Original address: http://stormzhang.com/openandroid/android/2014/01/12/android-butterknife/

As the saying goes, "A programmer who is not lazy is not a good programmer!" As an Android developer, are you often tired of a lot of findViewById and setOnClickListener code? ButterKnife It's a View Injection Framework that focuses on Android systems, freeing you from all this cumbersome code. Let's start with a code example to illustrate how ButterKnife simplifies the code:

Note: If you are using Eclipse to reference the library, you need to refer to it here. Eclipse Configuration Make some configurations, or you'll run incorrectly.

class ExampleActivity extends Activity {
  TextView title;
  TextView subtitle;
  TextView footer;

  @Override public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.simple_activity);
    title = (TextView) findViewById(R.id.title);
    subtitle = (TextView) findViewById(R.id.subtitle);
    footer = (TextView) findViewById(R.id.footer);

    // TODO Use views...
  }
}

The code after using ButterKnife is as follows:

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

  @Override public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.simple_activity);
    ButterKnife.inject(this);
    // TODO Use "injected" views...
  }
}

Is it very simple and easy to use? Here is a systematic introduction to the use of ButterKnife.

Characteristics of Butter Knife

1. Support View Injection in Activity

2. Support View Injection in View

3. Support for View Event Callback Function Injection

The following event callback functions are currently supported:

• View: @OnLongClick and @OnFocusChanged.

• TextView: @OnEditorAction.

• AdapterView: @OnItemClick and @OnItemLongClick.

• CompoundButton: @OnCheckedChanged.

Let's look at some injected sample code:

Injection into Activity

Injection in Fragment

Injection in ViewHolder mode

Injection callback function

Following are several examples of methods for injecting callback functions:

// With Button parameter
@OnClick(R.id.submit)
public void sayHi(Button button) {
  button.setText("Hello!");
}
 
// Without parameters
@OnClick(R.id.submit)
public void submit() {
  // TODO submit data to server...
}
 
// Injecting multiple View events at the same time
@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();
  }
}

Reset function

If you need to set the injected View to Null when the interface is destroyed, you can use the reset function:

public class FancyFragment extends Fragment {
  @InjectView(R.id.button1) Button button1;
  @InjectView(R.id.button2) Button button2;
 
  @Override View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fancy_fragment, container, false);
    ButterKnife.inject(this, view);
    // TODO Use "injected" views...
    return view;
  }
 
  @Override void onDestroyView() {
    super.onDestroyView();
    Views.reset(this);
  }
}

Optional View Injection is also supported. If the View does not exist, it will not:

@Optional @InjectView(R.id.might_not_be_there) TextView mightNotBeThere;
 
@Optional @OnClick(R.id.maybe_missing) void onMaybeMissingClicked() {
  // TODO ...
}

There are also two findViewById functions to simplify the way you look for Views. If none of them meets your needs, you can use them:

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

Finally, if you use Android Studio as an IDE, there is a ButterKnife plug-in android-butterknife-zelezny This plug-in allows you to manually generate the injection code mentioned above, thus making yourself a lazier programmer. Let's take a screenshot.