1，配置

工程 gradle

buildscript {
  repositories {
    mavenCentral()
    google()
   }
  dependencies {
    classpath 'com.jakewharton:butterknife-gradle-plugin:10.1.0'
  }
}

在 module 中添加

apply plugin: 'com.android.library'
apply plugin: 'com.jakewharton.butterknife'

依赖中添加

implementation 'com.jakewharton:butterknife:10.1.0'
annotationProcessor 'com.jakewharton:butterknife-compiler:10.1.0'
// 如果是 Kotlin，请用 annotationProcessor 替换掉 kapt

tip：在使用中请注意使用 R2 而不是 R
github 地址： https://github.com/JakeWharton/butterknife

2，绑定 View

注意在 onCreate 调用 ButterKnife.bind

class ExampleActivity extends Activity {
  @BindView(R.id.title) TextView title;
  @BindView(R.id.subtitle) TextView subtitle;
  @BindView(R.id.footer) TextView footer;

  @Override public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.simple_activity);
    ButterKnife.bind(this);
    // TODO Use fields...
  }
}

3，Resource 绑定

class ExampleActivity extends Activity {
  @BindString(R.string.title) String title;
  @BindDrawable(R.drawable.graphic) Drawable graphic;
  @BindColor(R.color.red) int red; // int or ColorStateList field
  @BindDimen(R.dimen.spacer) Float spacer; // int (for pixel size) or float (for exact value) field
  // ...
}

4，Non-Activity 绑定

只要 bind 了View Root，你也可以在任意object中进行绑定，如 Fragment

public class FancyFragment extends Fragment {
  @BindView(R.id.button1) Button button1;
  @BindView(R.id.button2) Button button2;

  @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fancy_fragment, container, false);
    ButterKnife.bind(this, view);
    // TODO Use fields...
    return view;
  }
}

或者listView 的adapter

public class MyAdapter extends BaseAdapter {
  @Override public View getView(int position, View view, ViewGroup parent) {
    ViewHolder holder;
    if (view != null) {
      holder = (ViewHolder) view.getTag();
    } else {
      view = inflater.inflate(R.layout.whatever, parent, false);
      holder = new ViewHolder(view);
      view.setTag(holder);
    }

    holder.name.setText("John Doe");
    // etc...

    return view;
  }

  static class ViewHolder {
    @BindView(R.id.title) TextView name;
    @BindView(R.id.job_title) TextView jobTitle;

    public ViewHolder(View view) {
      ButterKnife.bind(this, view);
    }
  }
}

5，View 列表

@BindViews({ R.id.first_name, R.id.middle_name, R.id.last_name })
List<EditText> nameViews;

还提供了 run 和 set 方法来修改列表属性

    static final butterknife.Action<View> DISABLE = new butterknife.Action<View>() {
        @Override public void apply(View view, int index) {
            view.setEnabled(false);
        }
    };
    static final butterknife.Setter<View, Boolean> ENABLED = new butterknife.Setter<View, Boolean>() {
        @Override public void set(View view, Boolean value, int index) {
            view.setEnabled(value);
        }
    };

    ViewCollections.run(nameViews, DISABLE);
    ViewCollections.set(nameViews, ENABLED, false);

6，Listener 绑定

@OnClick(R.id.submit)
public void submit(View view) {
  // TODO submit data to server...
}

// 参数可以省略掉
@OnClick(R.id.submit)
public void submit() {
  // TODO submit data to server...
}

// 如果是指定类型也会cast到相应的类型
@OnClick(R.id.submit)
public void sayHi(Button button) {
  button.setText("Hello!");
}

// 也可以binding到多个View上
@OnClick({ R.id.door1, R.id.door2, R.id.door3 })
public void pickDoor(DoorView door) {
  if (door.hasPrizeBehind()) {
    Toast.makeText(this, "You win!", LENGTH_SHORT).show();
  } else {
    Toast.makeText(this, "Try again", LENGTH_SHORT).show();
  }
}

// 在自定义View中不需要指定View ID
public class FancyButton extends Button {
  @OnClick
  public void onClick() {
    // TODO do something!
  }
}

7，unbind

对于不同生命周期的bind，需要的退出的时候 unbind

public class FancyFragment extends Fragment {
  @BindView(R.id.button1) Button button1;
  @BindView(R.id.button2) Button button2;
  private Unbinder unbinder;

  @Override public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fancy_fragment, container, false);
    unbinder = ButterKnife.bind(this, view);
    // TODO Use fields...
    return view;
  }

  @Override public void onDestroyView() {
    super.onDestroyView();
    unbinder.unbind();
  }
}

8，可选bind

在bind listener的时候，如果 View 找不到我们可以在变量中添加 @Nullable，或者在方法上添加 @Optional

@Nullable @BindView(R.id.might_not_be_there) TextView mightNotBeThere;

@Optional @OnClick(R.id.maybe_missing) void onMaybeMissingClicked() {
  // TODO ...
}

9，多个Listener

有的View 的Listener 会有多个回调函数，这个时候我们可以使用 callback 来指定相应的回调

@OnItemSelected(R.id.list_view)
void onItemSelected(int position) {
  // TODO ...
}

@OnItemSelected(value = R.id.maybe_missing, callback = NOTHING_SELECTED)
void onNothingSelected() {
  // TODO ...
}

10，原理

通过编译时注解，使用 javapoet 库生成相应的java文件
在我们调用 ButterKnife.bind(view) 方法的时候，根据类的全限定类型，来执行相应的代码

  @NonNull @UiThread
  public static Unbinder bind(@NonNull View target) {
    return bind(target, target);
  }

  @NonNull @UiThread
  public static Unbinder bind(@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);
    }
  }

  @Nullable @CheckResult @UiThread
  private static Constructor<? extends Unbinder> findBindingConstructorForClass(Class<?> cls) {
    Constructor<? extends Unbinder> bindingCtor = BINDINGS.get(cls);
    if (bindingCtor != null || BINDINGS.containsKey(cls)) {
      if (debug) Log.d(TAG, "HIT: Cached in binding map.");
      return bindingCtor;
    }
    String clsName = cls.getName();
    if (clsName.startsWith("android.") || clsName.startsWith("java.")
        || clsName.startsWith("androidx.")) {
      if (debug) Log.d(TAG, "MISS: Reached framework class. Abandoning search.");
      return null;
    }
    try {
      Class<?> bindingClass = cls.getClassLoader().loadClass(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;
  }

通过代码我们看到，这些方法都是执行的 UIThread 的，并且一般都是以 "_ViewBinding" 结尾，生成的文件我们可以在 build/generated/source/debug 下面看到

参考：
http://jakewharton.github.io/butterknife/