Profile

Cover photo
Tom Hume
Works at Google
Attended University of Sussex
Lives in San Francisco, US
896 followers|1,189,864 views
AboutPostsPhotosYouTubeReviews

Stream

Tom Hume

Shared publicly  - 
1
Add a comment...

Tom Hume

Shared publicly  - 
 
Truth, yo.
 
"How should I design my Android application? What kind of MVC pattern should I use? What should I use for an event bus?"

We often see questions from developers that are asking from the Android platform engineers about the kinds of design patterns and architectures they use in their apps. But the answer, maybe surprisingly, is we often don't have a strong opinion or really an opinion at all.

Should you use MVC? Or MVP? Or MVVM? I have no idea. Heck, I only know about MVC from school and had to do a Google search to find other options to put here.

This may be surprising, because Android could feel like it has strong opinions on how apps should be written. With its Java language APIs and fairly high-level concepts, it can look like a typical application framework that is there to say how applications should be doing their work. But for the most part, it is not.

It is probably better to call the core Android APIs a "system framework." For the most part, the platform APIs we provide are there to define how an application interacts with the operating system; but for anything going on purely within the app, these APIs are often just not relevant.

That said, the Android APIs can often look different (or higher level) from what one typically expects in an operating system, which may easily lead to confusion about how they should be used.

For an example of this, let's consider how an operating system defines "how to run an app." In a classic system, this is basically the contract it has with an application about when it should run:

int main(...) {
// My app goes here!
}

So the operating system starts the app, calls its main() function, and the app goes off and runs and does what it wants until it decides it is done. And clearly it is not saying anything here about what the app should be doing or how it should be designed within that main function -- it's a pretty pure blank slate.

In Android, however, we explicitly decided we were not going to have a main() function, because we needed to give the platform more control over how an app runs. In particular, we wanted to build a system where the user never needed to think about starting and stopping apps, but rather the system took care of this for them... so the system had to have some more information about what is going on inside of each app, and be able to launch apps in various well-defined ways whenever it is needed even if it currently isn't running.

To accomplish this, we decomposed the typical main entry point of an app into a few different types of interactions the system can have with it. And these are the Activity, BroadcastReceiver, Service, and ContentProvider APIs that Android developers quickly become familiar with.

These classes may look like they are telling you how the internals of your app should work, but they are not! In fact, they are all about how your app needs to interact with the system (and how the system can coordinate its interaction with other apps). As long as that interaction with the system happens, we don't really care what goes on inside of the app.

To illustrate, let's briefly look at these different APIs and what they really mean to the Android system.

Activity

This is the entry into an application for interacting with the user. From the system's perspective, the key interactions it provides with the app are:

• Keep track of what the user currently cares about (what is on screen) to ensure the process hosting that is kept running.
• Know that previously used processes contain things the user may return to (stopped activities), and thus more highly prioritize keeping those processes around.
• Help the application deal with the situation where its process is killed so the user can return to activities with their previous state restored.
• Provide a way for applications to implement user flows between each other, coordinated by the system. (The most classic example here being share.)

What we don't care about:

Once we have gotten in to this entry-point to your UI, we really don't care how you organize the flow inside. Make it all one activity with manual changes to its views, use fragments (a convenience framework we provide) or some other framework, or split it into additional internal activities. Or do all three as needed. As long as you are following the high-level contact of activity (it launches in the proper state, and saves/restores in the current state), it doesn't matter to the system.

BroadcastReceiver

This is a mechanism for the system to deliver events to the application that may be outside of a regular user flow. Most importantly, because this is another well-defined entry into the app, the system can deliver broadcasts to apps even if they aren't currently running. So, for example, an app can schedule an alarm to post a notification to tell the user about an upcoming event... and by delivering that alarm to a BroadcastReceiver of the app, there is no need for the app to remain running until the alarm goes off.

What we don't care about:

Dispatching events within an app is an entirely different thing. Whether you use some event bus framework, implement your own callback system, whatever... there is no reason to use the system's broadcasting mechanism, since you aren't dispatching events across apps. (In fact there is good reason not to -- there is a lot of unnecessary overhead and many potential security issues if using a global broadcast mechanism for the internal implementation of an app.) We do provide the LocalBroadcastManager convenience class that implements a purely in-process intent dispatching system with a similar API to the system's APIs, if you happen to like them. But again, there is no reason to use that over something else for things going on purely within your app.

Service

A general-purpose entry point for keeping an app running in the background for all kinds of reasons. There are actually two very distinct semantics services tell the system about how to manage an app:

Started services are simply telling the system to, for some reason, "keep me running until I say I am done." This could be to sync some data in the background or play music even after the user leaves the app. Those also represent two different types of started services that modify how the system handles them:

• Music playback is something the user is directly aware of, so the app tells the system this by saying it wants to be foreground with a notification to tell the user about it; in this case the system knows that it should try really hard to keep that service's process running, because the user will be unhappy if it goes away.

• A regular background service is not something the user is directly aware as running, so the system has more freedom in managing its process. It may allow it to be killed (and then restarting the service sometime later) if it needs RAM for things that are of more immediate concern to the user.

Bound services are running because some other app (or the system) has said that it wants to make use of the service. This is basically the service providing an API to another process. The system thus knows there is a dependency between these processes, so if process A is bound to a service in process B, it knows that it needs to keep process B (and its service) running for A. Further, if process A is something the user cares about, than it also knows to treat process B as something the user also cares about.

Because of their flexibility (for better or worse), services have turned out to be a really useful building block for all kinds of higher-level system concepts. Live wallpapers, notification listeners, screen savers, input methods, accessibility services, and many other core system features are all built as services that applications implement and the system binds to when they should be running.

What we don't care about:

Android doesn't care about things going on within your app that don't have any impact on how it should manage your process, so there is no reason to use services in these cases. For example, if you want to start some background operation to download data for your UI, you should not use a service for this -- it is actually important to not be telling the system to keep your process running while doing this, because it really doesn't need to be and the system would be better off having more freedom in managing it with other things the user is doing.

If you just make a simple background thread (or whatever non-service mechanism you want) to do the downloading, you will get the semantics you want: while the user is in your UI, the system will keep your process running for that, so the download will never be interrupted. When they leave your UI, your process will still be kept around (cached) and able to continue downloading, as long as its RAM isn't needed elsewhere.

Likewise for connecting different parts of your app together, there is no reason to bind to a service that is running in the same process as the one binding to it. Doing so is not actively harmful -- the system just sees a dependency from the process to itself so doesn't try to keep it around any more than usual -- but it is a bunch of unnecessary work for both you and the system. Instead, you can just use singletons or other normal in-process patterns for connecting pieces of your app together.

ContentProvider

Finally, the ContentProvider is a fairly specialized facility for publishing data from an app to other places. People generally think of them as an abstraction on a database, because there is a lot of API and support built in to them for that common case... but from the system design perspective, that isn't their point.

What these are to the system is an entry-point into an app for publishing named data items, identified by a URI scheme. Thus an app can decide how it wants to map the data it contains to a URI namespace, handing out those URIs to other entities which can in turn use them to access the data. There are a few particular things this allows the system to do in managing an app:

• Handing out a URI doesn't require the app remain running, so these can go all over the place with the owning app being dead. Only at the point where someone tells the system, "hey give me the data for this URI" does it need to make sure the app owning that data is running, so it can ask the app to retrieve and return the data.

• These URIs also provide an important fine-grained security model. For example, an application can place the URI for an image it has on the clipboard, but leave its content provider locked up so nobody can freely access it. When another app pulls that URI off the clipboard, the system can give it a temporary "URI permission grant" so that it is allowed to access the data only behind that URI, but nothing else in the app.

What we don't care about:

It doesn't really matter how you implement the data management behind a content provider; if you don't need structured data in a SQLite database, don't use SQLite. For example, the FileProvider helper class is an easy way to make raw files in your app available through a content provider.

Also, if you are not publishing data from your app for others to use, there is no need to use a content provider at all. It is true, because of the various helpers built around content providers, this can be an easy way to put data in a SQLite database and use it to populate UI elements like a ListView. But if any of this stuff makes what you are trying to do more difficult, then feel free to not use it and instead use a more appropriate data model for your app.
69 comments on original post
1
Add a comment...

Tom Hume

Shared publicly  - 
Guardian photographer David Levene travelled across the San Francisco Bay Area photographing the sites that transformed one of the great cities of the world
1
Diana Hume's profile photo
 
Fascinating pics
Add a comment...

Tom Hume

Shared publicly  - 
 
Love the comparison long-exposure photography in this review of the new Roomba. The pseudo-random way the older models chunk around was super-disappointing when I noticed ours doing it. I expect my robot slaves to be SMART, dammit!

http://spectrum.ieee.org/automaton/robotics/home-robots/review-irobot-roomba-980
An expensive new Roomba with features and performance to match
1
Add a comment...

Tom Hume

Shared publicly  - 
Students from Cornell University have created a GPS top hat that uses directional sound cues to help users find their destination hands free.
5
Add a comment...
In his circles
602 people
Have him in circles
896 people
Miles Sabin's profile photo
Dupe Olaoye's profile photo
Andy Nesbitt's profile photo
Tim Fletcher's profile photo
Raphael Agyekum-Darkwa's profile photo
James Page's profile photo
Adrian Bigland's profile photo
Darren Hodder's profile photo
Mark Louie's profile photo

Tom Hume

Shared publicly  - 
 
We popped into the Smart Home exhibition at Target today. It's a display of technology from a ton of different partners: from the obvious SmartThings from Samsung, through door locks from August to some fairly ridiculous items: a smart basketball, networked ear thermometer, and the Parrot plant monitor (which I'd probably use).

Kudos to them for not just highlighting the big brands, but the resulting picture of IoT, and the way it was presented, was a dreadful cacophony of needy devices, screaming for attention, shouting out their cleverness with twee "personalities", and relying on an bewildering set of apps and infrastructure to configure and use. The silver lining: after seeing all this, efforts like Thington seem less like nice-to-haves and more essential.

www.thington.com
1
Add a comment...

Tom Hume

Shared publicly  - 
 
“Organ donor” Aibo robot dogs made by Sony Corp. are honored in a funeral at Kofuku-ji temple in Chiba, near Tokyo. Parts from these robot dogs are used to repair other Aibo.
2
Add a comment...

Tom Hume

Shared publicly  - 
 
"No master plan, urban design, zoning ordinance, construction law or expert knowledge can claim any stake in the prosperity of Dharavi. It was built entirely by successive waves of immigrants fleeing rural poverty, political oppression and natural disasters. They have created a place that is far from perfect but has proved to be amazingly resilient and able to upgrade itself. In the words of Bhau Korde, a social worker who lives there, “Dharavi is an economic success story that the world must pay attention to during these times of global depression.”

Understanding such a place solely by the generic term “slum” ignores its complexity and dynamism."

http://designmuseumdharavi.org/Design_Museum_Dharavi/The_s_word.html
It does not take much to galvanize protest against a movie in India, but few thought the word “slumdog” would cause so much anger — especially as hundreds of Bollywood titles translate into much worse slurs. We had to pay attention, though, when friends from Mumbai's sprawling Dharavi area ...
1
Add a comment...

Tom Hume

Shared publicly  - 
1
Add a comment...

Tom Hume

Shared publicly  - 
 
http://www.theverge.com/2016/1/4/10712550/parrot-pot-automatic-watering-to-keep-your-plants-alive

Would it be worth having one which rotates your plant to ensure even sunlight?
Parrot's flashiest announcement of CES is without question its new drone, but it's shown up with one other neat — but much tamer — product, too: a self-watering pot for houseplants. The pot holds...
1
Add a comment...

Tom Hume

Shared publicly  - 
 
" if the thought of a large blinking eyeball that swivels around to look at you when you speak — and talks back — makes you feel at all uneasy, well, this may not be the bot for you."

http://techcrunch.com/2015/12/07/olly/
1
Add a comment...
People
In his circles
602 people
Have him in circles
896 people
Miles Sabin's profile photo
Dupe Olaoye's profile photo
Andy Nesbitt's profile photo
Tim Fletcher's profile photo
Raphael Agyekum-Darkwa's profile photo
James Page's profile photo
Adrian Bigland's profile photo
Darren Hodder's profile photo
Mark Louie's profile photo
Work
Occupation
Product Manager
Skills
"A janitor, essentially": https://medium.com/p/664d83ee702e
Employment
  • Google
    Product Manager, 2012 - present
    Started out in the Android Apps team. Took Auto Awesome Movies from concept to launch, shipped Quickoffice for Android Kitkat, merged it with Google Docs for Android. Moved to Android Platform team in 2014, working on System UI. Responsible for Android home screen and setup experiences.
  • Future Platforms
    2000 - 2011
    Co-founded, ran, and eventually sold this software company, which built gorgeous mobile apps for Palm Pilot to Android and iPhone, and everything in between. EVERYTHING.
  • Good Technology
    1995 - 2000
    Graduated from web all-rounder to technical dogsbody, before spending a year spinning off a division looking at mobile apps in 1999.
Places
Map of the places this user has livedMap of the places this user has livedMap of the places this user has lived
Currently
San Francisco, US
Previously
San Jose, US - London, UK - Brighton, UK - Reading, UK
Links
YouTube
Other profiles
Story
Tagline
Long-time squawk box software chap. Snagged on frowns, and slowly dawns.
Introduction
Internet and mobile software guy, wannabe AI geek.

Career path: BBC Micro (8) -> BBSs (16) -> FidoNet (17) -> Linux (18) -> Web (20) -> WAP (26) (sorry) -> mobile apps (27) -> University (38) -> Google (39)

Hobbies: running, reading, (writing), Aikido, airsoft.

Living in the Bay Area since 2013. Heart still in Brighton, UK.
Bragging rights
Built, ran and sold Future Platforms, (once) one of the UK's first and best mobile software houses. Wrote Java for Kylie, back in the day.
Education
  • University of Sussex
    MSc Advanced Computer Science, 2011 - 2012
  • Lancing College
    1987 - 1992
Basic Information
Gender
Male
Birthday
September 22
Incredible food. I had the ravioli, black cod and chocolate fondant with the recommended wines. Couldn't fault it; all perfect.
Food: ExcellentDecor: ExcellentService: Excellent
Public - 3 years ago
reviewed 3 years ago
Really interesting and well prepared food, great service. Try the prawns on curry ice cream...
Public - 3 years ago
reviewed 3 years ago
Incredible food, great atmosphere.
Food: ExcellentDecor: ExcellentService: Very Good
Public - 4 years ago
reviewed 4 years ago
4 reviews
Map
Map
Map
Very basic, pretty filthy. Oddly psychedelic mural depicting child sacrifice on bedroom wall.
Quality: GoodFacilities: GoodService: Good
Public - 4 years ago
reviewed 4 years ago