Compose LazyColumn laggy while scrolling

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05-10-2024

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Smooth Scrolling with LazyColumn: Conquering Performance Lag

The Jetpack Compose LazyColumn is a powerful tool for displaying long lists of data efficiently. However, you may encounter performance issues, particularly lagging during scrolling, if not implemented correctly. This article will delve into the common reasons behind this lag and provide practical solutions to ensure smooth scrolling in your Compose applications.

Scenario: The Lagging LazyColumn

Imagine you have a screen displaying a list of items, potentially containing images or complex layouts, using a LazyColumn. Upon scrolling, you notice a noticeable lag, causing a jerky and unpleasant user experience. This is a common problem, and it's often due to a combination of factors.

Original Code:

@Composable
fun ItemList() {
    LazyColumn {
        items(items = (1..100).toList()) { item ->
            // Complex layout with Image and Text
            ItemRow(item) 
        }
    }
}

@Composable
fun ItemRow(item: Int) {
    //  Complex layout with an image and text
    Row(
        modifier = Modifier
            .fillMaxWidth()
            .padding(8.dp)
    ) {
        Image(
            painter = painterResource(id = R.drawable.placeholder_image), 
            contentDescription = null, 
            modifier = Modifier
                .size(50.dp)
        )
        Spacer(modifier = Modifier.width(8.dp))
        Text(text = "Item $item")
    }
}

In this example, ItemList displays 100 items, each containing an image and text within a row. If ItemRow involves computationally expensive operations, such as image loading or complex layout calculations, the LazyColumn may start to lag during scrolling.

Insights & Solutions: Optimizing for Smooth Scrolling

Here's a breakdown of common causes for LazyColumn lag and their solutions:

1. Excessive Compositions:

• Issue: The LazyColumn's items block is being recomposed too frequently. Each recomposition can be computationally expensive, especially with complex layouts.

• Solution:

  • remember: Use remember composable to cache the ItemRow composable if it's not dependent on the item's data:

  @Composable
  fun ItemRow(item: Int) {
      val row = remember {
          Row(
              modifier = Modifier
                  .fillMaxWidth()
                  .padding(8.dp)
          ) {
              Image(
                  painter = painterResource(id = R.drawable.placeholder_image), 
                  contentDescription = null, 
                  modifier = Modifier
                      .size(50.dp)
              )
              Spacer(modifier = Modifier.width(8.dp))
              Text(text = "Item $item")
          }
      }
      row
  }
  

  • key: Provide a unique key for each item using the key parameter in items:

  LazyColumn {
      items(items = (1..100).toList(), key = { it }) { item ->
          ItemRow(item) 
      }
  }
  

2. Complex Item Layouts:

• Issue: Complex layouts with expensive operations (like image loading) can cause a significant performance bottleneck.
• Solution:
  • LazyColumn for Sub-Lists: If your item layout contains multiple sub-lists, consider using a nested LazyColumn to render those sub-lists lazily.
  • LazyRow for Sub-Items: Use LazyRow to render sub-items horizontally if applicable.
  • Image Loading Optimization: Use libraries like Coil or Glide to efficiently load and cache images, reducing image loading times. Consider using placeholders or low-resolution images until high-resolution images are loaded.

3. Excessive Data:

• Issue: Loading and displaying a large dataset can strain your app's resources.
• Solution:
  • Pagination: Implement pagination to load data in smaller chunks.
  • Pre-Fetching: Load data for the next set of items before they become visible, minimizing delays when scrolling.
  • Data Filtering: Allow the user to filter the list to reduce the amount of data displayed.

4. Consider Async Operations:

• Issue: Performing long-running operations within the composition can block the UI thread and cause lag.

• Solution: Use coroutines or LaunchedEffect to perform operations asynchronously:

  @Composable
  fun ItemRow(item: Int) {
      // ...
      LaunchedEffect(key1 = item) {
          // Perform long-running operation asynchronously
          // ...
      }
  }
  

5. Minimize Offscreen Compositions:

• Issue: Composing items that are off-screen can waste resources.
• Solution:

  • itemContent: Use the itemContent parameter within LazyColumn to only compose items that are visible or about to become visible:

    LazyColumn {
        items(items = (1..100).toList(), key = { it }) { item ->
            itemContent {
                ItemRow(item) 
            }
        }
    }
    

Conclusion: Crafting a Smooth User Experience

Following these guidelines and optimizing your LazyColumn will significantly improve scrolling performance in your Compose applications, providing a smooth and responsive user experience. By understanding the common causes of lag and applying these solutions, you can ensure that your lists are displayed efficiently and seamlessly.