The document discusses good practices, bad habits, and ugly issues that can arise when developing Android applications.
The good section covers clean code practices, using libraries, XML resources, and lifecycle methods. The bad section notes lazy practices like ignoring lifecycles and leaving cursors open. The ugly section describes ANRs, memory issues like bitmaps and strings, and overuse of logs and notifications. Developers are advised to follow proper patterns, manage resources carefully, and leverage tools like TraceView and MAT to debug problems.
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The Good, the Bad and the Ugly things to do with android
1. The Good,
The Bad,
Mobile2Days
and The Ugly…
Things to do with Android
Stanojko Markovik
03.11.2011@Java2Days
2. Your presenter…
• Speaks a few languages (Java, C++, Python…)
• Currently works at the ARTEMIS R&D
department at SudParis Telecom Institute
• Worked with android from v1.1
both for app development and custom ROMs
• Linux geek
• JUGMK member
7. What will we talk about??
• Good practices and the
1 proper way to do things
• Bad things people tend
2 to do and how to evade…
• The ugly things no one
3 wants to talk about.
9. The standard stuff first
• Always keep Clean and concise code
• DRY KISS - Always
• Be weary of memory usage
• Try to use libraries as external JAR files.
- modularity
- easier development sloop
• If you comment something out.. Erase it..
You will probably never use it again
10. Android Specific stuff - UI
• Android uses a modified version of
the MVC patter,
Views are made in XML.
Populated by code
• Android is aware of the display size.
So use this, and have different
graphics. For each size of the screen
11. Android Specific stuff - UI
• Try to utilize the 9patch drawables as much as
possible
Example 1 Example 2
12. Android Specific stuff - UI
• If the shapes are simple.. Write them in XML
Sample Round shape definition in XML
13. Android Specific stuff - Code
• Differentiate the LinkedList from the ArrayList
in the mobile world, it matters…
• Android uses a Google re-written Java,
so most of the standard java classes you use are “optimized”, optimizations
have bugs .
• Cleanup code before using it..
The Android compiler does not exclude unused classes. This will greatly
reduce your application size
14. Android Specific stuff - SDK
• Always have a target SDK, and a target device.
Maybe the code can be uniform and meant for all device, but the UI cannot.
• Forget String-s use StringBuilders
• Use a Debug condition for your Log statements.
Remember that : logs concat strings and are NOISY!
• Android has a GC, but System.gc() doesn’t work!
Have it in mind…
15. Android Specific stuff
Visual Scaling
• Try to get used to thinking in DIPs and SP.
• A good developer always wraps his content!
• Android has a GC, but System.gc() doesn’t work!
Have it in mind…
16. View.getTag() method
This is the “hidden” pocket meant for the object to
which the view is refering
• Use it on buttons to hold a state, or reference
• Use it with cursor adapters to hold an object or
database ID
• Use it with custom views to hold misc data for the
extra data you need.
17. notifyChange() method
Very often you have to write applications that use
adapters from databases or webservices.
The notifyChange() method is very important for
automatic update and/or content change.
Whenever you insert/update any data in the source it is
important to call this method to tell all the users to
refresh or re-query their data.
20. Database Cursors
• Database connections are often left open or half open
- This wreaks havoc in the android heap and memory
management, Never forget to cursor.close()
- If this is hard, then either call the manageCursor to
link the cursor to the activity lifecycle or use cursor
helper.
21. Use XML resources with care
XML layouts are a very handy, but developers over or
under use them very often.
- Handle the system services (layoutInflater)
- Inflate to combine layouts, much better and easier
than writing it in code.
- Don’t forget to recycle the Inflated layouts !
- Externalize ALL Strings to strings.xml
- Use values for system configurations
22. Don’t over nest
“Lazy” developers tend to overuse the LinearLayout
Instead of using RelativeLayout
Eclipse Demo here…
23. Cursor adapters and lists
• Use relative layout for the list items
• Use recyclable views and adapter
• Load images in the backgroud
Eclipse Demo here…
24. Background and Services
• Differentiate when to use binded and unbinded
services.
• Understand the onStartCommand() method and it’s
return statement.
• Differentiate threads and asynctasks
• Never use Toast or Dialog from a service
25. View Hierarchy
Developers tend to create complex view hierarchies
which are difficult for the GPU to render and refresh.
Views should be simple and a better resolution is for the
view hierarchy to be wide than tall.
Use the HierarchyViewer tool to find the skeleton of
your activity.
29. ANR
• Affected :
Activity, Service, BroadcastReceiver
• Reason :
Lifecycle rules broken
• Fix
Run heavy processing outside of the main thread, use
asynctask or another thread.
31. Fantom Apps - The Cause
In general this is a very difficult error to trace
- No Java StackTrace
- No Error screen
However if you look at the debug dump, you can see
That the heap is being overflowed.
To check
Runtime.getRuntime().maxMemory() – heap size
32. Fantom Apps - The Solution
VMRuntime
.getRuntime().setMinimumHeapSize(BIGGER_SIZE)
(how googers help them self with memory)
Or:
- Avoid operations that require threadpools.
Control your background processes.
- Try to find out if you overuse strings since + is a
very heavy duty operation!
- Use MemoryAnalyzer to find the “memory hoag”
33. Bitmaps and Graphics
Android 2.x does not work with bitmaps well
• VM does not load Bitmaps in heap,
• Bitmaps are immutable
• Matrix transformations are EXTREMELY risky
34. Bitmaps and Graphics
Repetitive problems
ERROR/AndroidRuntime(7906):
java.lang.OutOfMemoryError:
bitmap size exceeds VM budget
ERROR/AndroidRuntime(7906):
at
android.graphics.BitmapFactory.decodeFile(Bit
mapFactory.java:295)
35. Other Memory issues
This is actually caused by unclosed cursors and huge bitmaps
java.lang.RuntimeException: No memory in memObj at
android.database.CursorWindow.native_init at
android.database.CursorWindow.<init> at
android.database.CursorWindow.<init> at
android.database.CursorWindow$1.createFromParcel at
android.database.CursorWindow$1.createFromParcel at
android.content.ContentProviderNative.onTransact at
android.os.Binder.execTransact at
dalvik.system.NativeStart.run
36. The problem
You are stranded with a slow application.
• Memory is failing
• Application is Slow
• Sometimes it fails
• Sometimes it just “dissapears”
37. The tools of trade!
• TraceView
• Eclipse MAT
• DDMS system
42. Again the notifyChange() method
This can sometimes wreak havoc.
An example (that happened to me):
I download news from a website, upon download I have
a list of 50 items. NotifyChange() is called 50 times!
Definition of an UGLY SCENARIO
43. The logging facility
Android Log is great, but People tend to
1. Overlog
2. Forget the logs
3. Concatenate a huge amount of strings
4. Leave logs in loops (for, while, do-while)
5. Add stupid tags
6. Offer the consumer private information
45. It’s Hard
No, It’s not!
It’s fun!
It’s easy! New
Employee
1 yr 2 yr 3 yr
It’s lucrative
It’s cool!
46. You only have to :
1. Be aware of the rules of engagement!
2. Know your target
3. Be weary of memory!
4. Remember that it’s a VM
5. Have Respect for the other platforms, and
you just might learn something new…
47. Q&A
CONTACT ME AT :
STANOJKO.MARKOVIK@GMAIL.COM
HTTP://TWITTER.COM/SMARKOVIK
