Question

I’m just learning Android programming. The way I understand it is that the services work like a stack, Is there a way for a activity to return to the first activity that started the app, instead of just the previous one.

Example, say I have 4 activities, a,b,c,d. Is there a way for activity d to have a button that would bring up activity a?? Instead of activity d going to c, and c going back to b???

Answer 1

You can start again activity a, but using a flag in your intent:

FLAG_ACTIVITY_REORDER_TO_FRONT

From android docs:

If set in an Intent passed to Context.startActivity(), this flag will cause the launched activity to be brought to the front of its task’s history stack if it is already running.

Using this, you’ll reuse the instance of activity a already running, instead of starting a new one. Note that doing this, the instances of activities b, c and d will remain in the back stack (now after activity a).

Otherwise, if you want to finish this activities (and remove them from the back stack) you can start activity a (from d) with this other flag:

FLAG_ACTIVITY_CLEAR_TOP

If set, and the activity being launched is already running in the current task, then instead of launching a new instance of that activity, all of the other activities on top of it will be closed and this Intent will be delivered to the (now on top) old activity as a new Intent.

EDIT: this is a good resource to read, if you haven’t did it yet:
Tasks and Back Stack.