I'm using the W3C validation service to check that the text I type into a TextBox is valid markup.
It's almost working. But, under particular conditions my input results in an error and then endless timeout exceptions. I have to close an re-open the program to get it working again.
Please glance over my code and help me to solve this issue.
I've got a pretty simple WPF application with a TextBox and a StatusBar. The StatusBar updates as I type to let me know if my typed markup is or is not valid. So that I'm not hammering the service, validations occur only after one second or longer has elapsed with no keystrokes.
It StatusBar may show: "Validating...", "Valid", "Invalid", or--if there's been one--an exception's message.
The following validates successfully:
XHTML Input
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xml:lang="en">
<head>
<title>Test</title>
</head>
<body>
<h1>Test</h1>
<p>This is a test</p>
</body>
</html>
If I break my paragraph like <p>This is a test</ then I get this exception while trying to process the response XML:
Name cannot begin with the '"' character, hexadecimal value 0x22. Line 86, position 40.
If validation fails like that twice in a row, then it seems I can't just fix my paragraph tags and continue on like normal. For some reason each subsequent validation fails with this exception:
The operation has timed out
This is very strange.
I'm sorry to post my whole project, but I don't know where my problem is coming from. It might be my threading, web service communication, exception handling... I just can't seem to find it. Am I closing my StreamWriter, HttpWebRequest, and ResponseStreams correctly?
XAML
<Window x:Class="Window1"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="W3C Validation"
Height="300"
Width="300"
Name="Window1">
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="*" />
<RowDefinition Height="Auto" />
</Grid.RowDefinitions>
<TextBox Grid.Row="0"
TextWrapping="Wrap"
AcceptsReturn="True"
VerticalScrollBarVisibility="Visible"
FontFamily="Consolas"
TextChanged="TextBox_TextChanged" />
<StatusBar Grid.Row="1">
<StatusBarItem>
<TextBlock x:Name="TextBlockResult" />
</StatusBarItem>
</StatusBar>
</Grid>
</Window>
Visual Basic
Imports System.ComponentModel
Imports <xmlns:env="http://www.w3.org/2003/05/soap-envelope">
Imports <xmlns:m="http://www.w3.org/2005/10/markup-validator">
Class Window1
Private WithEvents Worker As BackgroundWorker
Private _WorkerArgument As String
Private Sub Window1_Loaded(ByVal sender As System.Object, ByVal e As System.Windows.RoutedEventArgs) Handles MyBase.Loaded
InitializeWorker()
End Sub
Private Sub InitializeWorker()
Worker = New BackgroundWorker
Worker.WorkerSupportsCancellation = True
AddHandler Worker.DoWork, AddressOf Worker_DoWork
AddHandler Worker.RunWorkerCompleted, AddressOf Worker_RunWorkerCompleted
End Sub
Private Sub TextBox_TextChanged(ByVal sender As System.Object, ByVal e As System.Windows.Controls.TextChangedEventArgs)
TryToWork(DirectCast(sender, TextBox).Text)
End Sub
Sub TryToWork(ByVal Argument As String)
If _WorkerArgument IsNot Nothing Then
_WorkerArgument = Argument
Exit Sub
End If
If Not Worker.IsBusy Then
TextBlockResult.Text = "Validating..."
Worker.RunWorkerAsync(Argument)
Exit Sub
End If
_WorkerArgument = Argument
Worker.CancelAsync()
Dim RetryTimer As New Windows.Threading.DispatcherTimer
AddHandler RetryTimer.Tick, AddressOf RetryTicker
RetryTimer.Interval = New TimeSpan(1) '1 tick'
RetryTimer.Start()
End Sub
Sub RetryTicker(ByVal sender As Object, ByVal e As System.EventArgs)
If Not Worker.IsBusy Then
DirectCast(sender, Windows.Threading.DispatcherTimer).Stop()
TextBlockResult.Text = "Validating..."
Worker.RunWorkerAsync(_WorkerArgument)
_WorkerArgument = Nothing
End If
End Sub
Private Sub Worker_DoWork(ByVal sender As Object, ByVal e As DoWorkEventArgs)
'wait for one second'
Dim StartTime As DateTime = DateTime.Now()
While Now.Subtract(StartTime) < New TimeSpan(0, 0, 1)
If DirectCast(sender, BackgroundWorker).CancellationPending Then
e.Cancel = True
Exit Sub
End If
System.Threading.Thread.Sleep(New TimeSpan(0, 0, 0, 0, 100)) 'tenth of a second'
End While
'then validate'
e.Result = Validate(DirectCast(e.Argument, String))
End Sub
Private Function Validate(ByVal Text As String) As String
Try
Dim Url As String = "http://validator.w3.org/check"
Dim Post As String = "&fragment=" + Web.HttpUtility.UrlEncode(Text) + "&output=soap12"
Dim ResponseDocument As XDocument = XDocument.Load(New Xml.XmlTextReader(Communicate(Url, Post)))
If ResponseDocument.Root.<env:Body>.<m:markupvalidationresponse>.<m:validity>.Value = "true" Then
Return "Valid"
Else
Return "Invalid"
End If
Catch ex As Exception
Return ex.Message
End Try
End Function
Private Function Communicate(ByVal Url As String, ByVal Post As String) As System.IO.Stream
Dim Writer As System.IO.StreamWriter = Nothing
Dim Request As System.Net.HttpWebRequest = System.Net.WebRequest.Create(Url)
Request.Method = "POST"
Request.ContentLength = Post.Length
Request.ContentType = "application/x-www-form-urlencoded"
Request.Timeout = 2000 '2 seconds'
Try
Writer = New System.IO.StreamWriter(Request.GetRequestStream())
Writer.Write(Post)
Catch
Finally
If Not Writer Is Nothing Then
Writer.Close()
End If
End Try
Return Request.GetResponse.GetResponseStream()
End Function
Private Sub Worker_RunWorkerCompleted(ByVal sender As Object, ByVal e As RunWorkerCompletedEventArgs)
If Not e.Cancelled Then
TextBlockResult.Text = DirectCast(e.Result, String)
End If
End Sub
End Class
Thanks for any help!
-
On a first glance, I would recomend not trying to validate every time the text is changed. That can, and does, get a bit overwhelming. I fear that is what is going on here. Good job on making it Async as that will keep it from blocking but I also suspect it is hiding your issue.
Try having the TextChanged event set a flag to execute the validator and then just have the DoWork method run in a tight(ish) loop checking that flag. That will allow it time to complete and not get confused. It might take a second or two to get the correct data but shouldn't lock up.
Good luck.
bendewey : Additionally you could get blocked if you do this. It says in their docs http://validator.w3.org/docs/api.html that excessive use will get blocked.Zack Peterson : I've built in a 1-second-or-greater delay between each validation per their suggestion.
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