使用annotationProcessor根据注解自动生成代码。本文先不讲原理，只讲实现过程。尝试了一下在模块化中使用注解自动生成代码，但是会报错：Attribute value must be constant。这是因为在library模块中使用该注解（即使用BindView绑定id）
image.png
而library构建时产生的R文件在壳模块app中，如下图所示：
image.png
所以在library中使用注解绑定id，该id就不是常量类型，因此会报错，目前不知道该如何解决，希望有大佬指点一二。
1 创建项目
-
项目结构
项目结构
annotation：注解类的java-library
app：主工程
compiler：主要用于根据注解类来生成对应代码的java-library
- 创建annotation的java-library
image.png
BindView.java
package com.example.annotation;
import androidx.annotation.IdRes;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
@Target(ElementType.FIELD)
@Retention(RetentionPolicy.SOURCE)
public @interface BindView {
@IdRes int value();
}
OnClick.java
package com.example.annotation;
import androidx.annotation.IdRes;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/**
* Created by yds
* on 2020/3/6.
*/
@Retention(RetentionPolicy.SOURCE)
@Target(ElementType.METHOD)
public @interface OnClick {
@IdRes int value();
}
Keep.java
package com.example.annotation;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
/**
* Created by yds
* on 2020/3/6.
*/
@Retention(RetentionPolicy.CLASS)
@Target(ElementType.TYPE)
public @interface Keep {
}
BindingSuffix.java
package com.example.annotation;
/**
* Created by yds
* on 2020/3/6.
*/
public class BindingSuffix {
public static final String GENERATED_CLASS_SUFFIX = "$Binding";
private BindingSuffix() {
}
}
build.gradle
apply plugin: 'java-library'
dependencies {
implementation fileTree(dir: 'libs', include: ['*.jar'])
implementation 'androidx.annotation:annotation:1.1.0'
}
sourceCompatibility = "1.8"
targetCompatibility = "1.8"
- 创建compiler库
compiler也是java-library类型的module
MyProcessor.java
package com.example.compiler;
import com.example.annotation.BindView;
import com.example.annotation.Keep;
import com.example.annotation.OnClick;
import com.google.auto.service.AutoService;
import com.squareup.javapoet.ClassName;
import com.squareup.javapoet.JavaFile;
import com.squareup.javapoet.MethodSpec;
import com.squareup.javapoet.TypeSpec;
import java.io.IOException;
import java.lang.annotation.Annotation;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.TreeSet;
import javax.annotation.processing.AbstractProcessor;
import javax.annotation.processing.Filer;
import javax.annotation.processing.Messager;
import javax.annotation.processing.ProcessingEnvironment;
import javax.annotation.processing.Processor;
import javax.annotation.processing.RoundEnvironment;
import javax.lang.model.SourceVersion;
import javax.lang.model.element.Element;
import javax.lang.model.element.ExecutableElement;
import javax.lang.model.element.Modifier;
import javax.lang.model.element.TypeElement;
import javax.lang.model.element.VariableElement;
import javax.lang.model.util.ElementFilter;
import javax.lang.model.util.Elements;
import javax.tools.Diagnostic;
@AutoService(Processor.class)
public class MyProcessor extends AbstractProcessor {
private Filer filer;
private Messager messager;
private Elements elementUtils;
//每个存在注解的类整理出来，key:package_classname value:被注解的类型元素
private Map<String, List<Element>> annotationClassMap = new HashMap<>();
@Override
public synchronized void init(ProcessingEnvironment processingEnv) {
super.init(processingEnv);
filer = processingEnv.getFiler();
messager = processingEnv.getMessager();
elementUtils = processingEnv.getElementUtils();
}
@Override
public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) {
if (!roundEnv.processingOver()) {
buildAnnotatedElement(roundEnv, BindView.class);
buildAnnotatedElement(roundEnv, OnClick.class);
}else {
for (Map.Entry<String, List<Element>> entry : annotationClassMap.entrySet()) {
String packageName = entry.getKey().split("_")[0];
String typeName = entry.getKey().split("_")[1];
ClassName className = ClassName.get(packageName, typeName);
ClassName generatedClassName = ClassName
.get(packageName, NameStore.getGeneratedClassName(typeName));
/*
创建要生成的类，如下所示
@Keep
public class MainActivity$Binding {}*/
TypeSpec.Builder classBuilder = TypeSpec.classBuilder(generatedClassName)
.addModifiers(Modifier.PUBLIC)
.addAnnotation(Keep.class);
/*添加构造函数
* public MainActivity$Binding(MainActivity activity) {
bindViews(activity);
bindOnClicks(activity);
}
*/
classBuilder.addMethod(MethodSpec.constructorBuilder()
.addModifiers(Modifier.PUBLIC)
.addParameter(className, NameStore.Variable.ANDROID_ACTIVITY)
.addStatement("$N($N)",
NameStore.Method.BIND_VIEWS,
NameStore.Variable.ANDROID_ACTIVITY)
.addStatement("$N($N)",
NameStore.Method.BIND_ON_CLICKS,
NameStore.Variable.ANDROID_ACTIVITY)
.build());
/*创建方法bindViews(MainActivity activity)
* private void bindViews(MainActivity activity) {}
*/
MethodSpec.Builder bindViewsMethodBuilder = MethodSpec
.methodBuilder(NameStore.Method.BIND_VIEWS)
.addModifiers(Modifier.PRIVATE)
.returns(void.class)
.addParameter(className, NameStore.Variable.ANDROID_ACTIVITY);
/*增加方法体
* activity.tvHello = (TextView)activity.findViewById(2131165326);
* */
for (VariableElement variableElement : ElementFilter.fieldsIn(entry.getValue())) {
BindView bindView = variableElement.getAnnotation(BindView.class);
if (bindView != null) {
bindViewsMethodBuilder.addStatement("$N.$N = ($T)$N.findViewById($L)",
NameStore.Variable.ANDROID_ACTIVITY,
variableElement.getSimpleName(),
variableElement,
NameStore.Variable.ANDROID_ACTIVITY,
bindView.value());
}
}
//将构建出来的方法添加到类里面
classBuilder.addMethod(bindViewsMethodBuilder.build());
/*以下构建如下代码
* private void bindOnClicks(final MainActivity activity) {
activity.findViewById(2131165218).setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
activity.onHelloBtnClick(view);
}
});
}
*/
ClassName androidOnClickListenerClassName = ClassName.get(
NameStore.Package.ANDROID_VIEW,
NameStore.Class.ANDROID_VIEW,
NameStore.Class.ANDROID_VIEW_ON_CLICK_LISTENER);
ClassName androidViewClassName = ClassName.get(
NameStore.Package.ANDROID_VIEW,
NameStore.Class.ANDROID_VIEW);
MethodSpec.Builder bindOnClicksMethodBuilder = MethodSpec
.methodBuilder(NameStore.Method.BIND_ON_CLICKS)
.addModifiers(Modifier.PRIVATE)
.returns(void.class)
.addParameter(className, NameStore.Variable.ANDROID_ACTIVITY, Modifier.FINAL);
for (ExecutableElement executableElement : ElementFilter.methodsIn(entry.getValue())) {
OnClick onClick = executableElement.getAnnotation(OnClick.class);
if (onClick != null) {
TypeSpec onClickListenerClass = TypeSpec.anonymousClassBuilder("")
.addSuperinterface(androidOnClickListenerClassName)
.addMethod(MethodSpec.methodBuilder(NameStore.Method.ANDROID_VIEW_ON_CLICK)
.addModifiers(Modifier.PUBLIC)
.addParameter(androidViewClassName, NameStore.Variable.ANDROID_VIEW)
.addStatement("$N.$N($N)",
NameStore.Variable.ANDROID_ACTIVITY,
executableElement.getSimpleName(),
NameStore.Variable.ANDROID_VIEW)
.returns(void.class)
.build())
.build();
bindOnClicksMethodBuilder.addStatement("$N.findViewById($L).setOnClickListener($L)",
NameStore.Variable.ANDROID_ACTIVITY,
onClick.value(),
onClickListenerClass);
}
}
classBuilder.addMethod(bindOnClicksMethodBuilder.build());
//将类写入文件中
try {
JavaFile.builder(packageName,
classBuilder.build())
.build()
.writeTo(filer);
} catch (IOException e) {
messager.printMessage(Diagnostic.Kind.ERROR, e.toString());
}
}
}
return true;
}
@Override
public Set<String> getSupportedAnnotationTypes() {
return new TreeSet<>(Arrays.asList(
BindView.class.getCanonicalName(),
OnClick.class.getCanonicalName(),
Keep.class.getCanonicalName()));
}
@Override
public SourceVersion getSupportedSourceVersion() {
return SourceVersion.latestSupported();
}
private void buildAnnotatedElement(RoundEnvironment roundEnv, Class<? extends Annotation> clazz) {
for (Element element : roundEnv.getElementsAnnotatedWith(clazz)) {
String className = getFullClassName(element);
List<Element> cacheElements = annotationClassMap.get(className);
if (cacheElements == null) {
cacheElements = new ArrayList<>();
annotationClassMap.put(className, cacheElements);
}
cacheElements.add(element);
}
}
private String getFullClassName(Element element) {
TypeElement typeElement = (TypeElement) element.getEnclosingElement();
String packageName = elementUtils.getPackageOf(typeElement).getQualifiedName().toString();
return packageName + "_" + typeElement.getSimpleName().toString();
}
}
这里的类上面一定要加上@AutoService(Processor.class)，如果不加上，你必须在main目录下面创建一个resources/META-INF/services/javax.annotation.processing.Processor，并在该文件里加入你所编写的Processor类，如下图所示：
image.png
否则，将不会自动生成类。
NameStore.java
package com.example.compiler;
import com.example.annotation.BindingSuffix;
/**
* Created by yds
* on 2020/3/5.
*/
public final class NameStore {
private NameStore(){}
public static String getGeneratedClassName(String clsName){
return clsName+ BindingSuffix.GENERATED_CLASS_SUFFIX;
}
public static class Package{
public static final String ANDROID_VIEW = "android.view";
}
public static class Class {
// Android
public static final String ANDROID_VIEW = "View";
public static final String ANDROID_VIEW_ON_CLICK_LISTENER = "OnClickListener";
}
public static class Variable{
public static final String ANDROID_ACTIVITY = "activity";
public static final String ANDROID_VIEW = "view";
}
public static class Method{
public static final String ANDROID_VIEW_ON_CLICK = "onClick";
// Binder
public static final String BIND_VIEWS = "bindViews";
public static final String BIND_ON_CLICKS = "bindOnClicks";
public static final String BIND = "bind";
}
}
build.gradle
apply plugin: 'java-library'
dependencies {
implementation fileTree(dir: 'libs', include: ['*.jar'])
implementation 'com.squareup:javapoet:1.11.1'
implementation project(path:':annotation')
implementation 'com.google.auto.service:auto-service:1.0-rc5'
annotationProcessor 'com.google.auto.service:auto-service:1.0-rc5'
}
sourceCompatibility = JavaVersion.VERSION_1_8
targetCompatibility = JavaVersion.VERSION_1_8
- app中类的编写
Binding.java
package com.example.binder;
import android.app.Activity;
import com.example.annotation.BindingSuffix;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
/**
* Created by yds
* on 2020/3/6.
*/
public class Binding {
private Binding(){}
private static <T extends Activity> void instantiateBinder(T target, String suffix){
Class<?> targetClass=target.getClass();
String className=targetClass.getName();
try {
Class<?>bindingClass =targetClass
.getClassLoader()
.loadClass(className+suffix);
Constructor<?> classConstructor=bindingClass.getConstructor(targetClass);
try {
classConstructor.newInstance(target);
} catch (IllegalAccessException e) {
throw new RuntimeException("Unable to invoke " + classConstructor, e);
} catch (InstantiationException e) {
throw new RuntimeException("Unable to invoke " + classConstructor, e);
} catch (InvocationTargetException e) {
Throwable cause = e.getCause();
if (cause instanceof RuntimeException) {
throw (RuntimeException) cause;
}
if (cause instanceof Error) {
throw (Error) cause;
}
throw new RuntimeException("Unable to create instance.", cause);
}
} catch (ClassNotFoundException e) {
throw new RuntimeException("Unable to find Class for " + className + suffix, e);
} catch (NoSuchMethodException e) {
throw new RuntimeException("Unable to find constructor for " + className + suffix, e);
}
}
public static <T extends Activity> void bind(T activity) {
instantiateBinder(activity, BindingSuffix.GENERATED_CLASS_SUFFIX);
}
}
MainActivity.java
package com.example.annotationdemo6;
import androidx.appcompat.app.AppCompatActivity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;
import com.example.annotation.BindView;
import com.example.annotation.OnClick;
import com.example.binder.Binding;
public class MainActivity extends AppCompatActivity {
@BindView(R.id.tv)
TextView mTextView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Binding.bind(this);
mTextView.setText("Hello world");
}
@OnClick(R.id.btn)
void clickByBtn(View v){
Intent intent = new Intent();
intent.setClass(MainActivity.this,JumpActivity.class);
startActivity(intent);
}
}
build.gradle
apply plugin: 'com.android.application'
android {
compileSdkVersion 29
buildToolsVersion "29.0.0"
defaultConfig {
applicationId "com.example.annotationdemo6"
minSdkVersion 21
targetSdkVersion 29
versionCode 1
versionName "1.0"
testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
}
buildTypes {
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
}
}
}
dependencies {
implementation fileTree(dir: 'libs', include: ['*.jar'])
implementation project(':annotation')
annotationProcessor project(':compiler')
implementation 'androidx.appcompat:appcompat:1.1.0'
implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
testImplementation 'junit:junit:4.12'
androidTestImplementation 'androidx.test:runner:1.2.0'
androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'
}
