FileWebRequest.BeginGetResponse Method (AsyncCallback, Object)

 

Begins an asynchronous request for a file system resource.

Namespace:   System.Net
Assembly:  System (in System.dll)

<HostProtectionAttribute(SecurityAction.LinkDemand, ExternalThreading := True)>
Public Overrides Function BeginGetResponse (
	callback As AsyncCallback,
	state As Object
) As IAsyncResult

Parameters

callback
Type: System.AsyncCallback

The AsyncCallback delegate.

state
Type: System.Object

An object that contains state information for this request.

Return Value

Type: System.IAsyncResult

An IAsyncResult that references the asynchronous request.

Exception Condition
InvalidOperationException

The stream is already in use by a previous call to BeginGetResponse.

WebException

The FileWebRequest was aborted.

The asynchronous callback method that implements the AsyncCallback delegate uses the EndGetResponse method to return the actual FileWebResponse.

The following code example uses the BeginGetResponse method to asynchronously access a file system resource.

Public Class RequestDeclare
    Public myFileWebRequest As FileWebRequest

    Public Sub New()
        myFileWebRequest = Nothing
    End Sub ' New
End Class ' RequestDeclare



Class FileWebRequest_resbeginend

    Public Shared allDone As New ManualResetEvent(False)

    ' Entry point which delegates to C-style main Private Function.
    Public Overloads Shared Sub Main()
        Main(GetCommandLineArgs())
    End Sub

    Overloads Shared Sub Main(args() As String)

        If args.Length < 2 Then
            Console.WriteLine(ControlChars.Cr + "Please enter the file name as command line parameter:")
            Console.WriteLine("Usage:FileWebRequest_resbeginend " + ChrW(60) + "systemname" + ChrW(62) + "/" + ChrW(60) + "sharedfoldername" + ChrW(62) + "/" + ChrW(60) + "filename" + ChrW(62) + ControlChars.Cr + "Example:FileWebRequest_resbeginend shafeeque/shaf/hello.txt")

        Else
            Try

                ' Place a webrequest.
                Dim myWebRequest As WebRequest = WebRequest.Create(("file://" + args(1)))
                ' Create an instance of the 'RequestDeclare' and associating the 'myWebRequest' to it.		
                Dim myRequestDeclare As New RequestDeclare()
                myRequestDeclare.myFileWebRequest = CType(myWebRequest, FileWebRequest)

                ' Begin the Asynchronous request for getting file content using 'BeginGetResponse()' method.	
                 Dim asyncResult As IAsyncResult = CType(myRequestDeclare.myFileWebRequest.BeginGetResponse(AddressOf RespCallback, myRequestDeclare), IAsyncResult)
                 allDone.WaitOne()


            Catch e As ArgumentNullException
                Console.WriteLine(("ArgumentNullException is :" + e.Message))
            Catch e As UriFormatException
                Console.WriteLine(("UriFormatException is :" + e.Message))
            End Try
        End If
    End Sub ' Main


    Private Shared Sub RespCallback(ar As IAsyncResult)



        ' State of request is asynchronous.
        Dim requestDeclare As RequestDeclare = CType(ar.AsyncState, RequestDeclare)

        Dim myFileWebRequest As FileWebRequest = requestDeclare.myFileWebRequest

        ' End the Asynchronus request by calling the 'EndGetResponse()' method.
        Dim myFileWebResponse As FileWebResponse = CType(myFileWebRequest.EndGetResponse(ar), FileWebResponse)

        ' Reade the response into Stream.
        Dim streamReader As New StreamReader(myFileWebResponse.GetResponseStream())


        Dim readBuffer(256) As [Char]

        Dim count As Integer = streamReader.Read(readBuffer, 0, 256)

        Console.WriteLine("The contents of the file are :"+ControlChars.Cr)

        While count > 0
            Dim str As New [String](readBuffer, 0, count)
            Console.WriteLine(str)
            count = streamReader.Read(readBuffer, 0, 256)
        End While
	     streamReader.Close()
        ' Release the response object resources.
	     myFileWebResponse.Close()
        allDone.Set()
        Console.WriteLine("File reading is over.")
    End Sub ' RespCallback 
End Class ' FileWebRequest_resbeginend

.NET Framework
Available since 1.1
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