android two-way Data Binding - data changes does not update UI views

Question

I am using android two-way data binding, but data changes does not update view elements. I have a simple string correctly displayed on an TextInputEditText, but when the bound viewmodel livedata variable is updated, the view is not updating. The variable info is supposed to show 'Hello my friend' on the radiobutton click listener..but it is not updating the ui.

fragment:

public class MainFragment extends Fragment {

private MainViewModel mViewModel;
private MainFragmentBinding mDataBinding;

public static MainFragment newInstance() {
    return new MainFragment();
}

@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container,
                         @Nullable Bundle savedInstanceState) {
    mDataBinding = DataBindingUtil.inflate(getLayoutInflater(), R.layout.main_fragment, container, false);
    return mDataBinding.getRoot();
}

@Override
public void onActivityCreated(@Nullable Bundle savedInstanceState) {
    super.onActivityCreated(savedInstanceState);
    mViewModel = new ViewModelProvider(this).get(MainViewModel.class);

    mViewModel.getInfo().observe(getViewLifecycleOwner(), info -> {
        Toast.makeText(getActivity().getApplicationContext(), "First in", Toast.LENGTH_SHORT).show();

    });

    mDataBinding.radioButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            mViewModel.getInfo().setValue("Hello my friend");
        }
    });

    mDataBinding.setViewModel(mViewModel);
}
}

viewmodel:

public class MainViewModel extends ViewModel {

private MutableLiveData<String> info;

public MutableLiveData<String> getInfo() {
    if (info == null) {
        info = new MutableLiveData<>();
        info.setValue("First Info Initialization");
    }

    return info;
}

public void setInfo(String info) {
    this.info.setValue(info);
}

and view is something like:

    <layout>...
    <data>

        <variable
        name="viewModel"
        type="com.example.temp.ui.main.MainViewModel" />
    </data>

    <com.google.android.material.textfield.TextInputLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        style="@style/Widget.MaterialComponents.TextInputLayout.OutlinedBox">

        <com.google.android.material.textfield.TextInputEditText
            android:id="@+id/info"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:hint="Info"
            android:text="@={viewModel.info}" />
    </com.google.android.material.textfield.TextInputLayout>
    </layout>

I found the solution. The activity hosting the fragment was the one bound to the binding class lyfecycle. The solution updated on the problem above — mantc_sdr

AndroidSam27 AndroidSam27 · Accepted Answer · 2020-05-13T11:53:00

To use a LiveData object with your binding class, you need to specify a lifecycle owner to define the scope of the LiveData object.

// Specify the current activity as the lifecycle owner.
    binding.setLifecycleOwner(this);

android two-way Data Binding - data changes does not update UI views

3 Answers