lblResult is listbox Control
我作测试时第一按过程进行时node.FirstChild.Value的有值,当第二次进行到node.FirstChild.Value时值为空的。请问怎么改呀
异常详细信息: System.NullReferenceException: 未将对象引用设置到对象的实例。源错误:
行 42: {
行 43: lblResult.Items.Add("node name;" +node.Name);
行 44: lblResult.Items.Add("node value:"+node.FirstChild.Value );
行 45: }
行 46: 源文件: c:\Inetpub\wwwroot\Chapter6\gg.aspx.cs I 行: 44Program:
protected void Page_Load(object sender, EventArgs e)
{
if (!Page.IsPostBack)
{
ddlExpression.Items.Add("//book/title");
ddlExpression.Items.Add("//book[@genre='novel']/title");
ddlExpression.Items.Add("//book/author/first-name");
ddlExpression.Items.Add("//book/[@genre='philosopohy']/title");
ddlExpression.Items.Add("//book/price");
ddlExpression.Items.Add("//book[3]/title");
ddlExpression.SelectedIndex = 0;
//set the default selection
UpdateDisplay();
} } public void UpdateDisplay()
{
lblResult.Items.Clear();//clear content
string xmlPath = @"C:\Inetpub\wwwroot\Chapter6\books.xml";
XmlDocument doc = new XmlDocument();
doc.Load(xmlPath);
XmlNodeList docList = doc.DocumentElement.SelectNodes(ddlExpression.SelectedItem.Text); foreach (XmlNode node in docList)
{
lblResult.Items.Add("node name;" +node.Name);
lblResult.Items.Add("node value:"+node.FirstChild.Value );//????????此句有问题不能通过编译 。
}
}
protected void ddlExpression_SelectedIndexChanged(object sender, EventArgs e)
{
UpdateDisplay();
}
我作测试时第一按过程进行时node.FirstChild.Value的有值,当第二次进行到node.FirstChild.Value时值为空的。请问怎么改呀
异常详细信息: System.NullReferenceException: 未将对象引用设置到对象的实例。源错误:
行 42: {
行 43: lblResult.Items.Add("node name;" +node.Name);
行 44: lblResult.Items.Add("node value:"+node.FirstChild.Value );
行 45: }
行 46: 源文件: c:\Inetpub\wwwroot\Chapter6\gg.aspx.cs I 行: 44Program:
protected void Page_Load(object sender, EventArgs e)
{
if (!Page.IsPostBack)
{
ddlExpression.Items.Add("//book/title");
ddlExpression.Items.Add("//book[@genre='novel']/title");
ddlExpression.Items.Add("//book/author/first-name");
ddlExpression.Items.Add("//book/[@genre='philosopohy']/title");
ddlExpression.Items.Add("//book/price");
ddlExpression.Items.Add("//book[3]/title");
ddlExpression.SelectedIndex = 0;
//set the default selection
UpdateDisplay();
} } public void UpdateDisplay()
{
lblResult.Items.Clear();//clear content
string xmlPath = @"C:\Inetpub\wwwroot\Chapter6\books.xml";
XmlDocument doc = new XmlDocument();
doc.Load(xmlPath);
XmlNodeList docList = doc.DocumentElement.SelectNodes(ddlExpression.SelectedItem.Text); foreach (XmlNode node in docList)
{
lblResult.Items.Add("node name;" +node.Name);
lblResult.Items.Add("node value:"+node.FirstChild.Value );//????????此句有问题不能通过编译 。
}
}
protected void ddlExpression_SelectedIndexChanged(object sender, EventArgs e)
{
UpdateDisplay();
}
foreach (XmlNode node in docList)
{
lblResult.Items.Add("node name;" +node.Name);
if(node.FirstChild != null)
{
lblResult.Items.Add("node value:"+node.FirstChild.Value );//????????此句有问题不能通过编译 。
}
}