ButterKnife is a library that reduces boilerplate code for Android views by using annotation processing. It allows binding views to fields, setting listeners to methods, and operating on multiple views at once. To use it, annotations like @BindView and @OnClick are added and ButterKnife handles finding and casting views and wiring up listeners. It also supports binding resources, non-activity classes, view lists, and resetting bindings on configuration changes to prevent memory leaks.

1. ButterKnife 8.2.1
Himanshu Dudhat

2. Intro
• Field and method binding for Android views which uses annotation processing to generate boilerplate
code for you.
• Eliminate findViewById calls by using @BindView on fields.
• Group multiple views in a list or array. Operate on all of them at once with actions, setters, or properties.
• Eliminate anonymous inner-classes for listeners by annotating methods with @OnClick and others.
• Eliminate resource lookups by using resource annotations on fields.

3. Configure ButterKnife
• Update Project-level build.gradle
• Apply “android-apt” in module-level build.gradle
buildscript {
repositories {
mavenCentral()
}
dependencies {
classpath 'com.neenbedankt.gradle.plugins:android-apt:1.8'
}
}
apply plugin: 'android-apt'
android {
...
}
dependencies {
compile 'com.jakewharton:butterknife:8.2.1'
apt 'com.jakewharton:butterknife-compiler:8.2.1'
}

4. Add in library module
• Add Butterknife plugin to project-level build.gradle
• Apply ButterKnife plugin in library module
• Note: If you applied ButterKnife in library project then you neeed to use R2 class instead of R class in
ButterKnife annotations.
buildscript {
repositories {
mavenCentral()
}
dependencies {
classpath 'com.jakewharton:butterknife-gradle-plugin:8.2.1'
}
}
apply plugin: 'com.android.library'
apply plugin: 'com.jakewharton.butterknife'

5. Features
• VIEW BINDING
• RESOURCE BINDING
• NON-ACTIVITY BINDING
• VIEW LISTS
• LISTENER BINDING
• BINDING RESET
• OPTIONAL BINDINGS
• MULTI-METHOD LISTENERS

6. VIEW BINDING
• Annotate fields with @BindView and a view ID for Butter Knife to find and automatically cast the
corresponding view in your layout
• You can also perform binding on arbitrary objects by supplying your own view root
@BindView(R.id.title) TextView title;
@BindView(R.id.subtitle) TextView subtitle;
@BindView(R.id.footer) TextView footer;
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.phot);

7. 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.
@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

8. VIEW LISTS
• You can group multiple views into a List or array
• Then apply method allows you to act on all the views in a list at once
@BindViews({ R.id.first_name, R.id.middle_name, R.id.last_name })
List<EditText> nameViews;
ButterKnife.apply(nameViews, DISABLE);
ButterKnife.apply(nameViews, ENABLED, false);

9. Continue…
• Action and Setter interfaces allow specifying simple behavior
• An Android Property can also be used with the apply method.
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);
}
};
ButterKnife.apply(nameViews, View.ALPHA, 0.0f);

10. LISTENER BINDING
• Listeners can also automatically be configured onto methods
• Specify multiple IDs in a single binding for common event handling.
@OnClick(R.id.submit)
public void submit(View view) {
// TODO submit data to server...
}
@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();
}
}

11. BINDING RESET
• Fragments have a different view lifecycle than activities. Views should set to be null in
onDestroyViews().
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();
}
}

12. OPTIONAL BINDINGS
• For Views, it is using android defined annotation, @Nullable
• For methods, it is using ButterKnife annotation - @Optional
@Nullable @BindView(R.id.might_not_be_there)
TextView mightNotBeThere;
@Optional @OnClick(R.id.maybe_missing) void onMaybeMissingClicked() {
// TODO ...
}

13. 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.
E.g.
@OnItemSelected(R.id.list_view)
void onItemSelected(int position) {
// TODO ...
}
@OnItemSelected(value = R.id.maybe_missing, callback = NOTHING_SELECTED)
void onNothingSelected() {
// TODO ...
}

14. References
• http://jakewharton.github.io/butterknife
• https://www.sitepoint.com/tidying-code-with-android-butterknife/
• https://guides.codepath.com/android/Reducing-View-Boilerplate-with-Butterknife

15. Questions?

16. Thanks!
+HimanshuDudhat
@HimanshuDudhat
himanshu.dudhat@gmail.com
Team Lead - Android @ Cygnet Infotech Pvt. Ltd.
Sr. Software Engineer @ Cygnet Infotech Pvt. Ltd
Himanshu Dudhat