LazyColumnFor is not smooth scrolling

user_10870164 0
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So, I have implemented a lazycolumnfor to work with a list of recipe elements, the thing is that it does not smooth scroll, if I just scroll fast it stutters till the last element appears and not smooth scroll.

Is this an error from my side or do I need to add something else?

    data class Recipe(
            @DrawableRes val imageResource: Int,
            val title: String,
            val ingredients: List<String>
    )
    
    val recipeList = listOf(
            Recipe(R.drawable.header,"Cake1", listOf("Cheese","Sugar","water")),
            Recipe(R.drawable.header,"Cake2", listOf("Cheese1","Sugar1","Vanilla")),
            Recipe(R.drawable.header,"Cake3", listOf("Bread","Sugar2","Apple")))
    
    class MainActivity : AppCompatActivity() {
        override fun onCreate(savedInstanceState: Bundle?) {
            super.onCreate(savedInstanceState)
            setContent {
                RecipeList(recipeList = recipeList)
            }
        }
    }
    
    @Composable
    fun RecipeCard(recipe:Recipe){
        val image = imageResource(R.drawable.header)
        Surface(shape = RoundedCornerShape(8.dp),elevation = 8.dp,modifier = Modifier.padding(8.dp)) {
            Column(modifier = Modifier.padding(16.dp)) {
                val imageModifier = Modifier.preferredHeight(150.dp).fillMaxWidth().clip(shape = RoundedCornerShape(8.dp))
                Image(asset = image,modifier = imageModifier,contentScale = ContentScale.Crop)
                Spacer(modifier = Modifier.preferredHeight(16.dp))
                Text(text = recipe.title,style = typography.h6)
                for(ingredient in recipe.ingredients){
                    Text(text = ingredient,style = typography.body2)
                }
            }
        }
    }
    
    @Composable
    fun RecipeList(recipeList:List<Recipe>){
        LazyColumnFor(items = recipeList) { item ->
            RecipeCard(recipe = item)
        }
    }

@Preview
@Composable
fun RecipePreview(){
    RecipeCard(recipeList[0])
}
android-jetpack-compose android-recyclerview kotlin android
2 Answers

Currently (version 1.0.0-alpha02) Jetpack Compose has 2 Composable functions for loading image resources:

  1. imageResource(): this Composable function, load an image resource synchronously.

  2. loadImageResource(): this function loads the image in a background thread, and once the loading finishes, recompose is scheduled and this function will return deferred image resource with LoadedResource or FailedResource

So your lazyColumn is not scrolling smoothly since you are loading images synchronously.

So you should either use loadImageResource() or a library named Accompanist by Chris Banes, which can fetch and display images from external sources, such as network, using the Coil image loading library.

UPDATE:

Using CoilImage :

First, add Accompanist Gradle dependency, then simply use CoilImage composable function:

    CoilImage(data = R.drawable.header)

Using loadImageResource() :

    val deferredImage = loadImageResource(
        id = R.drawable.header,
    )

    val imageModifier = Modifier.preferredHeight(150.dp).fillMaxWidth()
        .clip(shape = RoundedCornerShape(8.dp))
    deferredImage.resource.resource?.let {
        Image(
            asset = it,
            modifier = imageModifier
        )
    }

Note: I tried both ways in a LazyColumnFor, and although loadImageResource() performed better than imageResource() but still it didn't scroll smoothly.

So I highly recommend using CoilImage

Note 2: To use Glide or Picasso, check this repository by Vinay Gaba

user_56002560

On the other note, LazyColumn haven't been optimised for scrolling performance yet, but I've just tested on 1.0.0-beta07 release and can confirm it's way smoother than 1.0.0-beta06

Compose.UI 1.0.0-beta07 relevant change log:

LazyColumn/Row will now keep up to 2 previously visible items active (not disposed) even when they are scrolled out already. This allows the component to reuse the active subcompositions when we will need to compose a new item which improves the scrolling performance. (Ie5555)

user_73683350
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