Kotlin Android - Unable to get @BindingAdapter to work

Question

I keep getting the binding error when trying to use the @BindingAdapter. Try for 3 days and follow numerous online articles on this subject, but still getting the below error.

@BindingAdapter("focusableColor")
fun setFocusableColor(v:CardView,  color:Int) {
    println("hello")
}

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
          super.onCreate(savedInstanceState)
          val binding:ActivityMainBinding  = 
              DataBindingUtil.setContentView(this,R.layout.activity_main)
          etc...
    }



In current_task_layout.xml

<layout xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:android="http://schemas.android.com/apk/res/android">
    <data>
            <variable name="task" type="com.edenhan.simplytask.Task">
            </variable>
    </data>

<android.support.v7.widget.CardView
  android:id="@+id/card_view">
  .....
  focusableColor="@{1}"/>

Error encountered:

Found data binding errors.

****/ data binding error ****msg:Cannot find the setter for attribute 'focusableColor' with parameter type int on android.support.v7.widget.CardView. file:D:\\…….\\app\\src\\main\\res\\layout\\current_task_layout.xml

Answer 1

Have you tried moving the binding out of the companion object? You should put it in a kotlin file and make it a top level function. For example:

Bindings.kt

@BindingAdapter("focusableColor")
fun setFocusableColor(v:CardView,  color:Int) {..}

And put the binding xml in the app namespace

Also, see Kotlin custom attribute databinding

edit: full example

MainActivity.kt

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
    }
}

@BindingAdapter("focusableColor")
fun setColor(card: CardView, @ColorInt color: Int) {
    // or whatever
    card.setBackgroundColor(color)
}

activity_main.xml

<?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"
    >
    <android.support.constraint.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".MainActivity">

        <android.support.v7.widget.CardView
            android:id="@+id/card"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            app:focusableColor="@{1}"/>
    </android.support.constraint.ConstraintLayout>
</layout>

Answer 2

Below defined full code for load image using BindingAdapter with Kotlin

ImageLoader.kt

import android.widget.ImageView
import androidx.databinding.BindingAdapter
import androidx.databinding.ObservableField

class ImageLoader {

    val imageResource = ObservableField(R.drawable.ic_launcher_background)

    companion object {
        @JvmStatic
        @BindingAdapter("android:src")
        fun setImage(imageView: ImageView, imageRes: Int) {
            imageView.setImageResource(imageRes)
        }
    }
}

activity_home.xml

<?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">
    <data>
        <variable name="imageLoader" type="com.sample.testdemo.ImageLoader"/>
    </data>
    <RelativeLayout
            android:orientation="vertical"
            android:layout_width="match_parent"
            android:layout_height="match_parent">

        <ImageView android:layout_width="wrap_content"
                   android:layout_height="wrap_content"
                   android:contentDescription="@string/app_name"
                   android:src="@{imageLoader.imageResource}"
                   android:layout_centerInParent="true"/>
    </RelativeLayout>
</layout>

HomeActivity.kt

import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity
import androidx.databinding.DataBindingUtil
import com.sample.testdemo.databinding.ActivityHomeBinding

class HomeActivity : AppCompatActivity() {

    lateinit var binding: ActivityHomeBinding

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        binding = DataBindingUtil.setContentView(this,  R.layout.activity_home)

        binding.imageLoader = ImageLoader()
    }
}

Note: Don't forget to add below line at the top of app level build.gradle

apply plugin: 'kotlin-kapt'