到此我们整个的流程算分析完了。

小超人

最后我们看下对外提供的API

bind 方法

那么还差一步，什么时候都要我们生成的java文件呢？答案是：
ButterKnife.bind(this);方法。
我们看一下ButterKnife对外提供的API

  
   /**
   * BindView annotated fields and methods in the specified {@link Activity}. The current content
   * view is used as the view root.
   *
   * @param target Target activity for view binding.
   */
  @NonNull @UiThread
  public static Unbinder bind(@NonNull Activity target) {
    View sourceView = target.getWindow().getDecorView();
    return createBinding(target, sourceView);
  }

  /**
   * BindView annotated fields and methods in the specified {@link View}. The view and its children
   * are used as the view root.
   *
   * @param target Target view for view binding.
   */
  @NonNull @UiThread
  public static Unbinder bind(@NonNull View target) {
    return createBinding(target, target);
  }

  /**
   * BindView annotated fields and methods in the specified {@link Dialog}. The current content
   * view is used as the view root.
   *
   * @param target Target dialog for view binding.
   */
  @NonNull @UiThread
  public static Unbinder bind(@NonNull Dialog target) {
    View sourceView = target.getWindow().getDecorView();
    return createBinding(target, sourceView);
  }

  /**
   * BindView annotated fields and methods in the specified {@code target} using the {@code source}
   * {@link Activity} as the view root.
   *
   * @param target Target class for view binding.
   * @param source Activity on which IDs will be looked up.
   */
  @NonNull @UiThread
  public static Unbinder bind(@NonNull Object target, @NonNull Activity source) {
    View sourceView = source.getWindow().getDecorView();
    return createBinding(target, sourceView);
  }

  /**
   * BindView annotated fields and methods in the specified {@code target} using the {@code source}
   * {@link View} as the view root.
   *
   * @param target Target class for view binding.
   * @param source View root on which IDs will be looked up.
   */
  @NonNull @UiThread
  public static Unbinder bind(@NonNull Object target, @NonNull View source) {
    return createBinding(target, source);
  }

  /**
   * BindView annotated fields and methods in the specified {@code target} using the {@code source}
   * {@link Dialog} as the view root.
   *
   * @param target Target class for view binding.
   * @param source Dialog on which IDs will be looked up.
   */
  @NonNull @UiThread
  public static Unbinder bind(@NonNull Object target, @NonNull Dialog source) {
    View sourceView = source.getWindow().getDecorView();
    return createBinding(target, sourceView);
  }

  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);
    }
  }

我们看到bind的一系列方法都会调用createBinding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);
    }
  }

Class<?> targetClass = target.getClass();获取类的实例，最后获取构造函数，最后constructor.newInstance方法来调用该类的构造函数。
而该类的构造函数是通过findBindingConstructorForClass方法，我们来看下此方法：

   @Nullable @CheckResult @UiThread
  private static Constructor<? extends Unbinder> findBindingConstructorForClass(Class<?> cls) {
  //缓存中查找，找到直接返回
    Constructor<? extends Unbinder> bindingCtor = BINDINGS.get(cls);
    if (bindingCtor != null) {
      if (debug) Log.d(TAG, "HIT: Cached in binding map.");
      return bindingCtor;
    }
    
     //检查合法性
    String clsName = cls.getName();
    if (clsName.startsWith("android.") || clsName.startsWith("java.")) {
      if (debug) Log.d(TAG, "MISS: Reached framework class. Abandoning search.");
      return null;
    }
    try {
    //构造一个class，可以看类名就是我们生成的。
      Class<?> bindingClass = Class.forName(clsName + "_ViewBinding");
      //noinspection unchecked
        // 获取我们的构造函数
      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);
    }
     //加入到缓存中
    BINDINGS.put(cls, bindingCtor);
    return bindingCtor;
  }

可以看到用到了简单的缓存。

unbind 方法

在新版的8.4.0中去除了 unbind方法。

ButterKnife.unbind(this);

采用了接口的形式。让生成的类来实现，比如：

 public final class SimpleAdapter$ViewHolder_ViewBinding implements Unbinder {
   @UiThread
  public SimpleAdapter$ViewHolder_ViewBinding(SimpleAdapter.ViewHolder target, View source) {
  //...
  }
 //...
  @Override
  public void unbind() {
  /...
  }
 ｝

那如何unbind呢？？
ButterKnife.bind(this)返回值是一个我们生成的java文件类的实例对象。返回的是一个Unbinder 正和此意。
so，你可以这么用：

  private  Unbinder unbinder;     
  @Override protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.simple_activity);
     unbinder=ButterKnife.bind(this);
     ｝
       @Override
  protected void onDestroy() {
    super.onDestroy();
    unbinder.unbind();
  }

到此我们就算完了。

哈哈