Window Handle Changes in Always-On-Top Window?

Hi egl1044,

I thought that I had a working method, but the example you gave (mutex) didn't work. I pasted it into my app exactly as you instructed.

It seems to detect the application itself even when another instance is not running, and prevents itself from loading. Can you please assist?

Thanks!

Hi ttobin,

My understanding from your last question was that you wanted to prevent multiple instances of your application from loading if you detected another instance you wanted to have your application show the first main instance even if it was in the system tray. The code I posted in your last post should work :). Just to be sure you need to test it in the compiled form rather executable form and not from the VB IDE.

It works by creating a block of memory in your application, I then write the first instance (hWnd) to this memory. Now if another instance was to be launched your application would read that block of memory and obtain the (hWnd). This (hWnd) is actually the first instance and not the (NEW) instance. This way you can use the (hWnd) with ShowWindow() API.

This what you were looking for? If I am completely wrong here just let me know what it is your doing and I can help you solve it :)

Thanks for your quick response, egl1044!

The concept is very logical...I will give it another try.

egl1044, it works great!

My mistake was, I was trying to run it from the VB IDE (duh).

Does the use of the memory block require any clean up when closing the app?

Thanks again!!!

Also, ShowWindow shows the app when it is minimized to the system tray, but not when it is minimized to the task bar. How can I show it in that case also?

In combination with your excellent mutex method, using the all of the following commands togethe, I can cover all possibilities.  I can now show the original instance window whether it is minimized to system tray or task bar, or if it is hiding behind other windows:

Public Const SW_NORMAL = 4
Public Const SW_SHOW = 5

 If AppPrevInstanceSecure("MyAppName") Then
    MainAppWindow = hWndFromMainApp
    ShowWindow(MainAppWindow, SW_SHOW)
    ShowWindow(MainAppWindow, SW_NORMAL)
    SetForegroundWindow (MainAppWindow)
    End
Else
    InitForMainApp Me.hwnd
End If

Is that OK or do you recommend a better way?
Please also comment on my clean up question.

Thanks!

Hi,

Great to to see it's working :)
IsIconic
http://msdn.microsoft.com/en-us/library/ms633527(VS.85).aspx
ShowWindow
http://msdn.microsoft.com/en-us/library/ms633548(VS.85).aspx

It looks good to me (untested) but from the documents SW_RESTORE seems to be the flag to use to show the window from the minimized state. You can try it and see if it works.

Private Declare Function IsIconic Lib "user32" (ByVal hWnd As Long) As Long
 
 If IsIconic(Me.hWnd) Then'your hwnd
    ' SW_RESTORE
    Else
    ' SW_SHOW
  End If

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<< Does the use of the memory block require any clean up when closing the app? >>

Nope. You should be fine here. It only allocates 4 bytes of memory this is the size of a single Long variable so nothing to worry about. When your main instance closes the memory will be released automatically.

Also here is the difference between VB's internal AppPrevInstance and the Mutex(AppPrevInstanceSecure) when using the VB method if someone renamed your executable or moved its location  multiple instances would still be launced. However with the Mutex approach a user can rename your executable or move it on the system and it will still block a second instance. So it's the much better option to use for making sure a second instance never spawns.

The reason it doesn't work in the VB IDE is for one we never call ReleaseMutex() and you can't really test multiple instance from VB IDE :)

Excellent!!! Thank you very much!