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

        #region Fields

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

        #endregion



        #region Constructors

        public ScanAsynchronouslyDemoForm()
        {
            InitializeComponent();

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

        #endregion



        #region Methods

        /// <summary>
        /// Starts the image acquisition from scanner.
        /// </summary>
        private void startImageAcquisitionButton_Click(object sender, System.EventArgs e)
        {
            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 Memory transfer mode
                device.TransferMode = Vintasoft.Twain.TransferMode.Memory;
                // enable UI
                device.ShowUI = true;

                // open the device
                device.Open();
                // specify that black-white images must be acquired
                device.PixelType = Vintasoft.Twain.PixelType.BW;
                // specify the threshold for acquired images
                device.Threshold = 128;
                // set the inches as unit of measure
                device.UnitOfMeasure = Vintasoft.Twain.UnitOfMeasure.Inches;
                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 acquisition is in progress.
        /// </summary>
        private void device_ImageAcquiringProgress(
            object sender,
            Vintasoft.Twain.ImageAcquiringProgressEventArgs e)
        {
            // update progress bar
            progressBar1.Value = e.Progress;
        }

        /// <summary>
        /// Image is acquired.
        /// </summary>
        private void device_ImageAcquired(object sender, Vintasoft.Twain.ImageAcquiredEventArgs e)
        {
            // dispose image stored in the picture box
            if (pictureBox1.Image != null)
            {
                pictureBox1.Image.Dispose();
                pictureBox1.Image = null;
            }

            // show acquired image in the picture box
            pictureBox1.Image = e.Image.GetAsBitmap(true);

            // add the acquired image to a TIFF file
            e.Image.Save(System.IO.Path.Combine(System.IO.Directory.GetCurrentDirectory(), "multipage.tif"));

            // dispose the acquired image
            e.Image.Dispose();
        }

        /// <summary>
        /// Scan is completed.
        /// </summary>
        private void device_ScanCompleted(object sender, System.EventArgs e)
        {
            System.Windows.Forms.MessageBox.Show("Scan is competed.");
        }

        /// <summary>
        /// Scan is canceled.
        /// </summary>
        private void device_ScanCanceled(object sender, System.EventArgs e)
        {
            System.Windows.Forms.MessageBox.Show("Scan is canceled.");
        }

        /// <summary>
        /// Scan is failed.
        /// </summary>
        private void device_ScanFailed(object sender, Vintasoft.Twain.ScanFailedEventArgs e)
        {
            System.Windows.Forms.MessageBox.Show(string.Format("Scan is failed: {0}", e.ErrorString));
        }

        /// <summary>
        /// User interface of device is closed.
        /// </summary>
        private void device_UserInterfaceClosed(object sender, System.EventArgs e)
        {
            System.Windows.Forms.MessageBox.Show("User Interface is closed.");
        }

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

            // unsubscribe from device events
            UnsubscribeFromDeviceEvents(device);

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

            System.Windows.Forms.MessageBox.Show("Scan is finished.");
        }

        /// <summary>
        /// Subscribes to the device events.
        /// </summary>
        private void SubscribeToDeviceEvents(Vintasoft.Twain.Device device)
        {
            device.ImageAcquiringProgress += new System.EventHandler<Vintasoft.Twain.ImageAcquiringProgressEventArgs>(device_ImageAcquiringProgress);
            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.ImageAcquiringProgress -= new System.EventHandler<Vintasoft.Twain.ImageAcquiringProgressEventArgs>(device_ImageAcquiringProgress);
            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 ScanAsynchronouslyDemoForm
    Inherits Form

#Region "Fields"

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

#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>
    ''' Starts the image acquisition from scanner.
    ''' </summary>
    Private Sub startImageAcquisitionButton_Click(ByVal sender As Object, ByVal e As EventArgs)
        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 Memory transfer mode
            device.TransferMode = Vintasoft.Twain.TransferMode.Memory
            ' enable UI
            device.ShowUI = True

            ' open the device
            device.Open()
            ' specify that black-white images must be acquired
            device.PixelType = Vintasoft.Twain.PixelType.BW
            ' specify the threshold for acquired images
            device.Threshold = 128
            ' set the inches as unit of measure
            device.UnitOfMeasure = Vintasoft.Twain.UnitOfMeasure.Inches
            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 acquisition is in progress.
    ''' </summary>
    Private Sub device_ImageAcquiringProgress(ByVal sender As Object, ByVal e As Vintasoft.Twain.ImageAcquiringProgressEventArgs)
        ' update progress bar
        progressBar1.Value = e.Progress
    End Sub

    ''' <summary>
    ''' Image is acquired.
    ''' </summary>
    Private Sub device_ImageAcquired(ByVal sender As Object, ByVal e As Vintasoft.Twain.ImageAcquiredEventArgs)
        ' dispose image stored in the picture box
        If pictureBox1.Image IsNot Nothing Then
            pictureBox1.Image.Dispose()
            pictureBox1.Image = Nothing
        End If

        ' show acquired image in the picture box
        pictureBox1.Image = e.Image.GetAsBitmap(True)

        ' add the acquired image to a TIFF file
        e.Image.Save(IO.Path.Combine(IO.Directory.GetCurrentDirectory(), "multipage.tif"))

        ' dispose the acquired image
        e.Image.Dispose()
    End Sub

    ''' <summary>
    ''' Scan is completed.
    ''' </summary>
    Private Sub device_ScanCompleted(ByVal sender As Object, ByVal e As EventArgs)
        MessageBox.Show("Scan is competed.")
    End Sub

    ''' <summary>
    ''' Scan is canceled.
    ''' </summary>
    Private Sub device_ScanCanceled(ByVal sender As Object, ByVal e As EventArgs)
        MessageBox.Show("Scan is canceled.")
    End Sub

    ''' <summary>
    ''' Scan is failed.
    ''' </summary>
    Private Sub device_ScanFailed(ByVal sender As Object, ByVal e As Vintasoft.Twain.ScanFailedEventArgs)
        MessageBox.Show(String.Format("Scan is failed: {0}", e.ErrorString))
    End Sub

    ''' <summary>
    ''' User interface of device is closed.
    ''' </summary>
    Private Sub device_UserInterfaceClosed(ByVal sender As Object, ByVal e As EventArgs)
        MessageBox.Show("User Interface is closed.")
    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

        MessageBox.Show("Scan is finished.")
    End Sub

    ''' <summary>
    ''' Subscribes to the device events.
    ''' </summary>
    Private Sub SubscribeToDeviceEvents(ByVal device As Vintasoft.Twain.Device)
        AddHandler device.ImageAcquiringProgress, New EventHandler(Of Vintasoft.Twain.ImageAcquiringProgressEventArgs)(AddressOf device_ImageAcquiringProgress)
        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.UserInterfaceClosed, New EventHandler(AddressOf device_UserInterfaceClosed)
        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.ImageAcquiringProgress, New EventHandler(Of Vintasoft.Twain.ImageAcquiringProgressEventArgs)(AddressOf device_ImageAcquiringProgress)
        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.UserInterfaceClosed, New EventHandler(AddressOf device_UserInterfaceClosed)
        RemoveHandler device.ScanFinished, New EventHandler(AddressOf device_ScanFinished)
    End Sub

#End Region

End Class