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。
2014-09-10 16:45:32.920 xmlforblog[3820:60b] start parse 12014-09-10 16:45:32.921 xmlforblog[3820:60b] start element2014-09-10 16:45:32.922 xmlforblog[3820:60b] found characters2014-09-10 16:45:32.922 xmlforblog[3820:60b] start element2014-09-10 16:45:32.922 xmlforblog[3820:60b] found characters2014-09-10 16:45:32.922 xmlforblog[3820:60b] start element2014-09-10 16:45:32.923 xmlforblog[3820:60b] found characters2014-09-10 16:45:32.923 xmlforblog[3820:60b] end element2014-09-10 16:45:32.923 xmlforblog[3820:60b] found characters2014-09-10 16:45:32.923 xmlforblog[3820:60b] start element2014-09-10 16:45:32.924 xmlforblog[3820:60b] found characters2014-09-10 16:45:32.924 xmlforblog[3820:60b] end element2014-09-10 16:45:32.924 xmlforblog[3820:60b] found characters2014-09-10 16:45:32.924 xmlforblog[3820:60b] start element2014-09-10 16:45:32.925 xmlforblog[3820:60b] found characters2014-09-10 16:45:32.925 xmlforblog[3820:60b] end element2014-09-10 16:45:32.925 xmlforblog[3820:60b] found characters2014-09-10 16:45:32.925 xmlforblog[3820:60b] end element2014-09-10 16:45:32.926 xmlforblog[3820:60b] found characters2014-09-10 16:45:32.926 xmlforblog[3820:60b] start element2014-09-10 16:45:32.928 xmlforblog[3820:60b] found characters2014-09-10 16:45:32.929 xmlforblog[3820:60b] start element2014-09-10 16:45:32.929 xmlforblog[3820:60b] found characters2014-09-10 16:45:32.929 xmlforblog[3820:60b] end element2014-09-10 16:45:32.930 xmlforblog[3820:60b] found characters2014-09-10 16:45:32.930 xmlforblog[3820:60b] start element2014-09-10 16:45:32.930 xmlforblog[3820:60b] found characters2014-09-10 16:45:32.930 xmlforblog[3820:60b] end element2014-09-10 16:45:32.931 xmlforblog[3820:60b] found characters2014-09-10 16:45:32.931 xmlforblog[3820:60b] start element2014-09-10 16:45:32.931 xmlforblog[3820:60b] found characters2014-09-10 16:45:32.931 xmlforblog[3820:60b] end element2014-09-10 16:45:32.931 xmlforblog[3820:60b] found characters2014-09-10 16:45:32.932 xmlforblog[3820:60b] end element2014-09-10 16:45:32.932 xmlforblog[3820:60b] found characters2014-09-10 16:45:32.932 xmlforblog[3820:60b] start element2014-09-10 16:45:32.932 xmlforblog[3820:60b] found characters2014-09-10 16:45:32.933 xmlforblog[3820:60b] start element2014-09-10 16:45:32.933 xmlforblog[3820:60b] found characters2014-09-10 16:45:32.933 xmlforblog[3820:60b] end element2014-09-10 16:45:32.933 xmlforblog[3820:60b] found characters2014-09-10 16:45:32.934 xmlforblog[3820:60b] start element2014-09-10 16:45:32.934 xmlforblog[3820:60b] found characters2014-09-10 16:45:32.934 xmlforblog[3820:60b] end element2014-09-10 16:45:32.934 xmlforblog[3820:60b] found characters2014-09-10 16:45:32.935 xmlforblog[3820:60b] start element2014-09-10 16:45:32.935 xmlforblog[3820:60b] found characters2014-09-10 16:45:32.935 xmlforblog[3820:60b] end element2014-09-10 16:45:32.935 xmlforblog[3820:60b] found characters2014-09-10 16:45:32.936 xmlforblog[3820:60b] end element2014-09-10 16:45:32.936 xmlforblog[3820:60b] found characters2014-09-10 16:45:32.936 xmlforblog[3820:60b] end element2014-09-10 16:45:32.936 xmlforblog[3820:60b] parse end2014-09-10 16:45:32.936 xmlforblog[3820:60b] ( { age = 22; firstName = Wythe; id = 1; lastName = xu; }, { age = 31; firstName = li; id = 2; lastName = si; }, { age = 24; firstName = Dipen; id = 3; lastName = Shah; })
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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