[iPhone]XML文件解析 parsing-xml-files NSXMLParser
NSXMLParser 实现的是sax方法解析xml文件。
参考资料：
【参考一】http://www.iphonesdkarticles.com/2008/11/parsing-xml-files.html
【参考二】http://codesofa.com/blog/archive/2008/07/23/make-nsxmlparser-your-friend.html
Introduction
NSXMLParser is a forward only reader or an event driven parser. What it means is, an event is raised whenever the parser comes across a start of an element, value, CDATA and so on. The delegate of NSXMLParser can then implement these events to capture XML data. Some of the events are raised multiple times like the start of an element, value of an element and so on. Since NSXMLParser is known as an event driven parser, we can only read data at the present node and cannot go back. The iPhone only supports NSXMLParser and not NSXMLDocument, which loads the whole XML tree in memory.
For example, say you have a simple XML file such as the following:
<?xml version= "1.0" encoding="UTF8"> |
<article author="John Doe"> |
<para>This is a very short article.</para> |
</article> |
The parser would report the following series of events to its delegate:
-
Started parsing document
-
Found start tag for element
article－－－<article > -
Found attribute
authorof elementarticle, value “John Doe”－－－－－author="John Doe" -
Found start tag for element
para －－－－－<para> -
Found characters －－－－－－
This is a very short article. 【element's value】 -
Found end tag for element
para－－－－－－</para> -
Found end tag for element
article－－－－</article> -
Ended parsing document
使用NSXMLParser步骤方法如下：
步骤一，确定从xml文件 解析出来的数据如何保存－－定义一个类（结构体）
小提示：可能一个xml文件解析出的数据包含多个对象，可以用NSMutableArray来保存。如参考一中提到的books
步骤二，自定义解析处理方法（主要三个方法）－－Delegate代理
为了使代码清晰 可以单独提出来作为一个类
方法一：
- (void)parser:(NSXMLParser *)parser didStartElement:(NSString *)elementName
namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qualifiedName
attributes:(NSDictionary *)attributeDict {
/*
* 处理一：start tag for element 根据不同的元素名，创建不同的用于保存对应数据信息的对象（结构体）
* 处理二：attribute of the element 保存数据信息到对象（结构体）
*/
if([elementName isEqualToString:@"Books"]) {
//Initialize the array.
appDelegate.books = [[NSMutableArray alloc] init];
}
aBook.bookID = [[attributeDict objectForKey:@"id"] integerValue];
}
方法二：主要处理element's value 主要一般都是如下处理保存value值到字符串
- (void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string {
if(!currentElementValue)
currentElementValue = [[NSMutableString alloc] initWithString:string];
else
[currentElementValue appendString:string];
NSLog(@"Processing Value: %@", currentElementValue);
}
方法三：
- (void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName
namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName {
/*
*处理end tag for element，判断不同的元素名，给予不同的处理 保存
*/
if([elementName isEqualToString:@"Book"]) {
[appDelegate.books addObject:aBook];
[aBook release];
aBook = nil;
}
}
步骤三 获取xml文件，并建立NSXMLParser对象，后解析
如参考一中实例，从url获取xml文件，并实例化NSXMLParser对象
NSURL *url = [[NSURL alloc] initWithString:@"http://sites.google.com/site/iphonesdktutorials/xml/Books.xml"];
NSXMLParser *xmlParser = [[NSXMLParser alloc] initWithContentsOfURL:url];
//Initialize the delegate.实例化解析处理方法的代理（步骤二中定义的代理）
XMLParser *parser = [[XMLParser alloc] initXMLParser];
//Set delegate 设置NSXMLParser对象的解析方法代理[xmlParser setDelegate:parser];
//Start parsing the XML file.调用代理解析NSXMLParser对象BOOL success = [xmlParser parse];
if(success)
NSLog(@"No Errors");
else
NSLog(@"Error Error Error!!!");
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