This article is based on the official Google documentation on two-way data binding, with a few modifications to address common challenges when implementing two-way binding for int fields.

Two-way data binding in Android allows UI elements like EditText to reflect and update the underlying model seamlessly. However, handling fields such as int can be tricky. This guide walks you through creating a two-way data binding converter for int fields.

Why Do We Need a Converter?

By default, two-way data binding in Android can bind String values easily. However, for types like int, a converter is required to convert the integer to a string (for display) and back to an integer (when user input is received). This is where two-way converters come into play.

Step 1: Create the Converter Class

First, you need to create a Converter class that will contain the logic for converting between an int and a String.

In the Google documentation, you might find examples with three parameters. However, in practice, using one parameter might work better for simple integer conversion, as described below.

package com.example.recordshop.util;

import androidx.databinding.InverseMethod;

public class Converter {

    // Converts integer to string for display in the EditText
    **@InverseMethod("stringToInt")**
    public static String intToString(int value) {
        // If the value is 0 (default), return an empty string
        return value == 0 ? "" : String.valueOf(value);
    }

    // Converts string input back to integer when user types into the EditText
    public static int stringToInt(String value) {
        try {
            // Try to parse the string to an integer, default to 0 if it's empty or invalid
            return value.isEmpty() ? 0 : Integer.parseInt(value);
        } catch (NumberFormatException e) {
            return 0; // Default value on error
        }
    }
}

Here’s how the two methods work:

• intToString: Converts the integer into a String and returns an empty string when the value is 0, which prevents EditText from displaying "0" by default.
• stringToInt: Converts the String input back to an integer. If the input is empty, it defaults to 0.

Step 2: Add the Converter to the XML Layout

Once the Converter class is set up, you need to import it into your XML layout where two-way data binding is applied.

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="<http://schemas.android.com/apk/res/android>"
    xmlns:app="<http://schemas.android.com/apk/res-auto>"
    xmlns:tools="<http://schemas.android.com/tools>">

    <data>
        <!-- Import the Converter class -->
        **<import type="com.example.recordshop.util.Converter" />**

        <!-- Variable for the album object -->
        <variable
            name="album"
            type="com.example.recordshop.model.Album" />
    </data>

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".ui.addnewalbum.AddNewAlbumActivity">

        <EditText
            android:id="@+id/albumReleaseYear"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:hint="Release Year"
            android:inputType="number"
            **android:text="@={Converter.intToString(album.releaseYear)}"**
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent" />
    </androidx.constraintlayout.widget.ConstraintLayout>
</layout>

Key Points:

• We import the Converter class using <import type="com.example.recordshop.util.Converter" />. This ensures that the converter methods can be used in the layout.
• The EditText field for album.releaseYear uses the two-way binding expression: @={Converter.intToString(album.releaseYear)}. This binds the releaseYear property from the Album model to the EditText and converts the value using the Converter methods.

Step 3: Inverse Method Annotation

The @InverseMethod annotation is crucial for enabling two-way data binding. It specifies which method is the inverse of the current one.

In the Converter class, we use: