ButterKnife的使用及其解析

本博客介绍ButterKnife的使用及其源码解析。

ButterKnife的使用

ButterKnife简介

添加依赖

在Project级别的build.gradle文件中添加为ButterKnife定制的Gradle插件：

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buildscript { repositories { jcenter() } dependencies { classpath 'com.android.tools.build:gradle:2.3.3' classpath 'com.jakewharton:butterknife-gradle-plugin:8.8.1' } }

在Application级别的build.gradle文件中添加ButterKnife插件和依赖代码：

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apply plugin: 'com.jakewharton.butterknife' ... dependencies{ annotationProcessor 'com.jakewharton:butterknife-compiler:8.8.1' compile 'com.android.support:recyclerview-v7:26.0.0-alpha1' }

使用ButterKnife

• 使用ButterKnife绑定控件

用注解@BindView()绑定单个控件id，用注解@BindViews()绑定多个控件id：

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(R.id.et_input) EditText etInput; (R.id.btn_send) Button btnSend; (R.id.lv_main) ListView lvMain;

在Activity中，需要在setContentView()之后添加：

1	mUnbinder = ButterKnife.bind(this);

切记在Activity的onDestroy()中进行解绑：

1	mUnbinder.unbind();

在Fragment中，需要在onCreateView()的return之前添加：

1	mUnbinder = ButterKnife.bind(this, view);

在Fragment的onDestroyView()中进行以下操作：

1	mUnbinder.unbind();

而在ListView或者RecyclerView的Adapter中也可以使用ButterKnife，需要做以下操作：

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public (View itemView) { super(itemView); ButterKnife.bind(this, itemView); }

• 使用ButterKnife绑定资源

ButterKnife提供了以下资源绑定方式：

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@BindAnim() //2、绑定数组资源id @BindArray() //3、绑定Bitmap相关的资源id @BindBitmap() //4、绑定boolean资源id @BindBool() //5、绑定color资源id @BindColor() //6、绑定尺寸资源id @BindDimen() //7、绑定drawable资源id @BindDrawable() //8、绑定float资源id @BindFloat //9、绑定字体资源id @BindFont //10、绑定int资源id @BindInt //11、绑定String资源id @BindString

• 使用ButterKnife绑定监听

ButterKnife提供了以下监听绑定方式：

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//1、为添加`OnCheckedChangeListener`的View绑定资源id @OnCheckedChanged() //2、为添加`OnClickListener`的View绑定资源id @OnClick() //3、为添加`OnEditorActionListener`的View绑定资源id @OnEditorAction() //4、为添加`OnFocusChangeListener`的View绑定资源id @OnFocusChange() //5、为添加`OnItemClickListener`的View绑定资源id @OnItemClick //6、为添加`OnItemLongClickListener`的View绑定资源id @OnItemLongClick() //7、为添加`OnItemSelectedListener`的View绑定资源id @OnItemSelected() //8、为添加`OnLongClickListener`的View绑定资源id @OnLongClick() //9、为添加`OnPageChangeListener`的View绑定资源id @OnPageChange() //10、为添加`TextWatcher`的View绑定资源id @OnTextChanged() //11、为添加`OnTouchListener`的View绑定资源id @OnTouch()

• 使用ButterKnife可选绑定

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//1、防止空指针异常 @Nullable //2、注入指定的视图不需要出现在该视图 @Optional

ButterKnife源码解析

ButterKnife采用的是编译时注解，自定义了很多常用注解，上文已经讲解在此不再赘述。以@BindView注解为例：

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@Retention(CLASS) @Target(FIELD) public @interface BindView { @IdRes int value(); }

其中@Retention(CLASS)用来声明注解的保留策略，表明@BindView注解是编译时注解，而@Target(FIELD)则表明@BindView注解作用于成员变量。

解析ButterKnife注解处理器ButterKnifeProcessor

要处理注解需要使用到注解处理器，ButterKnife的注解处理器是ButterKnifeProcessor，继承自AbstractProcessor。

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@AutoService(Processor.class) public final class ButterKnifeProcessor extends AbstractProcessor { ... }

在注解处理器ButterKnifeProcessor中注解处理的主要逻辑都在process()中：

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@Override public boolean process(Set<? extends TypeElement> elements, RoundEnvironment env) { //1、查找和解析传入的目标`RoundEnvironment`对象并将其存入Map中 Map<TypeElement, BindingSet> bindingMap = findAndParseTargets(env); //2、遍历Map集合 for (Map.Entry<TypeElement, BindingSet> entry : bindingMap.entrySet()) { //3、获取键TypeElement TypeElement typeElement = entry.getKey(); //4、获取值BindingSet BindingSet binding = entry.getValue(); //5、产生JavaFile JavaFile javaFile = binding.brewJava(sdk, debuggable); try { //6、向JavaFile写入Filer javaFile.writeTo(filer); } catch (IOException e) { error(typeElement, "Unable to write binding for type %s: %s", typeElement, e.getMessage()); } } return false; }

接下来查看在process()中调用的findAndParseTargets()：

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private Map<TypeElement, BindingSet> findAndParseTargets(RoundEnvironment env) { //1、创建LinkedHashMap用于存储BindingBuilder Map<TypeElement, BindingSet.Builder> builderMap = new LinkedHashMap<>(); //2、创建Set用于存储builderMap键 Set<TypeElement> erasedTargetNames = new LinkedHashSet<>(); scanForRClasses(env); //3、解析每个@BindAnim注解 for (Element element : env.getElementsAnnotatedWith(BindAnim.class)) { if (!SuperficialValidation.validateElement(element)) continue; try { //4、动画资源相应的解析方法 parseResourceAnimation(element, builderMap, erasedTargetNames); } catch (Exception e) { logParsingError(element, BindAnim.class, e); } } ...(此处省略n多个@BindXxx注解) //5、创建ArrayDeque用于存储BindingSet.Builder对象 Deque<Map.Entry<TypeElement, BindingSet.Builder>> entries = new ArrayDeque<>(builderMap.entrySet()); //6、创建LinkedHashMap用于存储绑定中元素 Map<TypeElement, BindingSet> bindingMap = new LinkedHashMap<>(); while (!entries.isEmpty()) { //7、移除第一个元素(出队) Map.Entry<TypeElement, BindingSet.Builder> entry = entries.removeFirst(); //8、获取移除元素的键 TypeElement type = entry.getKey(); //9、获取移除元素的值 BindingSet.Builder builder = entry.getValue(); //10、在提供的Set中找到父binder类型 TypeElement parentType = findParentType(type, erasedTargetNames); if (parentType == null) { bindingMap.put(type, builder.build()); } else { BindingSet parentBinding = bindingMap.get(parentType); if (parentBinding != null) { builder.setParent(parentBinding); bindingMap.put(type, builder.build()); } else { //11、入队 entries.addLast(entry); } } } return bindingMap; }

接下来查阅parseResourceAnimation()代码：

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private void parseResourceAnimation(Element element, Map<TypeElement, BindingSet.Builder> builderMap, Set<TypeElement> erasedTargetNames) { boolean hasError = false; TypeElement enclosingElement = (TypeElement) element.getEnclosingElement(); //1、验证目标类型是动画 if (!ANIMATION_TYPE.equals(element.asType().toString())) { error(element, "@%s field type must be 'Animation'. (%s.%s)", BindAnim.class.getSimpleName(), enclosingElement.getQualifiedName(), element.getSimpleName()); hasError = true; } //2、验证常见的生成代码限制 hasError |= isInaccessibleViaGeneratedCode(BindAnim.class, "fields", element); hasError |= isBindingInWrongPackage(BindAnim.class, element); if (hasError) { return; } //3、收集信息在成员变量中 String name = element.getSimpleName().toString(); int id = element.getAnnotation(BindAnim.class).value(); QualifiedId qualifiedId = elementToQualifiedId(element, id); BindingSet.Builder builder = getOrCreateBindingBuilder(builderMap, enclosingElement); builder.addResource(new FieldAnimationBinding(getId(qualifiedId), name)); erasedTargetNames.add(enclosingElement); }

其中，parseResourceAnimation()中isInaccessibleViaGeneratedCode()代码如下：

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大专栏  ButterKnife的使用及其解析="code"> private boolean isInaccessibleViaGeneratedCode(Class<? extends Annotation> annotationClass, String targetThing, Element element) { boolean hasError = false; TypeElement enclosingElement = (TypeElement) element.getEnclosingElement(); //1、方法修饰符不能为private和static Set<Modifier> modifiers = element.getModifiers(); if (modifiers.contains(PRIVATE) || modifiers.contains(STATIC)) { error(element, "@%s %s must not be private or static. (%s.%s)", annotationClass.getSimpleName(), targetThing, enclosingElement.getQualifiedName(), element.getSimpleName()); hasError = true; } //2、包含类型不能为非class if (enclosingElement.getKind() != CLASS) { error(enclosingElement, "@%s %s may only be contained in classes. (%s.%s)", annotationClass.getSimpleName(), targetThing, enclosingElement.getQualifiedName(), element.getSimpleName()); hasError = true; } //3、包含类的修饰符不能为private if (enclosingElement.getModifiers().contains(PRIVATE)) { error(enclosingElement, "@%s %s may not be contained in private classes. (%s.%s)", annotationClass.getSimpleName(), targetThing, enclosingElement.getQualifiedName(), element.getSimpleName()); hasError = true; } return hasError; }

其中，parseResourceAnimation()中isBindingInWrongPackage()代码如下：

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private boolean isBindingInWrongPackage(Class<? extends Annotation> annotationClass, Element element) { TypeElement enclosingElement = (TypeElement) element.getEnclosingElement(); String qualifiedName = enclosingElement.getQualifiedName().toString(); //1、判断类的包名不能以android开头 if (qualifiedName.startsWith("android.")) { error(element, "@%s-annotated class incorrectly in Android framework package. (%s)", annotationClass.getSimpleName(), qualifiedName); return true; } //2、判断类的包名不能以java开头 if (qualifiedName.startsWith("java.")) { error(element, "@%s-annotated class incorrectly in Java framework package. (%s)", annotationClass.getSimpleName(), qualifiedName); return true; } return false; }

解析ButterKnife的bind()

ButterKnife的bind()运行在UI线程，在指定的Activity中注释变量和方法，当前的内容视图被用作根视图。

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@NonNull @UiThread public static Unbinder bind(@NonNull Activity target) { //1、获取根视图 View sourceView = target.getWindow().getDecorView(); //2、创建绑定 return createBinding(target, sourceView); }

接下来查阅createBinding()代码：

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private static Unbinder createBinding(@NonNull Object target, @NonNull View source) { //1、获取目标Class Class<?> targetClass = target.getClass(); if (debug) Log.d(TAG, "Looking up binding for " + targetClass.getName()); //2、为Class查找Binding构造方法 Constructor<? extends Unbinder> constructor = findBindingConstructorForClass(targetClass); if (constructor == null) { return Unbinder.EMPTY; } //noinspection TryWithIdenticalCatches Resolves to API 19+ only type. try { //3、返回构造方法实例对象 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); } }

下面查阅findBindingConstructorForClass()代码：

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@Nullable @CheckResult @UiThread private static Constructor<? extends Unbinder> findBindingConstructorForClass(Class<?> cls) { //1、根据传入的Class从Map中获取Constructor对象 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(); //2、类名称如果以android或java开头返回null if (clsName.startsWith("android.") || clsName.startsWith("java.")) { if (debug) Log.d(TAG, "MISS: Reached framework class. Abandoning search."); return null; } try { //3、生成<类名>_ViewBinding的类 Class<?> bindingClass = cls.getClassLoader().loadClass(clsName + "_ViewBinding"); 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); } //4、将Constructor放入Map并返回 BINDINGS.put(cls, bindingCtor); return bindingCtor; }

而上段代码中多次出现的BINDINGS是什么样的数据结构呢？

1 2	@VisibleForTesting static final Map<Class<?>, Constructor<? extends Unbinder>> BINDINGS = new LinkedHashMap<>();

解析ButterKnife生成辅助类

在上问分析中已经生成了<类名>_ViewBinding的类，下面分析<类名>_ViewBinding类中的代码：

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public class MainActivity_ViewBinding implements Unbinder { private MainActivity target; private View view2131427424; @UiThread public MainActivity_ViewBinding(MainActivity target) { //1、构造方法分钟传入了MainActivity的DecorView this(target, target.getWindow().getDecorView()); } @UiThread public MainActivity_ViewBinding(final MainActivity target, View source) { this.target = target; View view; //2、根据类型查找到需要的View target.etInput = Utils.findRequiredViewAsType(source, R.id.et_input, "field 'etInput'", EditText.class); //3、查找需要的View view = Utils.findRequiredView(source, R.id.btn_send, "field 'btnSend' and method 'OnClick'"); //4、View类型转换 target.btnSend = Utils.castView(view, R.id.btn_send, "field 'btnSend'", Button.class); view2131427424 = view; view.setOnClickListener(new DebouncingOnClickListener() { @Override public void doClick(View p0) { target.OnClick(); } }); } @Override @CallSuper public void unbind() { MainActivity target = this.target; if (target == null) throw new IllegalStateException("Bindings already cleared."); this.target = null; target.etInput = null; target.btnSend = null; view2131427424.setOnClickListener(null); view2131427424 = null; } }

下面查阅Utils中的findRequiredViewAsType()：

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public static <T> T findRequiredViewAsType(View source, @IdRes int id, String who, Class<T> cls) { //1、获取需要的View View view = findRequiredView(source, id, who); //2、View类型转换 return castView(view, id, who, cls); }

下面查阅Utils中findRequiredView()代码：

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public static View findRequiredView(View source, @IdRes int id, String who) { //1、最终还是通过findViewById() 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."); }

下面查阅Utils中castView()代码：

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public static <T> T castView(View view, @IdRes int id, String who, Class<T> cls) { try { //1、类型转换类似于(TextView)findViewById() 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); } }