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ButterKnife官方介绍

2015-08-11 22:41 513 查看

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 {
@Bind(R.id.title) TextView title;
@Bind(R.id.subtitle) TextView subtitle;
@Bind(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);
}

NON-ACTIVITY BINDING

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

public class FancyFragment extends Fragment {
@Bind(R.id.button1) Button button1;
@Bind(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 {
@Bind(R.id.title) TextView name;
@Bind(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.

@Bind({ 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 has an

unbind

method to do this automatically.

public class FancyFragment extends Fragment {
@Bind(R.id.button1) Button button1;
@Bind(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;
}

@Override public void onDestroyView() {
super.onDestroyView();
ButterKnife.unbind(this);
}
}

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 the
field or method.

Note: Any annotation named

@Nullable

can be used for this purpose. It is encouraged to use
the

@Nullable

annotation from Android's "support-annotations" library, see Android
Tools Project.

@Nullable @Bind(R.id.might_not_be_there) TextView mightNotBeThere;

@Nullable @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.

Download

ButterKnife JAR

The source code to the library and sample application as well as this website is available on GitHub. The Javadoc is also available
to browse.

MAVEN

If you are using Maven for compilation you can declare the library as a dependency.

<dependency>
<groupId>com.jakewharton</groupId>
<artifactId>butterknife</artifactId>
<version>(insert latest version)</version>
</dependency>

GRADLE

compile 'com.jakewharton:butterknife:(insert latest version)'

Be sure to suppress this lint warning in your

build.gradle

lintOptions {
disable 'InvalidPackage'
}

Some configurations may also require additional exclusions.

packagingOptions {
exclude 'META-INF/services/javax.annotation.processing.Processor'
}

IDE CONFIGURATION

Some IDEs require additional configuration in order to enable annotation processing.

IntelliJ IDEA — If your project uses an external configuration (like a Maven

pom.xml

)
then annotation processing should just work. If not, try manual configuration.
Eclipse — Set up manual configuration.

PROGUARD

Butter Knife generates and uses classes dynamically which means that static analysis tools like ProGuard may think they are unused. In order to prevent them from being removed, explicitly mark them to be kept. To prevent ProGuard renaming classes that use @Bind
on a member field the

keepclasseswithmembernames

option is used.

-keep class butterknife.** { *; }
-dontwarn butterknife.internal.**
-keep class **$$ViewBinder { *; }

-keepclasseswithmembernames class * {
@butterknife.* <fields>;
}

-keepclasseswithmembernames class * {
@butterknife.* <methods>;
}

License

Copyright 2013 Jake Wharton

Licensed under the Apache License, Version 2.0 (the "License");

you may not use this file except in compliance with the License.

You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software

distributed under the License is distributed on an "AS IS" BASIS,

WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

See the License for the specific language governing permissions and

limitations under the License.

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

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