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Butter Knife

2016-05-11 10:13 507 查看

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 in

onCreateView

,
set the views to

null

onDestroyView

.
Butter Knife returns an

Unbinder

instance 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

Make sure you have latest Butterknife lib on your classpath
Right click on usage of desired layout reference (e.g. R.layout.main in your Activity or Fragment), then

Generate

and

Generate
ButterKnife Injections

Pick injections you want, you also have an option to create ViewHolder for adapters.
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 Železný 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.

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