Jetpack Compose LazyColumn 的 ItemDecoration 是什么？

Question

In JetpackCompose, we can use LazyColumnFor as RecyclerView .

In RecyclerView , to have a proper margin/padding between items, we need to use ItemDecoration , as per this article

Like below

class MarginItemDecoration(private val spaceHeight: Int) : RecyclerView.ItemDecoration() {
    override fun getItemOffsets(outRect: Rect, view: View,
                                parent: RecyclerView, state: RecyclerView.State) {
        with(outRect) {
            if (parent.getChildAdapterPosition(view) == 0) {
                top = spaceHeight
            }
            left =  spaceHeight
            right = spaceHeight
            bottom = spaceHeight
        }
    }
}

For JetpackCompose LazyColumnFor , what's the equivalent of ItemDecoration ?

Answer 1

With 1.0.0 (tested with 1.0.0-rc01 ) you can use Arrangement.spacedBy() to add spacing in-between items.

Something like:

LazyColumn(
    verticalArrangement = Arrangement.spacedBy(8.dp),
) {
    // ...
}

The example below adds 8.dp of space in-between each item

Before and after:

If you want to add padding around the edges of the content you can use the contentPadding parameter.

  LazyColumn(
        verticalArrangement = Arrangement.spacedBy(8.dp),
        contentPadding = PaddingValues(horizontal = 24.dp, vertical = 8.dp)
  ){ ...  }

In the example above, the first item will add 8.dp padding to it's top, the last item will add 8.dp to its bottom, and all items will have 24.dp padding on the left and the right.

Answer 2

You can use LazyColumn with itemsIndexed (formerly LazyColumnForIndexed , deprecated) and apply the padding depending on the index.

LazyColumn {
  itemsIndexed(items = ...) { index, item ->
    Box(Modifier.padding(
      start = 16.dp, end = 16.dp, bottom = 16.dp, top = if (index == 0) 16.dp else 0.dp
    ))
  }
}

Answer 3

I kind of workaround using contentPadding of LazyColumnFor for top, start and end padding, and Spacer as the bottom padding for all items.

@Composable
fun MyComposeList(
    modifier: Modifier = Modifier,
    listItems: List<String>,
) {
    LazyColumnFor(
        modifier = modifier, items = listItems,
        contentPadding = PaddingValues(16.dp, 16.dp, 16.dp)
    ) { itemText ->
        ViewItem(
            itemText = itemText
        )
        Spacer(modifier = Modifier.fillMaxWidth().height(16.dp))
    }
}

This seems to get the result I needed, as the contentPadding can be scrolled together within the LazyColumnFor

Answer 4

The tutorial comes from the code lab you should refer to for a good plan https://developer.android.com/codelabs/jetpack-compose-layouts?continue=https%3A%2F%2Fdeveloper.android.com%2Fcourses%2Fpathways%2Fjetpack-compose-for-android-developers-1%23codelab-https%3A%2F%2Fdeveloper.android.com%2Fcodelabs%2Fjetpack-compose-layouts#6

LazyRow(
    modifier = modifier.padding(top = 16.dp, bottom = 16.dp),
    horizontalArrangement = Arrangement.spacedBy(8.dp),
    contentPadding = PaddingValues(horizontal = 8.dp)
) {
    items(alignYourBodyData) { item ->
        AlignYourBodyElement(
            drawable = item.drawable,
            text = item.text
        )
    }
}