It is likely that the Mobu viewport/rendering is on a separate thread from normal scene processing. Which would explain why the scene navigator updates and the viewport does not. The viewport only seems to update if the application is the focused application. With this in mind I decided to force change the application focus to get the results I wanted.
When the python tool makes a connection to the specific dcc app I will call the following:
import win32gui, win32con def enum_callback(self, hwnd, results): self.winlist.append((hwnd, win32gui.GetWindowText(hwnd))) def get_dcc_hwnd(self, app_name): self.toplist =  self.winlist =  win32gui.EnumWindows(self.enum_callback, self.toplist) # look for the specific application window name dcc = [(hwnd, title) for hwnd, title in self.winlist if app_name in title.lower()] if dcc != None and dcc != None: dcc = dcc self.dcc_hwnd = dcc get_dcc_hwnd( 'motionbuilder')This will return self.dcc_hwnd and all that really is is a window process handle or long integer. In this example it is. DCC Handle: 3214530
Now that I have stored the window handle when I select an object in my listview it will call the following:
def set_dcc_focus(self): if self.dcc_hwnd != None: # store the current python tool window handle current_hwnd = win32gui.GetForegroundWindow() # use the window handle to set focus win32gui.SetForegroundWindow(self.dcc_hwnd) # important to sleep here as to allow Mobu time to draw time.sleep(0.03) try: # set the focus back to the python tool win32gui.SetForegroundWindow(current_hwnd) except: returnWith this I can click on all the objects in my external tool and see the select update 'realtime' within the MotionBuilder viewport. The code will change the window focus momentarily and just long enough to redraw the MotionBuilder viewport then immediately return focus back to the python tool. With the sleep time I have set here it is fast enough that I can be pressing down on the keyboard to step between items in the listview without noticing the app focus switching. However, I have noticed that if Motionbuilder doesn't have enough time to redraw, some things have the possibility of not rendering when the viewport is redrawn. So the sleep here could become variable and dependent on the amount of objects within the viewport.
In the comments below, Kevin pointed out that you can skip all of this and modify the application.txt by adding the following line under [Timing]
NoFastIdleOnDeactivate = No