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Simple example of using Fragments in Kotlin | Android

Here is the simple example of using Fragments with Activity in Android.

MainActivity.kt
  
class MainActivity : AppCompatActivity(), BlankFragment.OnFragmentInteractionListener {

    override fun onFragmentInteraction(uri: Uri) {
        TODO("not implemented") //To change body of created functions use File | Settings | File Templates.
    }

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

        if (savedInstanceState == null) {
            supportFragmentManager.beginTransaction().
                    add(R.id.fragment, BlankFragment.newInstance("Param1", "Param2"), "Second").commit()
        }

        fab.setOnClickListener { view ->
            //Here we will replace the BlanckFragment with SecondFragment.
            supportFragmentManager.beginTransaction().replace(R.id.fragment, SecondFragment(), "Second").commit()
        }
    }
}

activity_main.xml
  
<android.support.design.widget.CoordinatorLayout 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"
    tools:context="com.guna.kotlinapplication.MainActivity">

    <android.support.design.widget.AppBarLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:theme="@style/AppTheme.AppBarOverlay">

        <android.support.v7.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="?attr/colorPrimary"
            app:popupTheme="@style/AppTheme.PopupOverlay" />

    </android.support.design.widget.AppBarLayout>

    <include layout="@layout/content_main" />

    <android.support.design.widget.FloatingActionButton
        android:id="@+id/fab"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom|end"
        android:layout_margin="@dimen/fab_margin"
        app:srcCompat="@android:drawable/ic_dialog_email" />

</android.support.design.widget.CoordinatorLayout>

content_main.xml
  
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/fragment"
    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"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"
    tools:context="com.guna.kotlinapplication.MainActivity"
    tools:showIn="@layout/activity_main"/>

We can add static fragment like this. content_main.xml
  
<fragment xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/fragment"
    class="com.guna.kotlinapplication.BlankFragment"
    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"
    app:layout_behavior="@string/appbar_scrolling_view_behavior"
    tools:context="com.guna.kotlinapplication.MainActivity"
    tools:showIn="@layout/activity_main"/>

BlankFragment.kt 
 
/**
 * A simple [Fragment] subclass.
 * Activities that contain this fragment must implement the
 * [BlankFragment.OnFragmentInteractionListener] interface
 * to handle interaction events.
 * Use the [BlankFragment.newInstance] factory method to
 * create an instance of this fragment.
 */
class BlankFragment : Fragment() {

    // TODO: Rename and change types of parameters
    private var mParam1: String? = null
    private var mParam2: String? = null

    private var mListener: OnFragmentInteractionListener? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        if (arguments != null) {
            mParam1 = arguments!!.getString(ARG_PARAM1)
            mParam2 = arguments!!.getString(ARG_PARAM2)
        }
    }

    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
                              savedInstanceState: Bundle?): View? {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_blank, container, false)
    }

    // TODO: Rename method, update argument and hook method into UI event
    fun onButtonPressed(uri: Uri) {
        if (mListener != null) {
            mListener!!.onFragmentInteraction(uri)
        }
    }

    override fun onAttach(context: Context?) {
        super.onAttach(context)
        if (context is OnFragmentInteractionListener) {
            mListener = context
        } else {
            throw RuntimeException(context!!.toString() + " must implement OnFragmentInteractionListener")
        }
    }

    override fun onDetach() {
        super.onDetach()
        mListener = null
    }

    /**
     * This interface must be implemented by activities that contain this
     * fragment to allow an interaction in this fragment to be communicated
     * to the activity and potentially other fragments contained in that
     * activity.
     *
     *
     * See the Android Training lesson [Communicating with Other Fragments](http://developer.android.com/training/basics/fragments/communicating.html) for more information.
     */
    interface OnFragmentInteractionListener {
        // TODO: Update argument type and name
        fun onFragmentInteraction(uri: Uri)
    }

    companion object {
        // TODO: Rename parameter arguments, choose names that match
        // the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
        private val ARG_PARAM1 = "param1"
        private val ARG_PARAM2 = "param2"

        /**
         * Use this factory method to create a new instance of
         * this fragment using the provided parameters.
         *
         * @param param1 Parameter 1.
         * @param param2 Parameter 2.
         * @return A new instance of fragment BlankFragment.
         */
        // TODO: Rename and change types and number of parameters
        fun newInstance(param1: String, param2: String): BlankFragment {
            val fragment = BlankFragment()
            val args = Bundle()
            args.putString(ARG_PARAM1, param1)
            args.putString(ARG_PARAM2, param2)
            fragment.arguments = args
            return fragment
        }
    }
}// Required empty public constructor

fragment_blank.xml
  
<FrameLayout 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"
    android:background="@color/colorPrimary"
    tools:context="com.guna.kotlinapplication.BlankFragment">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:text="@string/hello_blank_fragment"
        android:textColor="#fff" />

</FrameLayout>

SecondFragment.kt 
 
/**
 * A simple [Fragment] subclass.
 */
class SecondFragment : Fragment() {


    override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
                              savedInstanceState: Bundle?): View? {
        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.fragment_second, container, false)
    }

}// Required empty public constructor

fragment_second.xml
  
<FrameLayout 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"
    android:background="#567891"
    tools:context="com.guna.kotlinapplication.SecondFragment">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:text="@string/hello_blank_fragment"
        android:textColor="#fff" />

</FrameLayout>


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