Android框架式编程之BufferKnife

Posted 2020-09-19 灰色飘零

android 开发过程中，我们需要写大量的findViewById()和setonclicktListener()等事件， 那么现在有一个框架可以很好的解决这个问题 ---- BufferKnife。BufferKnife可以大量精简代码，而且不影响性能，可以通过查看Butter Knife了解到，其自定义注解的实现都是限定为RetentionPolicy.CLASS，也就是到编译出.class文件为止有效，在运行时不会额外消耗性能。

下面是说明一下如何使用Butter Knife ：

基本的使用方法如下：

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); // 必须在设置好布局事件后绑定当前的Activity
    // TODO Use fields...
  }
}

上面的慢反射代码执行下来生成的class代码如下：

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);
}

另外Butter Knife 也可以用于资源绑定:

可以使用@BindBool, @BindColor, @BindDimen, @BindDrawable, @BindInt, @BindString来预绑定一些资源到对应的字段。

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
  // ...
} 

那么有人会问，非Activity的类如何绑定呢？其实只需要比Activity绑定时多传递一个参数即可，即根View：

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;
  }
}

 

Butter Knife 还有另一个用途就是简化List的Adapter的ViewHolder部分的代码：

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);
    }
  }
}

基本上你想调用findViewById的方法的地方应该都是可以设置ButterKnife.bind的。

使用ButterKnife.bind（这）将视图的孩子绑定到字段中。 如果您在布局中使用<merge>标签，并在自定义视图构造函数中展开，则可以立即调用它。 或者，从XML扩展的自定义视图类型可以在onFinishInflate（）回调中使用它。

提供的其他的绑定的APIs：

• 使用Activity作为视图根来绑定任意对象。如果你使用类似MVC 的模式，你可以使用ButterKnife.bind(this, activity)来绑定控制器。

 

ButterKnife还可以处理View Lists：

你可以将多个view分组到列表或者数组：

View Lists

You can group multiple views into a List or array.

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

The apply method allows you to act on all the views in a list at once.

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

Listeners can also automatically be configured onto methods.

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

All arguments to the listener method are optional.

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

Define a specific type and it will automatically be cast.

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

Specify multiple IDs in a single binding for common event handling.

@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();
  }
}

Custom views can bind to their own listeners by not specifying an ID.

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

Binding Reset

Fragments have a different view lifecycle than activities. When binding a fragment in onCreateView, set the views to null in onDestroyView. Butter Knife returns an Unbinderinstance when you call bind to do this for you. Call its unbind method in the appropriate lifecycle callback.

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();
  }
}

Optional Bindings

By default, both @Bind and listener bindings are required. An exception will be thrown if the target view cannot be found.

To suppress this behavior and create an optional binding, add a @Nullable annotation to fields or the @Optional annotation to methods.

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

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

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

Multi-Method Listeners

Method annotations whose corresponding listener has multiple callbacks can be used to bind to any one of them. Each annotation has a default callback that it binds to. Specify an alternate using the callback parameter.

@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);

Add a static import for ButterKnife.findById and enjoy even more fun.

Download

Gradle

compile ‘com.jakewharton:butterknife:(insert latest version)‘
annotationProcessor ‘com.jakewharton:butterknife-compiler:(insert latest version)‘