How to databind to onTextChanged for an EditText on Android?

To extend @Nilzors answer, it is also possible to pass text and/or other parameters in the layout:

View:

<EditText
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/username"
    android:text="Enter username:"
    android:onTextChanged="@{(text, start, before, count) -> viewModel.onUsernameTextChanged(text)}" />

ViewModel:

public void onUsernameTextChanged(CharSequence text) {
    // TODO do something with text
}

You always need to pass either zero or all parameters.

Actually it works out of the box. I think my mistake was using an old version of the data binding framework. Using the latest, this is the procedure:

View:

<EditText
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/username"
    android:text="Enter username:"
    android:onTextChanged="@{data.onTextChanged}" />

Model:

public void onTextChanged(CharSequence s, int start, int before, int count) {
    Log.w("tag", "onTextChanged " + s);
}

Make also sure that you have assigned model into DataBinding

For ex. in your activity

lateinit var activityMainDataBinding: ActivityMainBinding

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    activityMainDataBinding = DataBindingUtil.setContentView(this, R.layout.activity_main) 
    val dataViewModel = ViewModelProvider(this).get(DataViewModel::class.java)
    activityMainDataBinding.dataModel = dataViewModel
}

Make sure you are referncing gradle build tools v1.5.0 or higher and have enabled databinding with android.dataBinding.enabled true in your build.gradle.

edit: Functioning demo project here. view. model.

The Easy Way

If you are using onTextChange() to update text in the model then you can use Two-way Binding directly.

<data>
    <variable
        name="user"
        type="com.package.User"/>
</data>

<EditText
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@={user.name}"/>

The model class will have a getter and setter:

public class User {
    private String name;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

Now the name in the model will be changed in realtime with user interaction. So using binding.getUser().getName() will get the latest text.

One-Way Binding will only gets updated when model value is changed. It does not update model back real time.

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

Two-Way Binding update model variable in real time with user input.

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

The ONLY difference is of = (equal sign) receives data changes to the property and listen to user updates at the same time.

If you just need text parameter after text has changed, you could use android:afterTextChanged binding adapter. for example:

android:afterTextChanged="@{(text) -> viewModel.onTextChange(text)}"

Then in your ViewModel just implement like this:

fun onTextChange(editable: Editable?) {
    Log.d("TAG","New text: ${editable.toString()}")
}

Furthermore, there is android:beforeTextChanged which used to know old text before text change event, usage is same as android:afterTextChanged.