Basic question...on switching windows

[John Clark]

If I know the "title" of an open window of an application running on the
same PC that my application is installed, say for example "Window abc",
what's the best method of getting my vb.net to "switch" to that window as if
I'd clicked on the taskbar or pressed ALT+TAB?

It should be simple, but I've had no luck so far ..

Thanks,

JC

 

[Arne Janning]

If I know the "title" of an open window of an application running on the
same PC that my application is installed, say for example "Window abc",
what's the best method of getting my vb.net to "switch" to that window as
if I'd clicked on the taskbar or pressed ALT+TAB?

It should be simple, but I've had no luck so far ..

Hi John,

get a handle of the window using Win32-API FindWindow
http://www.pinvoke.net/default.aspx/user32.FindWindow

and bring it to front using
http://www.pinvoke.net/default.aspx/user32.SetForegroundWindow

or BringWindowToTop
http://www.pinvoke.net/default.aspx/user32.BringWindowToTop

Cheers

Arne Janning

 

[Tom Shelton]

Hi John,

get a handle of the window using Win32-API FindWindow
http://www.pinvoke.net/default.aspx/user32.FindWindow

and bring it to front using
http://www.pinvoke.net/default.aspx/user32.SetForegroundWindow

or BringWindowToTop
http://www.pinvoke.net/default.aspx/user32.BringWindowToTop

Cheers

Arne Janning

Actually, to make SetForegroundWindow work reliably, you'll also need to
use GetWindowThreadProcessId and AttachThreadInput as well...

findwindow 'get the window handle
getwindowthreadprocessid 'get the thread handle for the window
attachthreadinput ' attach to it's input queue
setforgroundwindow ' set it to the foreground
attachthreadinput ' detach from thread's input queue

This is because of changes made to the way SetForegroundWindow works in
Win98/Win2k and greater. The idea was to keep applications from stealing
the focus....

According to msdn SetForegroundWindow only works if one of the following is
true:

The process is the foreground process.
The process was started by the foreground process.
The process received the last input event.
There is no foreground process.
The foreground process is being debugged.
The foreground is not locked (see LockSetForegroundWindow).
The foreground lock time-out has expired (see SPI_GETFOREGROUNDLOCKTIMEOUT
in SystemParametersInfo).
Windows 2000/XP: No menus are active.

Using the above sequence seems to circumvent these restrictions and forces
the window to the top...

 

[Arne Janning]

According to msdn SetForegroundWindow only works if one of the following
is
true:

The process is the foreground process.
The process was started by the foreground process.
The process received the last input event.
There is no foreground process.
The foreground process is being debugged.
The foreground is not locked (see LockSetForegroundWindow).
The foreground lock time-out has expired (see SPI_GETFOREGROUNDLOCKTIMEOUT
in SystemParametersInfo).
Windows 2000/XP: No menus are active.

Using the above sequence seems to circumvent these restrictions and forces
the window to the top...

Hi Tom,

thanks for the feedback. You are right, of course, but I don't know if it
helps John.
As I couldn't find a working implementation in VB.NET on groups.google.com
or somewhere else on the net here is some code that worked for me and might
work for John as well:

Private Declare Function GetForegroundWindow _
Lib "user32" () As IntPtr
Private Declare Function SetForegroundWindow _
Lib "user32" (ByVal hWnd As IntPtr) As Boolean
Private Declare Function GetWindowThreadProcessId _
Lib "user32" (ByVal hWnd As IntPtr, _
ByVal lpdwProcessId As IntPtr) As Integer
Private Declare Function AttachThreadInput _
Lib "user32" (ByVal idAttach As Integer, _
ByVal idAttachTo As Integer, ByVal fAttach As Boolean _
) As Boolean
Private Declare Function FindWindow _
Lib "user32" Alias "FindWindowA" (ByVal lpClassName As String, _
ByVal lpWindowName As String) As IntPtr

Private Sub Button1_Click( _
ByVal sender As System.Object, _
ByVal e As System.EventArgs) _
Handles Button1.Click

Dim hwndApp As IntPtr
Dim hwndForeground As IntPtr
Dim ThreadForeground As Integer

hwndApp = FindWindow("Notepad", "Untitled - Notepad")
If Not hwndApp.Equals(IntPtr.Zero) AndAlso _
Not hwndApp.Equals(GetForegroundWindow) Then
ThreadForeground = GetWindowThreadProcessId(hwndForeground,
IntPtr.Zero)
AttachThreadInput(ThreadForeground, 0, True)
SetForegroundWindow(hwndApp)
AttachThreadInput(ThreadForeground, 0, False)
End If
End Sub

One may have to use Spy++ to get more details about the window that shall be
set to the foreground.

Cheers

Arne Janning

 

[Tom Shelton]

Hi Tom,

thanks for the feedback. You are right, of course, but I don't know if it
helps John.
As I couldn't find a working implementation in VB.NET on groups.google.com
or somewhere else on the net here is some code that worked for me and might
work for John as well:

Private Declare Function GetForegroundWindow _
Lib "user32" () As IntPtr
Private Declare Function SetForegroundWindow _
Lib "user32" (ByVal hWnd As IntPtr) As Boolean
Private Declare Function GetWindowThreadProcessId _
Lib "user32" (ByVal hWnd As IntPtr, _
ByVal lpdwProcessId As IntPtr) As Integer
Private Declare Function AttachThreadInput _
Lib "user32" (ByVal idAttach As Integer, _
ByVal idAttachTo As Integer, ByVal fAttach As Boolean _
) As Boolean
Private Declare Function FindWindow _
Lib "user32" Alias "FindWindowA" (ByVal lpClassName As String, _
ByVal lpWindowName As String) As IntPtr

Private Sub Button1_Click( _
ByVal sender As System.Object, _
ByVal e As System.EventArgs) _
Handles Button1.Click

Dim hwndApp As IntPtr
Dim hwndForeground As IntPtr
Dim ThreadForeground As Integer

hwndApp = FindWindow("Notepad", "Untitled - Notepad")
If Not hwndApp.Equals(IntPtr.Zero) AndAlso _
Not hwndApp.Equals(GetForegroundWindow) Then
ThreadForeground = GetWindowThreadProcessId(hwndForeground,
IntPtr.Zero)
AttachThreadInput(ThreadForeground, 0, True)
SetForegroundWindow(hwndApp)
AttachThreadInput(ThreadForeground, 0, False)
End If
End Sub

One may have to use Spy++ to get more details about the window that shall be
set to the foreground.

Cheers

Arne Janning

Good example Arne...

 

[JC - home]

Many thanks for all the assistance here Very much appreciated!

JC