Tasks are purely there for UI navigation -- they basically take on the roll of an "application" for the user, in lieu of a more rigid 1 apk == 1 process == 1 icon == 1 app model. A task really has little identity of its own -- without some activity, a task doesn't exist. It is just a way to group related activities together for purposes of managing flow through the UI.
For launch mode, I would strongly discourage from using singleTask unless you understand what that is, why the default interaction model doesn't work for your app, and how singleTask changes it to do what you want. The vast majority of apps don't need it. The Browser does use it, but I would argue that this is as much to its detriment as to its advantage. As far as the thought process... well, first there were activities, and that was all. A single linear activity stack was not enough for the UI navigation we ended up doing, though, so the concept of tasks was created as a way to group related activities together so they could be moved around in the history. If you look at the activity manager implementation, you can still see many remnants of the fact that tasks were a later addition -- the activity manager is still all oriented around a single global stack of activities, and the implementation of "tasks" is actually just re-ordering operations on that single list. So while the model we present is that each task has its own activity stack, the implementation hasn't actually caught up to that. (Actually this global list ends up being useful to have, anyway, to give the window manager a single holistic Z-ordering of all windows... but if we had started with tasks as a formal concept from the start, it is unlikely we would have ended up with the current implementation.) On Thu, May 7, 2009 at 11:59 AM, devi prasad <dpras...@gmail.com> wrote: > > I've been trying to understand the key concepts that make up the > Android programming model. I'm impressed as well as intrigued by > 'tasks' that stack up activities. I do not really appreciate why and > how one assigns a particular launch mode to an activity. For instance, > I'd like to define a few necessary conditions for marking an activity > the root of a new task. I'm focusing particularly on the 'singleTask' > launch mode. I'd like to know, for example, whether security, user > experience, and such factors decide the launch modes... > > Can someone educate me about the rationale behind Android tasks? I'm > also curious to know the thought process behind their design when they > were originally conceived? > > thanks > > > > -- Dianne Hackborn Android framework engineer hack...@android.com Note: please don't send private questions to me, as I don't have time to provide private support, and so won't reply to such e-mails. All such questions should be posted on public forums, where I and others can see and answer them. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Android Developers" group. To post to this group, send email to android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers-unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/android-developers?hl=en -~----------~----~----~----~------~----~------~--~---
