastName>xu</lastName>
   ​    ​    ​    ​    ​
    ​    ​    ​    ​    ​ <age>22</age>  ​    ​    ​    ​

    ​    ​    ​    ​ </person>
  ​    ​    ​
   ​    ​    ​    ​ <person id="2">
   ​    ​    ​    ​
    ​    ​    ​    ​    ​ <firstName>li</firstName>
    ​    ​    ​    ​    ​
    ​    ​    ​    ​    ​ <lastName>si</lastName>
    ​    ​    ​    ​    ​
    ​    ​    ​    ​    ​ <age>31</age>
  ​    ​    ​    ​
    ​    ​    ​    ​ </person>
    ​    ​    ​    ​
    ​    ​    ​    ​    ​<person id="3">
   ​    ​    ​    ​    ​
    ​    ​    ​    ​    ​ <firstName>Dipen</firstName>
    ​    ​    ​    ​    ​
    ​    ​    ​    ​    ​ <lastName>Shah</lastName>
    ​    ​    ​    ​    ​
    ​    ​    ​    ​    ​ <age>24</age>
    ​    ​    ​    ​
    ​    ​    ​    ​ </person>
    ​    ​    ​    ​
    ​    ​    ​</root>

接来来是一个头文件 "ViewController.h"

#import <UIKit/UIKit.h>

@interface ViewController : UIViewController<NSXMLParserDelegate>

@property NSXMLParser *parser;
@property NSMutableArray *person;
@property NSString *currenttag;

@end

然后是它的实现文件  "ViewController.m"

#import "ViewController.h"

@interface ViewController ()

@end

@implementation ViewController

@synthesize  parser = _parser , person = _person , currenttag = _currenttag;

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
    }
    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];

    NSString *xmlFilePath = [[NSBundle mainBundle]pathForResource:@"info"ofType:@"xml"];

    NSData *data = [[NSData alloc]initWithContentsOfFile:xmlFilePath];

    self.parser = [[NSXMLParser alloc]initWithData:data];

    self.parser.delegate = self;

    [self.parser parse];

    NSLog(@"%@",_person);

}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

#pragma mark delegate method

-(void)parserDidStartDocument:(NSXMLParser *)parser
{
    _person = [[NSMutableArray alloc]init];
    NSLog(@"start parse 1");
}

-(void)parser:(NSXMLParser *)parser didStartElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName attributes:(NSDictionary *)attributeDict
{
    _currenttag = elementName;

    if ([_currenttag isEqualToString:@"person"]) {
        NSString *_id = [attributeDict objectForKey:@"id"];
        NSMutableDictionary *dict = [[NSMutableDictionary alloc]init];
        [dict setObject:_id forKey:@"id"];
        [_person addObject:dict];
    }

    NSLog(@"start element");
}

-(void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string
{
    NSMutableDictionary *dict = [_person lastObject];

    if ([_currenttag isEqualToString:@"firstName"] && dict) {
        [dict setObject:string forKey:@"firstName"];

    }
    if ([_currenttag isEqualToString:@"lastName"] && dict) {
        [dict setObject:string forKey:@"lastName"];
    }
    if ([_currenttag isEqualToString:@"age"] && dict) {
        [dict setObject:string forKey:@"age"];
    }

    NSLog(@"found characters");
}

-(void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName
{
    _currenttag = nil;

    NSLog(@"end element");
}

-(void)parserDidEndDocument:(NSXMLParser *)parser
{
    NSLog(@"parse end");
}
@end

通过断电和输出信息，我们可以知道整个解析过程是 开始解析文档、开始标签、找到字符串、结束标签、文档结束。

-- ::32.920 xmlforblog[:60b] start parse
-- ::32.921 xmlforblog[:60b] start element
-- ::32.922 xmlforblog[:60b] found characters
-- ::32.922 xmlforblog[:60b] start element
-- ::32.922 xmlforblog[:60b] found characters
-- ::32.922 xmlforblog[:60b] start element
-- ::32.923 xmlforblog[:60b] found characters
-- ::32.923 xmlforblog[:60b] end element
-- ::32.923 xmlforblog[:60b] found characters
-- ::32.923 xmlforblog[:60b] start element
-- ::32.924 xmlforblog[:60b] found characters
-- ::32.924 xmlforblog[:60b] end element
-- ::32.924 xmlforblog[:60b] found characters
-- ::32.924 xmlforblog[:60b] start element
-- ::32.925 xmlforblog[:60b] found characters
-- ::32.925 xmlforblog[:60b] end element
-- ::32.925 xmlforblog[:60b] found characters
-- ::32.925 xmlforblog[:60b] end element
-- ::32.926 xmlforblog[:60b] found characters
-- ::32.926 xmlforblog[:60b] start element
-- ::32.928 xmlforblog[:60b] found characters
-- ::32.929 xmlforblog[:60b] start element
-- ::32.929 xmlforblog[:60b] found characters
-- ::32.929 xmlforblog[:60b] end element
-- ::32.930 xmlforblog[:60b] found characters
-- ::32.930 xmlforblog[:60b] start element
-- ::32.930 xmlforblog[:60b] found characters
-- ::32.930 xmlforblog[:60b] end element
-- ::32.931 xmlforblog[:60b] found characters
-- ::32.931 xmlforblog[:60b] start element
-- ::32.931 xmlforblog[:60b] found characters
-- ::32.931 xmlforblog[:60b] end element
-- ::32.931 xmlforblog[:60b] found characters
-- ::32.932 xmlforblog[:60b] end element
-- ::32.932 xmlforblog[:60b] found characters
-- ::32.932 xmlforblog[:60b] start element
-- ::32.932 xmlforblog[:60b] found characters
-- ::32.933 xmlforblog[:60b] start element
-- ::32.933 xmlforblog[:60b] found characters
-- ::32.933 xmlforblog[:60b] end element
-- ::32.933 xmlforblog[:60b] found characters
-- ::32.934 xmlforblog[:60b] start element
-- ::32.934 xmlforblog[:60b] found characters
-- ::32.934 xmlforblog[:60b] end element
-- ::32.934 xmlforblog[:60b] found characters
-- ::32.935 xmlforblog[:60b] start element
-- ::32.935 xmlforblog[:60b] found characters
-- ::32.935 xmlforblog[:60b] end element
-- ::32.935 xmlforblog[:60b] found characters
-- ::32.936 xmlforblog[:60b] end element
-- ::32.936 xmlforblog[:60b] found characters
-- ::32.936 xmlforblog[:60b] end element
-- ::32.936 xmlforblog[:60b] parse end
-- ::32.936 xmlforblog[:60b] (
        {
        age = ;
        firstName = Wythe;
        id = ;
        lastName = xu;
    },
        {
        age = ;
        firstName = li;
        id = ;
        lastName = si;
    },
        {
        age = ;
        firstName = Dipen;
        id = ;
        lastName = Shah;
    }
)

执行结果

而我们的处理主要是在 开始标签、找到字符串 （

-(void)parser:(NSXMLParser *)parser didStartElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName attributes:(NSDictionary *)attributeDict 

-(void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string

） 中。

遇到开始标签时，我们现判断标签，名字，如果是person，表明接下来就是person的信息，这样我们就先创建一个可变字典，以便将来存放它的值。

-(void)parser:(NSXMLParser *)parser didStartElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName attributes:(NSDictionary *)attributeDict
{
    _currenttag = elementName;

    if ([_currenttag isEqualToString:@"person"]) {
        NSString *_id = [attributeDict objectForKey:@"id"];
        NSMutableDictionary *dict = [[NSMutableDictionary alloc]init];
        [dict setObject:_id forKey:@"id"];
        [_person addObject:dict];
    }

    NSLog(@"start element");
}

在找到字符串时，我们就是通过判断当前标签名，将对应的信息保存到刚刚创建的字典中

-(void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string
{
    NSMutableDictionary *dict = [_person lastObject];

    if ([_currenttag isEqualToString:@"firstName"] && dict) {
        [dict setObject:string forKey:@"firstName"];

    }
    if ([_currenttag isEqualToString:@"lastName"] && dict) {
        [dict setObject:string forKey:@"lastName"];
    }
    if ([_currenttag isEqualToString:@"age"] && dict) {
        [dict setObject:string forKey:@"age"];
    }

    NSLog(@"found characters");
}

不断循环这样的过程，最后我们就可以解析出整个XML文档。

另外说一句，这只是解析一般的文档，如果你跟我曾经一样学会这个就去解析豆瓣API的XML文档，会发现行不通。这时因为许多网站因为它的数据较多，为了避免标签的重复，使用了命名空间，带有命名空间的XML文档解析和这稍有不同。

以后我会写带命名空间的XML文档解析，敬请期待。

拖了快一个月了，今天终于写完。以后不能这么懒了

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