Acquire images from TWAIN image scanner asynchronously

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

Here are steps, which should be made for asynchronous acquisition of images from TWAIN device:

Open TWAIN device manager.
Select TWAIN device.
Subscribe to the events of TWAIN device: Device.ImageAcquired, Device.ScanFinished, etc.
Open TWAIN device.
Set TWAIN device settings.
Start the asynchronous acquisition of images from TWAIN device by calling Device.Acquire method.
Retrieve acquired image one by one while the Device.ImageAcquired event occurs.
Stop image acquisition process when the Device.ScanCompleted event occurs.

Here is an example that demonstrates how to acquire images from TWAIN device and save acquired images to a multipage TIFF file:

static bool _isScanningFinished;


/// <summary>
/// Asynchronously acquires images from TWAIN device.
/// </summary>
public static void AsynchronouslyAcquireImageFromTwainDevice()
{
    _isScanningFinished = false;

    // create the device manager
    using (Vintasoft.Twain.DeviceManager deviceManager = new Vintasoft.Twain.DeviceManager())
    {
        deviceManager.IsTwain2Compatible = true;
        // open the device manager
        deviceManager.Open();

        // get the device
        string deviceName = "KODAK Scanner: i5000";
        Vintasoft.Twain.Device device = deviceManager.Devices.Find(deviceName);
        if (device == null)
            throw new System.ApplicationException(string.Format("Device '{0}' is not found.", deviceName));

        // subscribe to device events
        SubscribeToDeviceEvents(device);

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

        // 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);

        // run asynchronous image acqusition
        device.Acquire();

        // wait while feeder will be stopped
        while (!_isScanningFinished)
        {
            System.Windows.Forms.Application.DoEvents();
        }

        // unsubscribe from device events
        UnsubscribeFromDeviceEvents(device);

        // close the device
        device.Close();
    }
}

/// <summary>
/// Image acquisition is in progress.
/// </summary>
private static void device_ImageAcquiringProgress(object sender, Vintasoft.Twain.ImageAcquiringProgressEventArgs e)
{
    // update progress bar
}

/// <summary>
/// Image is acquired.
/// </summary>
private static void device_ImageAcquired(object sender, Vintasoft.Twain.ImageAcquiredEventArgs e)
{
    // 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 static void device_ScanCompleted(object sender, System.EventArgs e)
{
    System.Console.WriteLine("Scan is completed.");
}

/// <summary>
/// Scan is canceled.
/// </summary>
private static void device_ScanCanceled(object sender, System.EventArgs e)
{
    System.Console.WriteLine("Scan is canceled.");
}

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

/// <summary>
/// Scan is finished.
/// </summary>
private static 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.Console.WriteLine("Scan is finished.");

    _isScanningFinished = true;
}

/// <summary>
/// Subscribes to the device events.
/// </summary>
private static 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.ScanFinished += new System.EventHandler(device_ScanFinished);
}

/// <summary>
/// Unsubscribes from the device events.
/// </summary>
private static 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.ScanFinished -= new System.EventHandler(device_ScanFinished);
}

VB.NET

Shared _isScanningFinished As Boolean


''' <summary>
''' Asynchronously acquires images from TWAIN device.
''' </summary>
Public Shared Sub AsynchronouslyAcquireImageFromTwainDevice()
    _isScanningFinished = False

    ' create the device manager
    Using deviceManager As New Vintasoft.Twain.DeviceManager()
        deviceManager.IsTwain2Compatible = True
        ' open the device manager
        deviceManager.Open()

        ' get the device
        Dim deviceName As String = "KODAK Scanner: i5000"
        Dim device As Vintasoft.Twain.Device = deviceManager.Devices.Find(deviceName)
        If device Is Nothing Then
            Throw New System.ApplicationException(String.Format("Device '{0}' is not found.", deviceName))
        End If

        ' subscribe to device events
        SubscribeToDeviceEvents(device)

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

        ' 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)

        ' run asynchronous image acqusition
        device.Acquire()

        ' wait while feeder will be stopped
        While Not _isScanningFinished
            System.Windows.Forms.Application.DoEvents()
        End While

        ' unsubscribe from device events
        UnsubscribeFromDeviceEvents(device)

        ' close the device
        device.Close()
    End Using
End Sub

''' <summary>
''' Image acquisition is in progress.
''' </summary>
Private Shared Sub device_ImageAcquiringProgress(sender As Object, e As Vintasoft.Twain.ImageAcquiringProgressEventArgs)
    ' update progress bar
End Sub

''' <summary>
''' Image is acquired.
''' </summary>
Private Shared Sub device_ImageAcquired(sender As Object, e As Vintasoft.Twain.ImageAcquiredEventArgs)
    ' 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()
End Sub

''' <summary>
''' Scan is completed.
''' </summary>
Private Shared Sub device_ScanCompleted(sender As Object, e As System.EventArgs)
    System.Console.WriteLine("Scan is completed.")
End Sub

''' <summary>
''' Scan is canceled.
''' </summary>
Private Shared Sub device_ScanCanceled(sender As Object, e As System.EventArgs)
    System.Console.WriteLine("Scan is canceled.")
End Sub

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

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

    ' unsubscribe from device events
    UnsubscribeFromDeviceEvents(device)

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

    System.Console.WriteLine("Scan is finished.")

    _isScanningFinished = True
End Sub

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

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

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