Butter Knife 在项目中的应用
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在使用注解是 变量 和方法 不能是静态和私有的,不然会报错,
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 putfindViewById
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 theonFinishInflate()
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
in 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 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);
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