android kotlin - Launch app programmatically

MainActivity.kt

package com.cfsuman.kotlinexamples

import android.content.Context
import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.widget.Toast
import kotlinx.android.synthetic.main.activity_main.*
import android.content.Intent


class MainActivity : AppCompatActivity() {

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

        // Package name of GMail app
        val packageName = "com.google.android.gm"

        // Click listener for button widget
        button.setOnClickListener{
            // Launch the app programmatically
            launchApp(packageName)
        }
    }


    // Custom method to launch an app
    private fun launchApp(packageName: String) {
        // Get an instance of PackageManager
        val pm = applicationContext.packageManager

        // Initialize a new Intent
        val intent:Intent? = pm.getLaunchIntentForPackage(packageName)

        // Add category to intent
        intent?.addCategory(Intent.CATEGORY_LAUNCHER)

        // If intent is not null then launch the app
        if(intent!=null){
            applicationContext.startActivity(intent)
        }else{
            toast("Intent null.")
        }
    }
}



// Extension function to show toast message
fun Context.toast(message: String) {
    Toast.makeText(this, message, Toast.LENGTH_SHORT).show()
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/root_layout"
    android:background="#bdd1b7"
    android:padding="16dp"
    android:orientation="vertical"
    >
    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Open Another App"
        android:layout_gravity="center_horizontal"
        />
</LinearLayout>