(VB.NET) Async TaskCompleted Callback

Demonstrates the use of the TaskCompleted callback for async method calls (i.e. for Chilkat asynchronous methods where the method name ends with "Async").

NOTE: This is very important: The TaskCompleted callback runs in the background thread. (All callbacks from an async task, such as AbortCheck, PercentDone, ProgressInfo, etc. are in the background thread.) An application that uses TaskCompleted must be very careful. For example, user interface elements (such as labels, text boxes, etc.) may not be directly accessible from a background thread, and could crash the application if directly accessed. Also, attempting to debug code running in a background thread from an IDE is likely to crash the IDE.

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' TaskCompleted callback method.
Private Sub http_OnTaskCompleted(sender As Object, args As Chilkat.TaskCompletedEventArgs) Handles http.OnTaskCompleted

    Dim completedTask As Chilkat.Task = args.Task;
        ' A finished task could be one that was canceled, aborted, or truly finished.  

    ' If the task was "canceled", it was canceled prior to actually starting.  This could
    ' happen if the task was canceled while waiting in a thread pool queue to be scheduled by Chilkat's
    ' background thread pool scheduler.  

    ' If the task was "aborted", it indicates that it was canceled while running in a background thread.  
    ' The ResultErrorText will likely indicate that the task was aborted.

    ' If the task "completed", then it ran to completion, but the actual success/failure of the method
    ' is determined by the result obtained via a GetResult* method.  (A "completed" task will
    ' have a StatusInt equal to 7.   If the task finished, but was not completed, then it must've
    ' been aborted or canceled:
    If (completedTask.StatusInt <> 7) Then
        Debug.WriteLine("Task did not complete.")
        Debug.WriteLine("task status: " & completedTask.Status)
        Exit Sub
    End If


    ' The synchronous call to QuickGetObj would return an HTTP response object.  To get this 
    ' response object for the async call, we instantiate a new/empty HTTP response object,
    ' and then load it from the completed task.
    Dim resp As New Chilkat.HttpResponse

    Dim success As Boolean = resp.LoadTaskResult(completedTask)
    If (success <> True) Then
        Debug.WriteLine(resp.LastErrorText)
        Exit Sub
    End If


    ' Now that we have the response, we can get all of the information:

    Debug.WriteLine("status code: " & resp.StatusCode)
    Debug.WriteLine("response header: " & resp.Header)

    Dim xmlResponse As New Chilkat.Xml
    xmlResponse.LoadXml(resp.BodyStr)
    Debug.WriteLine(xmlResponse.GetXml())
End Sub

private Sub ChilkatExample()

    ' This example requires the Chilkat API to have been previously unlocked.
    ' See Global Unlock Sample for sample code.




    Dim WithEvents http As New Chilkat.Http

    Dim success As Boolean

    Dim soapXml As New Chilkat.Xml

    soapXml.Tag = "soap12:Envelope"
    success = soapXml.AddAttribute("xmlns:xsi","http://www.w3.org/2001/XMLSchema-instance")
    success = soapXml.AddAttribute("xmlns:xsd","http://www.w3.org/2001/XMLSchema")
    success = soapXml.AddAttribute("xmlns:soap12","http://www.w3.org/2003/05/soap-envelope")

    soapXml.NewChild2("soap12:Body","")
    success = soapXml.GetChild2(0)
    soapXml.NewChild2("GetCityWeatherByZIP","")
    success = soapXml.GetChild2(0)
    success = soapXml.AddAttribute("xmlns","http://ws.cdyne.com/WeatherWS/")
    soapXml.NewChild2("ZIP","60187")
    soapXml.GetRoot2()


    Debug.WriteLine(soapXml.GetXml())

    Dim req As New Chilkat.HttpRequest
    req.HttpVerb = "POST"
    req.SendCharset = False
    req.AddHeader("Content-Type","application/soap+xml; charset=utf-8")
    req.AddHeader("SOAPAction","http://ws.cdyne.com/WeatherWS/GetCityWeatherByZIP")
    req.Path = "/WeatherWS/Weather.asmx"
    success = req.LoadBodyFromString(soapXml.GetXml(),"utf-8")

    http.FollowRedirects = True

    ' The name of "SynchronousRequestAsync" method is somewhat confusing. This is explained here:

    ' Any Chilkat method that utilizes callbacks will have an Async version of the method.
    ' The name of the Async method is the method name appended with "Async".  For example,
    ' if the method is named "Abc", then the async method is "AbcAsync".
    ' The Async method always returns a Chilkat Task object.

    ' In the years prior to Chilkat introducing the Async functionality, this particular method's
    ' name was already "SynchronousRequest".  The async versionof the method is therefore
    ' "SynchronousRequestAsync" (just like "Abc" --> "AbcAsync").  Yes, it's confusing and we apologize.. 
    Dim task As Chilkat.Task = http.SynchronousRequestAsync("wsf.cdyne.com",80,False,req)
    If (http.LastMethodSuccess <> True) Then
        Debug.WriteLine(http.LastErrorText)
        Exit Sub
    End If


    ' Schedule the task for running on the thread pool.  This changes the task's state
    ' from Inert to Live.
    success = task.Run()
    If (success <> True) Then
        Debug.WriteLine(task.LastErrorText)

        Exit Sub
    End If


    ' The application is now free to do anything else
    ' while the HTTP request is in progress.  When the task
    ' is completed, the TaskCompleted method is called.



    ' -------------------------------------------------------------------------------
    ' The following is a general note that applies to all programming languages:
    ' -------------------------------------------------------------------------------

    ' NOTE: This is very important:  The TaskCompleted callback runs in the background thread.  
    ' (All callbacks from an async task, such as AbortCheck, PercentDone, ProgressInfo, etc. are in the background thread.) 
    ' An application that uses TaskCompleted must be very careful.  
    ' For example, user interface elements (such as labels, text boxes, etc.) may not be directly
    ' accessible from a background thread, and could crash the application if directly accessed.  Also, attempting to debug
    ' code running in a background thread from an IDE, especially an older IDE (such as VB6) is likely to crash the IDE.

End Sub