Office Hours — Today, March 1

← Tuesday, February 28

Mar 1
8:55 AM
Mark M.
has entered the room
9:00 AM
Jumana A.
has entered the room
Jumana A.
Hi Mark!
HOpe you are well after your flu
Mark M.
howdy, Jumana!
I am a bit better, but this cold is still bothering me
Brent K.
has entered the room
Jumana A.
tell me about it!
Mark M.
howdy, Brent!
Brent K.
howdy!
Mark M.
Jumana, you arrived first: do you have a question?
Jumana A.
quick question - how do i implement a randomizer ...i want my app to pick up words randomly from a file
just tell me the classes and i can do the digging
Mark M.
use the standard Java rand() function
Jumana A.
oh !
Mark M.
sorry
Jumana A.
ok
Mark M.
Random is a class
java.util.Random
Jumana A.
ya got it
Mark M.
Brent: do you have a question?
Jumana A.
also im having trouble installing updates on eclipse
sorry , Brent go ahead
9:05 AM
Jumana A.
im just posing the question before hand before my 2 year old pulls me away
seem to have some dependency issue when im updating eclispse 3.6.1 to 3.6.2
Mark M.
I am no Eclipse expert, so it is unlikely I can be of much assistance
Jumana A.
ok no prob, mark
Brent K.
Ok, so I'm trying to figure out how to create something like a "running operations" page for a file browser. When the user initiates large operations, I want them to be able to view the progress of those operations from a dedicated activity. File operations are handled via asyncTasks of course.
Mark M.
um, OK
that's kinda broad
do you have a more specific question>?
(modulo a >)
Jumana A.
picking up words randomly from a file in the project directory structure and displaying on the screen are pure java functionalities right, mark?
Brent K.
lets see if I can be more specific
Mark M.
Jumana: off the cuff, I would say yes
9:10 AM
Brent K.
Is there a way that I can make a second activity aware of any asyncTasks started by a first activity?
Mark M.
more likely, those tasks should not be owned by either activity
for the purposes of this chat, let's call the activity that is starting the tasks Activity A
Brent K.
ok
Mark M.
and the activity that is the list of running tasks is Activity B
now, the user is in Activity A, they start off some task, and then press BACK
what is the user's expectation in terms of whether that task should complete?
Brent K.
Excellent question
Mark M.
I kinda liked it myself... :-)
if the answer is "the task should continue", then you probably should be using an IntentService (if one task at a time is sufficient) or a regular Service managing the AsyncTasks
9:15 AM
Brent K.
If, for example, the user decided to copy a ROM file from one folder to another using my file explorer app, I think that they would expect it to complete itself, even if the app had been closed
Mark M.
OK
that calls for a Service of some form to be in charge of the work
Brent K.
And it is entirely possible that there would be multiple operations going simultaneosly
Mark M.
that would eliminate IntentService
next question:
Brent K.
This is good stuff. So I start up a service when I start my app, and pass any file operations to it from the main activity
Mark M.
does the user need to be informed of task completion, even if there are no activities of yours running?
Jumana A.
Thats it from my side as of now
Mark M.
(Jumana: OK)
Brent K.
That would probably be a good idea for at least one of the different file operation types. Maybe my app could throw up a notification if wasn't currently up?
Mark M.
right
my general recommendation would then be to use an ordered broadcast
have the Service (or its AsyncTask) send an ordered broadcast when key events occur in the task lifecycle
Jumana A.
has left the room
Mark M.
(at least when the task ends)
9:20 AM
Mark M.
Activity B can register a high-priority receiver for the broadcast
and if it gets the broadcast, it can update itself accordingly
you also have a manifest-registered receiver for the same broadcast, at normal priority
that receiver will only get control of Activity B wasn't around
and it can display a Notification
that way, the service is oblivious to whether Activity B is or is not around
Brent K.
makes sense
Mark M.
I blogged about this a ways back: http://commonsware.com/blog/2010/08/11/act…
here's a sample project: https://github.com/commonsguy/cw-advandroi…
and I'll finally be covering this in _The Busy Coder's Guide to Advanced Android Development_ in the next update
now, in your case, the story is a bit more complicated, as Activity B will somehow need to query to find out if there are outstanding tasks
there are a few approaches for that:
1. have your service use the binding pattern (onBind()) and supply a query API
2. have the roster of tasks as a static data member that Activity B peeks at
3. have a ContentProvider interface to hide that static roster, and have Activity B use the Provider
Brent K.
Activity B should also be able to remember completed tasks too, so maybe the service can keep a running list somewhere for Activity B to look at?
Mark M.
in that case, I'd lean towards #3
9:25 AM
Mark M.
or #1
well, actually, any of them could work for that, now that I think about it
the disadvantage of #2 is that it implies that the whole roster of completed tasks in is memory, which may or may not be practical for you, depending on how much history you have
Brent K.
True
emil10001
has entered the room
Mark M.
Brent: let me take a question from emil10001, and I can swing back to you in a bit
tunneling
has entered the room
Mark M.
emil10001: do you have a question?
(BTW, howdy, tunneling!)
tunneling
hello
emil10001
hello Mark, I'm having an issue that I can't seem to get rid of in my app, and I haven't had much luck getting it answered elsewhere: http://stackoverflow.com/questions/9490558…
Mark M.
first, apply StrictMode to see if you are doing anything obviously wrong on the main application thread (disk I/O, network I/O, etc.)
then, use Traceview to see where your time is being spent
(assuming StrictMode didn't identify your problem, that is)
emil10001
what does StrictMode do?
Mark M.
StrictMode is covered in _The Busy Coder's Guide to Android Development_
emil10001
ah, ok
i'll look it up there
Mark M.
it will report if you try to do disk I/O, network I/O, and such on the main application thread
Traceview is covered in _Tuning Android Applications_
9:30 AM
emil10001
ok
9:30 AM
Mark M.
otherwise, it's really tough to give you general advice on this sort of problem
emil10001
I sort of figured that out, but I was stumped
Mark M.
but if touch events are slow to respond, usually it's a matter of spending too much time on the main application thread
emil10001
well, i did try to break things off onto a service thread
seemed to help a little bit, but not as much as I'd hoped
Mark M.
yeah, that's where using Traceview can help, to more scientifically determine the source of your difficulty
emil10001
i'll look into StrictMode, and also see if I've done anything stupid in the UI thread
Mark M.
OK
tunneling: do you have a question?
emil10001
ok, sounds good, thank you
tunneling
yea, i was wanting to disccus a little more the Plugin
I loaded up your sample code, and ran it in the emulator
Mark M.
which sample is this?
tunneling
works fine, i modified it to send over a ArrayList, works fine too
RemoveView
RemoteView
sorry
Host and Plugin
Frank
has entered the room
tunneling
Chapter 22 - Introspection and Integration
Mark M.
tunneling: OK, what is your question?
9:35 AM
tunneling
is this pattern adequate for replacing an API?
Mark M.
that's impossible to answer in the abstract
Frank
Hi everybody!
Mark M.
it's akin to asking if a brick is adequate for replacing a toothbrush
(howdy, Frank!)
tunneling
well, the last time we discussed this I was on the path of using ServiceLoader to load "drivers"
Mark M.
it all depends on what the toothbrush was being used for
right
tunneling
so, where in the API i use a DriverManager to get a list of drivers
in the Plugin, I would broadcast an intent and get a list of available plugins
Mark M.
the pattern I outline in the RemoteView samples can certainly be used for driver discovery
whether ongoing communications with the driver should be via broadcasts, or service commands, or service binding, or a ContentProvider, is indeterminate
tunneling
so it's possible to bind to a service from another app?
Mark M.
sure: see Remote Services sections in the "Advanced Services" chapter in _The Busy Coder's Guide to Advanced Android Development_
9:40 AM
tunneling
ok, that should get me going. I was concerned with the "back and forth" being done with intents
9:40 AM
tunneling
thanks.
Mark M.
Frank: do you have a question?
Frank
Yes!
First of all thanks for doing this when Western Europe is awake. I really appreciate it.
Mark M.
that's why I try to rotate through a few different times
(though usually the morning slot starts an hour later)
Frank
View paste 
My situation is the following:
1 - User requests some information 
2 - Service waits for network connection, then queries backend
3 - UI updates with information requested by user
View paste 
The thing is it can sometimes take quit a while a while to reach step 3.
When the user is no longer actively using the App, I would like to Notify him.
Mark M.
ha! we just got through talking about that
Frank
How would you go about dealing with this?
ah sorry I got here late
Mark M.
I really wish Campfire would let people scroll through a bit of history from before they entered the room...
anyway, ordered broadcasts are one solution for this problem
read: http://commonsware.com/blog/2010/08/11/act…
sample code: https://github.com/commonsguy/cw-advandroi…
Frank
Reading...
Mark M.
and this will be covered a bit more in the next update to _The Busy Coder's Guide to Advanced Android Development_, which (hopefully) will be released next week
9:45 AM
Mark M.
your service would send an ordered broadcast at the completion of #2
your activity, if it is in the foreground, would receive the ordered broadcast in #3 and update the UI
your manifest-registered receiver for the same broadcast -- which would only get control if the activity did not handle the broadcast -- would raise a Notification
Frank
Sounds great!
Perfect
Mark M.
Brent: do you have another question?
Brent K.
At least one ;)
Mark M.
go ahead with one
Brent K.
I'm grappling with whether or not this "operation queue" should remember things that it has done before
so the question is:
If I decide that the app/service should not forget completed operations whenever it is unloaded from memory, what would be the best way to persist that?
A small database?
Mark M.
that's a likely candidate
some sort of JSON or XML file could work as well
I'm not a big fan of using SharedPreferences for structures like that
Brent K.
Yeah, that doesn't seem like it would be the best idea
9:50 AM
emil10001
has left the room
Brent K.
So basically, I would wrap the service, its minions, and the database/JSON or XML file that it writes to in a content provider?
which would provide a more abstract way of retrieving this stuff for Activity B?
Mark M.
well, technically the service wouldn't be wrapped by the ContentProvider
they would work more in tandem
the ContentProvider would provide the API for manipulating your task queue and history
the Service would be executing the tasks
Brent K.
Would there be an easy way for Activity B to display realtime progress using this setup?
Mark M.
use a ContentObserver, perhaps
we're running a bit low on time
Brent K.
I'll have to read up on those
Mark M.
if anyone has other questions, fire away
Frank
OK
View paste 
I have an IntentService that updates a DB. Currently the Service Broadcasts the update and then an Activity reads the DB and updates the UI.

Is this an appropriate architecture? If so, why isn't it described in the Service patterns in your Android dev. book?
Mark M.
the use of broadcasts to have a service notify others is covered in _The Busy Coder's Guide to Android Development_ in the theory chapter
Frank
What are the pros and cons of this approach?
ah ok, missed that
Mark M.
I do not cover every possible permutation of options in the patterns, because I don't have that kind of time
Frank
I only looked in the service patterns section.
Mark M.
this will get more coverage in the next update to the Advanced Android book, as previously mentioned
Frank
What are the pros and cons compared with the approaches you do cover directly in the service patterns?
9:55 AM
Mark M.
broadcasts are public, unless you are only supporting 2.2 and can use setPackage()
broadcasts involve RPC (unless you use LocalBroadcastManager, also covered in the next Advanced Android update)
Frank
broadcasts are 1-n, so there can be several receivers...
Mark M.
that too
Frank
Not sure if that's the case with the patterns in the book
Mark M.
the book samples are more focused on 1-(0/1)
Frank
It should become important when you have several Fragements onscreen, right?
Mark M.
only if all those fragments care
Frank
Well, if at least 2 Fragments care...
Mark M.
and since fragments can't receive broadcasts, it's really more a question for their hosting activities
Frank
Ah! I didn't know that!
Well maybe Broadcasts are a bit of overkill then.
Mark M.
well, there is no registerReceiver() on Fragment AFAIK
Jumana A.
has entered the room
Jumana A.
has left the room
10:00 AM
Frank
Thanks Mark. The Ordered Broadcasts are just what the doctor ordered!
Mark M.
OK, that's a wrap for today's chat
Brent K.
Thanks for the help Mark
Mark M.
next week's are at 7:30pm Eastern (with appropriate apologies to Western Europe)
Frank
Looking forward to the transcipt
tunneling
has left the room
Brent K.
has left the room
Frank
has left the room
Mark M.
turned off guest access

← Tuesday, February 28

 

Office Hours

People in this transcript

  • Brent Kensey
  • emil10001
  • Frank
  • Jumana AM
  • Mark Murphy
  • tunneling