I'm trying to get clear about task/back stack on Android at http://developer.android.com/design/patterns/navigation.html.
When reach the part below i have some question. Please take a look on it first (or go to the link above to read all the post)
However, by touching Up from the compose activity, the user indicates a desire to remain within Gmail. Gmail's conversation list activity appears, and a new Task B is created for it. New tasks are always rooted to Home, so touching Back from the conversation list returns there.
Task A persists in the background, and the user may return to it later (for example, via the Recents screen). If Gmail already had its own task running in the background, it would be replaced with Task B—the prior context is abandoned in favor of the user's new goal.
Now, get back to this question.
- Why does it create new task B in this case? (when user touching Up from the compose activity)
- What does it means by "it would be replaced with Task B"
Could you help to make it clear, please!?