app 的 build.gradle 导入
implementation 'com.jakewharton:butterknife:10.2.1'
annotationProcessor 'com.jakewharton:butterknife-compiler:10.2.1'在 Activity 使用
public class MainActivity extends AppCompatActivity {
@BindView(R.id.tv_name)
TextView mTvName;
@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ButterKnife.bind(this);
mTvName.setText("ButterKnife");
}
}在基本使用的，很明显，ButterKnife.bind(this) 应该是 ButterKnife 工作的入口。
//ButterKnife 和 Activity 建立绑定关系的过程
@NonNull @UiThread
public static Unbinder bind(@NonNull Activity target) {
View sourceView = target.getWindow().getDecorView();
return bind(target, sourceView);
}
//最终调到以下函数
@NonNull @UiThread
public static Unbinder bind(@NonNull Object target, @NonNull View source) {
Class<?> targetClass = target.getClass();
if (debug) Log.d(TAG, "Looking up binding for " + targetClass.getName());
//代码1 Class 中查找 constructor 本例子 MainActivity_ViewBinding
Constructor<? extends Unbinder> constructor = findBindingConstructorForClass(targetClass);
if (constructor == null) {
return Unbinder.EMPTY;
}
try {
//执行构造函数 本例子使用例子，就是生成 MainActivity_ViewBinding 类
return constructor.newInstance(target, source);
}
//下面抛出一些异常
...
} 代码1 ButterKnife#findBindingConstructorForClass
//1.LinkedHashMap 保存 MainActivity 与 MainActivity_ViewBinding 的构造器对象
@VisibleForTesting
static final Map<Class<?>, Constructor<? extends Unbinder>> BINDINGS = new LinkedHashMap<>();
@Nullable @CheckResult @UiThread
private static Constructor<? extends Unbinder> findBindingConstructorForClass(Class<?> cls) {
//2.根据 key 获取 xxx_ViewBinding
Constructor<? extends Unbinder> bindingCtor = BINDINGS.get(cls);
if (bindingCtor != null || BINDINGS.containsKey(cls)) {
if (debug) Log.d(TAG, "HIT: Cached in binding map.");
return bindingCtor;
}
//3.忽略 android、androidx、java 原生文件
String clsName = cls.getName();
if (clsName.startsWith("android.") || clsName.startsWith("java.")
|| clsName.startsWith("androidx.")) {
if (debug) Log.d(TAG, "MISS: Reached framework class. Abandoning search.");
return null;
}
try {
Class<?> bindingClass = cls.getClassLoader().loadClass(clsName + "_ViewBinding");
bindingCtor = (Constructor<? extends Unbinder>) bindingClass.getConstructor(cls, View.class);
...
} catch (ClassNotFoundException e) {
...
//4.父类寻找
bindingCtor = findBindingConstructorForClass(cls.getSuperclass());
} catch (NoSuchMethodException e) {
throw new RuntimeException("Unable to find binding constructor for " + clsName, e);
}
//put 进去 MainActivity 与 MainActivity_ViewBinding 之间的映射
BINDINGS.put(cls, bindingCtor);
return bindingCtor;
}通过以上代码，有一个问题 xxx_ViewBinding 这个类哪里来，涉及以下技术。
- JavaPoet：用来生成.java文件
- Annotation Processor + APT（Annotation Processing Tool ）：编译时扫描和解析 Java 注解的工具
public class MainActivity_ViewBinding implements Unbinder {
private MainActivity target;
@UiThread
public MaintActivity_ViewBinding(MainActivity target) {
this(target, target.getWindow().getDecorView());
}
@UiThread
public MainActivity_ViewBinding(MainActivity target, View source) {
this.target = target;
target.mTvName = Utils.findRequiredViewAsType(source, R.id.tv_name, "field 'mTvName'", TextView.class);
}
@Override
@CallSuper
public void unbind() {
MainActivity target = this.target;
if (target == null) throw new IllegalStateException("Bindings already cleared.");
this.target = null;
target.mTvName = null;
}
}在 butterknife-compiler 这个模块中有一个 ButterKnifeProcessor，这个类用来完成了注解处理器的核心逻辑。
@AutoService(Processor.class)
@IncrementalAnnotationProcessor(IncrementalAnnotationProcessorType.DYNAMIC)
@SuppressWarnings("NullAway") // TODO fix all these...
public final class ButterKnifeProcessor extends AbstractProcessor {//注解处理器
...
//init 入口
@Override public synchronized void init(ProcessingEnvironment env) {
super.init(env);
//判断最低的支持的 sdk 版本
String sdk = env.getOptions().get(OPTION_SDK_INT);
if (sdk != null) {
try {
this.sdk = Integer.parseInt(sdk);
} catch (NumberFormatException e) {
...
}
}
typeUtils = env.getTypeUtils();
filer = env.getFiler();
}
...
//重点：目标类注解信息的收集并生成对应 java 类
@Override public boolean process(Set<? extends TypeElement> elements, RoundEnvironment env) {
//注解信息的扫描收集
Map<TypeElement, BindingSet> bindingMap = findAndParseTargets(env);
for (Map.Entry<TypeElement, BindingSet> entry : bindingMap.entrySet()) {
TypeElement typeElement = entry.getKey();
BindingSet binding = entry.getValue();
//---> 收集完注解信息之后 得到 java 类源码 开始生成 java 文件
JavaFile javaFile = binding.brewJava(sdk, debuggable);
try {
//生成 java 文件
javaFile.writeTo(filer);
} catch (IOException e) {
error(typeElement, "Unable to write binding for type %s: %s", typeElement, e.getMessage());
}
}
return false;
}
}ButterKnifeProcessor#findAndParseTargets
private Map<TypeElement, BindingSet> findAndParseTargets(RoundEnvironment env) {
Map<TypeElement, BindingSet.Builder> builderMap = new LinkedHashMap<>();
Set<TypeElement> erasedTargetNames = new LinkedHashSet<>();
//获取 BindView 注解
for (Element element : env.getElementsAnnotatedWith(BindView.class)) {
// we don't SuperficialValidation.validateElement(element)
// so that an unresolved View type can be generated by later processing rounds
try {
parseBindView(element, builderMap, erasedTargetNames);
} catch (Exception e) {
logParsingError(element, BindView.class, e);
}
}
...
//将 builderMap 中的数据添加到队列中
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, classpathBindings.keySet());
if (parentType == null) {
bindingMap.put(type, builder.build());
} else {
BindingInformationProvider parentBinding = bindingMap.get(parentType);
if (parentBinding == null) {
parentBinding = classpathBindings.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;
} ButterKnifeProcessor#parseBindView
//解析 BindView 元素
private void parseBindView(Element element, Map<TypeElement, BindingSet.Builder> builderMap,
Set<TypeElement> erasedTargetNames) {
TypeElement enclosingElement = (TypeElement) element.getEnclosingElement();
//下面就是开始校验数据合法性
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;
}
//获取元素使用 BindView 注解时设置的属性值，View 对应的 xml 中 id 值
int id = element.getAnnotation(BindView.class).value();
//获取父元素对应的 BindingSet.Builder
//BindingSet 保存要生成目标类的基本特征信息，和 ButterKnife 注解的元素的信息
//BindingSet 和 ButterKnife 类对应起来
BindingSet.Builder builder = builderMap.get(enclosingElement);
//资源 id
Id resourceId = elementToId(element, BindView.class, id);
if (builder != null) {
String existingBindingName = builder.findExistingBindingName(resourceId);
//如果id已经被绑定，会抛出异常
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 {
//创建一个新的 BindingSet.Builder 并返回，
builder = getOrCreateBindingBuilder(builderMap, enclosingElement);
}
String name = simpleName.toString();
TypeName type = TypeName.get(elementType);
//判断当前元素是否使用 Nullable 注解
boolean required = isFieldRequired(element);
//FieldViewBinding 包含元素名、类型等，和元素id一起添加到 BindingSet.Builder
builder.addField(resourceId, new FieldViewBinding(name, type, required));
//记录当前元素的父类元素
erasedTargetNames.add(enclosingElement);
}当收集完目标类的基本信息，就会使用 JavaPoet生成相关的 java 类文件。
ButterKnifeProcessor#init
public final class ButterKnifeProcessor extends AbstractProcessor {//注解处理器
...
//重点：目标类注解信息的收集并生成对应 java 类
@Override public boolean process(Set<? extends TypeElement> elements, RoundEnvironment env) {
//注解信息的扫描收集
Map<TypeElement, BindingSet> bindingMap = findAndParseTargets(env);
for (Map.Entry<TypeElement, BindingSet> entry : bindingMap.entrySet()) {
TypeElement typeElement = entry.getKey();
BindingSet binding = entry.getValue();
//---> 收集完注解信息之后 得到 java 类源码 开始生成 java 文件
JavaFile javaFile = binding.brewJava(sdk, debuggable);
try {
//生成 java 文件
javaFile.writeTo(filer);
} catch (IOException e) {
error(typeElement, "Unable to write binding for type %s: %s", typeElement, e.getMessage());
}
}
return false;
}
}