How to use button to slide between pages in Kotlin ViewPager

In this android kotlin source code example, we are going to use button to slide between pages in Kotlin ViewPager.

You can copy and adopt this source code example to your Kotlin android project without reinventing the wheel.

Below is a step by step source code to use button to slide between pages in Kotlin ViewPager.

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<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:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".ViewPager.ViewPagerActivity6">

    <androidx.viewpager.widget.ViewPager
        android:id="@+id/viewpager"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        app:layout_constraintBottom_toTopOf="@id/slideButton"
        app:layout_constraintTop_toTopOf="parent"/>

    <androidx.appcompat.widget.AppCompatButton
        android:id="@+id/slideButton"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Slide ViewPager"
        android:textColor="@color/white"
        android:background="@color/colorAccent"
        app:layout_constraintBottom_toBottomOf="parent"/>

</androidx.constraintlayout.widget.ConstraintLayout>

MainActivity.kt

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import androidx.appcompat.widget.AppCompatButton
import androidx.fragment.app.Fragment
import androidx.fragment.app.FragmentManager
import androidx.fragment.app.FragmentPagerAdapter
import androidx.viewpager.widget.ViewPager
import com.bluapp.kotlinview.R

class ViewPagerActivity6 : AppCompatActivity() {
    private var viewPager: ViewPager? = null
    private var slideButton: AppCompatButton? = null
    private var currentViewPager = 0
    private val int_items = 5

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_view_pager6)
        viewPager = findViewById(R.id.viewpager) as ViewPager
        slideButton = findViewById(R.id.slideButton) as AppCompatButton
        viewPager!!.adapter = MyAdapter(supportFragmentManager)
        slideButton!!.setOnClickListener {
            if(currentViewPager == int_items){
                currentViewPager = 0
            }
            viewPager!!.setCurrentItem(currentViewPager++, true)
        }
        viewPager!!.addOnPageChangeListener(object : ViewPager.OnPageChangeListener{
            override fun onPageSelected(position: Int) {
                currentViewPager = position
            }

            override fun onPageScrolled(position: Int, positionOffset: Float, positionOffsetPixels: Int) {
            }

            override fun onPageScrollStateChanged(state: Int) {

            }
        })
    }

    private inner class MyAdapter(fm: FragmentManager?) : FragmentPagerAdapter(fm!!, FragmentPagerAdapter.BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT) {

        override fun getItem(position: Int): Fragment {
            var fragment: Fragment? = null
            when (position) {
                0 -> fragment = ViewPagerFragment()
                1 -> fragment = ViewPagerFragment()
                2 -> fragment = ViewPagerFragment()
                3 -> fragment = ViewPagerFragment()
                4 -> fragment = ViewPagerFragment()
            }
            return fragment!!
        }

        override fun getCount(): Int {
            return int_items
        }
    }
}

fragment_view_pager.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.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"
    android:background="#000000"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    tools:context=".ViewPager.ViewPagerFragment">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="ViewPagerFragment"
        android:textSize="20sp"
        android:textColor="@color/white"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintBottom_toBottomOf="parent"/>

</androidx.constraintlayout.widget.ConstraintLayout>

ViewPagerFragment.kt

import android.os.Bundle
import androidx.fragment.app.Fragment
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import com.bluapp.kotlinview.R

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

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