Binding Views using ButterKnife
we can annotate fields with @BindView
and a view ID for Butter Knife to find and automatically cast the corresponding view in our layout.
Binding Views
Binding Views in Activity
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... } }
Binding Views in Fragments
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; } // in fragments or non activity bindings we need to unbind the binding when view is about to be destroyed @Override public void onDestroy() { super.onDestroy(); unbinder.unbind(); } }
Binding Views in Dialogs
We can use ButterKnife.findById
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);
Binding Views in ViewHolder
static class ViewHolder { @BindView(R.id.title) TextView name; @BindView(R.id.job_title) TextView jobTitle; public ViewHolder(View view) { ButterKnife.bind(this, view); } }
Binding Resources
Apart from being useful for binding views, one could also use ButterKnife to bind resources such as those defined within strings.xml
, drawables.xml
, colors.xml
, dimens.xml
, etc.
public 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
@Override public void onCreate(Bundle savedInstanceState) {
// ... ButterKnife.bind(this);
}
}
Binding View Lists
You can group multiple views into a List or array. This is very helpful when we need to perform one action on multiple views at once.
@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);
//We can use 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); } };
Optional Bindings
By default, both @Bind
and listener bindings are required. An exception is thrown if the target view cannot be found. But if we are not sure if a view will be there or not then we can add a @Nullable
annotation to fields or the @Optional
annotation to methods to suppress this behavior and create an optional binding.
@Nullable @BindView(R.id.might_not_be_there) TextView mightNotBeThere; @Optional @OnClick(R.id.maybe_missing) void onMaybeMissingClicked() { // TODO ... }