#StackBounty: #android #scroll #android-recyclerview #interpolation Why doesn't smooth scroll of RecyclerView work well with some I…

Bounty: 200

Background

In an effort to make a nice&short overview of the items on a horizontal RecyclerView, we want to have a bounce-like animation , that starts from some position, and goes to the beginning of the RecyclerView (say, from item 3 to item 0) .

The problem

For some reason, all Interpolator classes I try (illustration available here) don’t seem to allow items to go outside of the RecyclerView or bounce on it.

More specifically, I’ve tried OvershootInterpolator , BounceInterpolator and some other similar ones. I even tried AnticipateOvershootInterpolator. In most cases, it does a simple scrolling, without the special effect. on AnticipateOvershootInterpolator , it doesn’t even scroll…

What I’ve tried

Here’s the code of the POC I’ve made, to show the issue:

MainActivity.kt

class MainActivity : AppCompatActivity() {
    val handler = Handler()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        val itemSize = resources.getDimensionPixelSize(R.dimen.list_item_size)
        val itemsCount = 6
        recyclerView.adapter = object : RecyclerView.Adapter<RecyclerView.ViewHolder>() {
            override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecyclerView.ViewHolder {
                val imageView = ImageView(this@MainActivity)
                imageView.setImageResource(android.R.drawable.sym_def_app_icon)
                imageView.layoutParams = RecyclerView.LayoutParams(itemSize, itemSize)
                return object : RecyclerView.ViewHolder(imageView) {}
            }

            override fun getItemCount(): Int = itemsCount

            override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {
            }
        }
        val itemToGoTo = Math.min(3, itemsCount - 1)
        val scrollValue = itemSize * itemToGoTo
        recyclerView.post {
            recyclerView.scrollBy(scrollValue, 0)
            handler.postDelayed({
                recyclerView.smoothScrollBy(-scrollValue, 0, BounceInterpolator())
            }, 500L)
        }
    }
}

activity_main.xml

<androidx.recyclerview.widget.RecyclerView
    android:id="@+id/recyclerView" xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto" android:layout_width="match_parent"
    android:layout_height="@dimen/list_item_size" android:orientation="horizontal"
    app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"/>

gradle file

apply plugin: 'com.android.application'
apply plugin: 'kotlin-android'
apply plugin: 'kotlin-android-extensions'

android {
    compileSdkVersion 28
    defaultConfig {
        applicationId "com.example.myapplication"
        minSdkVersion 15
        targetSdkVersion 28
        versionCode 1
        versionName "1.0"
        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
    }
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation"org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
    implementation 'androidx.appcompat:appcompat:1.0.0-rc02'
    implementation 'androidx.core:core-ktx:1.0.0-rc02'
    implementation 'androidx.constraintlayout:constraintlayout:1.1.2'
    implementation 'androidx.recyclerview:recyclerview:1.0.0-rc02'
}

And here’s an animation of how it looks for BounceInterpolator , which as you can see doesn’t bounce at all :

enter image description here

Sample POC project available here

The question

Why doesn’t it work as expected, and how can I fix it?

Could RecyclerView work well with Interpolator for scrolling ?


EDIT: seems it’s a bug, as I can’t use any “interesting” interpolator for RecyclerView scrolling, so I’ve reported about it here .


Get this bounty!!!

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