具有“指定强制转换无效”的Vb多线程错误 [英] Vb multithreading with “specified cast is not valid” error

问题描述

大家好..

如果我在没有线程的情况下运行下面的代码，那么一切都应该如此，但是当我以新线程启动时，我会收到System.InvalidCastException错误并显示已指定演员无效



预先感谢您提供任何帮助。

  Dim  thread1  As  新线程（ AddressOf  th10）
 
 私有  Sub  Form3_Load（发件人作为 对象， e  As  EventArgs）句柄  MyBase 。载荷
 CheckForIllegalCrossThreadCalls =  False  
 Button1.PerformClick（）
 结束  Sub  
 
 私有  Sub  Button1_Click（发件人作为 对象，e  As  EventArgs）句柄 Button1.Click 
 thread1.Start（）
 结束  Sub  
 
 公共  Sub  th10（）
 WebBrowser3.Navigate（  https：// www .somewebsite.com）
   WebBrowser3.ReadyState<> WebBrowserReadyState.Complete 
 Application.DoEvents（）
 结束   
 
  Dim  pos4 作为 长 
  Dim  bp2 作为 字符串 
 
  Dim  value1  As   String  = WebBrowser3.Document.Body.InnerText 
 
 pos4 = InStr（pos4 +  1 ，value1，  sometextfromwebsite，vbTextCompare）
 bp2 = value1.Substring（pos4）
  Dim  startIndex1 作为 整数 =  17  
  Dim  length1 作为 整数 =  16  
  Dim  substring1  As  字符串 = bp2.Substring（startIndex1，length1）
 
 TextBox3.Text = substring1 
 结束  Sub  
 

我有什么试过：



此错误显示在While WebBrowser3.ReadyState ...以及我将其更改为;

 静态 start 作为 单 
 start = VB.Timer（）
   而 VB.Timer（）< start +  5  
 Application.DoEvents（）
  Loop  

（我不喜欢指定页面加载时间的想法，在某些情况下可能需要更长时间）



......似乎没问题，但是我在Dim value1 As String = WebBrowser3.Document.Body.InnerText

解决方案

错误报告！

您忘记了URL末尾的引用

 公共  Sub  th10（）
 WebBrowser3.Navigate（  https://somewebsite.com）
 '  ^缺失引用此处 

此代码无效。

Hi all..
If I run the code below without threading everything works like it should, but when I start it as a new thread then I receive ‘System.InvalidCastException’ error with "Specified cast is not valid"

Thanks in advance for any help you can provide.

Dim thread1 As New Thread(AddressOf th10)

Private Sub Form3_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    CheckForIllegalCrossThreadCalls = False
    Button1.PerformClick()
End Sub

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    thread1.Start()
End Sub

Public Sub th10()
    WebBrowser3.Navigate("https://www.somewebsite.com")
    While WebBrowser3.ReadyState <> WebBrowserReadyState.Complete
        Application.DoEvents()
    End While

    Dim pos4 As Long
    Dim bp2 As String

    Dim value1 As String = WebBrowser3.Document.Body.InnerText

    pos4 = InStr(pos4 + 1, value1, "sometextfromwebsite", vbTextCompare)
    bp2 = value1.Substring(pos4)
    Dim startIndex1 As Integer = 17
    Dim length1 As Integer = 16
    Dim substring1 As String = bp2.Substring(startIndex1, length1)

    TextBox3.Text = substring1
End Sub

What I have tried:

This error shows at "While WebBrowser3.ReadyState…" and when I change it to;

Static start As Single
start = VB.Timer()
Do While VB.Timer() < start + 5
Application.DoEvents()
Loop

(I don’t like the idea to specify a time for page load, in some cases it might take longer)

…it seems to be fine, but then I receive the same error on "Dim value1 As String = WebBrowser3.Document.Body.InnerText"

解决方案

Bug report !
you forgot a quote at the end of URL

Public Sub th10()
       WebBrowser3.Navigate("https://somewebsite.com")
       '                                            ^ missing quote here

this code can't have worked.

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