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 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，我们在方法里注释效果会比较好。

private void parseListenerAnnotation(Class<? extends Annotation> annotationClass, Element element,
Map<TypeElement, BindingClass> targetClassMap, Set 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ExecutableElement
if (!(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value
Method 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()

《Android学习笔记总结+最新移动架构视频+大厂安卓面试真题+项目实战源码讲义》

开源分享完整内容戳这里

;
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BindingClass
BindingClass 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 };