B4J Question Is there an event that triggers when a B4J [UI] application loses focus?

Private Sub MainForm_FocusChanged (HasFocus As Boolean)
    TextAreaLog.Text = TextAreaLog.Text & HasFocus & CRLF 'This is a TextArea on the MainForm...
End Sub

'need a special library... the jna... easy to get it from the internet !!!
    #AdditionalJar: jna-5.2.0
    #AdditionalJar: jna-platform-5.2.0


Sub Process_Globals
    Private fx As JFX
    Private MainForm As Form
    Private xui As XUI
    Private Button1 As B4XView
'you will need the timer:
    Private tm As Timer
End Sub

Sub AppStart (Form1 As Form, Args() As String)
    MainForm = Form1
    MainForm.RootPane.LoadLayout("Layout1")
    MainForm.Show
   
'you can have this in b4xpages to check every 0.5 sec:
    tm.Initialize("Timer1",500)
    tm.Enabled=True
   
End Sub

'and this sub to check what is in front:
Sub Timer1_tick
tm.Enabled=False
    Dim user32 As JavaObject
    user32 = user32.InitializeStatic("com.sun.jna.platform.win32.User32").GetField("INSTANCE")
   
    Dim hwnd1 As JavaObject = user32.RunMethod("GetForegroundWindow",Null)

    Dim Rect As JavaObject
    Rect.InitializeNewInstance("com.sun.jna.platform.win32.WinDef.RECT",Null)
    user32.runmethod("GetWindowRect",Array(hwnd1,Rect))
   
    Dim title(512) As Char
    user32.RunMethod("GetWindowText", Array(hwnd1,title,512))
    Dim native As JavaObject
    Dim activewindowtitle As String = native.InitializeStatic("com.sun.jna.Native").RunMethod("toString", Array(title))
    activewindowtitle = activewindowtitle.Trim
'check for it:
    Log(activewindowtitle)
'you can even get the height or width of form... or the position... you can play with magic..
    Log(Rect.GetField("left") & " " & (Rect.GetField("right")-Rect.GetField("left")))
tm.Enabled=True
End Sub

Sub MainForm_FocusChanged (HasFocus As Boolean)