Why ListView Can Hurt Your App’s Performance (and What to Use Instead) ⚡

#flutter #dart #programming #list

If you’ve been building Flutter apps for a while, you’ve probably used ListView countless times. It’s one of the most common widgets for displaying scrollable content. But here’s the catch: not all ListViews are created equal, and if you’re not careful, they can absolutely tank your app’s performance.

In this blog, we’ll break down why ListView can be bad for performance, common mistakes developers make, and what you should use instead.

1. The Problem With Default ListView 🛑

By default, ListView tries to build all of its children at once.

That means:

If you have 1000 items, Flutter will render all 1000 widgets immediately.
This leads to laggy scrolling, high memory usage, and dropped frames.
On older devices, the app may even crash due to memory pressure.

2. The Hidden Cost of Widgets 💸

Every widget in Flutter comes with a rendering cost.

When you use ListView(children: [...]), all items are kept in memory.
Flutter has to calculate layouts, paint objects, and handle gestures for each.
As your list grows, performance drops exponentially.

Think of it this way: showing 10 cards is fine. Showing 10,000? That’s a nightmare.

3. Common Mistakes Developers Make ❌

Using ListView(children: [...]) instead of a builder.
Nesting multiple ListViews (leading to unbounded rendering).
Placing heavy widgets (images, charts) without lazy loading.
Forgetting to use caching for images in long lists.

4. The Right Way: ListView.builder ✅

Flutter provides builder constructors that render items lazily:

ListView.builder(
  itemCount: 1000,
  itemBuilder: (context, index) {
    return ListTile(
      title: Text('Item $index'),
    );
  },
);

✅ Only the visible items + a few off-screen buffers are built.

✅ As you scroll, Flutter recycles widgets.

✅ Memory and CPU usage remain stable.

5. For Complex Scenarios: ListView.separated & Slivers 🧩

ListView.separated → Great when you need dividers between items.
CustomScrollView + SliverList → Perfect for advanced layouts (sticky headers, grids, mixed content).

📌 Example with SliverList:

CustomScrollView(
  slivers: [
    SliverList(
      delegate: SliverChildBuilderDelegate(
        (context, index) => ListTile(title: Text("Item $index")),
        childCount: 1000,
      ),
    ),
  ],
);