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 1
2014-09-10 16:45:32.921 xmlforblog[3820:60b] start element
2014-09-10 16:45:32.922 xmlforblog[3820:60b] found characters
2014-09-10 16:45:32.922 xmlforblog[3820:60b] start element
2014-09-10 16:45:32.922 xmlforblog[3820:60b] found characters
2014-09-10 16:45:32.922 xmlforblog[3820:60b] start element
2014-09-10 16:45:32.923 xmlforblog[3820:60b] found characters
2014-09-10 16:45:32.923 xmlforblog[3820:60b] end element
2014-09-10 16:45:32.923 xmlforblog[3820:60b] found characters
2014-09-10 16:45:32.923 xmlforblog[3820:60b] start element
2014-09-10 16:45:32.924 xmlforblog[3820:60b] found characters
2014-09-10 16:45:32.924 xmlforblog[3820:60b] end element
2014-09-10 16:45:32.924 xmlforblog[3820:60b] found characters
2014-09-10 16:45:32.924 xmlforblog[3820:60b] start element
2014-09-10 16:45:32.925 xmlforblog[3820:60b] found characters
2014-09-10 16:45:32.925 xmlforblog[3820:60b] end element
2014-09-10 16:45:32.925 xmlforblog[3820:60b] found characters
2014-09-10 16:45:32.925 xmlforblog[3820:60b] end element
2014-09-10 16:45:32.926 xmlforblog[3820:60b] found characters
2014-09-10 16:45:32.926 xmlforblog[3820:60b] start element
2014-09-10 16:45:32.928 xmlforblog[3820:60b] found characters
2014-09-10 16:45:32.929 xmlforblog[3820:60b] start element
2014-09-10 16:45:32.929 xmlforblog[3820:60b] found characters
2014-09-10 16:45:32.929 xmlforblog[3820:60b] end element
2014-09-10 16:45:32.930 xmlforblog[3820:60b] found characters
2014-09-10 16:45:32.930 xmlforblog[3820:60b] start element
2014-09-10 16:45:32.930 xmlforblog[3820:60b] found characters
2014-09-10 16:45:32.930 xmlforblog[3820:60b] end element
2014-09-10 16:45:32.931 xmlforblog[3820:60b] found characters
2014-09-10 16:45:32.931 xmlforblog[3820:60b] start element
2014-09-10 16:45:32.931 xmlforblog[3820:60b] found characters
2014-09-10 16:45:32.931 xmlforblog[3820:60b] end element
2014-09-10 16:45:32.931 xmlforblog[3820:60b] found characters
2014-09-10 16:45:32.932 xmlforblog[3820:60b] end element
2014-09-10 16:45:32.932 xmlforblog[3820:60b] found characters
2014-09-10 16:45:32.932 xmlforblog[3820:60b] start element
2014-09-10 16:45:32.932 xmlforblog[3820:60b] found characters
2014-09-10 16:45:32.933 xmlforblog[3820:60b] start element
2014-09-10 16:45:32.933 xmlforblog[3820:60b] found characters
2014-09-10 16:45:32.933 xmlforblog[3820:60b] end element
2014-09-10 16:45:32.933 xmlforblog[3820:60b] found characters
2014-09-10 16:45:32.934 xmlforblog[3820:60b] start element
2014-09-10 16:45:32.934 xmlforblog[3820:60b] found characters
2014-09-10 16:45:32.934 xmlforblog[3820:60b] end element
2014-09-10 16:45:32.934 xmlforblog[3820:60b] found characters
2014-09-10 16:45:32.935 xmlforblog[3820:60b] start element
2014-09-10 16:45:32.935 xmlforblog[3820:60b] found characters
2014-09-10 16:45:32.935 xmlforblog[3820:60b] end element
2014-09-10 16:45:32.935 xmlforblog[3820:60b] found characters
2014-09-10 16:45:32.936 xmlforblog[3820:60b] end element
2014-09-10 16:45:32.936 xmlforblog[3820:60b] found characters
2014-09-10 16:45:32.936 xmlforblog[3820:60b] end element
2014-09-10 16:45:32.936 xmlforblog[3820:60b] parse end
2014-09-10 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;
}
)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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