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。

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：辅助Processor自动发现
javapoet：生成代码服务类
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。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 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 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 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 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->Build0->Make Project就可以了

injectview

生成的class类会继承ViewBinder :

package com.znn.injectview;
public interface ViewBinder {
  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);进行注解。

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

全部代码 http://git.oschina.net/zhangningning/AndroidRentation

源地址：https://www.zhangningning.com.cn/blog/Android/android_rentention_sample.html

坑太多了 搞了两晚上才搞出来。。。