Simple example of using ViewPager in Kotlin | Android

Though Kotlin has lot of massive features to speedup the development time, here is the simple example of using ViewPager in Android. In Kotlin we don't need to declare and initialize Views. We can simply access the id of Views from xml.

Ex:
activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<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:id="@+id/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.TabLayout
            android:id="@+id/tabs"
            android:layout_width="match_parent"
            android:layout_height="wrap_content" />
    </android.support.design.widget.AppBarLayout>

    <android.support.v4.view.ViewPager
        android:id="@+id/pager"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:layout_behavior="@string/appbar_scrolling_view_behavior" />
</android.support.design.widget.CoordinatorLayout>

MainActivity.kt

import android.os.Bundle
import android.support.v4.app.Fragment
import android.support.v4.app.FragmentManager
import android.support.v4.app.FragmentPagerAdapter
import android.support.v4.view.ViewPager
import android.support.v7.app.AppCompatActivity
import kotlinx.android.synthetic.main.activity_main.*

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

        setupViewPager(pager)
        tabs.setupWithViewPager(pager)
    }

    private fun setupViewPager(pager: ViewPager?) {
        val adapter = Adapter(supportFragmentManager)

        val f1 = BlankFragment.newInstance("One")
        adapter.addFragment(f1, "TAB 1")

        val f2 = BlankFragment.newInstance("Two")
        adapter.addFragment(f2, "TAB 2")

        val f3 = BlankFragment.newInstance("Three")
        adapter.addFragment(f3, "TAB 3")

        pager?.adapter = adapter
    }

    private class Adapter(manager: FragmentManager) : FragmentPagerAdapter(manager) {
        val fragments = ArrayList()
        val titles = ArrayList()
        override fun getItem(position: Int): Fragment = fragments.get(position)

        override fun getCount(): Int = fragments.size

        override fun getPageTitle(position: Int): CharSequence? = titles.get(position)

        fun addFragment(fragment: Fragment, title: String) {
            fragments.add(fragment)
            titles.add(title)
        }
    }
}

BlankFragment.kt

import android.os.Bundle
import android.support.v4.app.Fragment
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import kotlinx.android.synthetic.main.fragment_blank.view.*

class BlankFragment : Fragment() {
    var text = ""

    companion object {
        fun newInstance(text: String): BlankFragment {
            val fragment = BlankFragment()
            val bundle = Bundle()
            bundle.putString("Text", text)
            fragment.arguments = bundle
            return fragment
        }
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        text = arguments?.get("Text").toString()
    }

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

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        view.textView.setText(text)
    }
}

Did you noticed, we never declare pager nor initialized, instead we directly accessed it from activity_main.
In BlankFragment also, we didn't declare and initialize textView

And also, unless Java, default constructor will come with class name itself; like Adapter(manager: FragmentManager).

So, If you think this is the right time to start with Kotlin, then start alongside with your current project. Yes, you can use Java and Kotlin in same project. If your current Activity is java, don't worry, you can create your next Activity in kotlin. Or you can convert your current Activity also to Kotlin and then continue learning Kotlin in same Activity.

Here is the full video tutorial

Interesting right?

If you are really interested in this code, then please share this post with your friends.

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