How to use itemAfter or itemBefore in PagingSource LoadResult Page Paging 3

Hey I am working on unlimited data with Viewpager 2 and Paging 3 library. I successfully created the logic to create unlimited pages by the help of paging source. I am swiping single pages by buttons in both direction.

Video Link to watch :- Youtube Video

Github Source: - ViewPager Repository

Problem what I am getting

When i click slowly on previous button it swipe single page, but if i click quickly multiple times on previous button it start scrolling more than we click and it's not stopping until we click on viewpager. It's kind of race condition.

I asked in issue tracker, they suggested me to use itemBefore and itemAfter IssueTracker. I implemented this, but i failed to achieve good outcome.

MainActivity.kt

package com.example.viewpagerexample

import android.os.Bundle
import androidx.activity.viewModels
import androidx.appcompat.app.AppCompatActivity
import androidx.lifecycle.lifecycleScope
import com.example.viewpagerexample.databinding.ActivityMainBinding
import kotlinx.coroutines.flow.collectLatest
import kotlinx.coroutines.launch

class MainActivity : AppCompatActivity() {

    private val viewModel by viewModels<ViewPagerViewModel>()
    private lateinit var binding : ActivityMainBinding

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        binding = ActivityMainBinding.inflate(layoutInflater)
        setContentView(binding.root)

        val adapter = ViewPagerAdapter()
        lifecycleScope.launch {
            viewModel.dataList.collectLatest {
                adapter.submitData(it)
            }
        }
        binding.viewpager.adapter = adapter

        binding.next.setOnClickListener {
            binding.viewpager.setCurrentItem(binding.viewpager.currentItem.plus(1), true)
        }

        binding.previous.setOnClickListener {
            binding.viewpager.setCurrentItem(binding.viewpager.currentItem.minus(1), true)
        }
    }
}

ViewPagerDataSource.kt

package com.example.viewpagerexample

import android.util.Log
import java.util.*

class ViewPagerDataSource(
    private val pageSize: Int,
    private val currentDate: Date
) {
    fun loadDataSource(pageNumber: Int): List<Date> {
        val dates = mutableListOf<Date>()
        val startingDate = startingDate(pageNumber)
        val tempCalendar = Calendar.getInstance()
        tempCalendar.time = startingDate

        Log.e("loadData startingDate", "" + startingDate)

        var index = 0;
        while (index++ < pageSize) {
            dates.add(tempCalendar.time)
            tempCalendar.add(Calendar.DATE, 1)
        }
        return dates
    }

    private fun startingDate(pageNumber: Int): Date {
        Calendar.getInstance().let {
            it.time = currentDate
            it.add(Calendar.DATE, (pageNumber * pageSize) + pageSize)
            return it.time
        }
    }
}

ViewPagerPagingSource.kt

This is my paging source and i don't get how to use itembefore and itemAfter in my condition. Also I didn't get getRefreshKey what is the use of this? If i pass null is it fine for that or what else do I need to pass.

package com.example.viewpagerexample

import androidx.paging.PagingSource
import androidx.paging.PagingState
import java.io.IOException
import java.util.*

class ViewPagerPagingSource(
    private val dataSource: ViewPagerDataSource
) : PagingSource<Int, Date>() {

    override suspend fun load(params: LoadParams<Int>): LoadResult<Int, Date> {
        val position = params.key ?: 0

        return try {
            val data = dataSource.loadDataSource(position)
            LoadResult.Page(
                data = data,
                prevKey = if (data.isEmpty()) null else position - 1,
                nextKey = if (data.isEmpty()) null else position + 1,
                itemsBefore = LoadResult.Page.COUNT_UNDEFINED,
                itemsAfter = LoadResult.Page.COUNT_UNDEFINED
            )
        } catch (exception: IOException) {
            LoadResult.Error(exception)
        }
    }

    override fun getRefreshKey(state: PagingState<Int, Date>): Int? {
        return null
    }
}

ViewPagerViewModel.kt

package com.example.viewpagerexample

import android.app.Application
import androidx.lifecycle.AndroidViewModel
import androidx.paging.Pager
import androidx.paging.PagingConfig
import java.util.*

class ViewPagerViewModel(app: Application) : AndroidViewModel(app) {

    private val dataSource = ViewPagerDataSource(10, currentDate())

    val dataList =
        Pager(config = PagingConfig(
            pageSize = 10,
            enablePlaceholders = true
        ), pagingSourceFactory = {
            ViewPagerPagingSource(dataSource)
        }).flow

    private fun currentDate(): Date {
        val calendar = Calendar.getInstance()
        return calendar.time
    }
}

Adapter and Holder are attached in Github Link please find if you need them.

build.Gradle

plugins {
    id 'com.android.application'
    id 'kotlin-android'
    id 'kotlin-kapt'
}

android {
    compileSdkVersion 30
    buildToolsVersion "30.0.3"

    defaultConfig {
        applicationId "com.example.viewpagerexample"
        minSdkVersion 16
        targetSdkVersion 30
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
    compileOptions {
        sourceCompatibility JavaVersion.VERSION_1_8
        targetCompatibility JavaVersion.VERSION_1_8
    }
    kotlinOptions {
        jvmTarget = '1.8'
    }
    buildFeatures {
        viewBinding true
    }
}

dependencies {

    implementation "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"
    implementation 'androidx.core:core-ktx:1.6.0'
    implementation 'androidx.appcompat:appcompat:1.3.1'
    implementation 'com.google.android.material:material:1.4.0'
    implementation 'androidx.constraintlayout:constraintlayout:2.1.0'

    implementation "androidx.viewpager2:viewpager2:1.0.0"

    implementation "androidx.paging:paging-runtime-ktx:3.0.1"

    implementation "androidx.lifecycle:lifecycle-viewmodel-ktx:2.3.1"
    implementation "androidx.lifecycle:lifecycle-livedata-ktx:2.3.1"
    implementation "androidx.lifecycle:lifecycle-runtime-ktx:2.3.1"
    implementation "android.arch.lifecycle:extensions:1.1.1"
    implementation 'androidx.fragment:fragment-ktx:1.3.6'

    //noinspection GradleDynamicVersion
    testImplementation 'junit:junit:4.+'
    androidTestImplementation 'androidx.test.ext:junit:1.1.3'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.4.0'
}

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