Private Sub Button1_Click
Dim PageRoot As B4XView = GetRootPanel(TabStrip1, TabStrip1.CurrentPage)
Dim seekbar As B4XSeekBar = dd.GetViewByName(PageRoot, "B4XSeekBar1").Tag 'tag is needed because it is a custom view (https://www.b4x.com/android/forum/threads/117992/#content)
seekbar.Value = Rnd(0, 100)
End Sub
Private Sub GetRootPanel(TabStrip As TabStrip, PageIndex As Int) As B4XView
Return TabStrip.As(JavaObject).GetFieldJO("pages").RunMethod("get", Array(PageIndex))
End Sub