hello, Vasanthi

how can I help you today?

Hello, Mark. Thank you.

I have a few questions and would appreciate if you could answer them

I can try

Thanks.

1. Simple_list_item_2 – how come that doesn’t have a layout as the root element?

hold on

OK, I am confused

If you are referring to android.R.layout.simple_list_item_two, it uses a TwoLineListItem as the root element, holding a pair of TextView widgets

er, sorry, android.R.layout.simple_list_item_2

That is the one.

I guess I do not understand your question, then

I thought if you have more than one widget in a layout, the root has to be a layout

no

Sorry, my laptop is very slow..

So, there is no rule that a layout has to be the root element?

or, rather, it depends upon what you mean by "the root has to be a layout"

Now I am confused

there are many things in Android that use the term "layout"

with respect to TwoLineListItem, it is a (now deprecated) subclass of RelativeLayout

OK, now I understand.

if by "a layout has to be the root element", you mean "a Java class that ends in Layout has to be the root element", that is most certainly not the case

Yup, now I understand. Thank you.

the root view element of a layout resource file could be a <fragment>, a <ViewPager>, a <TextView>, etc.

OK. Can it be a class I have extended from one of the Layout classes?

I do not know what "one of the Layout classes" means

Sorry for my wording. a widget extending one of the Layouts?

I do not know what "one of the Layouts" means

for e.g.RelativeLayout or LinearLayout

try asking a question that does not involve the word "layout" used on its own, as there are many things in Android that are called "layouts"

those classes are not magic

in a layout XML resource file, the parent of view element is going to be a subclass of ViewGroup in most cases

RelativeLayout happens to inherit from ViewGroup

ViewPager happens to inherit from ViewGroup

Now, I understand.

That has cleared my doubt.

some subclasses of ViewGroup do not use child elements in layout XML resource files (e.g., ListView)

2. What will happen if we don’t use Adapters? Say for e.g. can I have a list of items and display them in a ListView? What does the Array Adapter provide us?

Sorry.

"can I have a list of items and display them in a ListView?" -- if you have an adapter somewhere, yes

Hi Rafael

an AdapterView, like ListView, works with Adapter objects to determine its contents

(BTW, hello, Refael -- I will be with you in a moment!)

Hi Vasanthi, Mark :)

Mark, I am trying to digest what you have written, so will take a few mins.

OK, let me take a question from Refael in the meantime, and I will be back with you shortly

Refael: your turn! do you have a question?

OK, thank you.

actually mark I have 3 :)

give me the first one for starters

sure, ok so first off I would like to ask, I was following your github project, it gave me TONS of help, the one regarding AlarmManager with the OnBoot receiver

I am using that code to start an alarm manager on repeat, that opens a service that runs a few actions for a few seconds and then closes. the alarm repeats every 10 minutes.

problem is, if my app crash, the alarm stops repeating itself

I've been doing some digging and I have no good idea as to how to solve it

what method are you calling on AlarmManager to set up the alarm?

one sec

alarmManager.setRepeating(AlarmManager.ELAPSED_REALTIME_WAKEUP, SystemClock.elapsedRealtime()+10000, TIME, pi);

TIME is 10 minutes

pi is my PendingIntent

I am not aware that an unhandled exception would unschedule an alarm

though you are the second person to mention this behavior in the past week or so

I'll need to run some experiments to see if I can reproduce the effect

every 10 minutes my service runs and among other things it writes a log into a .txt file of the exact time it did it's job

for some reason I noticed when i'm crashing

the alarm stops

what version(s) of Android are you seeing this on, and what is your targetSdkVersion?

minSdk 14, targetSdk 21

I am testing it on the latest android version, on Nexus 6

OK, I'll run some tests as part of my overall "OMG M!" battery of work I need to get done

let me take a question from Vasanthi, and I'll be back with you in a bit

Vasanthi: your turn! do you have a question?

sure thing

Yes, have some more. So, according to your answer about adapters, without an adapter, I can't display a list of items in a view?

to use an AdapterView, you need an Adapter

you can use RecyclerView, but it needs a RecyclerView.Adapter

OK. What does the Array Adapter provide us? Does it provide pagination?

Or is the pagination provided by the ListView that I am using?

neither; there is no pagination

presumably, you are a subscriber to my book (by virtue of being in this chat)

YES.

then I suggest that you read "AdapterViews and Adapter"

it starts on page 249 of Version 6.6 of the book

Yes, I have read that chapter and did the examples as well.

then I don't know what I can tell you

According to page 233, ListView knows how to scroll. Then why is my ListViewDemo not scrolling?

perhaps you don't have enough data that it needs to scroll

No, I have more items than what it displays.

then there is a problem with your device/emulator, or something

I am using the emulator. If I want to debug, can I debug? Where should I place the break point?

I have no idea

OK. I have few more questions, so if you want to answer Refael's and come back to me?

OK

Refael: your turn! do you have another question?

yup

Another problem I've been having this week is with design, I need to create a facebook like card item, but the whole card has to present an imageview, and it needs to have rounded corners, and a shadow

Once again, I never come to you with a problem before I got my hands really dirty first..

sounds like a CardView wrapped around an ImageView

How am I supposed to also get rounded corners and shadow too? I tried several way that I saw on stackoverflow, none of them seemed to work

CardView has rounded corners and a shadow

CardView?

googling

it came out as part of the Android Support package last yaer

er, year

it's a stock implementation of the card-style UI that you describe, as a subclass of FrameLayout (IIRC)

on Android 5.0+, it uses the system-supplied elevation-based drop shadow

on older devices, it emulates a drop-shadow using a nine-patch PNG or something

wow, never heard of it before, and didn't found any trace of it in my search..

I have some examples of it in my RecyclerView chapter

it's pretty much just a decorating container class -- wrap it around something else to give it the card-like look

yeah I saw the elevation one, works really well, but I have to support threw to api 14

hmmm so, wait, cardview can be supported to api 14?

it works back to API Level 7

wow amazing

looks neat

anyway, it's worth trying for your use case

ok so thats good for me, ill play around with it, Vasanthi? you're up? or should I fire away my 3rd question?

Yup.

Vasanthi: your turn! do you have another question?

the ArrayAdaptor’s getView

a. What are the parameters int position (I assume that it is the position of chosen item within the list), View convertView and ViewGroup parent ?

again, this is covered in the chapter that you read

position is the index into your collection of model data

Just wanted to figure out whether this gets called for for each and every item in the list to be displayed?

convertView is either null or a previous View that you returned from an earlier call to getView(), for recycling purposes

parent is the ListView itself

yes, it is called for each item in the list

at least, when those need to be shown, or possibly cached

Thank you.

Its Refael's turn

so, in a 25-item ListView, where 8 rows are visible, getView() will be called at the outset 8+ times, but not all 25

OK.

Refael: back to you!

so, my last question.. I have a layout in my main screen, I need to present a list of users inside those card views with just talked about, the list view is vertical, my problem is.. at the top of that screen I need to have another listview, this one is horizontal, and it has only 10 items displaying my top10 users. I'm wrapping all that screen in a scrollview so I can scroll the entire screen down.

but that's creating a problem using the horizontal scrolling

have the horizontal thingy be a row in the ListView

you scroll to the sides and also pull the scrollview down/up on the same time

rather than wrapping the whole structure in a ScrollView

or use addHeaderView() on the ListView to add your horizontal thingy

hmm, interesting approach

you're just brilliant Mark! how come I didn't think of it

I will go to great lengths to avoid trying to do the touch event hacking necessary to have a vertically scrollable thingy in a ScrollView

now, that may not completely solve your problem, but it gets rid of one item (the ScrollView) that's fighting over the touch events

yeah, but i will also be able to scroll down in that list

it may clear up your problem entirely, or you may still have issues, because ListView interferes with the horizontal thingy's touch events too

I haven't tried putting horizontally-scrollable content into a ListView, so I don't know how well that works

ok, i'll try that and see for myself =]

as for the first question I had, regarding the alarm manager, is there a way to check if an alarm manager is now active?

adb shell dumpsys alarm

it will show you all scheduled alarms

if yours is scheduled, it will show up in the list

note that in your case, setRepeating() is inexact

would you recommend that as a solution? to check if there's a scheduled alarm, and if not, then to reschedule?

oh, I thought you meant for debugging

I am not aware of a reliable way to determine if your alarm exists at runtime

and, given changes coming in M, frankly, the whole "do stuff periodically in the background" area is a serious mess

hmm, then how would you approach such a problem? I only run this schedule once when user signs up, and then the only time it goes back is after reboot, I restart the alarm OnBoot..

and M has a lot of time until it reaches market, I am not worried about this yet ;]

well, my old recommendation would be to not only log your events, but check those logs

if the last time you got control was plausible (e.g., you want every 10 minutes, you last got control 8 minutes ago), you just continue on

if the last time you got control is implausible (e.g., you want every 10 minutes, you last got control two weeks ago), you set up your alarms again

you need this for Force Stop at minimum

and, apparently, in some unhandled exception scenarios

hmmm

that's actually a decent fix

M invalidates this technique, though

let me take a question from Vasanthi, and if there's time, I'll be back with you before the chat ends

Vasanthi: any last questions?

It is about the min requirement for the system to run Android Studio. My laptop is extremely slow once I start Android Studio

My laptop has Intel core i3-3217U CPU at 1.80GHz smart cache 3MB with installed memory 4.0GB (3.89GB usable) 64bit op sys windows 8.1. Disk space available 340 GB.

that's pretty light

I have a high-end Core i7, 8GB of RAM, and Linux, and it runs fairly well

I have looked at what your book say

Is yours a laptop?

yes

I was not sure about buying an i7 laptop as I read that it gets heated up due to turbo boost

that probably depends on the notebook model

I rarely have mine actually in my lap, but from what I can tell, it doesn't get ridiculously hot

Which model would you recommend?

I have not really looked at current models

mine is a few-years-old Dell

OK. The Linux, do I need to install that?

because CPUs just haven't gotten any better, and I can put in my own SSD, so until 8GB becomes a limiting factor, this will suffice

you don't need to

plenty of people develop on Windows

I think it runs a bit leaner in terms of RAM usage than do modern versions of Windows

Yes, I thought so.

Refael: any last questions?

Thank you very much, Mark.

you're welcome!

Mark, you were incredibly helpful as always, your tips are gold!

thanks a lot !

you too are welcome!

btw , are you in Google I/O ?

no, I am not at I|O

here in my office

nothing like home then =)

watched some of the I|O live streams yesterday, and will do so again today

it's a lot less crowded here :-)

yeah me too, been pretty nice to watch

that's a wrap for today's chat

the transcript will be posted to https://commonsware.com/office-hours/ shortly

Mark, the answers to my first few questions aren't visible now. Is there a way, I could get them?

okie, i'll be leaving. thanks a lot again Mark

the next chat is Tuesday, also at 9am US Eastern

Vasanthi: visit https://commonsware.com/office-hours/ in a few minutes, and you can get access to the whole chat transcript

have a pleasant day, all!

Thank you, Mark. Bye to Refael and you.