@auditty +AudreyTroutt Android Annotation Processors Audrey Troutt

@auditty +AudreyTroutt @Override // An annotation! protected void onResume() { super.onResume(); … } Have you used them? Yes, you have

@auditty +AudreyTroutt Why use Annotations? // BEFORE class AndroidWay extends Activity { TextView name; ImageView thumbnail; LocationManager loc; Drawable icon; String myName; public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); name = (TextView) findViewById(R.id.name); thumbnail = (ImageView) findViewById(R.id.thumbnail); loc = (LocationManager) getSystemService(Activity.LOCATION_SERVICE); icon = getResources().getDrawable(R.drawable.icon); myName = getString(R.string.app_name); name.setText( "Hello, " + myName ); } } // AFTER @ContentView(R.layout.main) class RoboWay extends RoboActivity { @InjectView(R.id.name) TextView name; @InjectView(R.id.thumbnail) ImageView thumbnail; @InjectResource(R.drawable.icon) Drawable icon; @InjectResource(R.string.app_name) String myName; @Inject LocationManager loc; public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); name.setText( "Hello, " + myName ); } } // example borrowed from RoboGuice :) https://github.com/roboguice/roboguice/wiki

@auditty +AudreyTroutt Why use Annotations? // BEFORE class AndroidWay extends Activity { TextView name; ImageView thumbnail; LocationManager loc; Drawable icon; String myName; public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); name = (TextView) findViewById(R.id.name); thumbnail = (ImageView) findViewById(R.id.thumbnail); loc = (LocationManager) getSystemService(Activity.LOCATION_SERVICE); icon = getResources().getDrawable(R.drawable.icon); myName = getString(R.string.app_name); name.setText( "Hello, " + myName ); } } // AFTER @ContentView(R.layout.main) class RoboWay extends RoboActivity { @InjectView(R.id.name) TextView name; @InjectView(R.id.thumbnail) ImageView thumbnail; @InjectResource(R.drawable.icon) Drawable icon; @InjectResource(R.string.app_name) String myName; @Inject LocationManager loc; public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); name.setText( "Hello, " + myName ); } } // example borrowed from RoboGuice :) https://github.com/roboguice/roboguice/wiki

@auditty +AudreyTroutt Who creates Annotations? ● Library developers, mostly

@auditty +AudreyTroutt #import "UILabel+TextMagic.h" // This is a category @implementation UILabel (TextMagic) - (CGFloat)bottomYCoordinate { return self.frame.origin.y + self.frame.size.height; } - (CGFloat)rightXCoordinate { return self.frame.origin.x + self.frame.size.width; } @end // from https://github.com/ArtisanMobile/ArtisanCategoryMagic Metaprogramming is easy* on iOS

@auditty +AudreyTroutt #import // This is method swizzling + (void)replaceOriginalInstanceMethod:(SEL)originalMethod from:(id)original withInstanceMethod:(SEL)replacementMethod from:(id)replacementObject { Method originalMethod = class_getInstanceMethod([original class], originalMethod); Method mockMethod = class_getInstanceMethod([replacementObject class], replacementMethod); method_exchangeImplementations(originalMethod, mockMethod); } // Don’t do this in production code! It’s more polite to always call the original code. Metaprogramming is easy* on iOS

@auditty +AudreyTroutt Annotations ● Define metadata about code

@auditty +AudreyTroutt Annotation Processing https://medium.com/@lgvalle/how-butterknife-actually-works-85be0afbc5ab

@auditty +AudreyTroutt 1. Annotation(s) ○ are interfaces 2. Processor(s) ○ extend javax.annotation.processing.AbstractProces sor 3. Additional API to leverage generated code Annotation Processor Project Parts

@auditty +AudreyTroutt

@auditty +AudreyTroutt import java.lang.annotation.*; @Target(ElementType.METHOD) @Retention(RetentionPolicy.RUNTIME) public @interface WatchedMethod { String eventName(); String logProperty() default ""; } Annotation

@auditty +AudreyTroutt import java.lang.annotation.*; @Target(ElementType.METHOD) @Retention(RetentionPolicy.RUNTIME) public @interface WatchedMethod { String eventName(); String logProperty() default ""; } Annotation

@auditty +AudreyTroutt import java.lang.annotation.*; @Target(ElementType.METHOD) @Retention(RetentionPolicy.RUNTIME) public @interface WatchedMethod { String eventName(); String logProperty() default ""; } Annotation

@auditty +AudreyTroutt import java.lang.annotation.*; @Target(ElementType.METHOD) @Retention(RetentionPolicy.RUNTIME) public @interface WatchedMethod { String eventName(); String logProperty() default ""; } Annotation

@auditty +AudreyTroutt import java.lang.annotation.*; @Target(ElementType.METHOD) @Retention(RetentionPolicy.RUNTIME) public @interface WatchedMethod { String eventName(); String logProperty() default ""; } // SAMPLE USAGE IN MY ACTIVITY @Override @WatchedMethod(eventName = "disappear", logProperty = "timeOnScreen") protected void onStop() { super.onStop(); } Annotation

@auditty +AudreyTroutt Annotation Processor import java.util.Set; import javax.annotation.processing.AbstractProcessor; import javax.annotation.processing.RoundEnvironment; import javax.lang.model.element.TypeElement; public class WatchedMethodProcessor extends AbstractProcessor { … // where all the processing happens @Override public boolean process(Set extends TypeElement> annotations, RoundEnvironment roundEnv) { return false; } }

@auditty +AudreyTroutt Annotation Processor import java.util.Set; import javax.annotation.processing.AbstractProcessor; import javax.annotation.processing.RoundEnvironment; import javax.lang.model.element.TypeElement; public class WatchedMethodProcessor extends AbstractProcessor { @Override public Set getSupportedAnnotationTypes() { return Collections.singleton("com.audreytroutt.WatchedMethod"); } @Override public SourceVersion getSupportedSourceVersion() { return SourceVersion.latestSupported(); } ...

@auditty +AudreyTroutt Annotation Processor import java.util.Set; import javax.annotation.processing.AbstractProcessor; import javax.annotation.processing.RoundEnvironment; import javax.lang.model.element.TypeElement; public class WatchedMethodProcessor extends AbstractProcessor { @Override public Set getSupportedAnnotationTypes() { return Collections.singleton("com.audreytroutt.WatchedMethod"); } @Override public SourceVersion getSupportedSourceVersion() { return SourceVersion.latestSupported(); } ...

@auditty +AudreyTroutt Annotation Processor import java.util.Set; import javax.annotation.processing.AbstractProcessor; import javax.annotation.processing.RoundEnvironment; import javax.lang.model.element.TypeElement; public class WatchedMethodProcessor extends AbstractProcessor { @Override public Set getSupportedAnnotationTypes() { return Collections.singleton("com.audreytroutt.WatchedMethod"); } @Override public SourceVersion getSupportedSourceVersion() { return SourceVersion.latestSupported(); } ...

@auditty +AudreyTroutt Annotation Processor package javax.annotation.processing; public abstract class AbstractProcessor implements Processor { public Set getSupportedAnnotationTypes() { ... } public SourceVersion getSupportedSourceVersion() { ... } public synchronized void init(ProcessingEnvironment processingEnv) { ... } public abstract boolean process(Set extends TypeElement> annotations, RoundEnvironment roundEnv); }

@auditty +AudreyTroutt javax.annotation.processing.Processor com.audreytroutt.WatchedMethodProcessor com.example.SomeOtherProcessor

@auditty +AudreyTroutt WatchedMethodProcessor.jar Two files: ● com/audreytroutt/WatchedMethodProcessor.class ● META-INF/services/javax.annotation.processing.Proces sor

@auditty +AudreyTroutt WatchedMethodAnnotations.jar ● com/audreytroutt/WatchedMethod.class

@auditty +AudreyTroutt Include in Project dependencies { compile files('libs/WatchedMethodAnnotations.jar') annotationProcessor files('libs/WatchedMethodProcessor.jar') ... }

@auditty +AudreyTroutt ● Can’t modify existing files Annotation Processors

@auditty +AudreyTroutt Additional API class ExampleActivity extends Activity { @BindView(R.id.user) EditText username; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.simple_activity); ButterKnife.bind(this); //... } }

@auditty +AudreyTroutt Additional API class ExampleActivity extends Activity { @BindView(R.id.user) EditText username; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.simple_activity); ButterKnife.bind(this); //... } }

@auditty +AudreyTroutt Generated Code public class ExampleActivity$$ViewBinder implements ViewBinder { @Override public void bind(final Finder finder, final T target, Object source) { View view; view = finder.findRequiredView(source, 21313618, “field ‘user’”); target.username = finder.castView(view, 21313618, “field ‘user’”); } @Override public void reset(T target) { target.username = null; } }

@auditty +AudreyTroutt Generated Code public class ExampleActivity$$ViewBinder implements ViewBinder { @Override public void bind(final Finder finder, final T target, Object source) { View view; view = finder.findRequiredView(source, 21313618, “field ‘user’”); target.username = finder.castView(view, 21313618, “field ‘user’”); } @Override public void reset(T target) { target.username = null; } }

@auditty +AudreyTroutt Generated Code public class ExampleActivity$$ViewBinder implements ViewBinder { @Override public void bind(final Finder finder, final T target, Object source) { View view; view = finder.findRequiredView(source, 21313618, “field ‘user’”); target.username = finder.castView(view, 21313618, “field ‘user’”); } @Override public void reset(T target) { target.username = null; } }

@auditty +AudreyTroutt Get Started ● Leverage existing libraries ● Peek inside and see how they work

@auditty +AudreyTroutt https://github.com/JakeWharton/butterknife class ExampleActivity extends Activity { @BindView(R.id.user) EditText username; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.simple_activity); ButterKnife.bind(this); //... } }

@auditty +AudreyTroutt https://github.com/airbnb/DeepLinkDispatch @DeepLink("foo://example.com/deepLink/{id}") public class MainActivity extends Activity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); Intent intent = getIntent(); if (intent.getBooleanExtra(DeepLink.IS_DEEP_LINK, false)) { Bundle parameters = intent.getExtras(); String idString = parameters.getString("id"); // Do something with idString } }

@auditty +AudreyTroutt Some good blog posts: ● http://hannesdorfmann.com/annotation-proc essing/annotationprocessing101 ● https://medium.com/@lgvalle/how-butterknif e-actually-works-85be0afbc5ab

@auditty +AudreyTroutt https://github.com/google/compile-testing Compilation compilation = javac() .withProcessors(new MyAnnotationProcessor()) .compile(JavaFileObjects.forResource("HelloWorld.java")); assertThat(compilation).succeeded(); assertThat(compilation) .generatedSourceFile("GeneratedHelloWorld") .hasSourceEquivalentTo(JavaFileObjects.forResource( "GeneratedHelloWorld.java"));

@auditty +AudreyTroutt https://github.com/square/javapoet MethodSpec main = MethodSpec.methodBuilder("main") .addModifiers(Modifier.PUBLIC, Modifier.STATIC) .returns(void.class).addParameter(String[].class, "args") .addStatement("$T.out.println($S)", System.class, "Hello, JavaPoet!").build(); TypeSpec helloWorld = TypeSpec.classBuilder("HelloWorld") .addModifiers(Modifier.PUBLIC, Modifier.FINAL).addMethod(main).build(); JavaFile javaFile = JavaFile.builder("com.example.helloworld", helloWorld).build(); javaFile.writeTo(System.out);