一开始看到这个名字，黄油刀？
添加依赖
implementation'com.jakewharton:butterknife:8.4.0'
annotationProcessor 'com.jakewharton:butterknife-compiler:8.4.0'
在这里有一个坑，如果看的教程较老，会有在proect的build中添加
classpath'com.neenbedankt.gradle.plugins:android-apt:1.8'
以及在app的的build中添加
apply plugin:'com.neenbedankt.android-apt'
apt'com.jakewharton:butterknife-coplier:8.4.0'
之后就会报错，根据提示改即可
初识ButterKnife
最简单的莫过于bindview 以及 onclick
这里以bindview为例，之后的源码分析也都建立在这个基础上
public class MainActivity extends AppCompatActivity {
@NonNull
@BindView(R.id.tv_text)
TextView textView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
ButterKnife.bind(this);
}
}
bindView注解
进入bindView 可以看到一个简单的注解
@Retention(CLASS) @Target(FIELD)
public @interface BindView {
/** View ID to which the field will be bound. */
@IdRes int value();
}
- 根据提示 可以看到里面的value变量用来存放绑定控件的id值
- class属性说明他是在编译时运行的注解
- field属性应用于成员变量
ButterKnifeProcessor 源码分析
首先根据对注解的处理器的理解 主要逻辑都在process方法中 于是找到process方法
@Override public boolean process(Set<? extends TypeElement> elements, RoundEnvironment env) {
Map<TypeElement, BindingSet> bindingMap = findAndParseTargets(env);//1
for (Map.Entry<TypeElement, BindingSet> entry : bindingMap.entrySet()) {//2
TypeElement typeElement = entry.getKey();
BindingSet binding = entry.getValue();//3
JavaFile javaFile = binding.brewJava(sdk, debuggable, useLegacyTypes);
try {
javaFile.writeTo(filer);//4
} catch (IOException e) {
error(typeElement, "Unable to write binding for type %s: %s", typeElement, e.getMessage());
}
}
return false;
}
查看注释1处的findAndParseTargets方法
private Map<TypeElement, BindingSet> findAndParseTargets(RoundEnvironment env) {
Map<TypeElement, BindingSet.Builder> builderMap = new LinkedHashMap<>();
Set<TypeElement> erasedTargetNames = new LinkedHashSet<>();
// Process each @BindView element.
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);//1
} catch (Exception e) {
logParsingError(element, BindView.class, e);
}
}
查看注释1处的方法
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);//1
// 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);//2
hasError = true;
}
}
if (hasError) {
return;
}
// Assemble information on the field.
int id = element.getAnnotation(BindView.class).value();
BindingSet.Builder builder = builderMap.get(enclosingElement);
Id resourceId = elementToId(element, BindView.class, id);
if (builder != null) {//3
String existingBindingName = builder.findExistingBindingName(resourceId);
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(resourceId, new FieldViewBinding(name, type, required));//4
// Add the type-erased version to the valid binding targets set.
erasedTargetNames.add(enclosingElement);
}
根据注释可以看到在注释1处判断了是否使用错误
- 方法修饰符 不能为private static
- 包含类型不能为非class
- 包含类不能为private
- isBindingInWrongPackage 说明类的包名
注释2则说明修饰的必须是一个view or interface（其实这段代码中前面的一大段都是在判断使用是否正确）。接下来在注释3处判断builder是否存在不存在则创建，然后再注释4处调用了builder的 addfield方法，这样子修饰的类型信息全部转移到了builer中。
接下来回到process中 在注释2处遍历bindingMap 取得bindingSet 调用 bingSet 的brewJava;
JavaFile brewJava(int sdk, boolean debuggable, boolean useLegacyTypes) {
TypeSpec bindingConfiguration = createType(sdk, debuggable, useLegacyTypes);
return JavaFile.builder(bindingClassName.packageName(), bindingConfiguration)
.addFileComment("Generated code from Butter Knife. Do not modify!")
.build();
}
从代码中可以看出 这段将注解类生成了一个javaFile,接下来调用writeTo的方法 输出Java文件。
butterknife的bind 方法
public static Unbinder bind(@NonNull Activity target) {
View sourceView = target.getWindow().getDecorView();
return createBinding(target, sourceView);
}
可以看到主要调用的时creatBinding方法
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);
}
}
主要是调用了findBindingConstructorForClass方法
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;
}//1
try {
Class<?> bindingClass = Class.forName(clsName + "_ViewBinding");//2
//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;
}
在注释1处又进行了包名判断，在注射2处通过反射机制获取Class，这个Class类就是之前生成的MainActivity_ViewBinding ,且一个类只会在第一次反射形成，（简单的安卓反射机制）以后直接在BINDINGS里面去取，之后将class 转换为constructor。接着在createBinding中生成Constructor实例。
生成的辅助类分析
public MainActivity_ViewBinding(T target, View source) {
this.target = target;
target.textView = Utils.findRequiredViewAsType(source, R.id.tv_text, "field 'textView'", TextView.class);
}
@Override
@CallSuper
public void unbind() {
T target = this.target;
if (target == null) throw new IllegalStateException("Bindings already cleared.");
target.textView = null;
this.target = null;
}
}
在createBinding中已经传入了decorView(即source),调用了findRequiredViewAsType()方法，在其中调用了findRequiredView(),castView();
public static View findRequiredView(View source, @IdRes int id, String who) {
View view = source.findViewById(id);
if (view != null) {
return view;
}
String name = getResourceEntryName(source, id);
throw new IllegalStateException("Required view '"
+ name
+ "' with ID "
+ id
+ " for "
+ who
+ " was not found. If this view is optional add '@Nullable' (fields) or '@Optional'"
+ " (methods) annotation.");
}
很简单，调用findViewById;
再看castView()
public static <T> T castView(View view, @IdRes int id, String who, Class<T> cls) {
try {
return cls.cast(view);
} catch (ClassCastException e) {
String name = getResourceEntryName(view, id);
throw new IllegalStateException("View '"
+ name
+ "' with ID "
+ id
+ " for "
+ who
+ " was of the wrong type. See cause for more info.", e);
}
}
将view强制转换为传入class值类型，再赋值给targer（即MainActivity)其他的绑定如onclick再理解了上面的之后就很好理解了。
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