Fragments In Android Kotlin

• Fragments Represent Reusable portion of your apps UI
•  Fragments are used to define and manage UI of a single screen or portion of screen.
• Fragments has it's own layout , Life cycle and can handle input events
• Fragments can not exist on its own it must be hosted by an Activity or another Fragment

Activities act as a frame that contains the fragment .Each fragment operates like a view in the activity but it has has it's own layout , Life cycle and can handle input events.

Activities are ideal place to put global elements around your app's UI like Navigation Drawer, Toolbar , Bottom Navigation and fragments are better suited to define UI of single screen or portion of screen. You can use multiple Fragments with single Activity ,  this gives more modularity and reusability to our code.

Add the following dependency in your app level build.gradle file to use fragments

implementation "androidx.fragment:fragment-ktx:1.3.6"

Now create a new fragment 

package com.arun.androidtutsforu.demofragment
import android.os.Bundle
import androidx.fragment.app.Fragment
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
class DemoFragment : Fragment() {
    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        return inflater.inflate(R.layout.fragment_demo, container, false)
    }
}

This is the layout of our fragment

<androidx.constraintlayout.widget.ConstraintLayout 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:id="@+id/frameLayout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".DemoFragment">
    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="This is a Fragment"
        android:textColor="#000000"
        android:textSize="24sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>

 Fragment can not exists on its own , it must be hosted by an Activity or another Fragment.

Add  Fragment to the Activity

<?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:orientation="vertical"
    tools:context=".MainActivity">
   <fragment
       android:id="@+id/demofragment"
       android:name="com.arun.androidtutsforu.demofragment.DemoFragment"
       android:layout_width="match_parent"
       android:layout_height="match_parent" />
</LinearLayout>

android:name="com.arun.androidtutsforu.demofragment.DemoFragment" --This should be fully-qualified  class name of the fragment

Following is the  MainActivity

package com.arun.androidtutsforu.demofragment
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
    }
}