close the twain scanner

Question

hi

I used the following code to read the scanner file and review it in the image box with twain scanner.
It works well if the scanner is connected to the computer.
If the scanner is not connected, the code stops the window form and does not close.
I want a way to check the scanner connection or cancel if the scanner is not connected to the device (pc)

 Try
            Dim s As Collection

            s = SCANNER.ScanImages()

            For Each k In s

                PictureBox1.Load(k)

            Next
        Catch ex As Exception
            MsgBox(ex.Message)
        End Try

Answer 1

You should use WIA for scanners ("Windows Image Acquisition Library v2.0" on the COM tab),
more recent than Twain

There is also STI
A test with IStillImage.GetDeviceList to check if there is a scanner connected (it returns 0x80070491 with my scanner when I disconnect it) :

        Dim CLSID_StillImage As New Guid("B323F8E0-2E68-11D0-90EA-00AA0060F86C")
        Dim StillImageType As Type = Type.GetTypeFromCLSID(CLSID_StillImage, True)
        Dim StillImage As Object = Activator.CreateInstance(StillImageType)
        pStillImage = DirectCast(StillImage, IStillImage)
        If (pStillImage IsNot Nothing) Then
            Dim nNbItems As UInteger = 0
            Dim pBuffer As IntPtr = IntPtr.Zero
            '  HRESULT = 0x80070491  Message = Aucune correspondance pour la clé indiquée dans l'index. (Exception de HRESULT : 0x80070491)
            Dim hr As HRESULT = pStillImage.GetDeviceList(0, 0, nNbItems, pBuffer)
            If (hr <> HRESULT.S_OK) Then
                MessageBox.Show("No scanner found", "Information", MessageBoxButtons.OK, MessageBoxIcon.Information)
            Else
                MessageBox.Show("Number of scanners detected : " & nNbItems.ToString(), "Information", MessageBoxButtons.OK, MessageBoxIcon.Information)
            End If
        End If

Simplified declarations :

    Public Enum HRESULT As Integer
        S_OK = 0
        S_FALSE = 1
        E_NOINTERFACE = &H80004002
        E_NOTIMPL = &H80004001
        E_FAIL = &H80004005
        E_UNEXPECTED = &H8000FFFF
        E_OUTOFMEMORY = &H8007000E
    End Enum

    <ComImport, Guid("641BD880-2DC8-11D0-90EA-00AA0060F86C"), InterfaceType(ComInterfaceType.InterfaceIsIUnknown)>
    Public Interface IStillImage
        Function Initialize(hinst As IntPtr, dwVersion As UInteger) As HRESULT
        <PreserveSig>
        Function GetDeviceList(dwType As UInteger, dwFlags As UInteger, ByRef pdwItemsReturned As UInteger, ByRef ppBuffer As IntPtr) As HRESULT
        ' incomplete, not used...
    End Interface

Answer 2

Try something like this:

Dim s As Collection

Dim t As New Thread(Sub()
                        s = SCANNER.ScanImages()
                    End Sub)
t.IsBackground = True

t.Start()

REM wait 20 seconds

If Not t.Join(TimeSpan.FromSeconds(20)) Then
    t.Abort()
    MsgBox("Scanner is not responding")
Else
    For Each k In s
        PictureBox1.Load(k)
    Next
End If

Or check the SCANNER object and the documentation. Maybe there are more suitable methods.