namespace TwainExamples_CSharp
{
    public partial class ScanAsynchronouslyDirectlyToDiskDemoForm : System.Windows.Forms.Form
    {

        #region Fields

        /// <summary>
        /// TWAIN device manager.
        /// </summary>
        Vintasoft.Twain.DeviceManager _deviceManager;

        /// <summary>
        /// Path to directory where acquired images will be saved.
        /// </summary>
        string _directoryForImages = @"d:\images\";
        /// <summary>
        /// Index of acquired image.
        /// </summary>
        int _imageIndex;

        #endregion



        #region Constructors

        public ScanAsynchronouslyDirectlyToDiskDemoForm()
        {
            InitializeComponent();

            // create and open device manager
            _deviceManager = new Vintasoft.Twain.DeviceManager(this);
            _deviceManager.Open();
        }

        #endregion



        #region Methods

        /// <summary>
        /// Scans images asynchronously.
        /// </summary>
        public void startImageAcquisitionButton_Click()
        {
            Vintasoft.Twain.Device device = null;
            try
            {
                // select the default device
                _deviceManager.ShowDefaultDeviceSelectionDialog();

                // get reference to the default device
                device = _deviceManager.DefaultDevice;
                // if device is not found
                if (device == null)
                    return;

                // subscribe to the device events
                SubscribeToDeviceEvents(device);

                // set the File transfer mode
                device.TransferMode = Vintasoft.Twain.TransferMode.File;
                // disable UI
                device.ShowUI = false;

                // open the device
                device.Open();
                // specify that gray images must be acquired
                device.PixelType = Vintasoft.Twain.PixelType.Gray;
                // set the inches as unit of measure
                device.UnitOfMeasure = Vintasoft.Twain.UnitOfMeasure.Inches;
                // set the desired resolution of acquired images
                device.Resolution = new Vintasoft.Twain.Resolution(300f, 300f);

                // acquire images asynchronously
                device.Acquire();
            }
            catch (Vintasoft.Twain.TwainException ex)
            {
                // if device is found
                if (device != null)
                {
                    // if device is opened
                    if (device.State >= Vintasoft.Twain.DeviceState.Opened)
                        // close the device
                        device.Close();

                    // unsubscribe from device events
                    UnsubscribeFromDeviceEvents(device);
                }

                System.Windows.Forms.MessageBox.Show(ex.Message);
            }
        }

        /// <summary>
        /// Image is acquiring.
        /// </summary>
        private void device_ImageAcquiring(object sender, Vintasoft.Twain.ImageAcquiringEventArgs e)
        {
            string fileExtension = "bmp";
            switch (e.FileFormat)
            {
                case Vintasoft.Twain.TwainImageFileFormat.Tiff:
                    fileExtension = "tif";
                    break;

                case Vintasoft.Twain.TwainImageFileFormat.Jpeg:
                    fileExtension = "jpg";
                    break;
            }

            e.Filename = System.IO.Path.Combine(_directoryForImages, string.Format("page{0}.{1}", _imageIndex, fileExtension));
        }

        /// <summary>
        /// Image is acquired.
        /// </summary>
        private void device_ImageAcquired(object sender, Vintasoft.Twain.ImageAcquiredEventArgs e)
        {
            statusTextBox.Text += string.Format("Image is saved to file '{0}'{1}", System.IO.Path.GetFileName(e.Filename), System.Environment.NewLine);
            _imageIndex++;
        }

        /// <summary>
        /// Scan is completed.
        /// </summary>
        private void device_ScanCompleted(object sender, System.EventArgs e)
        {
            statusTextBox.Text += string.Format("Scan is completed{0}", System.Environment.NewLine);
        }

        /// <summary>
        /// Scan is canceled.
        /// </summary>
        private void device_ScanCanceled(object sender, System.EventArgs e)
        {
            statusTextBox.Text += string.Format("Scan is canceled{0}", System.Environment.NewLine);
        }

        /// <summary>
        /// Scan is failed.
        /// </summary>
        private void device_ScanFailed(object sender, Vintasoft.Twain.ScanFailedEventArgs e)
        {
            statusTextBox.Text += string.Format("Scan failed: {0}{1}", e.ErrorString, System.Environment.NewLine);
        }

        /// <summary>
        /// User interface of device is closed.
        /// </summary>
        private void device_UserInterfaceClosed(object sender, System.EventArgs e)
        {
            statusTextBox.Text += string.Format("User Interface is closed{0}", System.Environment.NewLine);
        }

        /// <summary>
        /// Scan is finished.
        /// </summary>
        private void device_ScanFinished(object sender, System.EventArgs e)
        {
            Vintasoft.Twain.Device device = sender as Vintasoft.Twain.Device;

            if (device != null)
            {
                // unsubscribe from device events
                UnsubscribeFromDeviceEvents(device);

                // if device is not closed
                if (device.State != Vintasoft.Twain.DeviceState.Closed)
                    // close the device
                    device.Close();
            }
        }

        /// <summary>
        /// Subscribes to the device events.
        /// </summary>
        private void SubscribeToDeviceEvents(Vintasoft.Twain.Device device)
        {
            device.ImageAcquiring += new System.EventHandler<Vintasoft.Twain.ImageAcquiringEventArgs>(device_ImageAcquiring);
            device.ImageAcquired += new System.EventHandler<Vintasoft.Twain.ImageAcquiredEventArgs>(device_ImageAcquired);
            device.ScanCompleted += new System.EventHandler(device_ScanCompleted);
            device.ScanCanceled += new System.EventHandler(device_ScanCanceled);
            device.ScanFailed += new System.EventHandler<Vintasoft.Twain.ScanFailedEventArgs>(device_ScanFailed);
            device.UserInterfaceClosed += new System.EventHandler(device_UserInterfaceClosed);
            device.ScanFinished += new System.EventHandler(device_ScanFinished);
        }

        /// <summary>
        /// Unsubscribes from the device events.
        /// </summary>
        private void UnsubscribeFromDeviceEvents(Vintasoft.Twain.Device device)
        {
            device.ImageAcquiring -= new System.EventHandler<Vintasoft.Twain.ImageAcquiringEventArgs>(device_ImageAcquiring);
            device.ImageAcquired -= new System.EventHandler<Vintasoft.Twain.ImageAcquiredEventArgs>(device_ImageAcquired);
            device.ScanCompleted -= new System.EventHandler(device_ScanCompleted);
            device.ScanCanceled -= new System.EventHandler(device_ScanCanceled);
            device.ScanFailed -= new System.EventHandler<Vintasoft.Twain.ScanFailedEventArgs>(device_ScanFailed);
            device.UserInterfaceClosed -= new System.EventHandler(device_UserInterfaceClosed);
            device.ScanFinished -= new System.EventHandler(device_ScanFinished);
        }

        #endregion

    }
}

Partial Public Class ScanAsynchronouslyDirectlyToDiskDemoForm
    Inherits Form

#Region "Fields"

    ''' <summary>
    ''' TWAIN device manager.
    ''' </summary>
    Private _deviceManager As Vintasoft.Twain.DeviceManager

    ''' <summary>
    ''' Path to directory where acquired images will be saved.
    ''' </summary>
    Private _directoryForImages As String = "d:\images\"
    ''' <summary>
    ''' Index of acquired image.
    ''' </summary>
    Private _imageIndex As Integer

#End Region



#Region "Constructors"

    Public Sub New()
        InitializeComponent()

        ' create and open device manager
        _deviceManager = New Vintasoft.Twain.DeviceManager(Me)
        _deviceManager.Open()
    End Sub

#End Region



#Region "Methods"

    ''' <summary>
    ''' Scans the images asynchronously.
    ''' </summary>
    Public Sub startImageAcquisitionButton_Click()
        Dim device As Vintasoft.Twain.Device = Nothing
        Try
            ' select the default device
            _deviceManager.ShowDefaultDeviceSelectionDialog()

            ' get reference to the default device
            device = _deviceManager.DefaultDevice
            ' if device is not found
            If device Is Nothing Then
                Exit Sub
            End If

            ' subscribe to the device events
            SubscribeToDeviceEvents(device)

            ' set the File transfer mode
            device.TransferMode = Vintasoft.Twain.TransferMode.File
            ' disable UI
            device.ShowUI = False

            ' open the device
            device.Open()
            ' specify that gray images must be acquired
            device.PixelType = Vintasoft.Twain.PixelType.Gray
            ' set the inches as unit of measure
            device.UnitOfMeasure = Vintasoft.Twain.UnitOfMeasure.Inches
            ' set the desired resolution of acquired images
            device.Resolution = New Vintasoft.Twain.Resolution(300.0F, 300.0F)

            ' acquire images asynchronously
            device.Acquire()
        Catch ex As Vintasoft.Twain.TwainException
            ' if device is found
            If device IsNot Nothing Then
                ' if device is opened
                If device.State >= Vintasoft.Twain.DeviceState.Opened Then
                    ' close the device
                    device.Close()
                End If

                ' unsubscribe from device events
                UnsubscribeFromDeviceEvents(device)
            End If

            MsgBox(ex.Message)
        End Try
    End Sub

    ''' <summary>
    ''' Image is acquiring.
    ''' </summary>
    Private Sub device_ImageAcquiring(ByVal sender As Object, ByVal e As Vintasoft.Twain.ImageAcquiringEventArgs)
        Dim fileExtension As String = "bmp"
        Select Case e.FileFormat
            Case Vintasoft.Twain.TwainImageFileFormat.Tiff
                fileExtension = "tif"
                Exit Select

            Case Vintasoft.Twain.TwainImageFileFormat.Jpeg
                fileExtension = "jpg"
                Exit Select
        End Select

        e.Filename = IO.Path.Combine(_directoryForImages, String.Format("page{0}.{1}", _imageIndex, fileExtension))
    End Sub

    ''' <summary>
    ''' Image is acquired.
    ''' </summary>
    Private Sub device_ImageAcquired(ByVal sender As Object, ByVal e As Vintasoft.Twain.ImageAcquiredEventArgs)
        statusTextBox.Text += String.Format("Image is saved to file '{0}'{1}", IO.Path.GetFileName(e.Filename), Environment.NewLine)
        _imageIndex += 1
    End Sub

    ''' <summary>
    ''' Scan is completed.
    ''' </summary>
    Private Sub device_ScanCompleted(ByVal sender As Object, ByVal e As EventArgs)
        statusTextBox.Text += String.Format("Scan is completed{0}", Environment.NewLine)
    End Sub

    ''' <summary>
    ''' Scan is canceled.
    ''' </summary>
    Private Sub device_ScanCanceled(ByVal sender As Object, ByVal e As EventArgs)
        statusTextBox.Text += String.Format("Scan is canceled{0}", Environment.NewLine)
    End Sub

    ''' <summary>
    ''' Scan is failed.
    ''' </summary>
    Private Sub device_ScanFailed(ByVal sender As Object, ByVal e As Vintasoft.Twain.ScanFailedEventArgs)
        statusTextBox.Text += String.Format("Scan failed: {0}{1}", e.ErrorString, Environment.NewLine)
    End Sub

    ''' <summary>
    ''' User interface of device is closed.
    ''' </summary>
    Private Sub device_UserInterfaceClosed(ByVal sender As Object, ByVal e As EventArgs)
        statusTextBox.Text += String.Format("User Interface is closed{0}", Environment.NewLine)
    End Sub

    ''' <summary>
    ''' Scan is finished.
    ''' </summary>
    Private Sub device_ScanFinished(ByVal sender As Object, ByVal e As EventArgs)
        Dim device1 As Vintasoft.Twain.Device = DirectCast(sender, Vintasoft.Twain.Device)

        ' unsubscribe from device events
        UnsubscribeFromDeviceEvents(device1)

        ' if device is not closed
        If device1.State <> Vintasoft.Twain.DeviceState.Closed Then
            ' close the device
            device1.Close()
        End If

        statusTextBox.Text += String.Format("Scan is finished{0}", Environment.NewLine)
    End Sub

    ''' <summary>
    ''' Subscribes to the device events.
    ''' </summary>
    Private Sub SubscribeToDeviceEvents(ByVal device As Vintasoft.Twain.Device)
        AddHandler device.ImageAcquiring, New EventHandler(Of Vintasoft.Twain.ImageAcquiringEventArgs)(AddressOf device_ImageAcquiring)
        AddHandler device.ImageAcquired, New EventHandler(Of Vintasoft.Twain.ImageAcquiredEventArgs)(AddressOf device_ImageAcquired)
        AddHandler device.ScanCompleted, New EventHandler(AddressOf device_ScanCompleted)
        AddHandler device.ScanCanceled, New EventHandler(AddressOf device_ScanCanceled)
        AddHandler device.ScanFailed, New EventHandler(Of Vintasoft.Twain.ScanFailedEventArgs)(AddressOf device_ScanFailed)
        AddHandler device.ScanFinished, New EventHandler(AddressOf device_ScanFinished)
    End Sub

    ''' <summary>
    ''' Unsubscribes from the device events.
    ''' </summary>
    Private Sub UnsubscribeFromDeviceEvents(ByVal device As Vintasoft.Twain.Device)
        RemoveHandler device.ImageAcquiring, New EventHandler(Of Vintasoft.Twain.ImageAcquiringEventArgs)(AddressOf device_ImageAcquiring)
        RemoveHandler device.ImageAcquired, New EventHandler(Of Vintasoft.Twain.ImageAcquiredEventArgs)(AddressOf device_ImageAcquired)
        RemoveHandler device.ScanCompleted, New EventHandler(AddressOf device_ScanCompleted)
        RemoveHandler device.ScanCanceled, New EventHandler(AddressOf device_ScanCanceled)
        RemoveHandler device.ScanFailed, New EventHandler(Of Vintasoft.Twain.ScanFailedEventArgs)(AddressOf device_ScanFailed)
        RemoveHandler device.ScanFinished, New EventHandler(AddressOf device_ScanFinished)
    End Sub

#End Region

End Class