深入理解ButterKnife源码并掌握原理（二）

好，我们接着parseBindView的步骤3 ，忘记了在哪里了，咦。

可以看下上一篇，哈哈。
步骤3

   BindingClass bindingClass = targetClassMap.get(enclosingElement);if (bindingClass != null) {ViewBindings viewBindings = bindingClass.getViewBinding(getId(id));if (viewBindings != null && viewBindings.getFieldBinding() != null) {FieldViewBinding existingBinding = viewBindings.getFieldBinding();error(element, "Attempt to use @%s for an already bound ID %d on '%s'. (%s.%s)",BindView.class.getSimpleName(), id, existingBinding.getName(),enclosingElement.getQualifiedName(), element.getSimpleName());return;}} else {bindingClass = getOrCreateTargetClass(targetClassMap, enclosingElement);}

如果map（缓存）中已经有了就直接到到这个BindingClass实例。BindingClass这个我们后面还会再说。

1.如果不为空，则根据id获取保存在bindingClass中的ViewBindings实例，
如果viewBindings不为空且viewBindings.getFieldBinding不为空则抛出异常，什么意思呢？就是说一个id不能bind多次。
2.如果为空，则bindingClass = getOrCreateTargetClass(targetClassMap, enclosingElement);
获取并返回，参数是最初的那个map和父节点。

  private BindingClass getOrCreateTargetClass(Map<TypeElement, BindingClass> targetClassMap,TypeElement enclosingElement) {BindingClass bindingClass = targetClassMap.get(enclosingElement);//再次判断if (bindingClass == null) {//获取父节点的类型名字，这个不用太关系TypeName targetType = TypeName.get(enclosingElement.asType());if (targetType instanceof ParameterizedTypeName) {targetType = ((ParameterizedTypeName) targetType).rawType;}//获取该enclosingElement就是父节点所在的包名称String packageName = getPackageName(enclosingElement);//类名字String className = getClassName(enclosingElement, packageName);//根据包名称和类名称获取bindingClassName实体//并且加入了_ViewBinding 哈哈，有点意思是了。不是吗？？ClassName bindingClassName = ClassName.get(packageName, className + "_ViewBinding");//是否是final 类 boolean isFinal = enclosingElement.getModifiers().contains(Modifier.FINAL);//创建了一个BindingClass实例bindingClass = new BindingClass(targetType, bindingClassName, isFinal);//加入集合，缓存targetClassMap.put(enclosingElement, bindingClass);}return bindingClass;}

到此我们的parseBindView的步骤3就完了。
步骤4：parseBindView步骤4

//@BindView(R.id.word)// TextView word;  //name就是wordString name = element.getSimpleName().toString();//类型的名字TypeName type = TypeName.get(elementType);//是否要求可为空boolean required = isFieldRequired(element);//生成FieldViewBinding实体FieldViewBinding binding = new FieldViewBinding(name, type, required);

步骤5.

添加到bindingClass中的成员变量的实体的集合中，方便生成java源文件也就是xxxxx_ViewBinding文件的成员变量的初始化存在
bindingClass.addField(getId(id), binding);

其它的注解都是一样的。至此查找并解析成员变量的流程就完了。
接下来是处理控件事件的监听的流程。

注解事件源码流程分析（OnClick，OnItemClick等）

我们回到findAndParseTargets方法。

   //... 省略成员变量的注解// Process each annotation that corresponds to a listener.//处理方法的比如一些OnClick，OnItemClick等for (Class<? extends Annotation> listener : LISTENERS) {findAndParseListener(env, listener, targetClassMap, erasedTargetNames);}// Try to find a parent binder for each.for (Map.Entry<TypeElement, BindingClass> entry : targetClassMap.entrySet()) {TypeElement parentType = findParentType(entry.getKey(), erasedTargetNames);if (parentType != null) {BindingClass bindingClass = entry.getValue();BindingClass parentBindingClass = targetClassMap.get(parentType);bindingClass.setParent(parentBindingClass);}}return targetClassMap;}

处理注解事件同样也分为查找和解析2个大步骤。
LISTENERS是butterknife支持的注解集合

  private static final List<Class<? extends Annotation>> LISTENERS = Arrays.asList(//OnCheckedChanged.class, //OnClick.class, //OnEditorAction.class, //OnFocusChange.class, //OnItemClick.class, //OnItemLongClick.class, //OnItemSelected.class, //OnLongClick.class, //OnPageChange.class, //OnTextChanged.class, //OnTouch.class //);

 private void findAndParseListener(RoundEnvironment env,Class<? extends Annotation> annotationClass, Map<TypeElement, BindingClass> targetClassMap,Set<TypeElement> erasedTargetNames) {for (Element element : env.getElementsAnnotatedWith(annotationClass)) {//检查合法性问题if (!SuperficialValidation.validateElement(element)) continue;try {//解析注解parseListenerAnnotation(annotationClass, element, targetClassMap, erasedTargetNames);} catch (Exception e) {StringWriter stackTrace = new StringWriter();e.printStackTrace(new PrintWriter(stackTrace));error(element, "Unable to generate view binder for @%s.\n\n%s",annotationClass.getSimpleName(), stackTrace.toString());}}}

我们看一下parseListenerAnnotation方法，传入了注解类annotationClass，该节点element，最初的那个集合targetClassMap。
比较长，我在方法里注释效果会比较好，哈哈

private void parseListenerAnnotation(Class<? extends Annotation> annotationClass, Element element,Map<TypeElement, BindingClass> targetClassMap, Set<TypeElement> erasedTargetNames)throws Exception {// This should be guarded by the annotation's @Target but it's worth a check for safe casting.//必需是方法类型的，节点元素为ExecutableElementif (!(element instanceof ExecutableElement) || element.getKind() != METHOD) {throw new IllegalStateException(String.format("@%s annotation must be on a method.", annotationClass.getSimpleName()));}//方法对应的是ExecutableElement，前文我们已经简单的说明了一下ExecutableElement executableElement = (ExecutableElement) element;//获取父节点TypeElement enclosingElement = (TypeElement) element.getEnclosingElement();// Assemble information on the method.// 获取注解信息Annotation annotation = element.getAnnotation(annotationClass);//该注解value方法，每一个注解都有（butterknife提供的都是数组）//为什么是数组？因为支持下面这种@OnClick(｛R.id.hello，R.id.hello2｝) void sayHello() {｝//反射注解方法valueMethod annotationValue = annotationClass.getDeclaredMethod("value");//不是数组抛出异常if (annotationValue.getReturnType() != int[].class) {throw new IllegalStateException(String.format("@%s annotation value() type not int[].", annotationClass));}//反射调用int[] ids = (int[]) annotationValue.invoke(annotation);//方法名字String name = executableElement.getSimpleName().toString();boolean required = isListenerRequired(executableElement);// Verify that the method and its containing class are accessible via generated code.//检查方法的修饰符，和成员变量一样，这里就不写了，嘻嘻boolean hasError = isInaccessibleViaGeneratedCode(annotationClass, "methods", element);hasError |= isBindingInWrongPackage(annotationClass, element);//一个注解的方法不能有形同的id，or抛出异常Integer duplicateId = findDuplicate(ids);if (duplicateId != null) {error(element, "@%s annotation for method contains duplicate ID %d. (%s.%s)",annotationClass.getSimpleName(), duplicateId, enclosingElement.getQualifiedName(),element.getSimpleName());hasError = true;}//获取该注解ListenerClass.class注解，什么意思呢？就是   //butterknife提供的方法注解 包含了另外一个注解//可以跳过代码看下面的文字说明。ListenerClass listener = annotationClass.getAnnotation(ListenerClass.class);if (listener == null) {throw new IllegalStateException(String.format("No @%s defined on @%s.", ListenerClass.class.getSimpleName(),annotationClass.getSimpleName()));}//检查id的合法性，里面有个Optional注解for (int id : ids) {//id 为 -1 ，不合法     if (id == NO_ID.value) {if (ids.length == 1) {//一个参数情况，且方法的参数适用了Optional注解，则抛出异常if (!required) {error(element, "ID-free binding must not be annotated with @Optional. (%s.%s)",enclosingElement.getQualifiedName(), element.getSimpleName());hasError = true;}} else {error(element, "@%s annotation contains invalid ID %d. (%s.%s)",annotationClass.getSimpleName(), id, enclosingElement.getQualifiedName(),element.getSimpleName());hasError = true;}}}／／获取实现的方法ListenerMethod method;ListenerMethod[] methods = listener.method();// methods就是OnItemClick 注解的ListenerClass注解的初始化值，比如下面这种，肯定是个//    method = @ListenerMethod(//   name = "onItemClick",//   parameters = {//   "android.widget.AdapterView<?>",//    "android.view.View",//        "int",//        "long"//    }//  )if (methods.length > 1) {//抛异常，不可能走到这因为butterknife提供的都是1个默认的，能骗到我，我可是上过小学的人，哈哈throw new IllegalStateException(String.format("Multiple listener methods specified on @%s.",annotationClass.getSimpleName()));} else if (methods.length == 1) {//如果有method属性值即这种onItemClick，则callbacks必须为空，也就是2者不能同时使用if (listener.callbacks() != ListenerClass.NONE.class) {throw new IllegalStateException(String.format("Both method() and callback() defined on @%s.",annotationClass.getSimpleName()));}method = methods[0];} else {// 否则使用callback//反射ListenerClass注解中的callback方法Method annotationCallback = annotationClass.getDeclaredMethod("callback");Enum<?> callback = (Enum<?>) annotationCallback.invoke(annotation);Field callbackField = callback.getDeclaringClass().getField(callback.name());method = callbackField.getAnnotation(ListenerMethod.class);//如果没有ListenerMethod.class注解 抛出异常，也就是说你使用了callback，则必须提供ListenerMethod.class注解if (method == null) {throw new IllegalStateException(String.format("No @%s defined on @%s's %s.%s.", ListenerMethod.class.getSimpleName(),annotationClass.getSimpleName(), callback.getDeclaringClass().getSimpleName(),callback.name()));}}//检查方法的合法性，就是你使用的注解的方法的参数不能butterknife的参数的个数（也就是android系统的那种）// Verify that the method has equal to or less than the number of parameters as the listener.List<? extends VariableElement> methodParameters = executableElement.getParameters();if (methodParameters.size() > method.parameters().length) {error(element, "@%s methods can have at most %s parameter(s). (%s.%s)",annotationClass.getSimpleName(), method.parameters().length,enclosingElement.getQualifiedName(), element.getSimpleName());hasError = true;}//检查返回值，就是你使用的注解的方法的参数不能butterknife的参数的个数（也就是android系统的那种）// Verify method return type matches the listener.TypeMirror returnType = executableElement.getReturnType();if (returnType instanceof TypeVariable) {TypeVariable typeVariable = (TypeVariable) returnType;returnType = typeVariable.getUpperBound();}if (!returnType.toString().equals(method.returnType())) {error(element, "@%s methods must have a '%s' return type. (%s.%s)",annotationClass.getSimpleName(), method.returnType(),enclosingElement.getQualifiedName(), element.getSimpleName());hasError = true;}if (hasError) {return;}//下面是方法参数的检查，不做分析了，太细了。记住一点就行了，你写的不和系统的实现方法一样就抛出异常Parameter[] parameters = Parameter.NONE;if (!methodParameters.isEmpty()) {parameters = new Parameter[methodParameters.size()];BitSet methodParameterUsed = new BitSet(methodParameters.size());String[] parameterTypes = method.parameters();for (int i = 0; i < methodParameters.size(); i++) {VariableElement methodParameter = methodParameters.get(i);TypeMirror methodParameterType = methodParameter.asType();if (methodParameterType instanceof TypeVariable) {TypeVariable typeVariable = (TypeVariable) methodParameterType;methodParameterType = typeVariable.getUpperBound();}for (int j = 0; j < parameterTypes.length; j++) {if (methodParameterUsed.get(j)) {continue;}if (isSubtypeOfType(methodParameterType, parameterTypes[j])|| isInterface(methodParameterType)) {parameters[i] = new Parameter(j, TypeName.get(methodParameterType));methodParameterUsed.set(j);break;}}if (parameters[i] == null) {StringBuilder builder = new StringBuilder();builder.append("Unable to match @").append(annotationClass.getSimpleName()).append(" method arguments. (").append(enclosingElement.getQualifiedName()).append('.').append(element.getSimpleName()).append(')');for (int j = 0; j < parameters.length; j++) {Parameter parameter = parameters[j];builder.append("\n\n  Parameter #").append(j + 1).append(": ").append(methodParameters.get(j).asType().toString()).append("\n    ");if (parameter == null) {builder.append("did not match any listener parameters");} else {builder.append("matched listener parameter #").append(parameter.getListenerPosition() + 1).append(": ").append(parameter.getType());}}builder.append("\n\nMethods may have up to ").append(method.parameters().length).append(" parameter(s):\n");for (String parameterType : method.parameters()) {builder.append("\n  ").append(parameterType);}builder.append("\n\nThese may be listed in any order but will be searched for from top to bottom.");error(executableElement, builder.toString());return;}}}//最后构造MethodViewBinding实体，形成方法的实体MethodViewBinding binding = new MethodViewBinding(name, Arrays.asList(parameters), required);//构造BindingClassBindingClass bindingClass = getOrCreateTargetClass(targetClassMap, enclosingElement);for (int id : ids) {//将生成的方法加入到bindingClass的方法集合中，一切都是为了生存java代码而准备。if (!bindingClass.addMethod(getId(id), listener, method, binding)) {error(element, "Multiple listener methods with return value specified for ID %d. (%s.%s)",id, enclosingElement.getQualifiedName(), element.getSimpleName());return;}}// Add the type-erased version to the valid binding targets set.erasedTargetNames.add(enclosingElement);}

ListenerClass／ListenerMethod 注解说明

@Target(METHOD)
@Retention(CLASS)
@ListenerClass(targetType = "android.widget.AdapterView<?>",setter = "setOnItemClickListener",type = "android.widget.AdapterView.OnItemClickListener",method = @ListenerMethod(name = "onItemClick",parameters = {"android.widget.AdapterView<?>","android.view.View","int","long"})
)
public @interface OnItemClick {/** View IDs to which the method will be bound. */@IdRes int[] value() default { View.NO_ID };
}

import java.lang.annotation.Retention;
import java.lang.annotation.Target;import static java.lang.annotation.ElementType.ANNOTATION_TYPE;
import static java.lang.annotation.RetentionPolicy.RUNTIME;@Retention(RUNTIME) @Target(ANNOTATION_TYPE)
public @interface ListenerClass {String targetType();/** Name of the setter method on the {@linkplain #targetType() target type} for the listener. */String setter();/*** Name of the method on the {@linkplain #targetType() target type} to remove the listener. If* empty {@link #setter()} will be used by default.*/String remover() default "";/** Fully-qualified class name of the listener type. */String type();/** Enum which declares the listener callback methods. Mutually exclusive to {@link #method()}. */Class<? extends Enum<?>> callbacks() default NONE.class;/*** Method data for single-method listener callbacks. Mutually exclusive with {@link #callbacks()}* and an error to specify more than one value.*/ListenerMethod[] method() default { };/** Default value for {@link #callbacks()}. */enum NONE { }
}

package butterknife.internal;import java.lang.annotation.Retention;
import java.lang.annotation.Target;import static java.lang.annotation.ElementType.FIELD;
import static java.lang.annotation.RetentionPolicy.RUNTIME;@Retention(RUNTIME) @Target(FIELD)
public @interface ListenerMethod {/** Name of the listener method for which this annotation applies. */String name();/** List of method parameters. If the type is not a primitive it must be fully-qualified. */String[] parameters() default { };/** Primitive or fully-qualified return type of the listener method. May also be {@code void}. */String returnType() default "void";/** If {@link #returnType()} is not {@code void} this value is returned when no binding exists. */String defaultReturn() default "null";
}

可以把这3个整体来看。ListenerMethod 这个注解包含了方法的返回值，名字，参数，是实现的那些方法；ListenerClass是set的那些方法属性，包含setter等，我们看到了OnItemClick设置的值就是我们平常写的那种，嘻嘻。

至此，我们的findAndParseTargets方法算是走完了。里面有很多细节。
为什么要分析有关细节呢？可以学习下大神的方法和理解有关处理的细节啊，哈哈。
深入理解ButterKnife源码并掌握原理（三)