Friday, June 17, 2011

What new Android developers need to know

Android is a new operating system. Apps are written in Java, which is a familiar language to many.  On the other hand, developing for mobile apps is a different beast than with other platforms.  Here are some things I've learned in my years of programming for Android, and I suggest if you are learning Android that you learn about these topics.  I think these make for great interview questions, so it would help to know about these topics if you are going for an Android related interview.

Android Topics

1.       Know what a task is in Android.
a.       How does the task and the navigation stack relate.
b.      What is the difference between default, singleTask, singleTop, etc.?
c.       What happens when you press BACK? 
d.      What happens when you press HOME?

2.       Know what activity lifecycles are. 
a.       When do you use onPause() vs. onDestroy()? 
b.      What are onConfigurationChange() and retainInstanceState() useful for? 
c.       What happens to static variables when you switch activities?

3.       Know what API levels are. 
a.       Unfortunately, the Android builder does not distinguish API levels.  You can build an application with minSdkVersion=3, targetSdkVersion=4 with code which uses methods only available on level 4.  This will build fine, but throw an exception when the class loader attempts to load your class files on an API level 3 phone.
b.      In Eclipse, change the API level to 3 briefly, just to see if the code can compile.
c.       We have to develop with API level 8 in order to use certain features in the manifest, so we have to be very careful about using API methods that are only API levels 1-3. 
d.      You can still use reflection and wrapper classes to prevent class loader from breaking, etc. to use newer classes; examples are available on the Android dev site.
e.      Be wary of the element in the Android manifest.
                                                               i.      An app may be filtered from the Marketplace based on these elements.
                                                             ii.      Bluetooth feature has special rules.

4.       Test your app in all sorts of UI configurations:
a.      Low density, extra large screens, landscape, etc.
b.      A layout may look good on a 320x480 screenshot in a mockup, but did the mockup address how it would look in landscape?
c.       Horizontally laid-out information isn’t good for mobile devices in general.  Keep the layouts flowing vertically.
d.      You get to create all sorts of UI configurations with emulators.

5.       Compress your graphics.  I use an open source program Paint.NET to adjust .PNG images. 
a.       PNG graphics can have unnecessary meta data from graphics programs which take up extra space.
b.      Sometimes encoding in 8-bit vs. 32-bit can save space, but careful that transparency is retained.
c.       If your business customer wants to give you graphics for every type of UI configuration, see if they can accept using a standard image size, and let Android scale the images.  It greatly increases the size of the app.  Android scales the images. 
d.      Use drawables defined in Android XML files when possible instead of bitmaps; they scale well in different sizes and take up less disk space.

6.       Don’t schedule services too often. 
a.       Do you really need to download data from the network every 15 minutes?  This is awful on battery life!
b.      You change the frequency of the service by rescheduling every time the service finishes instead of scheduling a periodic service.

Java in Android

1.       Learn what a strong reference, a weak reference, and a soft reference are.  Weak references are especially useful in Android.
a.       Use weak references when dealing with separate threads and timed operations: WeakReference. 
b.      Both WeakReference and SoftReferences can be useful for some types of caches.

2.       Always use separate threads when doing network operations, disk operations, and other long-running operations.
a.       It turns out that the same code which takes 5 ms can take 5000 ms when Android is out of memory or waiting for other processes to finish file I/O, killing and starting processes, and doing a GC on your app.
                                                               i.      Get used to doing lazy initialization.  It seems unnecessary until you get 500 ANRs on the Marketplace reports.
                                                             ii.      In startup methods, don’t initialize variables.  Wait until an accessor method such as getVariable().
b.      IntentServices, Handlers, Threads.  They are useful in different situations.
c.       IntentServices guarantee a separate thread and that multiple intents handled by the service are synchronized to be processed one after another.
d.      Handlers are useful for transferring messages from the network/etc. threads to the UI thread in an activity.
e.      Threads may be useful in some situations, but remember that a running thread is not a guarantee to keep your process alive; if all activities/services/etc. are closed, then a running thread can (and will) legally be destroyed by the OS.

3.       Be wary of static variables: you don’t have knowledge of their lifecycle, unlike instanced variables accessible through activities and services with onCreate() and onDestroy().
a.       Their value can be reset but
b.      Static variables are notorious for causing memory leaks.
c.      They are useful in some situations still.  For example, preventing code from executing more than once when your process has already started.

4.       Do you know what a memory leak in Java is?  It’s not the same as it is in C.  It refers to keeping strong references to objects which shouldn’t be used anymore (should be GC-able), but programming error has kept them strongly reachable.
a.       In Android especially, you never want to keep references to Activities and Services in variables, especially static variables. 
b.      Sometimes you do need contexts; you can either use Application as a context, or if you have to have the Activity context then 1. Use a weak reference, or 2. Don’t let the object which has a reference to the Activity be referenced by anything else: make sure the Activity completely “owns” the object.

5.       Don’t ever keep static references to Activities, Services, Views, or BroadcastReceivers.
a.       This causes memory leaks!
b.      You can use a global (static) context from the Application. 
c.       This is useful for getting resources, files, etc. Be careful; you can’t create dialogs from this context, and any activities started with the application context will always create a new task.
d.      If you have to use a static reference, use a WeakReference.


1.       Build machine is good.
a.       You can create custom Ant scripts.
b.      I use them to copy files based on build properties, and to change variables in the class.
c.       I also change AndroidManifest.xml using a script based on QA or release builds.
                                                               i.      No worry about developer forgetting to change items.
                                                             ii.      Add/remove debuggable attribute, permissions for logging to SD card, etc.

2.       Always use ProGuard in any app released to the Android Marketplace.
a.       Reduces app size by removing unused variables and methods.
b.      Obfuscates code, which theoretically cannot prevent hackers from snooping but does slow them down.
c.       Allows you to have code  like:
if (Config.LOGGING) print(“The data is: “ + data);
The above statement is completely removed when Config.LOGGING is false.

3.       Code formatters are useful
a.       Standardization is nice.
b.      Simple whitespace differences can cause merges to break.
c.       If you are using Eclipse, you can check in the project settings into the source repository.
d.      Deciding some standards can be akin to a religious war; after 50 years, lots and lots of smart people have debated this and they haven’t come to the same conclusion on what’s best.  Just go with something.

4.       Hungarian notation is used in Android OS and in some of our apps.
a.       It can be useful, but a developer can easily mess up.  In a strongly-typed symbolic language such as Java, source code formatters do a better job of telling you the data type of a variable.
b.      You don’t have to use the Android OS coding style, but it is an example of a coding style:
                                                               i.      mVariable means instanced field (member variable)
                                                             ii.      sVariable means non-final static field.
                                                            iii.      ALL_CAPS means a constant (final static)
c.       Hungarian Notation was originally meant to describe the type of data as in network response or pixel measurements.  It has been incorrectly used as data type as in “final static” or “DWORD LONG *”.

5.       Use themes and styles in your layouts. 
a.       It makes it easier to make changes.
b.      You’ll probably not use styles the first time you make your layouts.  Then when you have to go back and change 25 layout files just to move some pixels to the right, you’ll start using styles.

6.       Put logs everywhere. 
a.       Make a standard for how it’s done. 
b.      No need to remove them or comment them out when using ProGuard if wrapped in a constant boolean; this is a good thing.
c.       I have many ways of dealing with logs:
                                                               i.      Log items to logcat, filterable by one single tag. 
                                                             ii.      Log items to the SD card.  Great because this persists after device resets and lets you observe behavior overnight or over a long time.
                                                            iii.      Added menu item in debug area of app which will automatically e-mail logs to an e-mail address.

Useful reading:


WrightRocket said...

Excellent post! So good I not only bookmarked it, I saved it to my disk for future reference.

Anonymous said...

@Keith Wrigth: Thằng bợ đít

White Label SEO said...

Thanks for the insightful post. Looking forward to reading more of your post

Top SEO Company said...

thanks for sharing this questions. We are on process of hire android developer for our Best SEO Servicescompany and we are looking for question set to ask from them and i am glad that i found this website of yours

Anonymous said...

Thanks, deeply instructive.

Blogger said...

Thanks for sharing this important information about android development, we will also follow your guide. we are expert in Digital Marketing and web designing work. if someone looking for these services they can hire us.

Prachi Kalra said...

Thanks for the incredible blog. Keep up the great work!
Web Design Company in India

rithiaanandh said...

This is a very good content you share on this blog. it's very informative and provide me future-related information. Thank you a lot for providing individuals with a very spectacular possibility to read critical reviews from this site.
Sql server dba online training

jothikumar said...

Great post! I am actually getting ready to across this information, It’s very helpful for this blog. Also great with all of the valuable information you have Keep up the good work you are doing well.
Selenium online training
Selenium certification training
Selenium online course
Selenium training course

prabhaa said...

This is a very good content you share on this blog. it's very informative and provide me future related information.
Data Science Online Training
Data Science Online Certification
learn Data Science Course

Gizdoc said...

Really great article, you guys are doing a great work, keep posting good stuff, If your audience is into Tech do share Best Instagram Story Saver Apps
Gizdoc Tech Paradise

Story saver said...

Instagram is one of the most popular social media out there and if you want to download story from Instagram you can have a look on story saver

Amy said...

Hi really thank you for this good information on Blogs. I agree with you. I always follow your blog site.
Reference: Minneapolis Web Design

John said...

مهدی احمدوند
Firstly, Thanks for all the useful insights. I would like to thank you for putting emphasis on how relevancy playing a big role in hosting industry. I appreciate your hard work. Keep posting new updates with us.
آرمین 2afm
Generous leads are cardinal for any business, this incorporates Digital Marketing Services in Chennai, medium and enormous undertakings. The ordinarily realized Online Marketing Company In Chennai web-based promoting program that common computerized Digital Marketing Agency in India can offer to its clients are Search Engine Optimization, Paid Marketing, Digital Marketing Services In Chennai
علی یاسینی

Golden Triangle India Tour said...

It is amazing post, i am really impressed of your post. Its really useful. Golden Triangle India Tour

Quirinus Solution Ltd said...

eCommerce Website Development Company
eCommerce Website Development Company
eCommerce Website Development
Quirinus Soft an eCommerce Website Development Company
Quirinus Soft Pvt Ltd an eCommerce Website Development Company
Ecommerce Website Development Company
Quirinus Soft an eCommerce Website Development Company
Ecommerce Website Development Company
Ecommerce Website Development Company
eCommerce Application Development Services

Online Front said...

Online Front is one of the trustworthy and leading Digital Marketing Company In Delhi. We are one stop solution for all Digital Requirements.


free youtube subscribers
Digital Consultancy Services In Delhi
Website Development Packages
Website Designing Company In Delhi

aivivu said...

Thanks for sharing your wealthy information. This is one of the excellent posts which I have seen. I go through your all of your blog, but this blog is the best one. It is really what I wanted to see hope in future you will continue for sharing such an excellent post
combo đi quy nhơn 4 ngày 3 đêm

combo hà nội đà lạt 4 ngày 3 đêm

phỏng vấn xin visa kết hôn Hàn Quốc

phỏng vấn xin visa thương mại Nhật Bản

Kestw said...

Greet to see this type of Articles every informative. Latest Mobiles

webscybernetics said...

Amazing Article learned a lot from here and motivative article to inspire ourself!!

Aryan said...

Boht hi mast information hai. Tum boht mast kaam krta hai Matt bhai. Zara mera lekh padho kis tarah maine android ko dekstop me convert kr diya. Chaunk jayega tu.

Anonymous said...

Thanks for your post! This post was really helpful and knowledgeable.

anne m rubeo said...

Thanks for sharing will help you in growing your site.


Frank said...

the same as it is in C. Write My Essay For Me Cheap It refers to keeping strong references to objects which shouldn’t be used anymore.