Hi Mark, how are you?

hello, Lucy!

how can I help you today?

Let's see...I have a couple of questions regarding navigating

I guess my first question is: is there a trick to using addToBackStack when adding Fragments in a transaction? It doesn't seem to do anything for me. Hit the Back button on the device and I go back to the first Fragment.

I guess I do not understand your question

addToBackStack() reverses the transaction when the user presses BACK

I beginTransaction and then addToBackStack. But clicking Back does not take me back to the last Fragment in the series of Fragments in the Activity such as: F1->F2->F3 and then hit Back. I go to F1.

are F2 and F3 being added in a single transaction, or in multiple transactions?

Multiple Transactions. User clicks Next in a Fragment and I create a new transaction and add or replace the existing fragment with a new one.

and both of those transactions have addToBackStack()?

that's correct

Maybe I am still doing something wrong. If it should "just work" then I will try again.

and both transactions are applied by the same FragmentManager?

it should "just work"

Yes. In fact, I replace/add the Fragments inside the Activity by calling mListener.switchMyFragment() kind of design.

then I cannot explain your results

I will try again.

OK next navigation topic!

I've read page 421 of Busy Coders and I also saw some SO posts of yours regarding use of the flags: FLAG_ACTIVITY_CLEAR_TOP and FLAG_ACTIVITY_SINGLE_TOP

In my case, I have the following progression of Activities: A->B->C

On Activity C the user can click one of several buttons that launch other Activities let's call them D1->E1 and D2->E2. Ideally I'd like to return to Activity C.

My question is: can I use those flags to return to any Activity I want in the progression?

FLAG_ACTIVITY_CLEAR_TOP should do that; also use FLAG_ACTIVITY_SINGLE_TOP if you want to use the existing C instance

otherwise, assuming you haven't messed with launchOptions in the manifest, C will be destroyed and recreated

Yes that is what I would like. So for A->B->C I pass no flags. Then for D1, E1 etc I pass those flags?

no

when you want to go back to C, you pass those flags

Yeah I tried using those manifest options. I will make sure they are all gone.

on your startActivity() that returns the user to C

OK cool I will try that!

the docs for FLAG_ACTIVITY_CLEAR_TOP are pretty close to describing your scenario: https://developer.android.com/reference/android...

Excellent, thanks!

I will study that flag further. Perhaps I should control things from the code rather than the manifest.

I prefer to control from code where I can, particularly for non-exported activities

I'll polish my navigation further as its a bit clunky right now.

you have greater flexibility

as there is but one manifest

yeah, navigation in a multi-activity app can get painful

great point.

Yeah I wrote those bits to be Activities because I might want the functionality to be called from somewhere else.

if by "somewhere else", you also mean "someONE else", then you need to think more about launch modes

as you cannot readily force a third-party app to use certain flags

Oh luckily I mean in my own app.

OK

Only myself calling them. They bring up a piece of data that can be handy on its own.

Another question. I hope it makes sense. I am sending a notification to the user. They tap it in the notification bar, my app opens ActivityXYZ. I want the user to have a one-time chance to do something in response. I don't have navigation to ActivityXYZ except when tapping a notification. I wondered if its enough to enforce the "one time" whereby user taps, opens ActivityXYZ, clicks a button and I call finish() on that button.

Is it enough to make something a "one time" opportunity to do XYZ in response to a Notification.

I suppose I am asking that without another way to navigate to ActivityXYZ they should not be able to call it.

well, users cannot get to any activity unless you provide a means for them to do so

s/call it/launch it/

what you need to do is ensure that XYZ does not wind up in its own task

OH.

as otherwise the user could get back to that task from the overview screen

and notifications historically required FLAG_ACTIVITY_NEW_TASK

I see. Interesting. I will research that.

or, if you really do need it in its own task, try finishAndClearTask()

I've been using an adb command to track how many activities are open.

Oh I'm not familiar with finishAndClearTask(). Will read about that.

sorry, finishAndRemoveTask()

new to API Level 21, though

Hm. Yeah my app will support 19+

Still, I did not know about this. I will read more.

When I figure out what I'm doing wrong for addToBackStack I'll come back and let you know! Ditto for Activity flags.

Thanks again!

you're welcome!