Butterknife使用详解

项目地址

GitHub地址:https://github.com/JakeWharton/butterknife

简介

ButterKnife这个开源库可以让我们从大量的findViewById和setOnClickListener中解放出来，其对性能的影响微乎其微（其自定义注解的实现都是限定为RetentionPolicy.CLASS，也就是编译出.class文件为止有效，在运行时不额外消耗性能，其实通过java注解自动生成java代码的形式来完成工作），但也有一个明显的缺点，那就是代码的可读性差些，凡事有利有弊，我们需要做到有的放矢。

应用

Activity Binding

class ExampleActivity extends Activity {
  @Bind(R.id.title) TextView title;
  @Bind(R.id.subtitle) TextView subtitle;
  @Bind(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...
  }
}

调用注解bind生成的代码是可见的并且能够调试，上面的示例通过Bind注解生成的代码相当于下面的代码：

public void bind(ExampleActivity activity) {
  activity.subtitle = (android.widget.TextView) activity.findViewById(2130968578);
  activity.footer = (android.widget.TextView) activity.findViewById(2130968579);
  activity.title = (android.widget.TextView) activity.findViewById(2130968577);
}

RESOURCE BINDING

Bind pre-defined resources with @BindBool, @BindColor, @BindDimen, @BindDrawable, @BindInt, @BindString, which binds an R.bool ID (or your specified type) to its corresponding field.

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
  // ...
}

NON-ACTIVITY BINDING

public class FancyFragment extends Fragment {
  @Bind(R.id.button1) Button button1;
  @Bind(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;
  }
}

ADAPTER BINDING

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 {
    @Bind(R.id.title) TextView name;
    @Bind(R.id.job_title) TextView jobTitle;

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

LIST OR ARRAY BINDING

@Bind({ R.id.first_name, R.id.middle_name, R.id.last_name })
List<EditText> nameViews;
//允许同时作用于list中的view
ButterKnife.apply(nameViews, DISABLE);
ButterKnife.apply(nameViews, ENABLED, false);

//Action and Setter interfaces allow specifying simple behavior.
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);
  }
};

//An Android Property can also be used with the apply method.
ButterKnife.apply(nameViews, View.ALPHA, 0.0f);

LISTENER BINDING

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

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

//带Button参数
@OnClick(R.id.submit)
public void sayHi(Button button) {
  button.setText("Hello!");
}

//同时注入多个View事件
@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();
  }
}

public class FancyButton extends Button {
  @OnClick
  public void onClick() {
    // TODO do something!
  }
}

BINDING RESET

相对于Activity，Fragment有与之不同的视图声明周期。当早onCreateView中bind一个Fragment的时候，需要在OnDestroyView中将views设置为null。Butter Knife 通过一个ButterKnife.Unbinder接口来自动完成这个过程. Simply bind an unbinder with @Unbinder to the fragment.

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

  @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;
  }

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

OPTIONAL BINDINGS

默认情况下,@Bind和绑定的目标是必须存在的，如果目标View不存在将会抛出异常。

为了避免这样情况并且创建一个可选的绑定目标，给变量增加@Nullable注解或者给方法增加 @Optional注解.

Note: Any annotation named @Nullable or can be used for fields. It is encouraged to use the @Nullable annotation from Android’s “support-annotations” library.

//给变量增加@Nullable注解
@Nullable @Bind(R.id.might_not_be_there) TextView mightNotBeThere;

//给方法增加@Optional注解
@Optional @OnClick(R.id.maybe_missing) void onMaybeMissingClicked() {
  // TODO ...
}

MULTI-METHOD LISTENERS

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

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

BONUS

Also included are findById methods which simplify code that still has to find views on a View, Activity, or Dialog. It uses generics to infer the return type and automatically performs the cast.

View view = LayoutInflater.from(context).inflate(R.layout.thing, null);
TextView firstName = ButterKnife.findById(view, R.id.first_name);
TextView lastName = ButterKnife.findById(view, R.id.last_name);
ImageView photo = ButterKnife.findById(view, R.id.photo);