Android - DataBinding - How and when the Binding classes will be generated?

Question

DataBinding Guide States

  By default, a Binding class will be generated based on the name of the layout 
file, converting it to Pascal case and suffixing “Bindi         


        

Answer 1

Try to rename layout to main_activity.xml.

In my case, it didn't work to generate binding class for "activity_main.xml".
But renaming the layout file to main_activity.xml worked just fine.

Answer 2

Did you update your layout file for data binding? They are generated only for layouts which have data binding.

It has to start with a layout tag which has 2 child tags (data & your root view).

Something like this:

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android">
   <data>
       <variable name="user" type="com.example.User"/>
   </data>
   <LinearLayout ...
   </LinearLayout>
</layout>

When your layout has this form, AndroidStudio should auto complete the class. Also, by default, it is generated in <your.app.package>.databinding package.

Answer 3

A weird "bug" in android-studio causes the generated BR.java file not to use the @Bindable fields and still only have the _all property if a res/layout directory doesn't exist.

It happened to me when I wanted to create a "No Activity" App to have a library that contained my different bindable data.

Answer 4

If you don't want to restart android studio, one way is to rename activity_main.xml to something else e.g activity_m.xml and then rename it back to activity_main.xml. It is much faster than restarting android studio.

To rename, right click on activity_main.xml and choose Refactor => Rename

Answer 5

I ran into a similar issue that hasn't been mentioned here yet. In my case, I incorrectly added <Layout> as the tag versus <layout>. <Layout> is apparently a valid tag because Android Studio didn't complain (other than requiring layout_width and layout_height which aren't required for <layout>). The capitalization difference will manifest in similar behavior where you cannot import the databinding class (import com.example.android.aboutme.databinding.ActivityMainBinding in my case) in the MainActivity class even though <Layout> is a valid tag and the build.gradle file is defined properly to support data binding.

In my case, I did not need the <data> tags defined yet in order for ActivityMainBinding to validly import and be referenced in:

private lateinit var binding: ActivityMainBinding

I was working through the this codelab when I ran into this behavior: https://developer.android.com/codelabs/kotlin-android-training-data-binding-basics/index.html

Answer 6

What is your layout name?

The above layout file was activity_main.xml so the generate class was ActivityMainBinding.

What this means is that the generated class name will depend on your layout's name

activity_main.xml -> ActivityMainBinding.java

I think your activity name is "main_activity", so the generated binding class name should be MainActivityBinding not ActivityMainBinding