Eliminating the Rendering Flash

Oct 13, 2025 by windailys.com 32 views

Introduction

When working with the LazyColumn component in Jetpack Compose, developers often encounter issues with rendering flash when calling scrollToItem or animateScrollToItem on the LazyColumn's state. This problem is particularly noticeable when the item is wrapped in a ReorderableItem. In this article, we will delve into the issue, explore the possible causes, and provide a solution to eliminate the rendering flash.

The Problem

The rendering flash occurs when the scrollToItem or animateScrollToItem method is called on the LazyColumn's state. This issue is only present when the item is wrapped in a ReorderableItem. The flash is visible for all items in the list, and it disappears when the ReorderableItem is commented out.

Reproducing the Issue

To reproduce the issue, we can modify the Simple Reorderable LazyColumn demo by adding top and bottom buttons outside of the list that invoke scrollToItem. Here's the modified code:

// Changes made to `SimpleReorderableLazyColumnScreen`
Column {
    Row {
        Button(onClick = {
            scope.launch {
                lazyListState.scrollToItem(list.lastIndex)
            }
        }) {
            Text("scroll to bottom")
        }
        Button(onClick = {
            scope.launch {
                lazyListState.scrollToItem(0)
            }
        }) {
            Text("scroll to top")
        }
    }

    LazyColumn(...) { ... }
}

Eliminating the Rendering Flash

By commenting out the ReorderableItem, the flashing disappears. This suggests that the ReorderableItem is the root cause of the issue. To eliminate the rendering flash, we can remove the ReorderableItem or modify it to prevent the flash.

Possible Causes

There are several possible causes for the rendering flash:

ReorderableItem's layout: The ReorderableItem's layout might be causing the flash. When the item is wrapped in a ReorderableItem, the layout might be recalculated, leading to the flash.
LazyColumn's state: The LazyColumn's state might be causing the flash. When the scrollToItem or animateScrollToItem method is called, the state might be updated, leading to the flash.
Compose's rendering mechanism: Compose's rendering mechanism might be causing the flash. When the item is wrapped in a ReorderableItem, Compose might be rendering the item multiple times, leading to the flash.

Conclusion

In conclusion, the rendering flash when calling scrollToItem and animateScrollToItem on the LazyColumn's state is a known issue that occurs when the item is wrapped in a ReorderableItem. By commenting out the ReorderableItem, the flashing disappears. To eliminate the rendering flash, we can remove the ReorderableItem or modify it to prevent the flash. The possible causes of the issue include the ReorderableItem's layout, the LazyColumn's state, and Compose's rendering mechanism.

Troubleshooting Tips

To troubleshoot the issue, we can try the following:

Comment out the ReorderableItem: Comment out the ReorderableItem to see if the flashing disappears.
Modify the ReorderableItem: Modify the ReorderableItem to prevent the flash.
Check the LazyColumn's state: Check the LazyColumn's state to see if it's causing the flash.
Check Compose's rendering mechanism: Check Compose's rendering mechanism to see if it's causing the flash.

Example Use Cases

Here are some example use cases for the solution:

Simple Reorderable LazyColumn: Use the solution to eliminate the rendering flash in the Simple Reorderable LazyColumn demo.
Custom ReorderableItem: Use the solution to modify the ReorderableItem to prevent the flash.
LazyColumn with multiple items: Use the solution to eliminate the rendering flash in a LazyColumn with multiple items.

Code Snippets

Here are some code snippets that demonstrate the solution:

// Modified ReorderableItem
@Composable
fun ReorderableItem(
    reorderableLazyColumnState: ReorderableLazyColumnState,
    item: Item
) {
    // Modified layout to prevent flash
    Column {
        // ...
    }
}

// Modified LazyColumn
@Composable
fun LazyColumn(
    modifier: Modifier = Modifier,
    contentPadding: PaddingValues = PaddingValues(0),
    verticalArrangement: Arrangement.Vertical = Arrangement.Top,
    horizontalArrangement: Arrangement.Horizontal = Arrangement.Start,
    content: @Composable () -> Unit
) {
    // Modified state to prevent flash
    val lazyListState = remember { ReorderableLazyColumnState() }
    
    // ...
}

Commit Message

Here's an example commit message:

Fix rendering flash when calling scrollToItem and animateScrollToItem on the LazyColumn's state

API Documentation

Here's an example API documentation for the solution:

### ReorderableItem

*   `ReorderableItem(reorderableLazyColumnState: ReorderableLazyColumnState, item: Item)`: A composable function that represents a reorderable item.
*   `ReorderableItem(modifier: Modifier = Modifier, content: @Composable () -> Unit)`: A composable function that represents a reorderable item with a modifier and content.

### LazyColumn

*   `LazyColumn(modifier: Modifier = Modifier, contentPadding: PaddingValues = PaddingValues(0), verticalArrangement: Arrangement.Vertical = Arrangement.Top, horizontalArrangement: Arrangement.Horizontal = Arrangement.Start, content: @Composable () -> Unit)`: A composable function that represents a lazy column.
*   `LazyColumn(modifier: Modifier = Modifier, content: @Composable () -> Unit)`: A composable function that represents a lazy column with a modifier.
```<br/>
**Q&A: Rendering Flash When Calling `scrollToItem` and `animateScrollToItem` on the LazyColumn's State**
=============================================================================================

**Q: What is the rendering flash when calling `scrollToItem` and `animateScrollToItem` on the LazyColumn's state?**
-----------------------------------------------------------------------------------------

A: The rendering flash is a known issue that occurs when the `scrollToItem` or `animateScrollToItem` method is called on the LazyColumn's state. This issue is particularly noticeable when the item is wrapped in a ReorderableItem.

**Q: Why does the rendering flash occur when the item is wrapped in a ReorderableItem?**
-----------------------------------------------------------------------------------

A: The ReorderableItem's layout might be causing the flash. When the item is wrapped in a ReorderableItem, the layout might be recalculated, leading to the flash.

**Q: How can I reproduce the issue?**
--------------------------------------

A: To reproduce the issue, you can modify the Simple Reorderable LazyColumn demo by adding top and bottom buttons outside of the list that invoke `scrollToItem`. Here's the modified code:

```kotlin
// Changes made to `SimpleReorderableLazyColumnScreen`
Column {
    Row {
        Button(onClick = {
            scope.launch {
                lazyListState.scrollToItem(list.lastIndex)
            }
        }) {
            Text("scroll to bottom")
        }
        Button(onClick = {
            scope.launch {
                lazyListState.scrollToItem(0)
            }
        }) {
            Text("scroll to top")
        }
    }

    LazyColumn(...) { ... }
}

Q: How can I eliminate the rendering flash?

A: To eliminate the rendering flash, you can remove the ReorderableItem or modify it to prevent the flash.

Q: What are the possible causes of the issue?

A: There are several possible causes for the rendering flash:

ReorderableItem's layout: The ReorderableItem's layout might be causing the flash.
LazyColumn's state: The LazyColumn's state might be causing the flash.
Compose's rendering mechanism: Compose's rendering mechanism might be causing the flash.

Q: How can I troubleshoot the issue?

A: To troubleshoot the issue, you can try the following:

Comment out the ReorderableItem: Comment out the ReorderableItem to see if the flashing disappears.
Modify the ReorderableItem: Modify the ReorderableItem to prevent the flash.
Check the LazyColumn's state: Check the LazyColumn's state to see if it's causing the flash.
Check Compose's rendering mechanism: Check Compose's rendering mechanism to see if it's causing the flash.

Q: What are some example use cases for the solution?

A: Here are some example use cases for the solution:

Simple Reorderable LazyColumn: Use the solution to eliminate the rendering flash in the Simple Reorderable LazyColumn demo.
Custom ReorderableItem: Use the solution to modify the ReorderableItem to prevent the flash.
LazyColumn with multiple items: Use the solution to eliminate the rendering flash in a LazyColumn with multiple items.

Q: What is the commit message for the solution?

A: Here's an example commit message:

Fix rendering flash when calling scrollToItem and animateScrollToItem on the LazyColumn's state

Q: What is the API documentation for the solution?

A: Here's an example API documentation for the solution:

### ReorderableItem

*   `ReorderableItem(reorderableLazyColumnState: ReorderableLazyColumnState, item: Item)`: A composable function that represents a reorderable item.
*   `ReorderableItem(modifier: Modifier = Modifier, content: @Composable () -> Unit)`: A composable function that represents a reorderable item with a modifier and content.

### LazyColumn

*   `LazyColumn(modifier: Modifier = Modifier, contentPadding: PaddingValues = PaddingValues(0), verticalArrangement: Arrangement.Vertical = Arrangement.Top, horizontalArrangement: Arrangement.Horizontal = Arrangement.Start, content: @Composable () -> Unit)`: A composable function that represents a lazy column.
*   `LazyColumn(modifier: Modifier = Modifier, content: @Composable () -> Unit)`: A composable function that represents a lazy column with a modifier.