Pause Image Acquisition (Stop Feeder)

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Many TWAIN image scanners have automatic document feeders. Some from these TWAIN image scanners allow to stop the feeder, i.e. pause the image acquisition process. Device.StopFeeder allows to stop the feeder.

Here is an example that demonstrates how to start asynchronous TWAIN image acquisition, stop the document feeder and continue asynchronous TWAIN image acquisition:

static bool _isScanningFinished;
static int _step;
static int _imageCount;


/// <summary>
/// Synchronously acquires one image from TWAIN device, stops the document feeder, scans the second image.
/// </summary>
public static void AsynchronouslyAcquireImageFromTwainDevice_StopFeeder_ContinueImageTransfer()
{
    _isScanningFinished = false;
    _step = 0;
    _imageCount = 0;

    // 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;
        // specify that device must be closed after scan
        device.DisableAfterAcquire = true;

        // open the device
        device.Open();
        // specify that 2 images must be acquired from scanner
        device.XferCount = 2;

        // run asynchronous image acqusition
        device.Acquire();
        // wait while feeder will be stopped
        while (!_isScanningFinished)
        {
            System.Windows.Forms.Application.DoEvents();
        }

        if (_imageCount != 1)
        {
            // unsubscribe from device events
            UnsubscribeFromDeviceEvents(device);

            throw new System.ApplicationException("Wrong acquired image count.");
        }

        if (device.State != Vintasoft.Twain.DeviceState.TransferReady)
        {
            // unsubscribe from device events
            UnsubscribeFromDeviceEvents(device);

            throw new System.ApplicationException("Feeder is NOT stopped.");
        }
        System.Console.WriteLine("Feeder is stopped.");

        _isScanningFinished = false;
        // run asynchronous image acqusition
        device.Acquire();
        // wait while image scan will be finished
        while (!_isScanningFinished)
        {
            System.Windows.Forms.Application.DoEvents();
        }

        // unsubscribe from device events
        UnsubscribeFromDeviceEvents(device);

        if (_imageCount != 2)
            throw new System.ApplicationException("Wrong acquired image count.");

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

/// <summary>
/// Image is acquired.
/// </summary>
private static void device_ImageAcquired(object sender, Vintasoft.Twain.ImageAcquiredEventArgs e)
{
    System.Console.WriteLine("Image is acquired.");
    // increment image count
    _imageCount++;

    // if we need stop the feeder
    if (_step == 0)
    {
        // get reference to the device
        Vintasoft.Twain.Device device = (Vintasoft.Twain.Device)sender;
        // stop the feeder
        device.StopFeeder();

        // specify that feeder is stopped
        _step = 1;
        _isScanningFinished = true;
    }
}

/// <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)
{
    _isScanningFinished = true;
}

/// <summary>
/// Subscribes to the device events.
/// </summary>
private static void SubscribeToDeviceEvents(Vintasoft.Twain.Device device)
{
    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.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
Shared _step As Integer
Shared _imageCount As Integer


''' <summary>
''' Synchronously acquires one image from TWAIN device, stops the document feeder, scans the second image.
''' </summary>
Public Shared Sub AsynchronouslyAcquireImageFromTwainDevice_StopFeeder_ContinueImageTransfer()
    _isScanningFinished = False
    _step = 0
    _imageCount = 0

    ' 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
        ' specify that device must be closed after scan
        device.DisableAfterAcquire = True

        ' open the device
        device.Open()
        ' specify that 2 images must be acquired from scanner
        device.XferCount = 2

        ' run asynchronous image acqusition
        device.Acquire()
        ' wait while feeder will be stopped
        While Not _isScanningFinished
            System.Windows.Forms.Application.DoEvents()
        End While

        If _imageCount <> 1 Then
            ' unsubscribe from device events
            UnsubscribeFromDeviceEvents(device)

            Throw New System.ApplicationException("Wrong acquired image count.")
        End If

        If device.State <> Vintasoft.Twain.DeviceState.TransferReady Then
            ' unsubscribe from device events
            UnsubscribeFromDeviceEvents(device)

            Throw New System.ApplicationException("Feeder is NOT stopped.")
        End If
        System.Console.WriteLine("Feeder is stopped.")

        _isScanningFinished = False
        ' run asynchronous image acqusition
        device.Acquire()
        ' wait while image scan will be finished
        While Not _isScanningFinished
            System.Windows.Forms.Application.DoEvents()
        End While

        ' unsubscribe from device events
        UnsubscribeFromDeviceEvents(device)

        If _imageCount <> 2 Then
            Throw New System.ApplicationException("Wrong acquired image count.")
        End If

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

''' <summary>
''' Image is acquired.
''' </summary>
Private Shared Sub device_ImageAcquired(sender As Object, e As Vintasoft.Twain.ImageAcquiredEventArgs)
    System.Console.WriteLine("Image is acquired.")
    ' increment image count
    _imageCount += 1

    ' if we need stop the feeder
    If _step = 0 Then
        ' get reference to the device
        Dim device As Vintasoft.Twain.Device = DirectCast(sender, Vintasoft.Twain.Device)
        ' stop the feeder
        device.StopFeeder()

        ' specify that feeder is stopped
        _step = 1
        _isScanningFinished = True
    End If
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)
    _isScanningFinished = True
End Sub

''' <summary>
''' Subscribes to the device events.
''' </summary>
Private Shared Sub SubscribeToDeviceEvents(device As Vintasoft.Twain.Device)
    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.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

Here is an example that demonstrates how to start synchronous TWAIN image acquisition, stop the document feeder and continue synchronous TWAIN image acquisition:

/// <summary>
/// Synchronously acquires one image from TWAIN device, stops the document feeder, scans the second image.
/// </summary>
public static void SynchronouslyAcquireImageFromTwainDevice_StopFeeder_ContinueImageTransfer()
{
    int imageCount = 0;

    // 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));

        // disable device UI
        device.ShowUI = false;
        // specify that device must be closed after scan
        device.DisableAfterAcquire = true;

        // open the device
        device.Open();
        // specify that 2 images must be acquired from scanner
        device.XferCount = 2;

        // run asynchronous image acquisition
        Vintasoft.Twain.AcquireModalState acquireModalState = Vintasoft.Twain.AcquireModalState.None;
        do
        {
            acquireModalState = device.AcquireModal();
            switch (acquireModalState)
            {
                case Vintasoft.Twain.AcquireModalState.ImageAcquired:
                    System.Console.WriteLine("Image is acquired.");
                    if (device.AcquiredImage != null)
                        device.AcquiredImage.Dispose();

                    imageCount++;

                    // stop the feeder
                    device.StopFeeder();
                    break;

                case Vintasoft.Twain.AcquireModalState.ScanCompleted:
                    System.Console.WriteLine("Scan is completed.");
                    break;

                case Vintasoft.Twain.AcquireModalState.ScanCanceled:
                    System.Console.WriteLine("Scan is canceled.");
                    break;

                case Vintasoft.Twain.AcquireModalState.ScanFailed:
                    System.Console.WriteLine(string.Format("Scan is failed: {0}.", device.ErrorString));
                    break;
            }
        }
        while (acquireModalState != Vintasoft.Twain.AcquireModalState.None);

        if (imageCount != 1)
            throw new System.ApplicationException("Wrong acquired image count.");

        if (device.State != Vintasoft.Twain.DeviceState.TransferReady)
            throw new System.ApplicationException("Feeder is NOT stopped.");
        System.Console.WriteLine("Feeder is stopped.");

        // continue asynchronous image acquisition
        do
        {
            acquireModalState = device.AcquireModal();
            switch (acquireModalState)
            {
                case Vintasoft.Twain.AcquireModalState.ImageAcquired:
                    System.Console.WriteLine("Image is acquired.");

                    if (device.AcquiredImage != null)
                        device.AcquiredImage.Dispose();

                    imageCount++;
                    break;

                case Vintasoft.Twain.AcquireModalState.ScanCompleted:
                    System.Console.WriteLine("Scan is completed.");
                    break;

                case Vintasoft.Twain.AcquireModalState.ScanCanceled:
                    System.Console.WriteLine("Scan is canceled.");
                    break;

                case Vintasoft.Twain.AcquireModalState.ScanFailed:
                    System.Console.WriteLine(string.Format("Scan is failed: {0}.", device.ErrorString));
                    break;
            }
        }
        while (acquireModalState != Vintasoft.Twain.AcquireModalState.None);

        if (imageCount != 2)
            throw new System.ApplicationException("Wrong acquired image count.");

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

VB.NET

''' <summary>
''' Synchronously acquires one image from TWAIN device, stops the document feeder, scans the second image.
''' </summary>
Public Shared Sub SynchronouslyAcquireImageFromTwainDevice_StopFeeder_ContinueImageTransfer()
    Dim imageCount As Integer = 0

    ' 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

        ' disable device UI
        device.ShowUI = False
        ' specify that device must be closed after scan
        device.DisableAfterAcquire = True

        ' open the device
        device.Open()
        ' specify that 2 images must be acquired from scanner
        device.XferCount = 2

        ' run asynchronous image acquisition
        Dim acquireModalState As Vintasoft.Twain.AcquireModalState = Vintasoft.Twain.AcquireModalState.None
        Do
            acquireModalState = device.AcquireModal()
            Select Case acquireModalState
                Case Vintasoft.Twain.AcquireModalState.ImageAcquired
                    System.Console.WriteLine("Image is acquired.")
                    If device.AcquiredImage IsNot Nothing Then
                        device.AcquiredImage.Dispose()
                    End If

                    imageCount += 1

                    ' stop the feeder
                    device.StopFeeder()
                    Exit Select

                Case Vintasoft.Twain.AcquireModalState.ScanCompleted
                    System.Console.WriteLine("Scan is completed.")
                    Exit Select

                Case Vintasoft.Twain.AcquireModalState.ScanCanceled
                    System.Console.WriteLine("Scan is canceled.")
                    Exit Select

                Case Vintasoft.Twain.AcquireModalState.ScanFailed
                    System.Console.WriteLine(String.Format("Scan is failed: {0}.", device.ErrorString))
                    Exit Select
            End Select
        Loop While acquireModalState <> Vintasoft.Twain.AcquireModalState.None

        If imageCount <> 1 Then
            Throw New System.ApplicationException("Wrong acquired image count.")
        End If

        If device.State <> Vintasoft.Twain.DeviceState.TransferReady Then
            Throw New System.ApplicationException("Feeder is NOT stopped.")
        End If
        System.Console.WriteLine("Feeder is stopped.")

        ' continue asynchronous image acquisition
        Do
            acquireModalState = device.AcquireModal()
            Select Case acquireModalState
                Case Vintasoft.Twain.AcquireModalState.ImageAcquired
                    System.Console.WriteLine("Image is acquired.")

                    If device.AcquiredImage IsNot Nothing Then
                        device.AcquiredImage.Dispose()
                    End If

                    imageCount += 1
                    Exit Select

                Case Vintasoft.Twain.AcquireModalState.ScanCompleted
                    System.Console.WriteLine("Scan is completed.")
                    Exit Select

                Case Vintasoft.Twain.AcquireModalState.ScanCanceled
                    System.Console.WriteLine("Scan is canceled.")
                    Exit Select

                Case Vintasoft.Twain.AcquireModalState.ScanFailed
                    System.Console.WriteLine(String.Format("Scan is failed: {0}.", device.ErrorString))
                    Exit Select
            End Select
        Loop While acquireModalState <> Vintasoft.Twain.AcquireModalState.None

        If imageCount <> 2 Then
            Throw New System.ApplicationException("Wrong acquired image count.")
        End If

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

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