在 NSXMLParser 中解析 xml

Question

我已经阅读了许多关于如何从 xml 文件中获取文本的示例，但只是不知道如何去做。这是一个示例 xml 文件：

<?xml version="1.0" encoding="UTF-8"?>
<questions>
    <set>
        <question>Question</question>
        <answer>Answer</answer>
    </set>
</questions>

使用-(void)parser:(NSXMLParser *)parser didStartElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI，获取值Question 和Answer 的最简单方法是什么？我已经连接了我的解析器委托等等。

Answer 1

要实现 NSXMLParser，你需要实现它的委托方法。

首先以这种方式启动NSXMLParser。

- (void)viewDidLoad {

    [super viewDidLoad];

    rssOutputData = [[NSMutableArray alloc]init];

    //declare the object of allocated variable
    NSData *xmlData=[[NSData alloc]initWithContentsOfURL:[NSURL URLWithString:@""]];// URL that given to parse.

    //allocate memory for parser as well as 
    xmlParserObject =[[NSXMLParser alloc]initWithData:xmlData];
    [xmlParserObject setDelegate:self];

    //asking the xmlparser object to beggin with its parsing
    [xmlParserObject parse];

    //releasing the object of NSData as a part of memory management
    [xmlData release];

}
//-------------------------------------------------------------


-(void)parser:(NSXMLParser *)parser didStartElement:(NSString *)elementName namespaceURI:(NSString *) namespaceURI qualifiedName:(NSString *)qName
   attributes: (NSDictionary *)attributeDict
{
    if( [elementName isEqualToString:@"question"])
    {

         strquestion = [[NSMutableString alloc] init];

    }
}


//-------------------------------------------------------------


-(void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string
{
       // init the ad hoc string with the value     
     currentElementValue = [[NSMutableString alloc] initWithString:string];
  } else {
     // append value to the ad hoc string    
    [currentElementValue appendString:string];
  }
  NSLog(@"Processing value for : %@", string);
}


//-------------------------------------------------------------


-(void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName
{
    if( [elementName isEqualToString:@"question"])
    {
        [strquestion setString:elementName];
    }

 [currentElementValue release];
  currentElementValue = nil;
}

上述委托方法由解析器对象在遇到特定元素的结尾时发送给它的委托。在didEndElement这个方法中，你会得到question的值。

Answer 2

// This one called out when it hit a starting tag on xml in your case <question>

  BOOL got = FALSE;

  - (void)parser:(NSXMLParser *)parser didStartElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI 

 {

      if([elementName isEqualToString:@"question"])
       {
         got = TRUE;
       }
}

// This is third one to called out which gives the end tag of xml in your case </question>


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



// This delegate is the second one to called out which gives the value of current read tag in xml

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

   if(got)
  {
    NSLog(@"your desired tag value %@",string);
    got = FALSE; 
  }
}

Answer 3

你需要实现方法

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

一旦你看到你想要抓取的（内部）文本的元素，在你的程序中设置一个标志，并用foundCharacters在标签之间找到的东西保留一个字符串。一旦你点击了didEndElement 方法，你就可以对字符串做你想做的事情并重置标志。

例如

-(void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string {
  if (sawQuestion) {
    // need to check here that self->myString has been initialized
    [self->myString appendString:string];
 }
}

在didEndElement 中，您可以重置标志sawQuestion

Answer 4

你必须为NSXMLParserDelegate实现回调

关键是：

// called when it found an element - in your example, question or answer
- (void)parser:(NSXMLParser *)parser didStartElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI 

// called when it hits the closing of the element (question or answer)
- (void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI

// called when it found the characters in the data of the element
- (void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string

因此，当您点击元素时，您可以根据您点击时设置的状态设置解析器当前是否在问题或答案元素中（使用 iVar），然后当您使用 foundCharacters 回调时元素，您知道将数据分配给哪个变量（问题或答案）。