Android 开发过程中,我们需要写大量的findViewById()和setonclicktListener()等事件, 那么现在有一个框架可以很好的解决这个问题 ---- BufferKnife。BufferKnife可以大量精简代码,而且不影响性能,可以通过查看Butter Knife了解到,其自定义注解的实现都是限定为RetentionPolicy.CLASS,也就是到编译出.class文件为止有效,在运行时不会额外消耗性能。
下面是说明一下如何使用Butter Knife :
基本的使用方法如下:
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); // 必须在设置好布局事件后绑定当前的Activity // TODO Use fields... } }
上面的慢反射代码执行下来生成的class代码如下:
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); }
另外Butter Knife 也可以用于资源绑定:
可以使用@BindBool
, @BindColor
, @BindDimen
, @BindDrawable
, @BindInt
, @BindString来预绑定一些资源到对应的字段。
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 // ... }
那么有人会问,非Activity的类如何绑定呢?其实只需要比Activity绑定时多传递一个参数即可,即根View:
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; } }
Butter Knife 还有另一个用途就是简化List的Adapter的ViewHolder部分的代码:
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); } } }
基本上你想调用findViewById的方法的地方应该都是可以设置ButterKnife.bind的。
使用ButterKnife.bind(这)将视图的孩子绑定到字段中。 如果您在布局中使用<merge>标签,并在自定义视图构造函数中展开,则可以立即调用它。 或者,从XML扩展的自定义视图类型可以在onFinishInflate()回调中使用它。
提供的其他的绑定的APIs:
- 使用Activity作为视图根来绑定任意对象。如果你使用类似MVC 的模式,你可以使用ButterKnife.bind(this, activity)来绑定控制器。
ButterKnife还可以处理View Lists:
你可以将多个view分组到列表或者数组:
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
in 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.
Download
Gradle
compile ‘com.jakewharton:butterknife:(insert latest version)‘ annotationProcessor ‘com.jakewharton:butterknife-compiler:(insert latest version)‘