Kotlin Android Extensions

Kotlin Android Extensions is an important Kotlin plugin that is similar to Butterknife. It will allow to recover views in android.

Implementation

Add the following plugins in your app level build.gradle file

apply plugin:'com.android.application'
apply plugin:'kotlin-android'
apply plugin:'kotlin-android-extensions'

Coding Part

Create a new layout file in res folder, name it as activity_main.xml and paste the following codes

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="center"
    android:orientation="vertical"
    tools:context="com.androidmads.kotlinsample_helloworld.MainActivity">

    <TextView
        android:id="@+id/helloTxtView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Hello World!" />

    <TextView
        android:id="@+id/helloAndroidExtension"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="10dp"
        android:text="Hello World!" />

    <ImageView
        android:id="@+id/imageView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="10dp"
        app:srcCompat="@mipmap/ic_launcher" />

</LinearLayout>

Create a new Kotlin file and name it as MainActivity.kt Import the following line, which is used to recover the views in android.

import kotlinx.android.synthetic.main.activity_main.*;

The following code refers that how to use Kotlin Extension. Here helloAndroidExtension is the Id of the textview and click listener for this textview is done as in below code

// Hello Program for Kotlin Android Extension 
// helloAndroidExtension is the id of the TextView
helloAndroidExtension.text = "Example for Kotlin Android Extension";

We can apply the same Approach with imageview by assigning ImageSource from Drawable folder and see the code below.

imageView.setImageResource(R.mipmap.ic_launcher_round)

Full Code

The following shows, how to use Kotlin Android extensions

package com.androidmads.kotlinsample_helloworld

import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.widget.TextView
import android.widget.Toast
import kotlinx.android.synthetic.main.activity_main.*;

class MainActivity : AppCompatActivity() {

    // Declaration
    var helloTextView: TextView? = null

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

        // Initialization
        helloTextView = findViewById(R.id.helloTxtView) as TextView
        // Assigning data to TextView in runtime
        helloTextView!!.text = "Hello Kotlin!";

        // Click Listener in Kotlin
        helloTextView!!.setOnClickListener({
            Toast.makeText(applicationContext, "Hello TextView Clicked",
                    Toast.LENGTH_LONG).show();
        })

        // Hello Program for Kotlin Android Extension
        helloAndroidExtension.text = "Example for Kotlin Android Extension";

        imageView.setImageResource(R.mipmap.ic_launcher_round)
    }
}

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