A guide to make crashproof libraries A tips and tricks presentation for Droidcon Berlin Barcamp 2016

1. Android Technical Lead
Applause Inc.
Przemek Jakubczyk
pjakubczyk
@pjakubczyk
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2. A guide to make crashproof libraries
It's always your fault
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3. Background
At Applause I am responsible for quality
Applause SDK is crash and bug reporting library
shipped to over 1000 customers
SDK works with apps around the world
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4. History
Joined 2 years ago to project with no QA
Today ~2200 unit tests covering 3k methods
82% lines covered
Last major problem was support for Marshmallow
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Other than that over 6 months of no customer complain

5. How your SDK should look like
Be universal
Work in every provided configuration
Be robust
Work in any environment
Be defensive
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6. GRADLE
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7. Just use it.
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because it’s the base for Android build system

8. Gradle
use simple tricks to protect your
styling
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android {
resourcePrefix 'applause_'
}
or pass custom values to source
code via DSL
defaultConfig {
resValue "string",
"applause_library_version”,
"$version"
}

9. Gradle
easier integration with your Groovy
scripts
for example create own distribution
task
task buildAll (
dependsOn: 'assembleRelease',
type: Copy) {
from “build/outputs/”
into “another_path”
}
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10. Gradle
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Not possible :)
Often heard question. How to pass arguments to tasks?

11. Create new task for each configuration.
Gradle
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task buildAll (
dependsOn:
["assembleFreeRelease,
assemblePaidRelease"]
)

12. Java
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13. Java
catching Exception doesn’t solve problem
often hides real cause
tempting but dangerous
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try {
network.getClients();
} catch (Exception e) {
// handle exception
}

14. Java
Null Object Pattern
instead constantly checking for not null
value
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public interface Api {
void post(String action);
Api NULL = new Api() {
void post(String action){}
};
}
getApi().post(“Works”)

15. Java
NPE
Null Pointer Exception is the most popular
exception thrown in runtime.
NullObject pattern partially solves the problem.
Use empty objects, collections etc;
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List<User> fetchUsers(){
try {
return api.getAllUsers();
} catch (IOException e){
return new
ArrayList<Users>();
}
}

16. Java
Usually library is started by one static method
… and next versions provide more functionality
Init interface becomes complex
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17. Java
public static void start(
String baseUrl,
String defaultUser,
String defaultPassword,
boolean cacheRequests,
boolean forceHttps,
int timeout
)
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Conf conf = new Conf.Builder()
.withUrl(“http://api.github.com”)
.withUser(“pjakubczyk”)
.withPassword(“droidcon2016Berlin”)
.withCache(false)
.withHttps(true)
.withTimeout(15)
.build();
Library.start(conf);

18. Java
Builder pattern organize configuration
Easier data validation
Pass only parameters user wants
Handling default values
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19. Examples
Retrofit retrofit = new Retrofit.Builder()
.baseUrl(BASE_URL)
.addConverterFactory(GsonConverterFactory.create())
.build();
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Stetho.newInitializerBuilder(context)
.enableWebKitInspector(myInspector)
.build()

20. Concurrency
New Thread is your enemy
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ExecutorService EXECUTOR =
Executors.newSingleThreadExecutor(new ThreadFactory() {
@Override
public Thread newThread(Runnable r) {
return new Thread(r, "NetworkExecutor");
}
});

21. The String
String is a bad information holder
Often passing 2 string parameters to method
Lead to simple mistakes
User vs Person
Instead of getters maybe method ‘serializeForAuth’ ?
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22. Android
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23. Android
View.inEditMode() determines if view is drawn in Android Studio
Usually to disable other components
Let’s invert the usage
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24. 24
public void onFinishInflate(){
TextView title = findViewById(R.id.title);
if(inEditMode()) {
int count = title.getText().length();
if(count > 30){
title.setTextSize(24.0f);
} else {
title.setTextSize(30.0f);
}
}
}

25. Android
Build.VERSION.SDK_INT
ApplicationInfo.targetSdkVersion
the library doesn’t know where it’s run
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26. Android
usually interface for loading pictures from to web to Widget looks like this:
pictureLoader.load(“url_to_resource”, imageView);
passing arguments extending from View, Activity etc.
often lead to Memory leak
queue is flooded with requests holding all references
Go back to javadoc and check java.lang.ref.WeakReference<T> :) 26

27. Android
Wrap OS Exceptions with your own implementation
BitmapFactory
Throws unchecked OutOfMemoryError
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28. 28
public static class BitmapCreatorException extends Exception {
public BitmapCreatorException(String detailMessage) {
super(detailMessage);
}
public BitmapCreatorException(Throwable throwable) {
super(throwable);
}
}

29. 29
Bitmap createScaled(Bitmap bitmap, int width, int height) throws
BitmapCreatorException {
try {
Bitmap scaledBitmap =
Bitmap.createScaledBitmap(bitmap, width, height, true);
return nullCheck(scaledBitmap);
} catch (OutOfMemoryError error) {
throw new BitmapCreatorException(error);
}
}
Bitmap Provider

30. 30
Bitmap nullCheck(Bitmap bitmap) throws BitmapCreatorException {
if (bitmap == null)
throw new BitmapCreatorException("Bitmap is empty");
else
return bitmap;
}
Bitmap Provider

31. Android
ProGuard is outstanding tool to shrink code and inject bytecode optimizations
While shipping your code you must either provide:
copy&paste configuration to ProGuard (latest plugin supports auto-configuration)
be transparent to ProGuard.
Configuration vs Transparency?
Transparency!
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32. Android
http://www.methodscount.com/
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Product Method count
com.squareup.okhttp3:okhttp:3.0.1 2704
io.relayr:android-sdk:1.0.2 5413
io.reactivex:rxjava:1.1.0 4605
com.google.code.gson:gson:2. 1341
com.applause:applause-sdk:3.4.0 5041
com.fasterxml.jackson.core:jackson-databind:2.7.0 10732
com.parse:parse-android:1.13.0 4543

33. The End
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34. License
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35. Licence
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by default you own the copyright
no licence doesn’t conclue you can use it in your project
open code (found online) != open source movement
transferring code goes along with transferring the ownership
Check the licence
Check if it infects yours
(Apache, MIT vs GPL v2, LGPL, BSD)

36. Thank you
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37. A guide to make crashproof libraries
It's always your fault
37