编译时注解Butterknife源码解析之深入篇刘永雷.docx

1、编译时注解Butterknife源码解析之深入篇刘永雷编译时注解Butterknife源码解析之深入篇（雷惊风）1.概述。上篇文章我对Butterknife实现做了一些基础的说明，本篇文章我将向大家详细分析BindView、OnClick解析流程、生成BindingSet对应Java文件流程及我们调用ButterKnife.bind(this)后ButterKnife与生成Java文件的建立连接过程。2.BindView解析流程。这篇文章将接着上篇文章的findAndParseTargets(RoundEnvironment env)方法，如果你看了上篇文章，那么你就知道，所有Butterkn

2、ife中注解的解析都是在这个方法中的。好的那么我们开始吧。我们这个方法的流程上篇文章已经说过了，这里就不再浪费口水了，我们把解析BindView的代码拷出来再看一下：/ Process each BindView element./* * 处理BindView（R.id.btn）注解； * 1.做了一系列验证；如：private static修饰符判断、BindView必须作用在View上或者interface上等等； * 2.id的处理;生成QualifiedId、缓存等； * 3.builder创建；一个id是否注解了多次 * 4.Nullable处理，创建FieldViewBinding

3、存入builder，将enclosingElement存入erasedTargetNames； */for (Element element : env.getElementsAnnotatedWith(BindView.class) / we dont SuperficialValidation.validateElement(element) / so that an unresolved View type can be generated by later processing roundstry parseBindView(element, builderMap, erasedTar

4、getNames); catch (Exception e) logParsingError(element, BindView.class, e); 很简单，获取了项目中所有的被BindView注解了的Element，通过for（）循环处理每一个，一个trycatch代码块，try中出问题，打印信息，关于在注解处理器中处理错误log信息，在这里就不讲了，可以在init（）方法中获取Messager辅助类。看来重点在parseBindView(element, builderMap, erasedTargetNames);方法中了，跟进去：private void parseBindView(

5、Element element, Map builderMap, Set erasedTargetNames) /获取父级Element；TypeElement enclosingElement = (TypeElement) element.getEnclosingElement();/ Start by verifying common generated code restrictions.boolean hasError = isInaccessibleViaGeneratedCode(BindView.class, fields, element) | isBindingInWron

6、gPackage(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 = enclosing

7、Element.getQualifiedName(); Name simpleName = element.getSimpleName();/BindView必须作用在View上或者interface上；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

8、 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 informa

9、tion on the field.int id = element.getAnnotation(BindView.class).value();/通过enclosingElement获取builder，每一个builder对应一个类，如activity；BindingSet.Builder builder = builderMap.get(enclosingElement);/将element所在包与id封装到QualifiedId中；QualifiedId qualifiedId = elementToQualifiedId(element, id);if (builder != null

10、) /判断当前BindView所修饰控件是否已经绑定过； /getId（）：将id存入Id对象，并存入symbols；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, existingBindingNa

11、me, enclosingElement.getQualifiedName(), element.getSimpleName();return; else /新建一个builder；builder = getOrCreateBindingBuilder(builderMap, enclosingElement); String name = simpleName.toString(); TypeName type = TypeName.get(elementType);/判断是否添加了Nullableboolean required = isFieldRequired(element);/通过

12、Id创建ViewBinding.Builder并setFieldBinding（fieldViewBinding）builder.addField(getId(qualifiedId), new FieldViewBinding(name, type, required);/ Add the type-erased version to the valid binding targets set.erasedTargetNames.add(enclosingElement);方法也还好，不到100行，来看看在这个方法中做了一些什么操作吧。咱们先拿出一部分来看：/获取父级Element；Type

13、Element 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 f

14、rom 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();/Bind

15、View必须作用在View上或者interface上；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,

16、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;这部分是对我们BindView注解应用的一个正确性的一个检查，首先获取了我们的element对应的外部类的TypeElement，比如，activity中用BindView注解了一个But

17、ton btn；获取了activity对应的TypeElement，如果你看了上篇文章你就会明白。然后调用了一个isInaccessibleViaGeneratedCode(BindView.class, fields, element)方法与一个isBindingInWrongPackage(BindView.class, element)方法进行判断操作。一个一个来看一下，第一个：/* * 检查annotation作用域是否正确； * * param annotationClass* param targetThing* param element* return*/private boo

18、lean isInaccessibleViaGeneratedCode(Class annotationClass, String targetThing, Element element) boolean hasError = false;/获取当前element所在类的TypeElement；TypeElement enclosingElement = (TypeElement) element.getEnclosingElement();/ Verify method modifiers.获取当前element的修饰符；Set modifiers = element.getModifie

19、rs();/修饰符不能是private或者static的，否则报告异常（error方法）； / Messager提供给注解处理器一个报告错误、警告以及提示信息的途径。 / 它不是注解处理器开发者的日志工具，而是用来写一些信息给使用此注解器的第三方开发者的。if (modifiers.contains(PRIVATE) | modifiers.contains(STATIC) error(element, %s %s must not be private or static. (%s.%s), annotationClass.getSimpleName(), targetThing, encl

20、osingElement.getQualifiedName(), element.getSimpleName(); hasError = true; / Verify containing type.element只能直接从属于类（不能修饰局部变量）；否则报错；if (enclosingElement.getKind() != CLASS) error(enclosingElement, %s %s may only be contained in classes. (%s.%s), annotationClass.getSimpleName(), targetThing, enclosing

21、Element.getQualifiedName(), element.getSimpleName(); hasError = true; / Verify containing class visibility is not private.element外层类不能是私有的，否则报错；if (enclosingElement.getModifiers().contains(PRIVATE) error(enclosingElement, %s %s may not be contained in private classes. (%s.%s), annotationClass.getSim

22、pleName(), targetThing, enclosingElement.getQualifiedName(), element.getSimpleName(); hasError = true; return hasError;在这个类中判断了三种非正常情况：1.BindView注解的Element为private或者static修饰报错，如下例子：BindView（R.id.btn） private Button btn; 这种情况下就会报错。2.当前Element不是直接在一个类里边，报错。如：在一个方法的局部变量上添加了注解。3.外部Element是private的报错。如：p

23、rivate class Activity extends . BindView（R.id.btn） private Button btn;再看一下isBindingInWrongPackage(BindView.class, element)方法：/* * 检查anitation注解是否作用在了系统类上； * * param annotationClass* param element* return*/private boolean isBindingInWrongPackage(Class annotationClass, Element element) TypeElement enc

24、losingElement = (TypeElement) element.getEnclosingElement(); String qualifiedName = enclosingElement.getQualifiedName().toString();/不能作用于Android系统类里；if (qualifiedName.startsWith(android.) error(element, %s-annotated class incorrectly in Android framework package. (%s), annotationClass.getSimpleName(

25、), qualifiedName);return true; /不能作用在java系统类中；if (qualifiedName.startsWith(java.) error(element, %s-annotated class incorrectly in Java framework package. (%s), annotationClass.getSimpleName(), qualifiedName);return true; return false;这个方法主要是检查我们是否用到了系统类上，这里注意我们自己定义的包名。接着回到上一个方法向下看，后续又检查了是否用在了View子类

26、上或者Interface上。我都加了注释，不在详细解释。如果上边检查有一步出问题，则return终止。到这里，检查我们应用BindView合法性就完了。再往下边走：/ Assemble information on the field.int id = element.getAnnotation(BindView.class).value();/通过enclosingElement获取builder，每一个builder对应一个类，如activity；BindingSet.Builder builder = builderMap.get(enclosingElement);/将element所

27、在包与id封装到QualifiedId中；QualifiedId qualifiedId = elementToQualifiedId(element, id);if (builder != null) /判断当前BindView所修饰控件是否已经绑定过； /getId（）：将id存入Id对象，并存入symbols；String existingBindingName = builder.findExistingBindingName(getId(qualifiedId);if (existingBindingName != null) error(element, Attempt to us

28、e %s for an already bound ID %d on %s. (%s.%s),BindView.class.getSimpleName(), id, existingBindingName, enclosingElement.getQualifiedName(), element.getSimpleName();return; else /新建一个builder；builder = getOrCreateBindingBuilder(builderMap, enclosingElement);首先获取到我们注解中指定的id，如下代码中的R.id.btn：BindView(R.i

29、d.btn)Button btn;查看builderMap中是否已经缓存了外部Element对应的BindingSet.Builder,通过id创建QualifiedId，看一下这个过程：private QualifiedId elementToQualifiedId(Element element, int id) return new QualifiedId(elementUtils.getPackageOf(element).getQualifiedName().toString(), id);这里用到了辅助类elementUtils获取element的包名，通过包名与id创建了Qual

30、ifiedId后边是builder判断，如果不为空，通过QualifiedId生成Id判断是否注解过相同id，注解过，则输出错误信息。Builder为空，调用getOrCreateBindingBuilder(builderMap, enclosingElement)创建或获取builder，看一下：private BindingSet.Builder getOrCreateBindingBuilder( Map builderMap, TypeElement enclosingElement) BindingSet.Builder builder = builderMap.get(enclosingElement);if (builder = null) /生成一个builder， / builder中保存了泛型信息、将要生成的类名称、是否Final修饰、是否View内部，是否Activity内部、是否Dialog内部；builder = BindingSet.newB