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Two-way DataBinding in Android

 3 years ago
source link: https://www.ravirupareliya.com/blog/two-way-databinding-in-android/
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Two-way DataBinding in Android

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In the earlier posts we have seen how to use DataBinding, Setting custom font and Image loading. Today we will discuss about two-way DataBinding.

What is Two-way DataBinding?

Till now we have seen how to set values to xml view, but in controls like EditText we need to fetch value. In simple term two-way DataBinding is setting values to that control and fetching it after having some changes.

ObservableField

ObservableField can be used instead of extending BaseObservable class. ObservableFields are self-contained observable objects that have a single field.

public class User
    public final ObservableField<String> userName =
            new ObservableField<>();
    public final ObservableField<String> password =
            new ObservableField<>();

There is no need to create getter setter methods when we are using ObservableFields. Now attach custom TextWatcher to get values of EditText control.

public TextWatcherAdapter userNameWatcher = new TextWatcherAdapter(userName);
public TextWatcherAdapter passwordWatcher = new TextWatcherAdapter(password);

TextWatcherAdapter is custom class which extends TextWatcher. It will be used to fetch updated value of EditText.

public class TextWatcherAdapter implements TextWatcher {
    public final ObservableField<String> value =
            new ObservableField<>();
    private final ObservableField<String> field;
    private boolean isInEditMode = false;
    public TextWatcherAdapter(ObservableField<String> f) {
        this.field = f;
        field.addOnPropertyChangedCallback(new Observable.OnPropertyChangedCallback(){
            @Override
            public void onPropertyChanged(Observable sender, int propertyId) {
                if (isInEditMode){
                    return;
                value.set(field.get());
    @Override
    public void onTextChanged(CharSequence s, int start, int before, int count) {
    @Override
    public void beforeTextChanged(CharSequence s, int start, int count, int after) {
    @Override public void afterTextChanged(Editable s) {
        if (!Objects.equals(field.get(), s.toString())) {
            isInEditMode = true;
            field.set(s.toString());
            isInEditMode = false;

Layout file is very simple for this, with 2 EditTexts and a button. We need to set addTextChangeListener to bind custom TextWatcher with EditText.

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools">
    <data>
        <variable
            name="user"
            type="com.androidgig.logindemo.Model.User"></variable>
        <variable
            name="handler"
            type="com.androidgig.logindemo.Handler.ClickHandler"></variable>
    </data>
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:gravity="center"
        android:padding="20dp"
        android:orientation="vertical">
        <EditText
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:hint="User name"
            android:singleLine="true"
            android:imeOptions="actionNext"
            android:addTextChangedListener="@{user.userNameWatcher}"/>
        <EditText
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:hint="Password"
            android:inputType="textPassword"
            android:singleLine="true"
            android:imeOptions="actionDone"
            android:layout_marginTop="10dp"
            android:addTextChangedListener="@{user.passwordWatcher}"/>
        <Button
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Login"
            android:layout_marginTop="20dp"
            android:onClick="@{handler.onClickLogin}"/>
    </LinearLayout>
</layout>

Here you have noticed handler.onClickLogin in a Button, that is nothing but an interface which we have binded to Button.

public interface ClickHandler {
    void onClickLogin(View view);

Finally we will write our Activity code to perform all the actions. Binding will be same as we have done earlier.

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    ActivityMainBinding binding= DataBindingUtil.setContentView(this, R.layout.activity_main);

we need to set Model/Pojo class to view and set handler for onClick event. Here is full code of our MainActivity.

public class MainActivity extends AppCompatActivity implements ClickHandler {
    ActivityMainBinding binding;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        binding= DataBindingUtil.setContentView(this, R.layout.activity_main);
        binding.setUser(new User());
        binding.setHandler(this);
    @Override
    public void onClickLogin(View view) {
        User user=binding.getUser();
        if(validate(user))
            Toast.makeText(MainActivity.this,"Hello " + user.userName.get() + " your password is : " + user.password.get(),Toast.LENGTH_SHORT).show();
    private boolean validate(User user)
        if(user.userName.get() == null || user.userName.get().trim().length()<=0)
            Toast.makeText(MainActivity.this,"Please enter username.",Toast.LENGTH_SHORT).show();
            return false;
        else if(user.password.get() == null || user.password.get().trim().length()<=0)
            Toast.makeText(MainActivity.this,"Please enter password.",Toast.LENGTH_SHORT).show();
            return false;
        return true;

With this you are done with your simple login screen using DataBinding.

two-way databinding

Download code

Update :

With the latest update of DataBinding announced in Google I/O16, you will be able to use Two-Way DataBinding with minimal number of code. You don’t need to write those listeners. Here is the thing you need to change in your xml file.

android:text="@={user.name}"

By adding = sign in your expression will support Two-Way DataBinding.

Ravi Rupareliya

He loves to explore new technologies and have worked on Android, React Native, Action on Google and Flutter.

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