Navigation with Up and Back buttons is quite complicated (at least for me) As the android documentation states,
You have the ability to make the Up behavior even smarter based on your knowledge of detail view. Extending the Play Store example from above, imagine the user has navigated from the last Book viewed to the details for the Movie adaptation. In that case, Up can return to a container (Movies) which the user hasn't previously navigated through. http://developer.android.com/design/media/navigation_between_siblings_market2.png
I am exploring Google IO 2013 application for best practices and as far as I can see the mentioned above navigation rules are not taken into consideration. Here is the picture: https://dl.dropboxusercontent.com/u/6129677/do_not_delete/iosched2013.png
I launch the app and the main screen opens (#1). I tap on 'Browse sessions' -> second screen opens. Then I tap on a session - its detailed view is opened (#3). UP button says that this is 'Google+' category, and I expect to navigate to list of 'Google+' sessions after clicking on this button. Instead, the first screen is opened again (see picture).
Is this a correct behaviour and I am missing something?
Android design says that the up button goes up to the container regardless of what the icon is. It also says that the icon in the top left should be of the app. So in this case you could say that it violates the design by having a g+ icon.
That being said it is okay to violate android design if you have a specific reason to, in this case Google decided that it would like to show the icon of the category to give the user an indication of what category is without having to show 2 icons. In this case, they didn't want to alter the design all the way so as to go back to g+, but to assume the user understands that they are replacing the app icon with the category icon. So while they could show your 4th screen, they aren't necessarily required to and it depends on what you think will be best for user flows. Android design is meant to guide your individual design and doesn't need to be followed strictly (though it should be most of the time).
Hope that helps, I'm happy to answer any follow up questions.
来源：https://stackoverflow.com/questions/18941913/is-navigation-in-iosched-13-application-correct