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：

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mUnbinder = ButterKnife.bind(this);

切记在Activity的onDestroy()中进行解绑：

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mUnbinder.unbind();

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

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mUnbinder = ButterKnife.bind(this, view);

在Fragment的onDestroyView()中进行以下操作：

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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？

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@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);
  }
}

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原文地址：https://www.cnblogs.com/lijianming180/p/12268257.html