Butter Knife
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Annotate fields with @InjectView
and a view ID for Butter Knife to find and automatically cast the corresponding view in your layout.
class ExampleActivity extends Activity { @InjectView(R.id.title) TextView title; @InjectView(R.id.subtitle) TextView subtitle; @InjectView(R.id.footer) TextView footer; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.simple_activity); ButterKnife.inject(this); // TODO Use "injected" views... }}
Instead of slow reflection, code is generated to perform the view look-ups. Calling inject
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 inject(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 INJECTION
You can also perform injection on arbitrary objects by supplying your own view root.
public class FancyFragment extends Fragment { @InjectView(R.id.button1) Button button1; @InjectView(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.inject(this, view); // TODO Use "injected" views... 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 { @InjectView(R.id.title) TextView name; @InjectView(R.id.job_title) TextView jobTitle; public ViewHolder(View view) { ButterKnife.inject(this, view); } }}
You can see this implementation in action in the provided sample.
Calls to ButterKnife.inject
can be made anywhere you would otherwise put findViewById
calls.
Other provided injection APIs:
- Inject arbitrary objects using an activity as the view root. If you use a pattern like MVC you can inject the controller using its activity with
ButterKnife.inject(this, activity)
. - Inject a view's children into fields using
ButterKnife.inject(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 theonFinishInflate()
callback.
VIEW LISTS
You can group multiple views into a List
or array.
@InjectViews({ 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 Action<View> DISABLE = new Action<>() { @Override public void apply(View view, int index) { view.setEnabled(false); }}static final Setter<View, Boolean> ENABLED = new Setter<>() { @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);
LISTENER INJECTION
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! }}
INJECTION RESET
Fragments have a different view lifecycle than activities. When injecting a fragment inonCreateView
, set the views to null
in onDestroyView
. Butter Knife has a reset
method to do this automatically.
public class FancyFragment extends Fragment { @InjectView(R.id.button1) Button button1; @InjectView(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.inject(this, view); // TODO Use "injected" views... return view; } @Override public void onDestroyView() { super.onDestroyView(); ButterKnife.reset(this); }}
OPTIONAL INJECTIONS
By default, both @InjectView
and listener injections are required. An exception will be thrown if the target view cannot be found.
To suppress this behavior and create an optional injection, add the @Optional
annotation to the field or method.
@Optional @InjectView(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 thecallback
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
Butter Knife 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 supress 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 @InjectView on a member field thekeepclasseswithmembernames
option is used.
-keep class butterknife.** { *; }-dontwarn butterknife.internal.**-keep class **$$ViewInjector { *; }-keepclasseswithmembernames class * { @butterknife.* <fields>;}-keepclasseswithmembernames class * { @butterknife.* <methods>;}
License
Copyright 2013 Jake WhartonLicensed 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-2.0Unless required by applicable law or agreed to in writing, softwaredistributed 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 andlimitations under the License.
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