ObservableViewModel

kotlin

import android.arch.lifecycle.ViewModel
import android.databinding.Bindable
import android.databinding.Observable
import android.databinding.PropertyChangeRegistry

/**
 * An [Observable] [ViewModel] for Data Binding.
 */
open class ObservableViewModel : ViewModel(), Observable {

    private val callbacks: PropertyChangeRegistry by lazy { PropertyChangeRegistry() }

    override fun addOnPropertyChangedCallback(callback: Observable.OnPropertyChangedCallback) {
        callbacks.add(callback)
    }

    override fun removeOnPropertyChangedCallback(callback: Observable.OnPropertyChangedCallback)     {
        callbacks.remove(callback)
    }

    /**
     * Notifies listeners that all properties of this instance have changed.
     */
    @Suppress("unused")
    fun notifyChange() {
        callbacks.notifyCallbacks(this, 0, null)
    }

    /**
     * Notifies listeners that a specific property has changed. The getter for the property
     * that changes should be marked with [Bindable] to generate a field in
     * `BR` to be used as `fieldId`.
     *
     * @param fieldId The generated BR id for the Bindable field.
     */
    fun notifyPropertyChanged(fieldId: Int) {
        callbacks.notifyCallbacks(this, fieldId, null)
    }
}

java

import android.arch.lifecycle.ViewModel;
import android.databinding.Observable;
import android.databinding.PropertyChangeRegistry;

/**
 * A ViewModel that is also an Observable,
 * to be used with the Data Binding Library.
 */
public class ObservableViewModel extends ViewModel implements Observable {
    private PropertyChangeRegistry callbacks = new PropertyChangeRegistry();

    @Override
    public void addOnPropertyChangedCallback(Observable.OnPropertyChangedCallback callback) {
        callbacks.add(callback);
    }

    @Override
    public void removeOnPropertyChangedCallback(Observable.OnPropertyChangedCallback callback) {
       callbacks.remove(callback);
    }

    /**
     * Notifies observers that all properties of this instance have changed.
     */
    public void notifyChange() {
        callbacks.notifyCallbacks(this, 0, null);
    }

    /**
     * Notifies observers that a specific property has changed. The getter for the
     * property that changes should be marked with the @Bindable annotation to
     * generate a field in the BR class to be used as the fieldId parameter.
     *
     * @param fieldId The generated BR id for the Bindable field.
     */
    public void notifyPropertyChanged(int fieldId) {
        callbacks.notifyCallbacks(this, fieldId, null);
    }
}