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Recycler View Like Google Play Store App | How to use SnapHelper Android, Kotlin

 If we see the google play store android app, we can see that the app list in horizontal recycler view hold a property that the first property hold always full visible or not visible, but a portion visible is not seeing.




This property is snap property. In this article I show you how to use it in our own application. Basically we use two type of snap. Center Snap and start snap. I show you both here. So read full article here.

The Key Moment code is here-

For center snap you need to write 2 lines code-

        //center Snap
        val snapHelper = LinearSnapHelper()
        snapHelper.attachToRecyclerView(recyclerView1)


For start snap, create a class in kotlin say StartSnapHelper.kt

package com.example.snaphelpersampleapp

import android.view.View
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.LinearSnapHelper
import androidx.recyclerview.widget.OrientationHelper
import androidx.recyclerview.widget.RecyclerView

class StartSnapHelper : LinearSnapHelper() {
    private var mVerticalHelper: OrientationHelper? = null
    private var mHorizontalHelper: OrientationHelper? = null
    @Throws(IllegalStateException::class)
    override fun attachToRecyclerView(recyclerView: RecyclerView?) {
        super.attachToRecyclerView(recyclerView)
    }

    override fun calculateDistanceToFinalSnap(
        layoutManager: RecyclerView.LayoutManager,
        targetView: View
    ): IntArray? {
        val out = IntArray(2)
        if (layoutManager.canScrollHorizontally()) {
            out[0] = distanceToStart(targetView, getHorizontalHelper(layoutManager))
        } else {
            out[0] = 0
        }
        if (layoutManager.canScrollVertically()) {
            out[1] = distanceToStart(targetView, getVerticalHelper(layoutManager))
        } else {
            out[1] = 0
        }
        return out
    }

    override fun findSnapView(layoutManager: RecyclerView.LayoutManager): View? {
        return if (layoutManager is LinearLayoutManager) {
            if (layoutManager.canScrollHorizontally()) {
                getStartView(layoutManager, getHorizontalHelper(layoutManager))
            } else {
                getStartView(layoutManager, getVerticalHelper(layoutManager))
            }
        } else super.findSnapView(layoutManager)
    }

    private fun distanceToStart(targetView: View, helper: OrientationHelper?): Int {
        return helper!!.getDecoratedStart(targetView) - helper.startAfterPadding
    }

    private fun getStartView(
        layoutManager: RecyclerView.LayoutManager,
        helper: OrientationHelper?
    ): View? {
        if (layoutManager is LinearLayoutManager) {
            val firstChild = layoutManager.findFirstVisibleItemPosition()
            val isLastItem = (layoutManager
                .findLastCompletelyVisibleItemPosition()
                    == layoutManager.getItemCount() - 1)
            if (firstChild == RecyclerView.NO_POSITION || isLastItem) {
                return null
            }
            val child = layoutManager.findViewByPosition(firstChild)
            return if (helper!!.getDecoratedEnd(child) >= helper.getDecoratedMeasurement(child) / 2
                && helper.getDecoratedEnd(child) > 0
            ) {
                child
            } else {
                if (layoutManager.findLastCompletelyVisibleItemPosition()
                    == layoutManager.getItemCount() - 1
                ) {
                    null
                } else {
                    layoutManager.findViewByPosition(firstChild + 1)
                }
            }
        }
        return super.findSnapView(layoutManager)
    }

    private fun getVerticalHelper(layoutManager: RecyclerView.LayoutManager): OrientationHelper? {
        if (mVerticalHelper == null) {
            mVerticalHelper = OrientationHelper.createVerticalHelper(layoutManager)
        }
        return mVerticalHelper
    }

    private fun getHorizontalHelper(layoutManager: RecyclerView.LayoutManager): OrientationHelper? {
        if (mHorizontalHelper == null) {
            mHorizontalHelper = OrientationHelper.createHorizontalHelper(layoutManager)
        }
        return mHorizontalHelper
    }
}


Now in your activity-

        //start snap
        val startSnapHelper = StartSnapHelper()
        startSnapHelper.attachToRecyclerView(recyclerView2)



Full Project Code-


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=".MainActivity">

    <TextView
        android:id="@+id/tvCenterSnap"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="10dp"
        android:text="Center Snap"
        android:layout_marginTop="135dp"
        android:textSize="16sp"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recyclerView1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"
        app:layout_constraintTop_toBottomOf="@id/tvCenterSnap"
        tools:listitem="@layout/rowview_snap" />

    <TextView
        android:id="@+id/tvStartSnap"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="10dp"
        android:text="Start Snap"
        android:textSize="16sp"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/recyclerView1" />

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recyclerView2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="horizontal"
        app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"
        app:layout_constraintTop_toBottomOf="@id/tvStartSnap"
        tools:listitem="@layout/rowview_snap" />

</androidx.constraintlayout.widget.ConstraintLayout>


rowview_snap.xml
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="260dp"
    android:layout_height="wrap_content"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:minHeight="160dp"
    android:background="@drawable/bg_rowview"
    android:layout_margin="5dp">


    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        android:text="Item 1"
        android:textSize="22sp"
        android:textColor="@color/white"
        android:textStyle="bold"/>





</androidx.constraintlayout.widget.ConstraintLayout>


bg_rowview.xml in drawable-

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle">

    <solid android:color="@color/teal_700" />
    <stroke
        android:width="1dp"
        android:color="#C3636363" />

    <corners android:radius="10dp" />

</shape>


TestAdapter.kt
package com.example.snaphelpersampleapp

import android.annotation.SuppressLint
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.recyclerview.widget.RecyclerView
import kotlinx.android.synthetic.main.rowview_snap.view.*


class TestAdapter(private val list: ArrayList<String>) :
    RecyclerView.Adapter<TestAdapter.ViewHolder>() {

    //this method is returning the view for each item in the list
    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
        val v = LayoutInflater.from(parent.context)
            .inflate(R.layout.rowview_snap, parent, false)
        return ViewHolder(v)
    }

    //this method is binding the data on the list
    override fun onBindViewHolder(holder: ViewHolder, position: Int) {
        holder.bindItems(list[position], position)


    }

    //this method is giving the size of the list
    override fun getItemCount(): Int {
        return list.size
    }

    //the class is hodling the list view
    class ViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView) {

        @SuppressLint("SetTextI18n")
        fun bindItems(item: String, position: Int) {

            itemView.textView.text = "Item $position"

        }
    }

}


MainActivity.kt

package com.example.snaphelpersampleapp

import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.LinearSnapHelper
import kotlinx.android.synthetic.main.activity_main.*

class MainActivity : AppCompatActivity() {
    private val context = this

    private val list1 = ArrayList<String>()

    private val adapter1 = TestAdapter(list1)


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

        recyclerView1.layoutManager =
            LinearLayoutManager(context, LinearLayoutManager.HORIZONTAL, false)
        recyclerView1.adapter = adapter1

        recyclerView2.layoutManager =
            LinearLayoutManager(context, LinearLayoutManager.HORIZONTAL, false)
        recyclerView2.adapter = adapter1

        //center Snap
        val snapHelper = LinearSnapHelper()
        snapHelper.attachToRecyclerView(recyclerView1)

        //start snap
        val startSnapHelper = StartSnapHelper()
        startSnapHelper.attachToRecyclerView(recyclerView2)


        //set Temp data
        for (x in 0 until 10) {
            list1.add("Item")
        }
        adapter1.notifyDataSetChanged()


    }
}


Others Files-
strings.xml
<resources>
    <string name="app_name">Snap helper sample app</string>
</resources>


themes.xml

<resources xmlns:tools="http://schemas.android.com/tools">
    <!-- Base application theme. -->
    <style name="Theme.SnapHelperSampleApp" parent="Theme.MaterialComponents.DayNight.DarkActionBar">
        <!-- Primary brand color. -->
        <item name="colorPrimary">@color/purple_500</item>
        <item name="colorPrimaryVariant">@color/purple_700</item>
        <item name="colorOnPrimary">@color/white</item>
        <!-- Secondary brand color. -->
        <item name="colorSecondary">@color/teal_200</item>
        <item name="colorSecondaryVariant">@color/teal_700</item>
        <item name="colorOnSecondary">@color/black</item>
        <!-- Status bar color. -->
        <item name="android:statusBarColor" tools:targetApi="l">?attr/colorPrimaryVariant</item>
        <!-- Customize your theme here. -->
    </style>

    <style name="AppTheme" parent="Theme.AppCompat.Light.NoActionBar">
        <!-- Customize your theme here. -->
        <item name="colorAccent">@color/purple_500</item>
        <item name="colorPrimary">@color/purple_500</item>
        <item name="colorPrimaryDark">@color/purple_500</item>
    </style>

</resources>

AndroidManifest.xml   
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.snaphelpersampleapp">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>



See the output in this video-








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