分析bind流程

Activity綁定
ButterKnife.bind(this);bind源碼如下 ：

/**
   * 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);
  }

return一個(gè)Unbinder對(duì)象，Unbinder是一個(gè)接口, 當(dāng)Activity 銷(xiāo)毀時(shí)取消綁定

package butterknife;

import android.support.annotation.UiThread;

/** An unbinder contract that will unbind views when called. */
public interface Unbinder {
  @UiThread void unbind();

  Unbinder EMPTY = new Unbinder() {
    @Override public void unbind() { }
  };
}

NOTE:UiThread是官方support annitation庫(kù)提供的一個(gè)注解

先獲取Activity的DecorView, 調(diào)用createBinding(),如下

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);
    }
  }

調(diào)用findBindingConstructorForClass獲取Constructor，通過(guò)反射再執(zhí)行newInstance生成Unbinder對(duì)象，關(guān)鍵函數(shù)findBindingConstructorForClass如下：

@Nullable @CheckResult @UiThread
  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;
    }
    try {
      Class<?> bindingClass = Class.forName(clsName + "_ViewBinding");
      //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;
  }

可以看出BINDINGS鍵值對(duì)映射了class和對(duì)應(yīng)的Constructor, 而Constructor是xxx_ViewBinding(xxx指某個(gè)Activity)的構(gòu)造器，這個(gè)xxx_ViewBinding并不是我們手寫(xiě)的java類(lèi)，是annotation processor生成的，這個(gè)單開(kāi)一篇來(lái)說(shuō)明

結(jié)論

ButterKnife.bind(this);返回一個(gè)Unbinder接口，實(shí)例化的是Activity_ViewBinding對(duì)象