Question

我正在编写一个xml阅读器，其中类结构将表示来自xml文件的数据..

举个例子：

<catalog>
<book id="bk101">
  <author>Gambardella, Matthew</author>
  <title>XML Developer's Guide</title>
  <genre>Computer</genre>
  <price>44.95</price>
  <publish_date>2000-10-01</publish_date>
  <description>An in-depth look at creating applications 
  with XML.</description>
</book>
</catalog>

如何找到节点包含子节点！我使用了isempty元素方法！但我得到了例外。

 public element read(XmlReader xml)
    {
        element elem = new element();
        while (xml.Read())
        {
            if (xml.IsEmptyElement)
            {
                elem.ElemName = xml.Name;
                if (xml.HasAttributes)
                {
                    for (int i = 0; i <= xml.AttributeCount; i++)
                    {
                        xml.MoveToNextAttribute();
                        attribute attrib = new attribute();
                        attrib.AttName = xml.Name;
                        attrib.AttValue = xml.Value;
                        elem.Attributes.Add(attrib);
                    }
                }
                return elem;
            }
            else
            {
                elem.ElemName = xml.Name;

                if (xml.HasAttributes)
                {
                    for (int i = 1; i < xml.AttributeCount; i++)
                    {
                        xml.MoveToNextAttribute();
                        attribute attrib = new attribute();
                        attrib.AttName = xml.Name;
                        attrib.AttValue = xml.Value;
                        elem.Attributes.Add(attrib);
                    }
                }

                elem.subElems.Add(read(xml)); -> Object reference not set to an instance of an object.
                return elem;
            }
        }
        return elem;
    }

我使用两个班级。一个叫做元素，一个叫做属性。我在这里做的是逐行，当我找到一个元素时，我创建了一个元素类型对象。然后我检查该元素是否包含任何属性。如果是这样，我为我遇到的属性创建属性类型对象，并将它们添加到元素对象中的属性列表中。然后我检查子元素，如果找到任何子元素，我将它们作为单独的元素对象添加到主元素对象的列表中。

  class element
{
    private String elemName;

    public String ElemName
    {
        get { return elemName; }
        set { elemName = value; }
    }
    private String elemValue;

    public String ElemValue
    {
        get { return elemValue; }
        set { elemValue = value; }
    }
    private List<attribute> attributes;

    internal List<attribute> Attributes
    {
        get { return attributes; }
        set { attributes = value; }
    }

    private List<element> SubElems;

    internal List<element> subElems
    {
        get { return SubElems; }
        set { SubElems = value; }
    }

}

class attribute
{
    private String Name;

    public String AttName
    {
        get { return Name; }
        set { Name = value; }
    }
    private String value;

    public String AttValue
    {
        get { return this.value; }
        set { this.value = value; }
    }
}

Answer 1

创建element elem = new element();时，您永远不会将值分配给subElems，只会分配给elem.ElemName = xml.Name。因此，您得到NullReferenceException因为在subElems上，您在创建对象后拥有null。我重构了你的代码（请注意，我对element class）

一无所知

public element read(XmlReader xml)
{
    element elem = new element();
    while (xml.Read())
    {
        elem.ElemName = xml.Name;
        if (xml.HasAttributes)
        {
            for (int i = 0; i <= xml.AttributeCount; i++)
            {
                xml.MoveToNextAttribute();
                attribute attrib = new attribute();
                attrib.AttName = xml.Name;
                attrib.AttValue = xml.Value;
                elem.Attributes.Add(attrib);
            }
        }
        if (xml.IsEmptyElement)
        {   
            return elem;
        }
        else
        {
            elem.subElems = new List<element>(); //create new List of subelements
            elem.subElems.Add(read(xml)); 
            return elem;
        }
    }
    return elem;

或者

在element初始化subElems和Attributes的构造函数中定义

public element()
{
    this.subElems = new List<element>();
    this.Attributes = new List<attribute>();
}

或者

将您的字段声明更改为

private List<element> SubElems = new List<element>();
private List<attribute> attributes = new List<attribute>();

如何检查节点是否具有子元素

1 个答案:

或者

或者