How to work with back button in android with multiple fragment

How to work with back button in android with multiple fragment

When I was developing the Android application I found the very common issue. That was, how to manage back button navigation if I am using multiple fragments.
On some particular fragment, I want to show the back button but on some fragment, I don’t want to show the back button. Something like this and it may be varied as per your requirement. Here I am just considering a basic example with three fragments. I hope this example will surely help you with your problem. And this tutorial is completely written in Kotlin Language.

In this example I have Three fragment and one activity. Here I am taking navigation like – Fragment One -> Fragment Two -> Fragment Three. This is forward Navigation.

Now the Back-word navigation will be like Fragment Three -> Fragment One & Fragment Two -> Fragment One.

Code for MainActivity in Kotlin – MainActivity.kt

import android.annotation.SuppressLint
import android.os.Build
import android.os.Bundle
import android.os.Handler
import android.support.design.widget.Snackbar
import android.support.v7.app.AppCompatActivity
import android.view.MenuItem

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        supportFragmentManager.beginTransaction().replace(R.id.container, OneFragment()).commit()
    }

    override fun onOptionsItemSelected(item: MenuItem?): Boolean {
        onBackPressed()
        return super.onOptionsItemSelected(item)
    }

    private var doubleBackToExitPressedOnce = false
    @SuppressLint("ObsoleteSdkInt")
    override fun onBackPressed() {
        val f = supportFragmentManager.findFragmentById(R.id.container)
        when (f) {
            is OneFragment -> {
                if (doubleBackToExitPressedOnce) {
                    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN) {
                        finishAffinity()
                    } else {
                        finish()
                    }
                }
                this.doubleBackToExitPressedOnce = true
                setSnackBar("Please click BACK again to exit")
                Handler().postDelayed({ doubleBackToExitPressedOnce = false }, 2000)
            }
            is ThreeFragment -> supportFragmentManager.beginTransaction()
                .replace(R.id.container, OneFragment())
                .addToBackStack("tag").commit()
            else -> super.onBackPressed()
        }

    }

    private fun setSnackBar(message: String) {
        val snackBar = Snackbar.make(this.findViewById(android.R.id.content), message, Snackbar.LENGTH_LONG)
        snackBar.show()
    }
}

XML Of Main Activity! activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
    <android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".MainActivity">

        <FrameLayout
            android:id="@+id/container"
            android:layout_width="match_parent"
            android:layout_height="match_parent" />

    </android.support.constraint.ConstraintLayout>

Now I am writhing the code of OnCreate() of Fragment One! OneFragment.kt

private var rootView: View? = null
override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
): View? {
    // Inflate the layout for this fragment
    rootView = inflater.inflate(R.layout.fragment_one, container, false)


    if (activity != null) {
        (activity as MainActivity).title = "Fragment One"
    }
    if ((activity as MainActivity).supportActionBar != null) {
        val actionBar = (activity as MainActivity).supportActionBar
        actionBar!!.setDisplayHomeAsUpEnabled(false)
        actionBar.setHomeButtonEnabled(false)
    }
    val button: Button = rootView!!.findViewById(R.id.btnClick)
    button.setOnClickListener {
        activity!!.supportFragmentManager.beginTransaction().replace(R.id.container, TwoFragment()).addToBackStack("tag").commit()
    }

    return rootView
}

XML Of Fragment one! fragment_one.xml

<?xml version="1.0" encoding="utf-8"?>
    <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".OneFragment">

        <Button
            android:id="@+id/btnClick"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_centerHorizontal="true"
            android:layout_centerVertical="true"
            android:layout_margin="20dp"
            android:text="Fragment Two"
            android:textSize="17sp"
            android:textStyle="bold" />

    </RelativeLayout>

Code for Fragment Two OnCreate() in Kotlin – TwoFragment.kt

private var rootView: View? = null
override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
): View? {
    // Inflate the layout for this fragment
    rootView = inflater.inflate(R.layout.fragment_two, container, false)

    if (activity != null) {
        (activity as MainActivity).title = "Fragment Two"
    }
    if ((activity as MainActivity).supportActionBar != null) {
        val actionBar = (activity as MainActivity).supportActionBar
        actionBar!!.setDisplayHomeAsUpEnabled(true)
        actionBar.setHomeButtonEnabled(true)
    }

    val button = rootView!!.findViewById<Button>(R.id.btnClick)
    button.setOnClickListener {
        activity!!.supportFragmentManager.beginTransaction().replace(R.id.container, ThreeFragment()).addToBackStack("tag").commit()
    }
    return rootView
}

Xml of Fragment Two! fragment_two.xml

<?xml version="1.0" encoding="utf-8"?>
    <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".TwoFragment">

        <Button
            android:id="@+id/btnClick"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_centerHorizontal="true"
            android:layout_centerVertical="true"
            android:layout_margin="20dp"
            android:text="Fragment Three"
            android:textSize="17sp"
            android:textStyle="bold" />

    </RelativeLayout>

Code for Fragment Three OnCreate() in Kotlin – ThreeFragment.kt

private var rootView: View? = null
override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
): View? {
    // Inflate the layout for this fragment
    rootView = inflater.inflate(R.layout.fragment_three, container, false)

    if (activity != null) {
        (activity as MainActivity).title = "Fragment Three"
    }
    if ((activity as MainActivity).supportActionBar != null) {
        val actionBar = (activity as MainActivity).supportActionBar
        actionBar!!.setDisplayHomeAsUpEnabled(true)
        actionBar.setHomeButtonEnabled(true)
    }
    return rootView
}

Here Xml of Fragment Three is default.