Download File Using Multithreading in Windows Forms

This article explains how to download's file using multi threading. Let's discuss about threading in brief? Whether you are developing for computers with one processor or several, you want your application to provide the most responsive interaction with the user, even if the application is currently doing other work. Using multiple threads of execution is one of the most powerful ways to keep your application responsive to the user and at the same time make use of the processor in between or even during user events. While this section introduces the basic concepts of threading, it focuses on managed threading concepts and using managed threading.

Let's start now first of all create a new window application.

' Threading namespace
Imports System.Threading
' Local variable declarations
Protected WebClient1 As System.Net.WebClient
Protected workerThread As Thread

Here is my start download button click event code:

    ''' <summary>
    ''' Start Button click event handler
    ''' </summary>
    ''' <param name="sender"></param>
    ''' <param name="e"></param>
    ''' <remarks></remarks>
    Private Sub StartButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles StartButton.Click

        ' Update Status
        'StatusListBox.Items.Add("Download Started.")

        ' Start worker thread that will call Download and Process methods
        Try
            workerThread = New Thread(New ThreadStart(AddressOf DownloadAndProcessFiles))
            workerThread.Start()
        Catch ex As Exception
            Dim str As String = ex.Message

        Finally

            '' If there is a problem
            'If workerThread.IsAlive Then
            '    workerThread.Abort()
            'End If
        End Try

        ' Update status
    End Sub

Here is download functions

Private Sub DownloadAndProcessFiles()
        Dim WebClient1 As New System.Net.WebClient
        If StatusListBox.InvokeRequired Then
            StatusListBox.Invoke(New MethodInvoker(AddressOf DownloadAndProcessFiles), New Object() {})
            Exit Sub
        End If
        StatusListBox.Items.Add("DownloadTest 1 Started")
        Try
            Thread.Sleep(5000)
            WebClient1.DownloadFile("http://www.c-sharpcorner.com/", "C:\Abc.txt")
        Catch ex As Exception
            Dim str As String
            str = ex.Message
        End Try
        StatusListBox.Items.Add("DownloadTest 1 Done")
        StatusListBox.Items.Add("Processing Finished.")
    End Sub

This function will download c-sharpcorner home page source in ABC.txt in C drive, you change whatever name you want.

This is form load event

    ''' <summary>
    ''' This event is fired when form is loading
    ''' Initialize your variables here
    ''' </summary>
    ''' <param name="sender"></param>
    ''' <param name="e"></param>
    ''' <remarks></remarks>
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        StatusListBox.Items.Add("Initializing Variables.")
        InitializeVariables()
        StatusListBox.Items.Add("Variables Initialized.")
    End Sub

This is form closing event

    ''' <summary>
    ''' This event is fired just before the  form closes.
    ''' You want to deinitialize all of your variables
    ''' </summary>
    ''' <param name="sender"></param>
    ''' <param name="e"></param>
    ''' <remarks></remarks>
    Private Sub Form1_FormClosing(ByVal sender As System.Object, _
                ByVal e As System.Windows.Forms.FormClosingEventArgs) Handles MyBase.FormClosing
        StatusListBox.Items.Add("Releasing Variables.")
        ReleaseVariables()
        StatusListBox.Items.Add("Variables Realsed.")
    End Sub
 
    ''' <summary>
    ''' Initialize all variables
    ''' </summary>
    ''' <remarks></remarks>
    Private Sub InitializeVariables()
        Me.WebClient1 = New System.Net.WebClient
    End Sub

    ''' <summary>
    ''' DeInitialize all variables
    ''' </summary>
    ''' <remarks></remarks>
    Private Sub ReleaseVariables()
        If Not Me.WebClient1 Is Nothing Then
            Me.WebClient1 = Nothing
        End If
    End Sub

Output will look like this:



Figure 1.

After click on Start button.



Figure 2.

Check your C drive there should be a ABC.txt file downloaded which has c-sharp corner homepage html source.