Android Data Binding

With the introduction of Android M, one big change that’s come slightly less noticed is the introduction of Android Data Binding library. In this tutorial we’ll look into it’s need and implement it in our application.

Android Data Binding Overview

How many times have you seen that the activities/fragments code has numerous similar lines that just hookup the code with the XML markup? Unanimously, it’s the most boring work for a developer to do. Besides, it comes up with it’s own set of problems such as readability issues, increased time in debugging and having to keep a close eye on the annoying boilerplate code that can give rise to mistakes.

Thanks to the ButterKnife Library we’re able to use Annotations that reduces significant lines of code. But it still requires us to use @BindView or @InjectView and use findViewById for each view manually one by one.

The introduction of DataBinding Library with Android M is a blessing in disguise. It gives us the freedom to minimize the code for app logic that’s binding to the view. The DataBinding Library comes up with a mechanism where it auto generates the field names in our code from the respective view IDs. We’ll look into it shortly. First let’s jump onto the integration aspect.

Android Data Binding Integration

To integrate DataBinding make sure your gradle build bool version is 1.5 or above

dependencies {
        classpath 'com.android.tools.build:gradle:2.1.2'
    }

To enable data binding, add the following code in the app module’s build.gradle.

android {
    ...
    dataBinding {
        enabled = true
    }
}

Syncing the Gradle makes Data Binding available for our project. Let’s proceed onto it’s implementation.

Android Data Binding Project Structure

We’ll use an empty Android Studio project for our implementation as shown below.

The Layout

The earlier activity_main.xml layout we used to create looked like this:

<RelativeLayout android:layout_width="match_parent"
    android:layout_height="match_parent"

    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.journaldev.databinding.MainActivity"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:android="http://schemas.android.com/apk/res/android">

    <TextView
        android:id="@+id/tvHeading"
        android:layout_width="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_height="wrap_content"
        android:text="JournalDev.com" />


    <TextView
        android:id="@+id/tvSubHeading"
        android:layout_width="wrap_content"
        android:layout_below="@+id/tvHeading"
        android:layout_centerHorizontal="true"
        android:layout_height="wrap_content"
        android:text="Android Tutorials" />
</RelativeLayout>

To use Data Binding we need to add a layout as the root tag.

We’ve modified the activity_main.xml layout to include the layout tags as shown below.

<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools">

<RelativeLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.journaldev.databinding.MainActivity">

    <TextView
        android:id="@+id/tvHeading"
        android:layout_width="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_height="wrap_content"
        android:text="JournalDev.com" />


    <TextView
        android:id="@+id/tvSubHeading"
        android:layout_width="wrap_content"
        android:layout_below="@+id/tvHeading"
        android:layout_centerHorizontal="true"
        android:layout_height="wrap_content"
        android:text="Android Tutorials" />
</RelativeLayout>
</layout>

Note: You need to build your project once now so that the auto-generated field names from the layout are available in the MainActivity.java

Code

We’ll replace the default MainActivity.java with the following one to bring DataBinding into use.

package com.journaldev.databinding;

import android.databinding.DataBindingUtil;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;

import com.journaldev.databinding.databinding.ActivityMainBinding;


public class MainActivity extends AppCompatActivity {

    ActivityMainBinding binding;

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

        binding.tvHeading.setText("Welcome to JournalDev.com");
        binding.tvSubheading.setText("Welcome to this Android Tutorial on DataBinding");
    }
}

Few new things to note in the above code are:

• The ActivityMainBinding class is generated from the xml layout file and it’s named this way because the xml layout file name is turned into Upper CamelCase and appended with Binding
• We’re invoking the xml layout in the setContentView (this is a static method) by calling

  
  DataBindingUtil.setContentView(this, R.layout.activity_main)
  

• The IDs of the views of the xml layout get converted into camelCase field names too as it’s seen in the code above. As you can see it’s so easy to change the texts of the TextView widgets now

Note: If the ActivityMainBinding is not available even after building the project, try restarting Android Studio. It maybe because of the cache.

Few interesting Case Scenarios:

In the present layout we’ve defined the IDs in camelCase. What happens if you assign the same id as
android:id=”@+id/tv_Heading”?
Data Binding converts it into camelCase too and the field name remains the same.

What happens when the two IDs are like
android:id=”@+id/tvHeading” and android:id=”@+id/tv_Heading”?

Ideally DataBinding is smart enough and should convert the android:id=”@+id/tv_Heading” into tvHeading1 field name. But there is no surety. Also it can lead to confusion in tracking the field names with their respective IDs. Hence it’s recommended to stay with one type of naming convention. Ideally camelCase.

The output of the application is given below.

This is just the power of DataBinding in the app code logic. There’s much more to it than this. We’ll look at them in later tutorials. You can download the final Android DataBinding Project from the link below.