如何使用 HtmlAgilityPack 获取表单中的所有输入元素而不会出现空引用错误 [英] How to get all input elements in a form with HtmlAgilityPack without getting a null reference error
问题描述
示例 HTML:
<html><body>
<form id="form1">
<input name="foo1" value="bar1" />
<!-- Other elements -->
</form>
<form id="form2">
<input name="foo2" value="bar2" />
<!-- Other elements -->
</form>
</body></html>
测试代码:
HtmlDocument doc = new HtmlDocument();
doc.Load(@"D: est.html");
foreach (HtmlNode node in doc.GetElementbyId("form2").SelectNodes(".//input"))
{
Console.WriteLine(node.Attributes["value"].Value);
}
语句 doc.GetElementbyId("form2").SelectNodes(".//input") 给了我一个空引用.
The statement doc.GetElementbyId("form2").SelectNodes(".//input") gives me a null reference.
我做错了什么吗?谢谢.
Anything I did wrong? thanks.
推荐答案
您可以执行以下操作:
HtmlNode.ElementsFlags.Remove("form");
HtmlDocument doc = new HtmlDocument();
doc.Load(@"D: est.html");
HtmlNode secondForm = doc.GetElementbyId("form2");
foreach (HtmlNode node in secondForm.Elements("input"))
{
HtmlAttribute valueAttribute = node.Attributes["value"];
if (valueAttribute != null)
{
Console.WriteLine(valueAttribute.Value);
}
}
默认情况下，HTML Agility Pack 将表单解析为空节点，因为它们可以与其他 HTML 元素重叠.第一行 (HtmlNode.ElementsFlags.Remove("form");) 禁用此行为，允许您在第二个表单中获取输入元素.
By default HTML Agility Pack parses forms as empty node because they are allowed to overlap other HTML elements. The first line, (HtmlNode.ElementsFlags.Remove("form");) disables this behavior allowing you to get the input elements inside the second form.
更新:表单元素重叠示例:
<table>
<form>
<!-- Other elements -->
</table>
</form>
元素在表格内部开始，但在表格元素外部关闭.这在 HTML 规范中是允许的，并且 HTML Agility Pack 必须处理它.
The element begins inside a table but is closed outside the table element. This is allowed in the HTML specification and HTML Agility Pack has to deal with it.
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