NSXMLParser - 空值

Question

我第一次尝试使用 NSXMLParser 从 XML 获取值。但是我有一个问题。

下面我的XML：

<Library>
    <Book>
        <ID>1</ID>
        <TITLE>Test</TITLE>
    </Book>
</Library>

和解析器代码：

-(void)parser:(NSXMLParser *)parser didStartElement:(NSString                                 *)   elementName namespaceURI:(NSString *)namespaceURI qualifiedNam(NSString *)qName attributes:(NSDictionary *)attributeDict
{
  if([elementName isEqualToString:@"Book"])
  {
    NSLog(@"%@", [attributeDict valueForKey:@"ID"]);
  }
}

结果ID为空。你能帮帮我吗？

Answer 1

不幸的是，NSXMLParser 不能这样工作。它按文档顺序遍历 XML 中的元素，因此当 "Book" 元素开始时，它还没有到达 "ID" 元素。如果 XML 看起来像

，您的代码将工作

<Book Id="1">
    ...
</Book>

但我想您无法控制 XML。那么你需要一个更复杂的解决方案。我相信以下方法会起作用：

添加这些实例变量

NSString *currentElement, *bookID, *bookTitle;
NSMutableString *elementValue;

执行以下方法：

- (void)parser:(NSXMLParser *)parser didStartElement:(NSString                                 *)   elementName namespaceURI:(NSString *)namespaceURI qualifiedNam(NSString *)qName attributes:(NSDictionary *)attributeDict {
    currentElement = elementName;
    elementValue = nil; 
}

- (void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string {
    // Append characters to element value
    if (!elementValue) elementValue = [NSMutableString stringWithCapacity:100];
    [elementValue appendString:string];
}

- (void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qualifiedName {
     if ([@"Id" isEqualToString:elementName]) {
          bookID = [elementValue copy];
     } else if ([@"Title" isEqualToString:elementName]) {
          bookTitle = [elementValue copy];
     } else if ([@"Book" isEqualToString:elementName]) {
          // end of Book element, do something with bookID and bookTitle
     }
}

Answer 2

跟着下面code.You就明白了

在你的 .h 部分

//第 1 步：添加委托类

     First of all you should add <NSXMLParserDelegate>

//第 2 步：创建必要的对象

     NSXMLParser *parser;
     NSMutableData *ReceviedData;
     NSMutableString *currentStringValue;

     NSMutableArray *arrayID;

在你的 .m 部分

 //Step 3 - Allocate your all  Arrays in your viewDidLoad method

     arrayId = [NSMutableArray alloc]init];


 //Step 4 - Create Connection in your viewDidLoad Like 

     [self createConnection:@"http://www.google.com"];//give your valid url.

-(void)createConnection:(NSString *)urlString
{
     NSURL *url = [NSURL URLWithString:urlString];

  //Step 5 - parser delegate methods are using NSURLConnectionDelegate class or not.
    BOOL success;
    if (!parser)
    {
      parser = [[NSXMLParser alloc] initWithContentsOfURL:url];
      parser.delegate = self;
      parser.shouldResolveExternalEntities = YES;
      success = [parser parse];
      NSLog(@"Success : %c",success);
    }
  }

   -(void)parser:(NSXMLParser *)parser didStartElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName attributes:(NSDictionary *)attributeDict
  {
      NSLog(@"Current Element Name : %@",elementName);

     if ([elementName isEqualToString:@"ID"])
     {
         NSLog(@"The Result is==%@",elementName);
     }

  }

  -(void)parser:(NSXMLParser *)parser foundCharacters:(NSString *)string
  {
    currentStringValue = [[NSMutableString alloc] initWithString:string];
     NSLog(@"Current String Value : %@",currentStringValue);
  }

  -(void)parser:(NSXMLParser *)parser didEndElement:(NSString *)elementName namespaceURI:(NSString *)namespaceURI qualifiedName:(NSString *)qName
   {
     if ([elementName isEqualToString:@"ID"])
     {
       [arrayResult addObject:currentStringValue];
     }
      currentStringValue = nil;
  }

NSXMLParser - 空值

NSXMLParser - empty value

xml-parsing

ios