Butter Knife

1.Butter Knife fuction

Field and method binding for Android views

2.Link

http://jakewharton.github.io/butterknife/

3.Introduction

Annotate fields with @Bind and a view ID for Butter Knife to find and automatically
cast the corresponding view in your layout.

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...
  }
}

Instead of slow reflection, code is generated to perform the view look-ups. Calling bind delegates
to this generated code that you can see and debug.

The generated code for the above example is roughly equivalent to the following:

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

You can also perform binding on arbitrary objects by supplying your own view root.

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;
  }
}

Another use is simplifying the view holder pattern inside of a list adapter.

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);
    }
  }
}

You can see this implementation in action in the provided sample.

Calls to ButterKnife.bind can be made anywhere you would otherwise put findViewById calls.

Other provided binding APIs:

• Bind arbitrary objects using an activity as the view root. If you use a pattern like MVC you can bind the controller using its activity with ButterKnife.bind(this,
activity).
• Bind a view‘s children into fields using ButterKnife.bind(this).
  If you use <merge> tags in a layout and inflate in a custom view constructor
  you can call this immediately after. Alternatively, custom view types inflated from XML can use it in the onFinishInflate() callback.

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 inonCreateView,
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.

4. Android ButterKnife Zelezny

Simple plug-in for Android Studio/IDEA that allows one-click creation of Butterknife view
injections.

How to install

• in Android Studio: go to Preferences → Plugins → Browse repositories and search for ButterKnife
Zelezny

or

• download it and install via Preferences
→ Plugins → Install plugin from disk

How to use it

1. Make sure you have latest Butterknife lib on your classpath
2. Right click on usage of desired layout reference (e.g. R.layout.main in your Activity or Fragment), then Generate andGenerate
ButterKnife Injections
3. Pick injections you want, you also have an option to create ViewHolder for adapters.
4. Click Confirm and enjoy injections in your code with no work!

Contributing

Pull requests are welcomed!

• make sure you stick to our coding
  style.
• follow Getting Started with Plugin
  Development
• make sure you have Java 6 installed if you want to publish it in the plugin repository
• initial project setup might be tricky (like editing iml files manually), don‘t hesitate to contact @destil if
  you run into troubles.

Common issue: The plugin is not working after I updated to new Android Studio

• AS promts you to update plugins after update, you need to update them before using
• Make sure you have Butterknife on your classpath
• Make sure that your cursor is on layout file in Activity on Fragment

Why ‘Zelezny‘?

Jan ?elezny is a famous Czech javelin thrower, Olympic champion and world record
holder. With Zelezny‘s javelin, your butter knife will be much sharper!

See our other Czech personalities who help with #AndroidDev.