如果 LazyColumn 为空，则将 LazyColumn 项目推送到屏幕末尾

Question

I want to add a footer to LazyColumn that only appears when all the items are scrolled, but if there are no items in the LazyColumn or no enough items to cover the whole screen, I want the footer to show at the bottom of the screen.

Since we cannot set weights in LazyColumn is there any other way to achieve this?

Answer 1

You can use the LazyListState#layoutInfo to know if the list is empty or if there is available space at the bottom.

val state = rememberLazyListState()

val isIniatialLoading by remember {
    derivedStateOf {
        state.layoutInfo.viewportSize  == IntSize.Zero
    }
}

//Empty list or empty space
val hasEmptySpace by remember {
    derivedStateOf {
        val layoutInfo = state.layoutInfo
        val visibleItemsInfo = layoutInfo.visibleItemsInfo
        if (layoutInfo.totalItemsCount == 0) {
            true
        } else {
            val lastVisibleItem = visibleItemsInfo.last()
            val viewportHeight = layoutInfo.viewportEndOffset + layoutInfo.viewportStartOffset
            
            (lastVisibleItem.index + 1 == layoutInfo.totalItemsCount &&
                    lastVisibleItem.offset + lastVisibleItem.size < viewportHeight)
        }
    }
}

Then wrap the LazyColumn with a Column and apply the weight modifier to the list.

Column(Modifier.fillMaxSize()) {

    LazyColumn(
        state = state,
        modifier = Modifier.weight(1f)
    ){
        items(itemsList) {
           //....
        }

        //Footer when the list covers the entire screen
        if (!hasEmptySpace){
            item(){
                //Footer()
            }
        }
    }
    
    // Display the Footer at the bottom of the screen if the list is empty or if there is an empty space
    if ( !isIniatialLoading && hasEmptySpace ){
       //Footer()
    }

}