Erick Chang

There are plenty of resources introducing the data binding library in Android–see Yigit’s talk at the Bay Area Android Dev Group or watch Jacob’s talk from Droidcon NYC 2015. Not many people are willing to buy into the whole MVVM architecture, especially if you’re already working on a large app. It doesn’t seem worth it to rip out the internals of your carefully constructed MVX setup to make room for this framework.

It probably isn’t.

But I still think there’s room to add the data binding library to every app. It works really nicely as a replacement for findViewById and Butterknife (sorry Jake).

The problem with findViewById

class ExampleActivity extends Activity {
  TextView title;
  TextView subtitle;
  TextView footer;

  @Override public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.simple_activity);
    title = (TextView) findViewById(R.id.title);
    subtitle = (TextView) findViewById(R.id.subtitle);
    footer = (TextView) findViewById(R.id.footer);
  }
}

Everyone is familiar with this common nuisance. Whenever you inflate an Activity or Fragment, you need to call findViewById(int id), cast it to the correct View you’re interested in, and if your view has the slightest bit of complexity involved, you need to hold a reference to the view in your class. This scales poorly, is prone to error, and adds extra clutter to your onCreate methods.

Butterknife aimed to solve this problem a while back:

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...
  }
}

It solves the automatic type casting, but we still have to hold each field manually. We clutter our Activity classes with these view references, turning our Activity into a big ViewHolder.

Just introducing the data binding library can remove this clutter for you:

class ExampleActivity extends Activity {
  SimpleActivityBinding binding;

  @Override public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    binding = DataBindingUtil.setContentView(this, R.layout.simple_activity);
    // TODO access any View with ids declared in the layout
    binding.title.setText("Hi I'm a TextView!");
    binding.subtitle.setText("I'm a subtitle.");
    binding.footer.setText("I'm a footer.");
  }
}

The generated ViewDataBinding object acts as the ViewHolder for you, doing automatic type casting for you. No need to jump into the MVVM aspect of it–the binding is incredibly invaluable as a ViewHolder in itself. All you need to do for this migration is to wrap your root layout in <layout> tags and move all the namespace definitions.

<?xml version="1.0" encoding="utf-8"?>
<layout 
  xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:tools="http://schemas.android.com/tools"
  xmlns:app="http://schemas.android.com/apk/res-auto"
  >
  <LinearLayout
      android:id="@+id/container"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      >
    <TextView
        android:id="@+id/title"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        />
    <TextView
        android:id="@+id/subtitle"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        />
    <TextView
        android:id="@+id/footer"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        />
  </LinearLayout>
</layout>

Every view with an id defined will be captured in the generated ViewDataBinding for you, with no additional casting or declaration necessary. Adding another view to this layout with an id defined will be immediately accessible in the binding field in the example above. It really is a first party solution to findViewById.