Android libraries I wish I knew when I started

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Android Libraries I wish I knew when I started github.com/ChrisGuzman/taasty

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Chris Guzman Developer Advocate Nexmo @speaktochris | chris-guzman.com

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Starting a new app? Not sure what libraries to use?

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A lot of apps do similar things → Manage multiple views → Load and display images → Fetch data from an API → Parse JSON → Start new activities with extras → Persist data to storage

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These libraries prevent you reinventing the wheel with every project. → Butter Knife v8.5.1 → Picasso v2.5.2 → Gson v2.8.0 → Retroﬁt v2.3.0 → Realm v3.3.1 → Dart & Henson v2.0.2

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The 45 Hour Minute Hackathon

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What should I make?

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Introducing TaaSTY

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Tacos as a Service To You

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Tinder for Tacos

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Step 1 Set up our views

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Step 2 Use views

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Butter Knife Use annotations to write less boilerplate code

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→ How many times have you wrote ﬁndViewById? → No additional cost at run-time - does not slow down your app at all! → Improved View lookups → Improved Listener attachments → Improved Resource lookups

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Bind views in an activity public class MainActivity extends Activity { @BindView(R.id.name) TextView name; @Override protected void onCreate(Bundle bundle) { ... ButterKnife.bind(this); name.setText("Tofu with Cheese on a tortilla"); } }

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ButterKnife.bind(this) Generates code that looks up views/resources and saves them as a property on the Activity. public void bind(MainActivity activity) { activity.description = (android.widget.TextView) activity.findViewById(2130968577); }

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Bind and unbind views in a fragment public class TacoFragment extends Fragment { @BindView(R.id.tags) EditText tags; @Override public View onCreateView(args...) { ... ButterKnife.bind(this, parentView); //Important! unbinder = ButterKnife.bind(this, parentView); tags.setHint("Add tags. Eg: Tasty!, Want to try") return view; } }

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@Override public void onDestroyView() { super.onDestroyView(); //sets the views to null unbinder.unbind(); }

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Event listeners @OnClick(R.id.save) public void saveTaco(Button button) { button.setText("Saved!"); } Arguments to the listener method are optional @OnClick(R.id.reject) public void reject() { Log.d("RejectBtn", "onClick") }

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Butter Knife also supports: - OnLongClick - OnEditorAction - OnFocusChange - OnItemClick - OnItemLongClick - OnItemSelected - OnPageChange - OnTextChanged - OnTouch - OnCheckedChanged

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Inject resources once, no need to save them as member variables! class MainActivity extends Activity { @BindString(R.string.title) String title; @BindDrawable(R.drawable.star) Drawable star; // int or ColorStateList @BindColor(R.color.guac_green) int guacGreen; // int (in pixels) or float (for exact value) @BindDimen(R.dimen.spacer) Float spacer; }

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Group views together: @OnClick({ R.id.save, R.id.reject}) public void saveOrReject(View view) { if (view.getId() == R.reject) { Toast.makeText(this, "Ew Gross!", LENGTH_SHORT).show(); } else { Toast.makeText(this, "Yummy :)", LENGTH_SHORT).show(); } //TODO: implement ButterKnife.apply(actionButtons, DISABLE); getNewTaco(); }

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Act on list of views at once with ButterKnife.apply. @BindViews({R.id.save, R.id.reject}) List actionButtons; ButterKnife.apply(actionButtons, View.ALPHA, 0.0f);

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Action and Setter interfaces allow specifying simple behavior. ButterKnife.apply(actionButtons, DISABLE); ButterKnife.apply(actionButtons, ENABLED, false); static final ButterKnife.Action DISABLE = new ButterKnife.Action() { @Override public void apply(View view, int index) { view.setEnabled(false); } }; static final ButterKnife.Setter ENABLED = new ButterKnife.Setter() { @Override public void set(View view, Boolean value, int index) { view.setEnabled(value); } };

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private void getNewTaco() { //TODO: implement setTacoImage(); }

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Step 3 Add pictures of tasty tacos

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Picasso Download and display images with ease!

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→ makes HTTP Requests → caches the images → easy resizing/cropping/centering/scaling → takes care of downloading off the main thread → properly recycles views in RecyclerView

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Pop quiz Which do you prefer?

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private Bitmap DownloadImage(String url) { Bitmap bitmap = null; InputStream in = null; try { in = OpenHttpGETConnection(url); bitmap = BitmapFactory.decodeStream(in); in.close(); } catch (Exception e) { Log.d("DownloadImage", e.getLocalizedMessage()); } return bitmap; }

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Or... Picasso.with(context) .load("http://placekitten.com/200/300") .into(imageView);

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But wait there's more! .placeholder(R.mipmap.loading) //can be a resource or a drawable .error(R.drawable.sad_taco) //fallback image if error .fit() //reduce the image size to the dimensions of imageView .resize(imgWidth, imgHeight) //resizes the image in pixels .centerCrop() //or .centerInside() .rotate(90f) //or rotate(degrees, pivotX, pivotY) .noFade() //don't fade all fancy-like

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Not just for loading images from the web Picasso.with(context).load(R.drawable.salsa).into(imageView1); Picasso.with(context).load("file:///asset/salsa.png").into(imageView2); Picasso.with(context).load(new File(...)).into(imageView3);

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//Butter Knife! @BindView(R.id.taco_img) ImageView tacoImg; private void setTacoImage() { Picasso.with(context) .load("http://tacoimages.com/random.jpg") .into(tacoImg); } private void getNewTaco() { setTacoImage(); //TODO: implement loadTacoDescription(); }

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Step 4 Set up models Get ready for models by setting up what JSON will look like

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Gson Convert JSON to a java object and vice versa!

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→ Without requiring you place Java annotations in your classes → Super performant → Commonly used

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Example time! class Taco { private String name; private String url; //not included in JSON serialization or deserialization private transient String imageUrl; Taco(args...) { ... } }

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// Serialize to JSON Taco breakfastTaco = new Taco( "Eggs with syrup on pancake", "tacofancy.com/breakfast", "imgur.com/123"); Gson gson = new Gson(); String json = gson.toJson(breakfastTaco); json = { "name":"Eggs with syrup on pancake", "url": "tacofancy.com/breakfast" } // Deserialize to POJO Taco yummyTaco = gson.fromJson(json, Taco.class); // ==> yummyTaco is just like breakfastTaco without imagUrl

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Beneﬁts → All ﬁelds in the current class (and from all super classes) are included by default → Supports multi-dimensional arrays

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Gotchas → While serializing, a null ﬁeld is skipped from the output → While deserializing, a missing entry in JSON results in setting the corresponding ﬁeld in the object to null

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Cool customization //Set properties to null instead of ignoring them Gson gson = new GsonBuilder().serializeNulls().create(); //Keep whitespace Gson gson = new GsonBuilder().setPrettyPrinting().create();

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Need to rename a variable from an API? public class Taco { @SerializedName("serialized_labels") private String tags; }

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Or use a custom date format? public String DATE_FORMAT = "yyyy-MM-dd"; GsonBuilder gsonBuilder = new GsonBuilder(); gsonBuilder.setDateFormat(DATE_FORMAT); Gson gson = gsonBuilder.create();

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private void getNextTaco() { setTacoImage(); //TODO: implement loadTacoDescription(); }

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Step 5 Get taco recipe from web API

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Retroﬁt Stop using AsyncTask Please, just stop.

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The better way → Typesafe → Built in support for: → Authentication → parse JSON to POJOs → Supports RxJava → Can be executed synchronously or asynchronously

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API Endpoints public interface TacoApi { // Request method and URL specified in the annotation // Callback for the parsed response is the last parameter @GET("random") Call randomTaco(@Query("full-taco") boolean full); @GET("contributions/{name}") Call getContributors(@Path("name") String username); @POST("recipe/new") Call createRecipe(@Body Recipe recipe); @GET("contributions") Call> getContributors(); }

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Getting JSON synchronously Retrofit retrofit = new Retrofit.Builder() .baseUrl("http://taco-randomizer.herokuapp.com/") .addConverterFactory(GsonConverterFactory.create()) .build(); // Create an instance of our TacoApi interface. TacoApi tacoApi = retrofit.create(TacoApi.class); // Create a call instance for a random taco Call call = tacoApi.randomTaco(false); // Fetch a random taco // Do this off the main thread Taco taco = call.execute().body();

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POSTing JSON Async Recipe recipe = new Recipe(); Call call = tacoApi.createRecipe(recipe); call.enqueue(new Callback() { @Override public void onResponse(Call call, Response response) { } @Override public void onFailure(Call call, Throwable t) { }

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Annotations → @Path: variable substitution for the API endpoint. → @Query: Add a query parameter. → @Body: Payload for the POST call (serialized from a Java object to a JSON string) → @Headers: Add a header to the HTTP call → @Url: Pass in a dynamic url

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Cool tricks //Change the base url @POST("http://taco-randomizer.herokuapp.com/v2/taco") private Call getFromNewAPI(); //Add headers @Headers({"User-Agent: tacobot"}) @GET("contributions") private Call> getContributors();

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private void getNextTaco() { ... loadTacoDescription(); } private void loadTacoDescription() { Call call = tacoApi.randomTaco(true); call.enqueue(new Callback() { @Override public void onResponse(Call call, Response response) { //Set description from response Taco taco = response.body; //TODO: implement saveTaco(taco); } @Override public void onFailure(Call call, Throwable t) { //Show error } }

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Save taco recipe for later!

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Realm Replacement for sqlite

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→ Works by extending your models → Made for mobile → Most queries in Realm are fast enough to be run synchronously → Can have multiple realm database in an app

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public class Taco extends RealmObject { private String name; private String imageUrl; private String url; //getters and setters }

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Set-up Realm Realm.init(this); // Get a Realm instance for this thread Realm realm = Realm.getDefaultInstance();

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Persist to db // Persist your data in a transaction realm.beginTransaction(); // Persist unmanaged objects final Taco managedTaco = realm.copyToRealm(unmanagedTaco); // Create managed objects directly Taco taco = realm.createObject(Taco.class); realm.commitTransaction();

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Accessing Data //find all favorite tacos final RealmResults likedTacos = realm.where(Taco.class).equalTo("favorite", true).findAll();

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Typical SQL relationships → One to One → One to Many → Many to One → Many to Many

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Conditions → between() → greaterThan(), lessThan() → greaterThanOrEqualTo() & lessThanOrEqualTo() → equalTo() & notEqualTo() → contains() → beginsWith() & endsWith()

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Writing data

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//Transaction block realm.executeTransaction(new Realm.Transaction() { @Override public void execute(Realm realm) { Taco taco = realm.createObject(Taco.class); taco.setName("Spaghetti Squash on Fresh Corn Tortillas"); taco.setUrl("http://tacofancy.com/squash"); } });

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//Async realm.executeTransactionAsync(new Realm.Transaction() { public void execute(Realm bgRealm) { Taco taco = bgRealm.createObject(Taco.class); taco.name("Spaghetti Squash on Fresh Corn Tortillas"); taco.setUrl("http://tacofancy.com/squash"); } }, new Realm.Transaction.OnSuccess() { public void onSuccess() { // Transaction was a success. } }, new Realm.Transaction.OnError() { public void onError(Throwable error) { // Transaction failed and was automatically canceled. } });

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Fact: Tacos have many ingredients

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public class Taco extends RealmObject { ... private List ... } public class Ingredient extends RealmObject { private String name; private URL url; }

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RealmResults limeTacos = realm.where(Taco.class) .equalTo("ingredients.name", "Lime") .findAll();

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Delete results // All changes to data must happen in a transaction realm.executeTransaction(new Realm.Transaction() { @Override public void execute(Realm realm) { // remove single match limeTacos.deleteFirstFromRealm(); //or limeTacos.deleteLastFromRealm(); // remove a single object Taco fishTaco = limeTacos.get(1); fishTaco.deleteFromRealm(); // Delete all matches limeTacos.deleteAllFromRealm(); } });

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Data change listeners Can be attached to RealmObject or RealmResults limeTacos.addChangeListener( new RealmChangeListener>() { @Override public void onChange(RealmResults tacosConLimon) { //tacosConLimon.size() == limeTacos.size() // Query results are updated in real time Log.d("LimeTacos", "Now we have" + limeTacos.size() + " tacos"); } } );

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Tips → @PrimaryKey allows the use of copyToRealmOrUpdate() → Works with Gson and Retrofit easily

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Prevent memory leaks @Override protected void onDestroy() { // Remove the listener. realm.removeChangeListener(realmListener); //or realm.removeAllChangeListeners(); // Close the Realm instance. realm.close(); ... }

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Gotchas → No support for list of String or primitives → In the meantime add this Gson adapter → Need to save data to realm after getting response from Retrofit → Large datasets or complex queries should be run on background thread

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//TODO: implement goToTacoDetailActivity();

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Dart + Henson Inspired by Butter Knife Inject intent extras as a property on an object

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Beneﬁts → readable DSL for passing extras to intent → stop wasting time and write less of this: intent.putExtra("TACO_NAME", "Salsa Verde"); tacoName = getIntent().getExtras().getString("TACO_NAME");

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public class TacoDetailActivity extends Activity { @InjectExtra String name; @Nullable @InjectExtra String imageUrl; //default value if left null @Nullable @InjectExtra String tag = "taco"; //Ingredient implements Parcelable @Nullable @InjectExtra Ingredient ingredient; @Override public void onCreate(Bundle bundle) { super.onCreate(bundle); Dart.inject(this); //TODO use member variables ... } }

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Generate intent builders //Start intent for TacoDetailActivity Intent intent = Henson.with(this) .gotoTacoDetailActivity() .name(taco.getName()) .url(taco.getUrl()) .imageUrl(taco.getImageUrl()) .build(); // tag is null startActivity(intent);

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Want to use Henson for an activity without injectable extras? Annotate the activity with @HensonNavigable

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Is that it?

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grep 'TODO: implement' => 0 results

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→ Butter Knife - Manage multiple views → Picasso - Load and display images → Gson - Parse JSON → Retroﬁt - Fetch data from an API → Realm - Persist data to storage → Dart & Henson - Start new activities with extras

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Questions? @speaktochris chris-guzman.com