Office Hours — Today, March 24

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Mar 24
8:20 AM
Mark M.
has entered the room
8:25 AM
Mark M.
turned on guest access
8:30 AM
Leora
has entered the room
Leora
Hi Mark!
Mark M.
hello, Leora!
how can I help you today?
Jan S.
has entered the room
Mark M.
and hello, Jan!
Leora
A regular ol' question in these interesting times:
Jan S.
Hello, everyone!
Leora
Hi Jan!
I have a recyclerView with a height of 0dp
Mark M.
is that in a ConstraintLayout, so the height is determined by constraints?
Leora
In my adapter I measure the height...it works great except for the first run on devices with a soft bottom navigation
Yes
Mark M.
why does your adapter need to measure the height?
Leora
So I check the height of the navigation and add it...this also works great
Oh, so the adapter takes the total height and does a calculation to determine the height of the items
Mark M.
so, you're trying to exactly fit the items to the available space?
Leora
Cause the number of items is set dynamically
Yes
Works excellent with hard nav buttons
And now excellent with soft with first app run
But
8:35 AM
Leora
when user clicks bottom nav, thus loading a new fragment, it STILL takes the height of the nav bar even though the bar is not visible
When I implement onSystemUiVisibilityChange() it's too late
(onBindViewHolder has already been called and the items already laid out)
Mark M.
will this RecyclerView scroll? or are you trying to show all items at once?
Leora
all items at once...static
Mark M.
then I would not use RecyclerView
no scrolling == no recyclingg
er, recycling
just put the items as children of the ConstraintLayout, and set up chains to allocate the whitespace
Leora
actually I discussed this with you last year and came to the conclusion recycler best in this case
Mark M.
OK
I'll defer to "past me", then :-)
Leora
i can't, the lite version shows banner adds and i animate the recyclerview children to smoosh them
Mark M.
"when user clicks bottom nav, thus loading a new fragment, it STILL takes the height of the nav bar even though the bar is not visible" -- first, isn't the list gone? if not, where did this new fragment go?
8:40 AM
Mark M.
second, to be clear, the bar in question is the classic Android HOME/BACK/RECENTS bar? or by "bottom navigation" do you mean the Material Design bottom tabs thing?
Leora
sorry, user clicks MY bottom toolbar
and bar in question (for height and visibility) is android home etc
the code i use to get the height is:
View paste 
  int resourceId = resources.getIdentifier("navigation_bar_height", "dimen", "android");
                if (resourceId > 0) {
                    navigationBarHeight = resources.getDimensionPixelSize(resourceId);
                }
but it gets the height even when not visible :/
Mark M.
you might want to look into the window insets stuff
I think there is a Jetpack edition of those
and I think it handles this scenario, more flexibly than relying on a magic resource
Leora
i started to but the documentation says its waiting for the feature to be fully 'baked'
Mark M.
even half-baked, it might help in your situation
Leora
ok i'll try to muddle through it
Mark M.
personally, I really try to avoid this full-screen stuff as much as possible, because it has always been a pain in various body parts
and so when there's a Google library that aims to simplify it, I'd be all over that
plus, the full-screen stuff is changing a bit in Android R
Leora
how to avoid it? i need to measure item height
Mark M.
I try to avoid that scenario, and when I can't, I try to let something else handle it (e.g., ConstraintLayout and chains)
8:45 AM
Mark M.
in your case, you may have no option
Leora
could i still animate the views when a banner appears?
Mark M.
with ConstraintLayout, yes -- you can animate the transition between ConsrtraintSets
er, ConstraintSets
(are typos a sign of COVID-19? if so, I'm doomed...)
Leora
yes they are hahaha
sorry to clear...
i can animate the height of the items??? or only the constraints (margins) between them?
Mark M.
I've used that sort of animation to animate the height of a bottom sheet, based upon changes in visibility of its contents
there is probably a recipe for changing the actual item heights, though I can't be completely certain of that
let me take a question from Jan, and I'll come back to you in a bit
Leora
sure!
Mark M.
Jan: your turn! do you have a question?
Jan S.
View paste 
Exploring Android: Could you have used savedIntanceState instead of the menuMap variable to save the filterMode in the version of the ToDO app that does the filtering of the list?
Mark M.
not directly
MenuItem cannot go in a Bundle
8:50 AM
Mark M.
some future update to this book may use SavedStateHandle to save the current filter selection, to hold onto that across short-term process termination
menuMap is just a cache for findItem() calls on the Menu, so I don't have to do that on the fly later on
Jan S.
okay. One other about that book's example: Is the MasterDetail template provided by Studio a good model to use? I couldn't find any example in your book though the exploring android book mentioned you'd show it on tablet.
Mark M.
doing a large-screen edition of this UI is another thing that I may add to some future version of the book
in terms of the Studio templates... generally, I do not like them, but I have not looked at that one specifically in quite some time
Jan S.
okay. Thanks.
Mark M.
Google has also been backing away from master-detail, though IMHO it is still a useful pattern in some cases, this app in particular
the problem with master-detail is for resizable windows, it makes for a harsh transition
Google is steering developers towards more flexible "master" UIs that can leverage the additional screen space, such as a grid that adds/removes columns based upon changing window size
and for some sorts of data, that works
8:55 AM
Mark M.
let me take another question from Leora, and I'll be back with you shortly
Leora: back to you! do you have another question?
Leora
nahhh i think i'm stuck looking at the insets for now
Mark M.
the nice thing is that if you get those to work, they should handle other scenarios, such as if the user has gesture nav enabled, the lack of intruding nav on freeform windows (Chrome OS), etc.
Leora
thanks Mark! Be safe :)
You too Jan
Mark M.
you too!
OK, Jan, back to you! do you have another question?
Jan S.
Storage Access Framework: any reason to use for read-only text files in app's local storage? AssetManager looks simpler to use and I presume has less overhead.
Leora
"the lack of intruding nav on freeform windows (Chrome OS), etc" ?????
Mark M.
Leora: IIRC, in Chrome OS, the nav bar is outside of your app window, so while the bar exists, you would not take it into account in your sorts of measurements
Jan: AssetManager is for stuff that you ship with your app. If that's how you plan to get the read-only text to users, AssetManager is cheap and easy.
Leora
ugh
Mark M.
however, it is very read-only, so the only direct way of replacing the text is to update the app
you can do stuff where you look for a local file (e.g., in getCacheDir()) that perhaps you downloaded, then fall back to an asset if that file does not exist
9:00 AM
Mark M.
and none of that would require the Storage Access Framework
(Leora: you're starting to see why I really try to avoid messing with this stuff...)
(it was never easy, and modern versions of Android really start to add to the combinations -- e.g., split-screen on phones, where once again the nav bar is not part of your window)
Leora
I'm thinking of moving the whole layout from Constraint to good ole Linear
Jan S.
The text files are shipping with app. But they may need to be updated without updating app. They will never be written by app due to something the user does.
Leora: Linear sounds easy compared to what you are going to have to deal with in future.
Mark M.
Jan: will the app be updating the text itself (e.g., downloading from a server)? or does the user download something themselves that serves as the update?
Leora
I tried to be a good android soldier but....
9:05 AM
Mark M.
Leora: while ConstraintLayout is more flexible, there is nothing wrong with simple LinearLayout structures. Just be careful about too much nesting. From the description of your problem, I'm unconvinced that switching to LinearLayout will eliminate your need to do the measurement work, though.
Leora
Me thinks you're correct
Jan S.
A new version of the text file. For example, the child goes to next grade so the text's vocabulary needs to be updated. Not sure yet how we'll deal with it.
Mark M.
if the app can handle downloading it directly, you would not need the Storage Access Framework -- just download to getCacheDir() and use the pre-packaged asset as the fallback
if the user needs to download it, then you will want to consider the Storage Access Framework, particularly on Android 10
9:10 AM
Jan S.
Thanks. Very helpful. Should I be using viewModel (not using RecyclerView and at moment see no need for LiveData) to restore data (the text from the text file) through lifecycle changes. I get a little confused about all that.
Mark M.
it would be faster than you re-loading it from the file or asset
and, since I/O takes time, I would use LiveData, so you can do that I/O on a background thread and update the UI once it is ready
Jan S.
Thanks. Mark. That's all I have. Have a great day!
Mark M.
you too!
Jan S.
has left the room
Leora
has left the room
9:25 AM
Mark M.
turned off guest access

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Office Hours

People in this transcript

  • Jan Smith
  • Leora
  • Mark Murphy