[转自:https://www.zhangningning.com.cn/blog/Android/android_rentention_sample.html]

使用编译时注解方式实现View注入(Android Studio)

ButterKnife是一个强大的View注入，事件注入的框架，现模仿ButterKnife的方式，使用编译时注解实现View的注入的Demo，做个精简版的ButterKnife。

基本的原理在上一篇文章中(https://www.zhangningning.com.cn/blog/Android/android_rentention.html已经做了说明，这篇主要是实现一个在Activity中实现Bind View的注解。

先整体说明一下：实例一共分为四个部分：

injectview-annotations：这是个Java Library，，主要来定义注解。
injectview-compiler：这个也是一个Java Library，一定不能为Android Library ，也不能被Android模块的dependencies中使用compile引用，不然会找不到javax相关的类。主要用来处理注解，并生成相关的代码。
injectview：这个是Android Library,被android模块调用实现View的Bind.
app: Android Application模块，应用的主模块。

使用的库有：
auto-common：注解处理辅助类
auto-service：使用它就不需要把processor在META-INF配置了，编译时配置的Processor能够自动被发现并处理。
javapoet：辅助生成代码，能够更简单的生成.java源文件
这三个库用在injectview-compiler中，不会存在于最终的apk包中。

android-apt:用来编译injectview-compiler生成需要的代码。

四个模块的关系：
app引用injectview,
injectview引用injectview-annotations,
injectview-compiler引用injectview-annotations,
app中使用APT执行injectview-compiler

injectview-annotations

新建一个Java Library(File->New->New Module 选择Java Library) 首先定义一个注解：

package com.znn.injectview.annotations;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.CLASS)public @interface BindView {    int value();}

injectview-compiler

再新建一个名为injectview-compiler的Java Library。修改build.gradle：

apply plugin: 'java'dependencies {    compile fileTree(include: ['*.jar'], dir: 'libs')    compile 'com.google.auto:auto-common:0.6'    compile 'com.google.auto.service:auto-service:1.0-rc2'    compile 'com.squareup:javapoet:1.7.0'    compile project(':injectview-annotations')    sourceCompatibility = 1.7    targetCompatibility = 1.7}

新建一个继承AbstractProcessor的BindViewProcessor。并且使用AutoService进行注解，这样系统就能够找到这个 Processor ，并在编译时对注解进行预处理。

重写getSupportedAnnotationTypes方法，将BindView添加到支持处理的注解中。

在process函数中对注解进行处理，并生成对应辅助class文件，这个class名是当前Activity名字拼接上$$ViewBinder，后面bind的时候会使用反射找到这个类，并执行它的bind方法。相应的代码如下： BindViewProcessor.java

@AutoService(Processor.class)public final class BindViewProcessor extends AbstractProcessor{    private Elements elementUtils;    private Types typeUtils;    private Filer filer;    private static final ClassName VIEW_BINDER = ClassName.get("com.znn.injectview", "ViewBinder");    private static final String BINDING_CLASS_SUFFIX = "$$ViewBinder";//生成类的后缀 以后会用反射去取    @Override public synchronized void init(ProcessingEnvironment env) {        super.init(env);        elementUtils = env.getElementUtils();        typeUtils = env.getTypeUtils();        filer = env.getFiler();    }    @Override    public Set getSupportedAnnotationTypes() {        Set types = new LinkedHashSet<>();        types.add(BindView.class.getCanonicalName());        return types;    }    @Override public SourceVersion getSupportedSourceVersion() {        return SourceVersion.latestSupported();    }    @Override    public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) {        Map> targetClassMap = new LinkedHashMap<>();        for (Element element: roundEnv.getElementsAnnotatedWith(BindView.class)){            if (!SuperficialValidation.validateElement(element))                continue;            // Start by verifying common generated code restrictions.            TypeElement enclosingElement = (TypeElement) element.getEnclosingElement();            boolean hasError = isInaccessibleViaGeneratedCode(BindView.class, "fields", element)                        || isBindingInWrongPackage(BindView.class, element);            // Verify that the target type extends from View.            TypeMirror elementType = element.asType();            if (elementType.getKind() == TypeKind.TYPEVAR) {                TypeVariable typeVariable = (TypeVariable) elementType;                elementType = typeVariable.getUpperBound();            }            if (!isSubtypeOfType(elementType, "android.view.View") && !isInterface(elementType)) {                processingEnv.getMessager().printMessage(Diagnostic.Kind.ERROR, String.format("@%s fields must extend from View or be an interface. (%s.%s)",                        BindView.class.getSimpleName(), enclosingElement.getQualifiedName(),                        element.getSimpleName()));                hasError = true;            }            if (hasError) {                continue;            }            // Assemble information on the field.            List fieldViewBindingList = targetClassMap.get(enclosingElement);            if (fieldViewBindingList == null) {                fieldViewBindingList = new ArrayList<>();                targetClassMap.put(enclosingElement, fieldViewBindingList);            }            String packageName = getPackageName(enclosingElement);            TypeName targetType = TypeName.get(enclosingElement.asType());            int id = element.getAnnotation(BindView.class).value();            String fieldName = element.getSimpleName().toString();            TypeMirror fieldType = element.asType();            FieldViewBinding fieldViewBinding = new FieldViewBinding(fieldName, fieldType, id);            fieldViewBindingList.add(fieldViewBinding);        }        for (Map.Entry> item : targetClassMap.entrySet()){            List list = item.getValue();            if (list == null || list.size() == 0){                continue;            }            TypeElement enclosingElement = item.getKey();            String packageName = getPackageName(enclosingElement);            ClassName typeClassName = ClassName.bestGuess(getClassName(enclosingElement, packageName));            TypeSpec.Builder result = TypeSpec.classBuilder(getClassName(enclosingElement, packageName) + BINDING_CLASS_SUFFIX)                    .addModifiers(Modifier.PUBLIC)                    .addTypeVariable(TypeVariableName.get("T", typeClassName))                    .addSuperinterface(ParameterizedTypeName.get(VIEW_BINDER, typeClassName));            result.addMethod(createBindMethod(list, typeClassName));            try {                JavaFile.builder(packageName, result.build())                        .addFileComment(" This codes are generated automatically. Do not modify!")                        .build().writeTo(filer);            } catch (IOException e) {                e.printStackTrace();            }        }        return true;    }    private MethodSpec createBindMethod(List list, ClassName typeClassName) {        MethodSpec.Builder result = MethodSpec.methodBuilder("bind")                .addModifiers(Modifier.PUBLIC)                .returns(TypeName.VOID)                .addAnnotation(Override.class)                .addParameter(typeClassName, "target", Modifier.FINAL);        for (int i = 0; i < list.size(); i++) {            FieldViewBinding fieldViewBinding = list.get(i);            String packageString = fieldViewBinding.getType().toString();//            String className = fieldViewBinding.getType().getClass().getSimpleName();            ClassName viewClass = bestGuess(packageString);            result.addStatement("target.$L=($T)target.findViewById($L)", fieldViewBinding.getName(), viewClass, fieldViewBinding.getResId());        }        return result.build();    }    private boolean isInaccessibleViaGeneratedCode(Class<? extends Annotation> annotationClass,                                                   String targetThing, Element element) {        boolean hasError = false;        TypeElement enclosingElement = (TypeElement) element.getEnclosingElement();        // Verify method modifiers.        Set modifiers = element.getModifiers();        if (modifiers.contains(Modifier.PRIVATE) || modifiers.contains(Modifier.STATIC)) {            processingEnv.getMessager().printMessage(Diagnostic.Kind.ERROR, String.format("@%s %s must not be private or static. (%s.%s)",                    annotationClass.getSimpleName(), targetThing, enclosingElement.getQualifiedName(),                    element.getSimpleName()));            hasError = true;        }        // Verify containing type.        if (enclosingElement.getKind() != ElementKind.CLASS) {            processingEnv.getMessager().printMessage(Diagnostic.Kind.ERROR, String.format("@%s %s may only be contained in classes. (%s.%s)",                    annotationClass.getSimpleName(), targetThing, enclosingElement.getQualifiedName(),                    element.getSimpleName()));            hasError = true;        }        // Verify containing class visibility is not private.        if (enclosingElement.getModifiers().contains(Modifier.PRIVATE)) {            processingEnv.getMessager().printMessage(Diagnostic.Kind.ERROR, String.format("@%s %s may not be contained in private classes. (%s.%s)",                    annotationClass.getSimpleName(), targetThing, enclosingElement.getQualifiedName(),                    element.getSimpleName()));            hasError = true;        }        return hasError;    }    private boolean isBindingInWrongPackage(Class<? extends Annotation> annotationClass,                                            Element element) {        TypeElement enclosingElement = (TypeElement) element.getEnclosingElement();        String qualifiedName = enclosingElement.getQualifiedName().toString();        if (qualifiedName.startsWith("android.")) {            processingEnv.getMessager().printMessage(Diagnostic.Kind.ERROR, String.format("@%s-annotated class incorrectly in Android framework package. (%s)",                    annotationClass.getSimpleName(), qualifiedName));            return true;        }        if (qualifiedName.startsWith("java.")) {            processingEnv.getMessager().printMessage(Diagnostic.Kind.ERROR, String.format("@%s-annotated class incorrectly in Java framework package. (%s)",                    annotationClass.getSimpleName(), qualifiedName));            return true;        }        return false;    }    private boolean isSubtypeOfType(TypeMirror typeMirror, String otherType) {        if (otherType.equals(typeMirror.toString())) {            return true;        }        if (typeMirror.getKind() != TypeKind.DECLARED) {            return false;        }        DeclaredType declaredType = (DeclaredType) typeMirror;        List<? extends TypeMirror> typeArguments = declaredType.getTypeArguments();        if (typeArguments.size() > 0) {            StringBuilder typeString = new StringBuilder(declaredType.asElement().toString());            typeString.append('<');            for (int i = 0; i < typeArguments.size(); i++) {                if (i > 0) {                    typeString.append(',');                }                typeString.append('?');            }            typeString.append('>');            if (typeString.toString().equals(otherType)) {                return true;            }        }        Element element = declaredType.asElement();        if (!(element instanceof TypeElement)) {            return false;        }        TypeElement typeElement = (TypeElement) element;        TypeMirror superType = typeElement.getSuperclass();        if (isSubtypeOfType(superType, otherType)) {            return true;        }        for (TypeMirror interfaceType : typeElement.getInterfaces()) {            if (isSubtypeOfType(interfaceType, otherType)) {                return true;            }        }        return false;    }    private boolean isInterface(TypeMirror typeMirror) {        return typeMirror instanceof DeclaredType                && ((DeclaredType) typeMirror).asElement().getKind() == ElementKind.INTERFACE;    }    private String getPackageName(TypeElement type) {        return elementUtils.getPackageOf(type).getQualifiedName().toString();    }    private static String getClassName(TypeElement type, String packageName) {        int packageLen = packageName.length() + 1;        return type.getQualifiedName().toString().substring(packageLen).replace('.', '$');    }}

生成的文件在app->build->generated->source->apt->debug下，如果没有实时显示出来，可以尝试clean，然后菜单栏->Build->Make Project就可以了

injectview

生成的class类会实现接口ViewBinder :

package com.znn.injectview;public interface ViewBinder<T> {  void bind(T target);}

在InjectView的bind函数在Activity中调用，这里会先找到该Activity对应的ViewBinder类，并执行它的bind方法，来对该Activity中添加注解的View进行"注入"。

InjectView.java

public class InjectView {    public static void bind(Activity activity){        String clsName = activity.getClass().getName();        try {            Class<?> viewBindingClass = Class.forName(clsName + "$$ViewBinder");            ViewBinder viewBinder = (ViewBinder)viewBindingClass.newInstance();            viewBinder.bind(activity);        } catch (ClassNotFoundException e) {            e.printStackTrace();        } catch (InstantiationException e) {            e.printStackTrace();        } catch (IllegalAccessException e) {            e.printStackTrace();        }    }}

app

在项目工程跟build.gradle添加APT支持：

buildscript {    repositories {        jcenter()        mavenCentral()    }    dependencies {        classpath 'com.android.tools.build:gradle:2.1.0'        classpath 'com.neenbedankt.gradle.plugins:android-apt:1.8'    }}allprojects {    repositories {        jcenter()        mavenCentral()    }}

在app的模块的build.gradle加载apt，并使用apt对injectview-compiler进行处理。另外还要讲模块injectview添加到依赖中，以此可以访问到注解的定义和进行注入的入口。

apply plugin: 'com.android.application'apply plugin: 'com.neenbedankt.android-apt'android {    compileSdkVersion 23    buildToolsVersion "23.0.2"    defaultConfig {        applicationId "com.znn.androidrentation"        minSdkVersion 15        targetSdkVersion 22        versionCode 1        versionName "1.0"    }    compileOptions {        sourceCompatibility JavaVersion.VERSION_1_7        targetCompatibility JavaVersion.VERSION_1_7    }    buildTypes {        release {            minifyEnabled false            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'        }    }}dependencies {    compile fileTree(include: ['*.jar'], dir: 'libs')    testCompile 'junit:junit:4.12'    compile 'com.android.support:appcompat-v7:23.4.0'    compile project(':injectview')    apt project(':injectview-compiler')}

在Activity中对View变量添加BindView注解，在setContentView后，使用View前添加InjectView.bind(this);进行注入。

public class MainActivity extends FragmentActivity {    @BindView(R.id.text)    TextView textView;    @BindView(R.id.text2)    TextView textView2;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        InjectView.bind(this);        textView.setText("text changged!");    }}

OK，完成

只做了Activity的注入，内部类,Fragment的都没做，仅作学习编译时注解用，正式用还是用ButterKnife吧~~~~

全部代码 https://github.com/qduningning/AndroidRentation

使用编译时注解方式实现View注入(Android(安卓)Studio)

使用编译时注解方式实现View注入(Android Studio)

injectview-annotations

injectview-compiler

injectview

app

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