Stale Closure — The State Capture Issue

Have you ever encountered a situation where your LazyList is updated from the backend, but when you try to click on a newly added item that replaced a previous one, the old elements gets added to the list?

So in this article we are going to understand what stale closures are, why they happen, and how to fix them using a simple example.\

1. What is a Stale Closure?

A stale closure happens when a function (lambda) remembers an old value of a variable and doesn’t update when the variable changes. This can lead to unexpected behavior in your app.

2. Understanding the Problem

LazyColumn {
    items(recommendations.size) { index -> 
        Row(
            modifier = Modifier
                .padding(8.dp)
                .clickable {
                    // Captures stale recommendations/list index
                    onIngredientAdd(recommendations[index]) 
            Text(recommendations[index])
            Icon(Icons.Default.Add, "Add")
        }
    }
}

So, I had a searchable list (recommendations: List<String>) displayed in a LazyColumn. When I:

1. Searched something new → The UI updated correctly (new items appeared).
2. Clicked an item → Instead of adding the currently visible item, it added an old item from the previous list.

Example Flow:

• First search: Shows ["Apple", "Banana"] → Clicking "Apple" worked.
• Second search: Shows ["Orange", "Mango"] → Clicking "Orange" added "Apple" (old item).

When the list updated, the click handler kept referencing the old recommendations or wrong index.

Why?

• Jetpack Compose recomposes the UI (updates the visible list), but the click handler lambda might capture stale data.
• Indices are unstable if the list changes (e.g., index = 0 could point to different items after updates).

Solution

items(
    recommendations.size,
    key = { index -> recommendations[index] } // Unique key per item
) { index -> ... }

Why it worked:

• The key forced Compose to track items correctly even when the list changed.
• Each row was now associated with a stable key (the string itself), preventing reuse of stale indices.

Solution 2

items(recommendations) { recommendation ->
    Modifier.clickable {
        onIngredientAdd(recommendation) // No stale data possible
    }
}

Advantages:

1. No index mismatches.
2. No risk of stale closures.
3. Cleaner and safer code.

Key Lessons

1. Avoid indices in click handlers → They become stale if the list updates.
2. Prefer items(list) over items(count) → Jetpack Compose handles updates automatically.
3. Use key if you must use indices → Ensures correct item tracking.

Analogy 😉

Think of your list as a bookshelf:

Old Approach (Broken):
You say, “Give me the 3rd book.” But if someone rearranges the shelf, the 3rd book is now different!

Fixed Approach:
You say, “Give me The pragmatic Programmer” You always get the right book, no matter its position.

Hope this Helped you…
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