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ButterKniffe源码阅读

ButterKniffe项目地址：https://github.com/JakeWharton/butterknife.git 项目基本分为两个最大的模块组成 * butterkniffe：用于项目运行时调用，为参数进行赋值操作 * butterkniffe-annotations、butterknife-annotations：用于执行代码注解，在编译时调用，java版本的butterkniffe将在build的apt目录生成相应的注解文件***_ViewBinder.java 注解部分注解部分，入口为：butterknife.compiler.ButterKnifeProcessor.java文件 @AutoService(Processor.class) public final class ButterKnifeProcessor extends AbstractProcessor { public synchronized void init(ProcessingEnvironment env){ } public boolean process(Set<? extends TypeElement> elements, RoundEnvironment env) { } } 注解入口，告诉编译器这个类为注解类，将在编译时执行。AbstractProcessor为虚处理器，所有编译时注解处理器都必须继承自AbstactProcessor。在它被注解工具调用时，首先执行的是init函数，传入处理环境相关的参数。process函数为当前注解处理器的主函数，在这里可以处理所有注解代码。 @Override public synchronized void init(ProcessingEnvironment env) { super.init(env); String sdk = env.getOptions().get(OPTION_SDK_INT); if (sdk != null) { try { this.sdk = Integer.parseInt(sdk); } catch (NumberFormatException e) { env.getMessager() .printMessage(Kind.WARNING, "Unable to parse supplied minSdk option '" + sdk + "'. Falling back to API 1 support."); } } debuggable = !"false".equals(env.getOptions().get(OPTION_DEBUGGABLE)); elementUtils = env.getElementUtils(); typeUtils = env.getTypeUtils(); filer = env.getFiler(); try { trees = Trees.instance(processingEnv); } catch (IllegalArgumentException ignored) { } } 在init函数中，butterkniffe做了环境检查和参数初始化的工作接下来，进入了主处理函数process中，butterkniffe的process代码如下： @Override public boolean process(Set<? extends TypeElement> elements, RoundEnvironment env) { Map<TypeElement, BindingSet> bindingMap = findAndParseTargets(env); for (Map.Entry<TypeElement, BindingSet> entry : bindingMap.entrySet()) { TypeElement typeElement = entry.getKey(); BindingSet binding = entry.getValue(); JavaFile javaFile = binding.brewJava(sdk, debuggable); try { javaFile.writeTo(filer); } catch (IOException e) { error(typeElement, "Unable to write binding for type %s: %s", typeElement, e.getMessage()); } } return false; } 从代码中可以提现，主处理函数一共做了两个事情：扫描所有文件中的注解使用情况，将这些事情情况保存在一个Map中，然后统一使用JavaFile生成注解类。扫描所有文件中的注解使用首先看butterkniffe是如何扫描所有文件中的注解使用情况的，以下是process函数的第一行，findAndParseTargets函数 private Map<TypeElement, BindingSet> findAndParseTargets(RoundEnvironment env) { Map<TypeElement, BindingSet.Builder> builderMap = new LinkedHashMap<>(); Set<TypeElement> erasedTargetNames = new LinkedHashSet<>(); scanForRClasses(env); // Process each @BindAnim element. for (Element element : env.getElementsAnnotatedWith(BindAnim.class)) { //parse BindAnim to builderMap and erasedTargetNames } // Process each @BindArray element. for (Element element : env.getElementsAnnotatedWith(BindArray.class)) { //parse BindArray to builderMap and erasedTargetNames } // Process each @BindBitmap element. for (Element element : env.getElementsAnnotatedWith(BindBitmap.class)) { //parse BindBitmap to builderMap and erasedTargetNames } // Process each @BindBool element. for (Element element : env.getElementsAnnotatedWith(BindBool.class)) { //parse BindBool to builderMap and erasedTargetNames } // Process each @BindColor element. for (Element element : env.getElementsAnnotatedWith(BindColor.class)) { //parse BindColor to builderMap and erasedTargetNames } // Process each @BindDimen element. for (Element element : env.getElementsAnnotatedWith(BindDimen.class)) { //parse BindDimen to builderMap and erasedTargetNames } // Process each @BindDrawable element. for (Element element : env.getElementsAnnotatedWith(BindDrawable.class)) { //parse BindDrawable to builderMap and erasedTargetNames } // Process each @BindFloat element. for (Element element : env.getElementsAnnotatedWith(BindFloat.class)) { //parse BindFloat to builderMap and erasedTargetNames } // Process each @BindFont element. for (Element element : env.getElementsAnnotatedWith(BindFont.class)) { //parse BindFont to builderMap and erasedTargetNames } // Process each @BindInt element. for (Element element : env.getElementsAnnotatedWith(BindInt.class)) { //parse BindInt to builderMap and erasedTargetNames } // Process each @BindString element. for (Element element : env.getElementsAnnotatedWith(BindString.class)) { //parse BindString to builderMap and erasedTargetNames } // Process each @BindView element. for (Element element : env.getElementsAnnotatedWith(BindView.class)) { //parse BindView to builderMap and erasedTargetNames } // Process each @BindViews element. for (Element element : env.getElementsAnnotatedWith(BindViews.class)) { //parse BindViews to builderMap and erasedTargetNames } // Process each annotation that corresponds to a listener. for (Class<? extends Annotation> listener : LISTENERS) { findAndParseListener(env, listener, builderMap, erasedTargetNames); } // Associate superclass binders with their subclass binders. This is a queue-based tree walk // which starts at the roots (superclasses) and walks to the leafs (subclasses). Deque<Map.Entry<TypeElement, BindingSet.Builder>> entries = new ArrayDeque<>(builderMap.entrySet()); Map<TypeElement, BindingSet> bindingMap = new LinkedHashMap<>(); while (!entries.isEmpty()) { Map.Entry<TypeElement, BindingSet.Builder> entry = entries.removeFirst(); TypeElement type = entry.getKey(); BindingSet.Builder builder = entry.getValue(); TypeElement parentType = findParentType(type, erasedTargetNames); if (parentType == null) { bindingMap.put(type, builder.build()); } else { BindingSet parentBinding = bindingMap.get(parentType); if (parentBinding != null) { builder.setParent(parentBinding); bindingMap.put(type, builder.build()); } else { // Has a superclass binding but we haven't built it yet. Re-enqueue for later. entries.addLast(entry); } } } return bindingMap; } 这段代码主要做了三件事情： 1. 通过scanForRClass搜索资源文件，通过扫描资源文件，将View和id绑定，在避免控件重复绑定时被使用 2. 对支持的注解进行循环解析，如“Element element : env.getElementsAnnotatedWith(BindView.class)”，就是获取所有BindView类型的注解 3. 检测是否包含父类的注解，如果存在，将父类和子类的注解合并，代码从Deque处起始，先通过findParentType来判断是否存在父类，如果有，使用setParent设置，findParentType通过TypeMirror类获取父类信息以parseBindView来看一下具体绑定操作是如何进行的 private void parseBindView(Element element, Map<TypeElement, BindingSet.Builder> builderMap,Set<TypeElement> erasedTargetNames) { TypeElement enclosingElement = (TypeElement) element.getEnclosingElement(); // Start by verifying common generated code restrictions. 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(); } Name qualifiedName = enclosingElement.getQualifiedName(); Name simpleName = element.getSimpleName(); if (!isSubtypeOfType(elementType, VIEW_TYPE) && !isInterface(elementType)) { if (elementType.getKind() == TypeKind.ERROR) { note(element, "@%s field with unresolved type (%s) " + "must elsewhere be generated as a View or interface. (%s.%s)", BindView.class.getSimpleName(), elementType, qualifiedName, simpleName); } else { error(element, "@%s fields must extend from View or be an interface. (%s.%s)", BindView.class.getSimpleName(), qualifiedName, simpleName); hasError = true; } } if (hasError) { return; } // Assemble information on the field. int id = element.getAnnotation(BindView.class).value(); BindingSet.Builder builder = builderMap.get(enclosingElement); QualifiedId qualifiedId = elementToQualifiedId(element, id); if (builder != null) { String existingBindingName = builder.findExistingBindingName(getId(qualifiedId)); if (existingBindingName != null) { error(element, "Attempt to use @%s for an already bound ID %d on '%s'. (%s.%s)", BindView.class.getSimpleName(), id, existingBindingName, enclosingElement.getQualifiedName(), element.getSimpleName()); return; } } else { builder = getOrCreateBindingBuilder(builderMap, enclosingElement); } String name = simpleName.toString(); TypeName type = TypeName.get(elementType); boolean required = isFieldRequired(element); builder.addField(getId(qualifiedId), new FieldViewBinding(name, type, required)); // Add the type-erased version to the valid binding targets set. erasedTargetNames.add(enclosingElement); } 首先，在isInaccessibleViaGengerateCode中检测变量有操作权限，不允许为private或static，不允许非类成员变量，不允许使用private class。然后在isBindingInWrongPackage检测包头，不允许以android.或java.起始的包出现接下来，检测变量类型是否正确，是否为view类型继续，将变量名，类名，是否包含其它注解保存到map中生成注解文件 for (Map.Entry<TypeElement, BindingSet> entry : bindingMap.entrySet()) { TypeElement typeElement = entry.getKey(); BindingSet binding = entry.getValue(); JavaFile javaFile = binding.brewJava(sdk, debuggable); try { javaFile.writeTo(filer); } catch (IOException e) { error(typeElement, "Unable to write binding for type %s: %s", typeElement, e.getMessage()); } } 遍历解析注解生成的map，使用JavaFile类进行文件生成。生成代码位于brewJava中 // brewJava JavaFile brewJava(int sdk, boolean debuggable) { return JavaFile.builder(bindingClassName.packageName(), createType(sdk, debuggable)) .addFileComment("Generated code from Butter Knife. Do not modify!") .build(); } brewJava继续调用createType函数，位于同类中，返回TypeSpec private TypeSpec createType(int sdk, boolean debuggable) { TypeSpec.Builder result = TypeSpec.classBuilder(bindingClassName.simpleName()) .addModifiers(PUBLIC); if (isFinal) { result.addModifiers(FINAL); } if (parentBinding != null) { result.superclass(parentBinding.bindingClassName); } else { result.addSuperinterface(UNBINDER); } if (hasTargetField()) { result.addField(targetTypeName, "target", PRIVATE); } if (isView) { result.addMethod(createBindingConstructorForView()); } else if (isActivity) { result.addMethod(createBindingConstructorForActivity()); } else if (isDialog) { result.addMethod(createBindingConstructorForDialog()); } if (!constructorNeedsView()) { // Add a delegating constructor with a target type + view signature for reflective use. result.addMethod(createBindingViewDelegateConstructor()); } result.addMethod(createBindingConstructor(sdk, debuggable)); if (hasViewBindings() || parentBinding == null) { result.addMethod(createBindingUnbindMethod(result)); } return result.build(); } 处理流程大致为，创建注解类，检测是否存在父类，如果有，设置之。以及添加设置相应的全局变量和成员函数（主要是构造函数和unbind）参考一个生成构造函数的函数createBindingConstructor private MethodSpec createBindingConstructor(int sdk, boolean debuggable) { MethodSpec.Builder constructor = MethodSpec.constructorBuilder() .addAnnotation(UI_THREAD) .addModifiers(PUBLIC); if (hasMethodBindings()) { constructor.addParameter(targetTypeName, "target", FINAL); } else { constructor.addParameter(targetTypeName, "target"); } if (constructorNeedsView()) { constructor.addParameter(VIEW, "source"); } else { constructor.addParameter(CONTEXT, "context"); } if (hasUnqualifiedResourceBindings()) { // Aapt can change IDs out from underneath us, just suppress since all will work at runtime. constructor.addAnnotation(AnnotationSpec.builder(SuppressWarnings.class) .addMember("value", "$S", "ResourceType") .build()); } if (hasOnTouchMethodBindings()) { constructor.addAnnotation(AnnotationSpec.builder(SUPPRESS_LINT) .addMember("value", "$S", "ClickableViewAccessibility") .build()); } if (parentBinding != null) { if (parentBinding.constructorNeedsView()) { constructor.addStatement("super(target, source)"); } else if (constructorNeedsView()) { constructor.addStatement("super(target, source.getContext())"); } else { constructor.addStatement("super(target, context)"); } constructor.addCode("\n"); } if (hasTargetField()) { constructor.addStatement("this.target = target"); constructor.addCode("\n"); } if (hasViewBindings()) { if (hasViewLocal()) { // Local variable in which all views will be temporarily stored. constructor.addStatement("$T view", VIEW); } for (ViewBinding binding : viewBindings) { addViewBinding(constructor, binding, debuggable); } for (FieldCollectionViewBinding binding : collectionBindings) { constructor.addStatement("$L", binding.render(debuggable)); } if (!resourceBindings.isEmpty()) { constructor.addCode("\n"); } } if (!resourceBindings.isEmpty()) { if (constructorNeedsView()) { constructor.addStatement("$T context = source.getContext()", CONTEXT); } if (hasResourceBindingsNeedingResource(sdk)) { constructor.addStatement("$T res = context.getResources()", RESOURCES); } for (ResourceBinding binding : resourceBindings) { constructor.addStatement("$L", binding.render(sdk)); } } return constructor.build(); } 真正执行对资源的绑定，如果是view类型的注解，继续调用addViewBinding依次对资源绑定 private void addViewBinding(MethodSpec.Builder result, ViewBinding binding, boolean debuggable) { if (binding.isSingleFieldBinding()) { // Optimize the common case where there's a single binding directly to a field. FieldViewBinding fieldBinding = binding.getFieldBinding(); CodeBlock.Builder builder = CodeBlock.builder() .add("target.$L = ", fieldBinding.getName()); boolean requiresCast = requiresCast(fieldBinding.getType()); if (!debuggable || (!requiresCast && !fieldBinding.isRequired())) { if (requiresCast) { builder.add("($T) ", fieldBinding.getType()); } builder.add("source.findViewById($L)", binding.getId().code); } else { builder.add("$T.find", UTILS); builder.add(fieldBinding.isRequired() ? "RequiredView" : "OptionalView"); if (requiresCast) { builder.add("AsType"); } builder.add("(source, $L", binding.getId().code); if (fieldBinding.isRequired() || requiresCast) { builder.add(", $S", asHumanDescription(singletonList(fieldBinding))); } if (requiresCast) { builder.add(", $T.class", fieldBinding.getRawType()); } builder.add(")"); } result.addStatement("$L", builder.build()); return; } List<MemberViewBinding> requiredBindings = binding.getRequiredBindings(); if (!debuggable || requiredBindings.isEmpty()) { result.addStatement("view = source.findViewById($L)", binding.getId().code); } else if (!binding.isBoundToRoot()) { result.addStatement("view = $T.findRequiredView(source, $L, $S)", UTILS, binding.getId().code, asHumanDescription(requiredBindings)); } // 执行对变量赋值 addFieldBinding(result, binding, debuggable); // 执行对事件绑定方法的注解 addMethodBindings(result, binding, debuggable); } 调用部分代码位于butterKniffe包下的ButterKnife.java文件中，通过查看源码得知，所有bind函数的调用，统一归纳到createBinding(context, view)调用中。 private static Unbinder createBinding(@NonNull Object target, @NonNull View source) { Class<?> targetClass = target.getClass(); if (debug) Log.d(TAG, "Looking up binding for " + targetClass.getName()); Constructor<? extends Unbinder> constructor = findBindingConstructorForClass(targetClass); if (constructor == null) { return Unbinder.EMPTY; } //noinspection TryWithIdenticalCatches Resolves to API 19+ only type. try { return constructor.newInstance(target, source); } catch (IllegalAccessException e) { throw new RuntimeException("Unable to invoke " + constructor, e); } catch (InstantiationException e) { throw new RuntimeException("Unable to invoke " + constructor, 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 binding instance.", cause); } } createBinding继续递归调用findBindingConstructorForClass @Nullable @CheckResult @UiThread private static Constructor<? extends Unbinder> findBindingConstructorForClass(Class<?> cls) { Constructor<? extends Unbinder> bindingCtor = BINDINGS.get(cls); if (bindingCtor != null) { if (debug) Log.d(TAG, "HIT: Cached in binding map."); return bindingCtor; } String clsName = cls.getName(); if (clsName.startsWith("android.") || clsName.startsWith("java.")) { if (debug) Log.d(TAG, "MISS: Reached framework class. Abandoning search."); return null; } try { Class<?> bindingClass = cls.getClassLoader().loadClass(clsName + "_ViewBinding"); //noinspection unchecked bindingCtor = (Constructor<? extends Unbinder>) bindingClass.getConstructor(cls, View.class); if (debug) Log.d(TAG, "HIT: Loaded binding class and constructor."); } catch (ClassNotFoundException e) { if (debug) Log.d(TAG, "Not found. Trying superclass " + cls.getSuperclass().getName()); bindingCtor = findBindingConstructorForClass(cls.getSuperclass()); } catch (NoSuchMethodException e) { throw new RuntimeException("Unable to find binding constructor for " + clsName, e); } BINDINGS.put(cls, bindingCtor); return bindingCtor; } 在此函数中，以类名+”_ViewBinding”的方式找到注解类，并调用它的构造函数，如果注解类存在父类，依次向上调用。尾只是粗浅的看懂了代码而已，butterkniffe代码难懂之处在于对AbstractProcessor和JavaFile不清楚，对于整体架构和代码结构来说，复杂程度不算很高，理解难度也在可接受的范围之内

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