VintaSoft Twain .NET SDK v10.2
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    Acquire images from scanner asynchronously
    In This Topic

    VintaSoft Twain .NET SDK allows to acquire images from a scanner asynchronously.

    Here is to do list for acquiring images asynchronously:

    1. Open TWAIN device manager.
    2. Select TWAIN device.
    3. Subscribe to the events of TWAIN device: Device.ImageAcquired, Device.ScanFinished, etc.
    4. Open TWAIN device.
    5. Set the scanning settings.
    6. Start the asynchronous acquisition process.
    7. Retrieve acquired image one by one while the Device.ImageAcquired event fires.
    8. Stop image acquisition process when the Device.ScanCompleted event fires.

    Example: Here is an example that shows how to scan images asynchronously using scanner's user interface and save scanned images into multipage TIFF file:
    Imports System.IO
    Imports System.Windows.Forms
    Imports Vintasoft.Twain
    
    Partial Public Class ScanAsynchronouslyDemoForm
        Inherits Form
    
    #Region "Fields"
    
        ''' <summary>
        ''' TWAIN device manager.
        ''' </summary>
        Private _deviceManager As DeviceManager
    
    #End Region
    
    
    
    #Region "Constructors"
    
        Public Sub New()
            InitializeComponent()
    
            ' create and open device manager
            _deviceManager = New 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 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 = TransferMode.Memory
                ' enable UI
                device.ShowUI = True
    
                ' open the device
                device.Open()
                ' specify that black-white images must be acquired
                device.PixelType = PixelType.BW
                ' specify the threshold for acquired images
                device.Threshold = 128
                ' set the inches as unit of measure
                device.UnitOfMeasure = UnitOfMeasure.Inches
                device.Resolution = New Resolution(300.0F, 300.0F)
    
                ' acquire images asynchronously
                device.Acquire()
            Catch ex As TwainException
                ' if device is found
                If device IsNot Nothing Then
                    ' if device is opened
                    If device.State >= 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(Path.Combine(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 Device = DirectCast(sender, Device)
    
            ' unsubscribe from device events
            UnsubscribeFromDeviceEvents(device1)
    
            ' if device is not closed
            If device1.State <> 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 Device)
            AddHandler device.ImageAcquiringProgress, New EventHandler(Of ImageAcquiringProgressEventArgs)(AddressOf device_ImageAcquiringProgress)
            AddHandler device.ImageAcquired, New EventHandler(Of 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 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 Device)
            RemoveHandler device.ImageAcquiringProgress, New EventHandler(Of ImageAcquiringProgressEventArgs)(AddressOf device_ImageAcquiringProgress)
            RemoveHandler device.ImageAcquired, New EventHandler(Of 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 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
                  
    
    using System;
    using System.IO;
    using System.Windows.Forms;
    using Vintasoft.Twain;
    
    namespace TwainExamples_CSharp
    {
        public partial class ScanAsynchronouslyDemoForm : Form
        {
    
            #region Fields
    
            /// <summary>
            /// TWAIN device manager.
            /// </summary>
            DeviceManager _deviceManager;
    
            #endregion
    
    
    
            #region Constructors
    
            public ScanAsynchronouslyDemoForm()
            {
                InitializeComponent();
    
                // create and open device manager
                _deviceManager = new DeviceManager(this);
                _deviceManager.Open();
            }
    
            #endregion
    
    
    
            #region Methods
    
            /// <summary>
            /// Starts the image acquisition from scanner.
            /// </summary>
            private void startImageAcquisitionButton_Click(object sender, EventArgs e)
            {
                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 = TransferMode.Memory;
                    // enable UI
                    device.ShowUI = true;
    
                    // open the device
                    device.Open();
                    // specify that black-white images must be acquired
                    device.PixelType = PixelType.BW;
                    // specify the threshold for acquired images
                    device.Threshold = 128;
                    // set the inches as unit of measure
                    device.UnitOfMeasure = UnitOfMeasure.Inches;
                    device.Resolution = new Resolution(300f, 300f);
    
                    // acquire images asynchronously
                    device.Acquire();
                }
                catch (TwainException ex)
                {
                    // if device is found
                    if (device != null)
                    {
                        // if device is opened
                        if (device.State >= DeviceState.Opened)
                            // close the device
                            device.Close();
    
                        // unsubscribe from device events
                        UnsubscribeFromDeviceEvents(device);
                    }
    
                    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(Path.Combine(Directory.GetCurrentDirectory(), "multipage.tif"));
    
                // dispose the acquired image
                e.Image.Dispose();
            }
    
            /// <summary>
            /// Scan is completed.
            /// </summary>
            private void device_ScanCompleted(object sender, EventArgs e)
            {
                MessageBox.Show("Scan is competed.");
            }
    
            /// <summary>
            /// Scan is canceled.
            /// </summary>
            private void device_ScanCanceled(object sender, EventArgs e)
            {
                MessageBox.Show("Scan is canceled.");
            }
    
            /// <summary>
            /// Scan is failed.
            /// </summary>
            private void device_ScanFailed(object sender, Vintasoft.Twain.ScanFailedEventArgs e)
            {
                MessageBox.Show(string.Format("Scan is failed: {0}", e.ErrorString));
            }
    
            /// <summary>
            /// User interface of device is closed.
            /// </summary>
            private void device_UserInterfaceClosed(object sender, EventArgs e)
            {
                MessageBox.Show("User Interface is closed.");
            }
    
            /// <summary>
            /// Scan is finished.
            /// </summary>
            private void device_ScanFinished(object sender, EventArgs e)
            {
                Device device = (Device)sender;
    
                // unsubscribe from device events
                UnsubscribeFromDeviceEvents(device);
    
                // if device is not closed
                if (device.State != DeviceState.Closed)
                    // close the device
                    device.Close();
    
                MessageBox.Show("Scan is finished.");
            }
    
            /// <summary>
            /// Subscribes to the device events.
            /// </summary>
            private void SubscribeToDeviceEvents(Device device)
            {
                device.ImageAcquiringProgress += new EventHandler(device_ImageAcquiringProgress);
                device.ImageAcquired += new EventHandler(device_ImageAcquired);
                device.ScanCompleted += new EventHandler(device_ScanCompleted);
                device.ScanCanceled += new EventHandler(device_ScanCanceled);
                device.ScanFailed += new EventHandler(device_ScanFailed);
                device.UserInterfaceClosed += new EventHandler(device_UserInterfaceClosed);
                device.ScanFinished += new EventHandler(device_ScanFinished);
            }
    
            /// <summary>
            /// Unsubscribes from the device events.
            /// </summary>
            private void UnsubscribeFromDeviceEvents(Device device)
            {
                device.ImageAcquiringProgress -= new EventHandler(device_ImageAcquiringProgress);
                device.ImageAcquired -= new EventHandler(device_ImageAcquired);
                device.ScanCompleted -= new EventHandler(device_ScanCompleted);
                device.ScanCanceled -= new EventHandler(device_ScanCanceled);
                device.ScanFailed -= new EventHandler(device_ScanFailed);
                device.UserInterfaceClosed -= new EventHandler(device_UserInterfaceClosed);
                device.ScanFinished -= new EventHandler(device_ScanFinished);
            }
    
            #endregion
    
        }
    }