Not Connecting to website in New Thread
I have hit a road bump. I have been piecing together bits of code that I have found and customized it to work with my app. Now the following code works find out of a separate thread, but as soon as I put it into its on threads it doesn't want to connect.
Any suggestions?
Code:
Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
getAlexaNow = New Thread(AddressOf ThreadTask)
getAlexaNow.IsBackground = True
getAlexaNow.Start()
End Sub
Private Sub ThreadTask()
Dim intList As Integer
Dim strAlexa As String
intList = "0"
strSearch = txtSearch.Text
Do Until intList = linksList.Items.Count
Dim linkUrl As String = "http://www.alexa.com/search?q=" & linksList.Items.Item(intList)
Try
Dim myResponse As Net.HttpWebResponse = Net.HttpWebRequest.Create(linkUrl).GetResponse '// connect.
Dim myStream As IO.Stream = myResponse.GetResponseStream() '// get.
Dim myReader As New IO.StreamReader(myStream) '// read.
Dim myWebFileInfo As String = myReader.ReadToEnd '// get innerHtml of Page.
myReader.Close() : myStream.Close() : myResponse.Close() '// close reader, information stream, and connection.
RichTextBox3.Text = myWebFileInfo
If InStr(myWebFileInfo, "No regional data") Then
alexaList.Items.Add((linksList.Items.Item(intList)) & ":" & "No Alexa rank")
Exit Try
End If
'// get location of <pre> by index.
Dim myStartIndex As Integer = myWebFileInfo.IndexOf(">US</a>:") + 8 '// add +5 to not add "<pre>" to final result.
'// get location of </pre> by index.
Dim myEndIndex As Integer = myWebFileInfo.IndexOf(" </li>")
'// subtract to get a total number for the substring length result.
Dim myStringLengthToExtract As Integer = myEndIndex - myStartIndex
'// display result.
strAlexa = myWebFileInfo.Substring(myStartIndex, myStringLengthToExtract)
If InStr(strAlexa, "XHTML") Then
alexaList.Items.Add((linksList.Items.Item(intList)) & ":" & "No Alexa rank")
Else
If InStr(strAlexa, "%%") Then
Else
alexaList.Items.Add((linksList.Items.Item(intList)) & ":" & strAlexa)
End If
End If
Catch ex As Exception
MsgBox("Connection Error.", MsgBoxStyle.Critical, "myCool Error Message")
End Try
intList = intList + 1
Loop
End Sub
Re: Not Connecting to website in New Thread
If you are using a control on a thread that is different from the one it was created upon, you will usually get an exception. ie. alexaList.Items.Add
You must do all work for a control on the thread it was created upon.
To add, this line here: Catch ex As Exception, tells you what the problem is, you are actually ignoring it. It tells you the real problem. Use this instead of your existing MsgBox.
Code:
MessageBox.Show("Connection Error - " & ex.Message)
Re: Not Connecting to website in New Thread
Quote:
Originally Posted by
Grimfort
If you are using a control on a thread that is different from the one it was created upon, you will usually get an exception. ie.
alexaList.Items.Add
You must do all work for a control on the thread it was created upon.
To add, this line here:
Catch ex As Exception, tells you what the problem is, you are actually ignoring it. It tells you the real problem. Use this instead of your existing MsgBox.
Code:
MessageBox.Show("Connection Error - " & ex.Message)
Ok great! Thanks so much for your response.
This is the detailed error message.
Code:
Connection error - crosss-thread operation not valid: Control 'alexList' accessed from a thread other than the thread it was created on.
I'm wondering what I have to change because alexaList is a simlpe list box.
Here is my entire code.
Code:
Imports System.Text.RegularExpressions
Imports System.Net
Imports System.Text
Imports System.Threading
Public Class Form1
Private Property str33 As Object
Dim strNum As Integer
Dim strSearch As String
Private getAlexaNow As Thread
Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
' Dim linkurl As String
'linkurl = "http://www.860designs.com/check.txt"
' Dim myResponse As Net.HttpWebResponse = Net.HttpWebRequest.Create(linkUrl).GetResponse '// connect.
'' Dim myStream As IO.Stream = myResponse.GetResponseStream() '// get.
' Dim myReader As New IO.StreamReader(myStream) '// read.
' Dim myWebFileInfo As String = myReader.ReadToEnd '// get innerHtml of Page.
' Dim strUser As String
'// close reader, information stream, and connection.
' myReader.Close() : myStream.Close() : myResponse.Close()
' strUser = InputBox("username")
' If InStr(myWebFileInfo, strUser) Then
' Else
' Me.Close()
' Exit Sub
' End If
End Sub
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
WebBrowser1.Navigate("http://www.google.com/search?tbm=blg&hl=en&source=hp&biw=&bih=&q=" & strSearch & "&btnG=Search")
strNum = 1
strNum = 10
tmrBroswer.Enabled = True
End Sub
Private Sub WebBrowser1_DocumentCompleted(ByVal sender As Object, ByVal e As System.Windows.Forms.WebBrowserDocumentCompletedEventArgs) Handles WebBrowser1.DocumentCompleted
'For every link in the current document...
For Each ele As HtmlElement In WebBrowser1.Document.Links
'Get whatever text there is in the 'href' attribute
Dim eletarget As String = ele.GetAttribute("href")
Dim eletargetNew As String
'Add it to the listbox
If InStr(eletarget, "google.com") Then
ElseIf InStr(eletarget, "youtube.com") Then
ElseIf InStr(eletarget, "wdyl.com") Then
ElseIf InStr(eletarget, "javascript") Then
Else
Dim myStartIndex As Integer = eletarget.IndexOf("h") + 1 '// add +5 to not add "<pre>" to final result.
'// get location of </pre> by index.
Dim myEndIndex As Integer = eletarget.IndexOf("com") + 3
'// subtract to get a total number for the substring length result.
Dim myStringLengthToExtract As Integer = myEndIndex - myStartIndex
'// display result.
eletargetNew = eletarget.Substring(myStartIndex, myStringLengthToExtract)
If eletargetNew = "t" Then
Else
linksList.Items.Add("h" & eletargetNew)
End If
End If
'Carry on to the next link
Next
'strNum = strNum + 10
' Dim strSearch As String
' strSearch = txtSearch.Text
' If strNum > 100 Then
'Exit Sub
' End If
If tmrBroswer.Enabled = False Then
tmrBroswer.Enabled = False
Exit Sub
End If
tmrBroswer.Enabled = True
End Sub
Private Sub tmrBroswer_Tick(ByVal sender As Object, ByVal e As System.EventArgs) Handles tmrBroswer.Tick
Dim intStop As Integer
strSearch = txtSearch.Text
If intStop >= 5 Then
Exit Sub
tmrBroswer.Enabled = False
End If
WebBrowser1.Navigate("http://www.google.com/search?tbm=blg&hl=en&source=hp&biw=&bih=&q=" & strSearch & "&btnG=Search&start=" & strNum)
intStop = intStop + 1
strNum = strNum + 10
End Sub
Private Sub cmdStop_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdStop.Click
tmrBroswer.Enabled = False
End Sub
Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
getAlexaNow = New Thread(AddressOf ThreadTask)
getAlexaNow.IsBackground = True
getAlexaNow.Start()
End Sub
Private Sub ThreadTask()
Dim intList As Integer
Dim strAlexa As String
intList = "0"
strSearch = txtSearch.Text
Do Until intList = linksList.Items.Count
Dim linkUrl As String = "http://www.alexa.com/search?q=" & linksList.Items.Item(intList)
Try
Dim myResponse As Net.HttpWebResponse = Net.HttpWebRequest.Create(linkUrl).GetResponse '// connect.
Dim myStream As IO.Stream = myResponse.GetResponseStream() '// get.
Dim myReader As New IO.StreamReader(myStream) '// read.
Dim myWebFileInfo As String = myReader.ReadToEnd '// get innerHtml of Page.
myReader.Close() : myStream.Close() : myResponse.Close() '// close reader, information stream, and connection.
If InStr(myWebFileInfo, "No regional data") Then
alexaList.Items.Add((linksList.Items.Item(intList)) & ":" & "No Alexa rank")
Exit Try
End If
'// get location of <pre> by index.
Dim myStartIndex As Integer = myWebFileInfo.IndexOf(">US</a>:") + 8 '// add +5 to not add "<pre>" to final result.
'// get location of </pre> by index.
Dim myEndIndex As Integer = myWebFileInfo.IndexOf(" </li>")
'// subtract to get a total number for the substring length result.
Dim myStringLengthToExtract As Integer = myEndIndex - myStartIndex
'// display result.
strAlexa = myWebFileInfo.Substring(myStartIndex, myStringLengthToExtract)
If InStr(strAlexa, "XHTML") Then
alexaList.Items.Add((linksList.Items.Item(intList)) & ":" & "No Alexa rank")
Else
If InStr(strAlexa, "%%") Then
Else
alexaList.Items.Add((linksList.Items.Item(intList)) & ":" & strAlexa)
End If
End If
Catch ex As Exception
MsgBox("Connection Error - " & ex.Message)
End Try
intList = intList + 1
Loop
End Sub
Private Sub alexaList_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles alexaList.SelectedIndexChanged
Dim aLink As String
Dim aLinkNew As String
aLink = alexaList.SelectedItem.ToString
Dim myStartIndex As Integer = aLink.IndexOf("h") + 1 '// add +5 to not add "<pre>" to final result.
'// get location of </pre> by index.
Dim myEndIndex As Integer = aLink.IndexOf("com") + 3
'// subtract to get a total number for the substring length result.
Dim myStringLengthToExtract As Integer = myEndIndex - myStartIndex
'// display result.
aLinkNew = aLink.Substring(myStartIndex, myStringLengthToExtract)
If aLinkNew = "t" Then
Else
alexaBrowser.Navigate("h" & aLinkNew)
End If
End Sub
End Class
Re: Not Connecting to website in New Thread
So the exception tells you that you are trying to change a control on a different thread then the one it was created upon :).
Here is an example on how to start doing this here, or you could use an extension (advanced, but makes it easier after).
Re: Not Connecting to website in New Thread
Quote:
Originally Posted by
Grimfort
So the exception tells you that you are trying to change a control on a different thread then the one it was created upon :).
Here is an example on how to start doing this
here, or you could use an
extension (advanced, but makes it easier after).
Thank you so much for all of your help. I have taken a look at the thread, but couldn't be more confused. :eek:
I will review it again, but I fear this may cause me to hit a road block.
Re: Not Connecting to website in New Thread
Do not be too worried. Instead of directly using threads, M$ have created the BackgroundWorker control that can do most of this stuff for you. It has special events where you can access controls without this error.
Re: Not Connecting to website in New Thread
Quote:
Originally Posted by
Grimfort
Do not be too worried. Instead of directly using threads, M$ have created the
BackgroundWorker control that can do most of this stuff for you. It has special events where you can access controls without this error.
Ok great! I will definetly read into the M$ solution. Thanks for all of your help!
Re: Not Connecting to website in New Thread
I have moved my task into a background worker sub, but I am still having the same error.
Code:
Imports System.Text.RegularExpressions
Imports System.Net
Imports System.Text
Imports System.Threading
Public Class Form1
Private Property str33 As Object
Dim strNum As Integer
Dim strSearch As String
Private getAlexaNow As Thread
Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
' Dim linkurl As String
'linkurl = "http://www.860designs.com/check.txt"
' Dim myResponse As Net.HttpWebResponse = Net.HttpWebRequest.Create(linkUrl).GetResponse '// connect.
'' Dim myStream As IO.Stream = myResponse.GetResponseStream() '// get.
' Dim myReader As New IO.StreamReader(myStream) '// read.
' Dim myWebFileInfo As String = myReader.ReadToEnd '// get innerHtml of Page.
' Dim strUser As String
'// close reader, information stream, and connection.
' myReader.Close() : myStream.Close() : myResponse.Close()
' strUser = InputBox("username")
' If InStr(myWebFileInfo, strUser) Then
' Else
' Me.Close()
' Exit Sub
' End If
End Sub
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
WebBrowser1.Navigate("http://www.google.com/search?tbm=blg&hl=en&source=hp&biw=&bih=&q=" & strSearch & "&btnG=Search")
strNum = 1
strNum = 10
tmrBroswer.Enabled = True
End Sub
Private Sub WebBrowser1_DocumentCompleted(ByVal sender As Object, ByVal e As System.Windows.Forms.WebBrowserDocumentCompletedEventArgs) Handles WebBrowser1.DocumentCompleted
'For every link in the current document...
For Each ele As HtmlElement In WebBrowser1.Document.Links
'Get whatever text there is in the 'href' attribute
Dim eletarget As String = ele.GetAttribute("href")
Dim eletargetNew As String
'Add it to the listbox
If InStr(eletarget, "google.com") Then
ElseIf InStr(eletarget, "youtube.com") Then
ElseIf InStr(eletarget, "wdyl.com") Then
ElseIf InStr(eletarget, "javascript") Then
Else
Dim myStartIndex As Integer = eletarget.IndexOf("h") + 1 '// add +5 to not add "<pre>" to final result.
'// get location of </pre> by index.
Dim myEndIndex As Integer = eletarget.IndexOf("com") + 3
'// subtract to get a total number for the substring length result.
Dim myStringLengthToExtract As Integer = myEndIndex - myStartIndex
'// display result.
eletargetNew = eletarget.Substring(myStartIndex, myStringLengthToExtract)
If eletargetNew = "t" Then
Else
linksList.Items.Add("h" & eletargetNew)
End If
End If
'Carry on to the next link
Next
'strNum = strNum + 10
' Dim strSearch As String
' strSearch = txtSearch.Text
' If strNum > 100 Then
'Exit Sub
' End If
If tmrBroswer.Enabled = False Then
tmrBroswer.Enabled = False
Exit Sub
End If
tmrBroswer.Enabled = True
End Sub
Private Sub tmrBroswer_Tick(ByVal sender As Object, ByVal e As System.EventArgs) Handles tmrBroswer.Tick
Dim intStop As Integer
strSearch = txtSearch.Text
If intStop >= 5 Then
Exit Sub
tmrBroswer.Enabled = False
End If
WebBrowser1.Navigate("http://www.google.com/search?tbm=blg&hl=en&source=hp&biw=&bih=&q=" & strSearch & "&btnG=Search&start=" & strNum)
intStop = intStop + 1
strNum = strNum + 10
End Sub
Private Sub cmdStop_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdStop.Click
tmrBroswer.Enabled = False
End Sub
Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
Me.BackgroundWorker1.RunWorkerAsync()
End Sub
Private Sub BackgroundWorker1_DoWork(ByVal sender As Object, _
ByVal e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork
Dim worker As System.ComponentModel.BackgroundWorker = DirectCast(sender, System.ComponentModel.BackgroundWorker)
For i As Integer = 1 To 100
'Raise the ProgressChanged event in the UI thread.
worker.ReportProgress(i, i & " iterations complete")
Dim intList As Integer
Dim strAlexa As String
intList = "0"
strSearch = txtSearch.Text
Do Until intList = linksList.Items.Count
Dim linkUrl As String = "http://www.alexa.com/search?q=" & Me.linksList.Items.Item(intList)
Try
Dim myResponse As Net.HttpWebResponse = Net.HttpWebRequest.Create(linkUrl).GetResponse '// connect.
Dim myStream As IO.Stream = myResponse.GetResponseStream() '// get.
Dim myReader As New IO.StreamReader(myStream) '// read.
Dim myWebFileInfo As String = myReader.ReadToEnd '// get innerHtml of Page.
myReader.Close() : myStream.Close() : myResponse.Close() '// close reader, information stream, and connection.
If InStr(myWebFileInfo, "No regional data") Then
Me.alexaList.Items.Add((Me.linksList.Items.Item(intList)) & ":" & "No Alexa rank")
Exit Try
End If
'// get location of <pre> by index.
Dim myStartIndex As Integer = myWebFileInfo.IndexOf(">US</a>:") + 8 '// add +5 to not add "<pre>" to final result.
'// get location of </pre> by index.
Dim myEndIndex As Integer = myWebFileInfo.IndexOf(" </li>")
'// subtract to get a total number for the substring length result.
Dim myStringLengthToExtract As Integer = myEndIndex - myStartIndex
'// display result.
strAlexa = myWebFileInfo.Substring(myStartIndex, myStringLengthToExtract)
If InStr(strAlexa, "XHTML") Then
Me.alexaList.Items.Add((Me.linksList.Items.Item(intList)) & ":" & "No Alexa rank")
Else
If InStr(strAlexa, "%%") Then
Else
Me.alexaList.Items.Add((Me.linksList.Items.Item(intList)) & ":" & strAlexa)
End If
End If
Catch ex As Exception
MsgBox("Connection Error - " & ex.Message)
End Try
intList = intList + 1
Loop
Threading.Thread.Sleep(250)
Next i
End Sub
Private Sub BackgroundWorker1_ProgressChanged(ByVal sender As Object, _
ByVal e As System.ComponentModel.ProgressChangedEventArgs) Handles BackgroundWorker1.ProgressChanged
Me.ProgressBar1.Value = e.ProgressPercentage
Me.lblStatus.Text = TryCast(e.UserState, String)
End Sub
'This method is executed in the UI thread.
Private Sub BackgroundWorker1_RunWorkerCompleted(ByVal sender As Object, _
ByVal e As System.ComponentModel.RunWorkerCompletedEventArgs) Handles BackgroundWorker1.RunWorkerCompleted
Me.lblStatus.Text = "Operation complete"
End Sub
Private Sub alexaList_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs)
Dim aLink As String
Dim aLinkNew As String
aLink = alexaList.SelectedItem.ToString
Dim myStartIndex As Integer = aLink.IndexOf("h") + 1 '// add +5 to not add "<pre>" to final result.
'// get location of </pre> by index.
Dim myEndIndex As Integer = aLink.IndexOf("com") + 3
'// subtract to get a total number for the substring length result.
Dim myStringLengthToExtract As Integer = myEndIndex - myStartIndex
'// display result.
aLinkNew = aLink.Substring(myStartIndex, myStringLengthToExtract)
If aLinkNew = "t" Then
Else
alexaBrowser.Navigate("h" & aLinkNew)
End If
End Sub
End Class
Any suggestions?
Re: Not Connecting to website in New Thread
Yes, read the documentation! Don't just read it, really read it! It has a note in bright yellow that specifically states:
Quote:
You must be careful not to manipulate any user-interface objects in your DoWork event handler. Instead, communicate to the user interface through the ProgressChanged and RunWorkerCompleted events.
All you have done is thrown your code into the DoWork method. You need to seperate out the links into a list/collection/array, then put the answers into another list/collection/array. When you are ready to .ReportProgress and then put the answers from the list into the controls on the form.
Re: Not Connecting to website in New Thread
The OP has sent me PM asking for more help, so I will repost in here some questions to help him/her out.
In your DoWork method, this is the first time you use a control. The answer is you don't.
Do Until intList = linksList.Items.Count
Dim linkUrl As String = "http://www.alexa.com/search?q=" & Me.linksList.Items.Item(intList)
Before you even start DoWork, you need to extract the data into a list:
Code:
Private Links As New Generic.List(Of String)
Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
For Each strItem As String Me.linksList.Items
Links.Add(strItem)
Next
Me.BackgroundWorker1.RunWorkerAsync()
End Sub
'Then in the DoWork you use the Links list not the control
For Each strItem As String In Links
.....
Next
Note, this is an example, you can use a string array instead of a List(Of) or you might use a queue instead, possibly you might use a Items.CopyTo. Different people use different methods depending on their use or preference.
