Android must have Injections (Roboguice, ButterKnife)

RoboGuice

RoboGuice is a framework that brings the simplicity and ease of Dependency Injection to Android, using Google’s own Guice library. If you’ve ever used Spring (the #1 enterprise framework on Java, now more popular than J2EE itself) or Guice, you already know how convenient this style of programming can be.

RoboGuice 3 smoothes out some of the wrinkles in your Android development experience and makes things simple and fun. Do you always forget to check for null when you getIntent().getExtras()? RoboGuice 3 will help you. Think casting findViewById() to a TextView shouldn’t be necessary? RoboGuice 3 is on it.

RoboGuice 3 takes the guesswork out of development. Inject your View, Resource, System Service, or any other object, and let RoboGuice 3 take care of the details.

RoboGuice 3 slims down your application code. Less code means fewer opportunities for bugs. It also makes your code easier to follow — no longer is your code littered with the mechanics of the Android platform, but now it can focus on the actual logic unique to your application.

There’s no “magic”. Everything you need is configured explicitly for you by RoboGuice 3 or can be overridden by you.

RoboGuice 3 applications have been Featured on the Android Market for years. It leverages the award-winning and production-ready Google Guice library to bring you simple dependency injection lightweight enough to use in a mobile application.

It works, and people are using it. Why not give it a spin?

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To give you an idea, take a look at this simple example of a typical Android activity:

 

class AndroidWay extends Activity { 
        TextView name; 
        ImageView thumbnail; 
        LocationManager loc; 
        Drawable icon; 
        String myName; 

        public void onCreate(Bundle savedInstanceState) { 
            super.onCreate(savedInstanceState); 
            setContentView(R.layout.main);
            name      = (TextView) findViewById(R.id.name); 
            thumbnail = (ImageView) findViewById(R.id.thumbnail); 
            loc       = (LocationManager) getSystemService(Activity.LOCATION_SERVICE); 
            icon      = getResources().getDrawable(R.drawable.icon); 
            myName    = getString(R.string.app_name); 
            name.setText( "Hello, " + myName ); 
        } 
    } 

This example is 19 lines of code. If you’re trying to read through onCreate(), you have to skip over 5 lines of boilerplate initialization to find the only one that really matters: name.setText(). And complex activities can end up with a lot more of this sort of initialization code.

Compare this to the same app, written using RoboGuice:

@ContentView(R.layout.main)
    class RoboWay extends RoboActivity { 
        @InjectView(R.id.name)             TextView name; 
        @InjectView(R.id.thumbnail)        ImageView thumbnail; 
        @InjectResource(R.drawable.icon)   Drawable icon; 
        @InjectResource(R.string.app_name) String myName; 
        @Inject                            LocationManager loc; 

        public void onCreate(Bundle savedInstanceState) { 
            super.onCreate(savedInstanceState); 
            name.setText( "Hello, " + myName ); 
        } 
    } 

In this example, onCreate() is much easier to take in at a glance. All the platform boilerplate is stripped away and you’re left with just your own app’s business logic. Do you need aSystemService? Inject one. Do you need a View or Resource? Inject those, too, and RoboGuice will take care of the details.

RoboGuice’s goal is to make your code be about your app, rather than be about all the initialization and lifecycle code you typically have to maintain in Android.

Visit the Installation pages for all the details on how to configure your first RoboGuice application.

 

ButterKnife

Licensed under the Apache License, Version 2.0 (the “License”);

logo
Annotate fields with @BindView 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 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 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:8.2.1'
apt 'com.jakewharton:butterknife-compiler:8.2.1'