选择divs并使用htmlagilitypack放入集合中不起作用 [英] select divs and put into collection using htmlagilitypack not working

问题描述

为什么这不起作用?在启动时，foreach循环上出现空引用异常错误

Why does this not work? I get a null reference exception error on the foreach loop as it starts

我正在尝试在页面上获取所有div文本，并将每个文本放入我自己的收藏夹中

I'm trying to get all the divs text on a page and put each one into my own collection

Imports HtmlAgilityPack
Imports System.Xml

Partial Class _Default
    Inherits System.Web.UI.Page

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

        Dim webGet As HtmlWeb = New HtmlWeb
        Dim htmlDoc As HtmlDocument = webGet.Load("http://www.mysite.com")

        Dim ids As New List(Of String)()

        For Each div As Object In htmlDoc.DocumentNode.SelectNodes("//div")

            ids.Add(div.InnerText)

        Next



    End Sub
End Class

例外

exception

对象引用未设置为对象的实例.说明: 当前Web执行期间发生未处理的异常 要求.请查看堆栈跟踪以获取有关以下内容的更多信息: 错误及其在代码中的起源.

Object reference not set to an instance of an object. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

异常详细信息:System.NullReferenceException:没有对象引用 设置为对象的实例.

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

源错误:

第12行:Dim ids作为新列表(字符串)() 第13行:
第14行:对于htmlDoc.DocumentNode.SelectNodes("//div")中的每个div作为对象 第15行:
第16行:ids.Add(div.InnerText)

Line 12: Dim ids As New List(Of String)() Line 13:
Line 14: For Each div As Object In htmlDoc.DocumentNode.SelectNodes("//div") Line 15:
Line 16: ids.Add(div.InnerText)

推荐答案

您的代码看起来正确. URL"http://www.mysite.com"可能未返回有效的HTML.

Your code looks correct. Perhaps the URL "http://www.mysite.com" is not returning a valid HTML.

以下代码有效:

Imports HtmlAgilityPack

Public Class _Default
    Inherits System.Web.UI.Page

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        Dim webGet As HtmlWeb = New HtmlWeb
        Dim htmlDoc As HtmlDocument = webGet.Load("http://stackoverflow.com/q/11528387/1350308")

        Dim ids As New List(Of String)()
        TextBox1.Text = ""
        For Each div As HtmlNode In htmlDoc.DocumentNode.SelectNodes("//div")
            TextBox1.Text += div.Id + Environment.NewLine
        Next
    End Sub

End Class

TextBox1中的结果是:

The result in TextBox1 is:

noscript-padding
notify-container
overlay-header
custom-header

header
portalLink
topbar
hlinks
hsearch

hlogo
hmenus


content

question-header
mainbar
question
adzerk1

















comments-11528387


answers
answers-header

tabs
answer-11528559








comments-11528559

post-editor

wmd-button-bar

draft-saved
draft-discarded
wmd-preview









sidebar
newuser-box



adzerk2
hireme



























feed-link
feed-link-text

prettify-lang
footer

footer-menu
footer-sites
footer-flair
svnrev
copyright
noscript-warning

完整源代码: Q11528387WebApp.7z

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