Don't forget about the Phone library. Its also good for changing orientation between activities.
SetScreenOrientation (Orientation As Int)
Changes the current activity orientation. This method cannot be called from a service module.
Orientation - -1 for unspecified, 0 for landscape and 1 for portrait.
B4X:
Dim p as phone
Sub Activity_Create(FirstTime As Boolean)
'somewhere in your code for example
p.SetScreenOrientation (0) 'Switch to landscape mode
End Sub