Reducing View Boilerplate with ViewBinding

Overview

The View Binding library makes it easy to reduce the need to use findViewById() lookups. Once this option is enabled in your project, special binding classes will be generated from any of your layout XML files. If you have a layout called activity_simple.xml, for instance, a special class called ActivitySimpleBinding will be generated that will have references automatically created for you. Some major advantages are:

  • improved null safety
  • better type safety
  • greater efficiency with complex views

NOTE: the View Binding library is separate from the Data Binding Library, which provides two-way and layout variables support.

Setup

Add the following to app/build.gradle file:

android {
  buildFeatures {
        viewBinding true
    }
}

Once you have enabled this option, make sure to click Rebuild Project. You will need to rebuild your entire project in order to make sure the view binding class are created.

Activity View Lookups

Once you have enabled and recompiled your project, the binding classes should be available to you. In this example, a ActivitySimpleBinding class should have been generated for a activity_simple.xml file. Instead of using setContentView(activity_simple.xml), we replace that line with a call with ActivitySimpleBinding.inflate():

class ExampleActivity extends AppCompatActivity {
  private TextView title;
  private ActivitySimpleBinding binding;

  @Override 
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    // activity_simple.xml -> ActivitySimpleBinding
    binding = ActivitySimpleBinding.inflate(getLayoutInflater());

    // layout of activity is stored in a special property called root
    View view = binding.getRoot();
    setContentView(view);

    // set bindings more efficiently through bindings
    title = binding.title;       // was title = findViewById(R.id.title);
    title.setText("My title");

    // alternately, access views through binding when needed, instead of variables
    binding.title.setText("My title");

  }
}
class ExampleActivity : AppCompatActivity() {
  private lateinit var title: TextView
  private lateinit var binding: ActivitySimpleBinding  

  override fun onCreate(savedInstanceState: Bundle?) {
      super.onCreate(savedInstanceState)
      
      // activity_simple.xml -> ActivitySimpleBinding
      binding = ActivitySimpleBinding.inflate(layoutInflater)
  
      // layout of activity is stored in a special property called root
      val view = binding.root
      setContentView(view)

      // set bindings more efficiently through bindings
      title = binding.title       // was title = findViewById(R.id.title)
      title.text = "My title"

      // alternately, access views through binding when needed, instead of variables
      binding.title.text = "My title"
  }
}

Fragment View Lookups

This can be done within Activity, Fragment, or Adapter classes. For example, fragment usage would look like:

public class FancyFragment extends Fragment {
  Button button1;
  Button button2;

  FancyFragmentBinding binding;

  @Override 
  public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { 
    
    // fancy_fragment.xml -> FancyFragmentBinding
    binding = FancyFragmentBinding.inflate(getLayoutInflater(), container, false);

    // layout of fragment is stored in a special property called root
    View view = binding.getRoot();
    			 
    // TODO Use fields...
    // binding.
    return view;
  }

  @Override 
  public void onDestroyView() {
    super.onDestroyView();
    binding = null;
  }
}
class FancyFragment : Fragment() {
  private lateinit var button1: Button
  private lateinit var button2: Button

  // Used to inflate and destroy the view
  private var _binding: FancyFragmentBinding? = null

  // Used throughout the class
  private val binding get() = _binding!!

  override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View {
    
    // fancy_fragment.xml -> FancyFragmentBinding
    _binding = FancyFragmentBinding.inflate(getLayoutInflater(), container, false)

    // layout of fragment is stored in a special property called root
    View view = binding.getRoot()
    			 
    // TODO Use fields...
    // binding.
    return view
  }

  override fun onDestroyView() {
    super.onDestroyView()
    _binding = null
  }
}

Troubleshooting

  • If you are missing a view binding class even though it is imported, try to Build -> Rebuild Project.

References

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