On the Android, is the expected action of the back button to navigate backward through menus, or does it just go "back" to the previous screen you came from?
I don't have an Android device to sample a number of applications to see what the norm is. I'm using phonegap to package an HTML5 app, so I need to manually handle any back button functionality.
The default behavior is to go to the previous screen no matter what it is.
For detailed information, see Task and Back Stack, Activity and Task Design Guidelines, and other topics about BACK button in Android Dev guide.
dnbrv and Pewpewarrows have it exactly right, but to point to the most definitive resource on the matter, the Android Design Guide says this:
The Up button is used to navigate within an application based on the hierarchical relationships between screens. For instance, if screen A displays a list of items, and selecting an item leads to screen B (which presents that item in more detail), then screen B should offer an Up button that returns to screen A.
If a screen is the topmost one in an app (i.e. the home of the app), it should not present an Up button.
The system Back key is used to navigate based on the history of screens the user has recently seen, in reverse chronological order—in effect, the temporal relationships between screens.
When the previously viewed screen is also the hierarchical parent of the current screen, pressing the Back key will have the same result as pressing an Up button -- this is a common occurrence. However, unlike the Up button, which ensures the user remains within your app, the Back key can return the user to the Home screen, or even to a different application.
This guide is new, but it is the best source for understanding how navigational patterns (and all other Android design constructs) should be applied to apps.
One more thing - if you're on the main screen of the App and there's no previous screen that you can go back to, pressing back button will close the app.
This is actually the only way to completely close the app. Silly pattern, as there is no warning in most of the apps (I've started to use alert box to let know user that it's going to shut down the app).
The expectation is that it acts as a global history within an app -- you can use it to go back from as many levels deep into a menu as you need to (and some apps will take you right back to the home screen that way, without exiting the app).
There is an option on android that affect this behavior. Under Developer options there is the option
"Do not keep activities"
If this is checked, then app instances are destroyed when they loose visability
Drove me crazy for a while, beieve me.
