Hello all,
I want to know how we can prevent a session of form(both Mdi and simple)if its session is already on.Is there any method or property available that tells us if the session of the same instance of the form is on.
I will be really thankful.
Thanks,
Misbah H. Ansari.

If I understand your question correctly, you can determine whether a WINDOW IS OPEN ALREADY using API calls. Here's some logic from an old VB6 program of mine that will iterate through all the open windows using a callback function and set a global boolean flag. Sorry if the formatting is off in this little window. Hopefully you can figure out how to put the code back together and change it to check for the title you're looking for:

Public Declare Function EnumWindows Lib "user32.dll" (ByVal _ lpEnumFunc As Long, ByVal lParam As Long) As Long
Public Declare Function GetWindowText Lib "user32.dll" _ Alias "GetWindowTextA" (ByVal hwnd As Long, ByVal lpString As _ String, ByVal nMaxCount As Long) As Long
Public Declare Function GetWindowTextLength Lib "user32.dll" _ Alias "GetWindowTextLengthA" (ByVal hwnd As Long) As Long

'************************************************* ********************' EnumWindowsProc enumerates through all of the open windows on the
' system to check for a specific title

Public Function EnumWindowsProc(ByVal lngHwnd As Long, _
                                ByVal lngParam As Long) As Long
Dim lngTitleLength As Long
Dim strBuffer As String ' title bar text length and strBuffer
Dim lngRetVal As Long ' return value

' get length of title bar text for current window

  lngTitleLength = GetWindowTextLength(lngHwnd) + 1

  If lngTitleLength > 1 Then
    strBuffer = Space(lngTitleLength) ' make room in the buffer

    ' get title bar text

    lngRetVal = GetWindowText(lngHwnd, strBuffer, lngTitleLength)
  End If

  If InStr(UCase$(Left(strBuffer, lngTitleLength - 1)), _
   "YOUR WINDOW TITLE GOES HERE") > 0 Then
   ' SET A GLOBAL BOOLEAN OR WHATEVER HERE
   ' TO INDICATE YOUR WINDOW WAS FOUND
  End If

  EnumWindowsProc = 1 ' return value of 1 means continue enumeration
End Function ' EnumWindowsProc

Then call the function using this whereveryou need to from your code

Dim lngRetVal As Long

  ' enumerate through the open windows

  lngRetVal = EnumWindows(AddressOf EnumWindowsProc, 0)

Actually there are several different ways to do this is .Net

For MIDI forms I usually us a private withevents variable that is local to the whole class and if it isn't nothing then I can't create a new form. You must handle the Closing or Closed event and set the variable to Nothing.

For other forms I use a simple bit of code.

#Region "PREVIOUS INSTANCE"
    Public Function PREVIOUS_INSTANCE() As Boolean
        If UBound(Diagnostics.Process.GetProcessesByName(Diag nostics.Process.GetCurrentProcess.ProcessName)) > 0 Then
            Return True
        Else
            Return False
        End If
    End Function
#End Region

OR YOU CAN USE A MUTEX

#Region "Declarations"
    Private Shared _config As AppStartConfiguration = Nothing
    Private Shared _exePath As String = ""
    Private Shared _process As Process
    Private Shared _appStartMutex As Mutex
    Private Shared _mutexGuid As New Guid(New Byte() {&H5F, &H4D, &H69, &H63, &H68, &H61, &H65, &H6C, &H20, &H53, &H74, &H75, &H61, &H72, &H74, &H5F})
#End Region
#Region "Main"
    <STAThread()> _
     Shared Sub Main()
        Dim isOwned As Boolean = False

        _appStartMutex = New Mutex(True, _config.ExePath + _mutexGuid.ToString(), isOwned)

        If Not isOwned Then
            MessageBox.Show(String.Format(CultureInfo.CurrentC ulture, "There is already a copy of the application '{0}' running. Please close that application before starting a new one.", _config.ExePath))
            Environment.Exit(1)
            Exit Sub
        End If

        StartApp_Process()
    End Sub
#End Region

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