How to deal with unwanted widget build

Question

For various reasons, sometimes the build method of my widgets is called again.

I know that it happens because a parent updated. But this causes undesired effects. A typical situation where it causes problems is when using FutureBuilder this way:

@override
Widget build(BuildContext context) {
  return FutureBuilder(
    future: httpCall(),
    builder: (context, snapshot) {
      // create some layout here
    },
  );
}

In this example, if the build method were to be called again, it would trigger another HTTP request. Which is undesired.

Considering this, how to deal with the unwanted build? Is there any way to prevent a build call?

Answer 1

There are a few strategies that you can use to deal with unwanted widget builds:

1. Use AutomaticKeepAliveClientMixin: This mixin can be used with a widget that needs to preserve its state across rebuilds. By default, Flutter will rebuild the widget tree whenever its parent widget changes, which can cause unwanted effects in some cases. However, with AutomaticKeepAliveClientMixin, you can prevent the widget from being rebuilt and preserve its state.

2. Use const widgets: If a widget is marked as const, then it won't be rebuilt unless its parameters change. This can be useful for widgets that don't change often, such as static layouts.

3. Use ValueKey: By using ValueKey with a widget, you can tell Flutter to reuse the same widget instance if the key remains the same. This can be useful for widgets that need to preserve their state across rebuilds.

4. Use StatefulWidget instead of StatelessWidget: If a widget needs to maintain some state, you can use StatefulWidget instead of StatelessWidget. The build method of a StatefulWidget is called whenever its state changes, but not when its parent changes. This can help to reduce unwanted rebuilds.

5. Use didUpdateWidget lifecycle method: You can use the didUpdateWidget method to detect when the widget is being rebuilt due to a parent widget update. This method is called whenever a widget is rebuilt, and you can use it to determine whether the widget needs to be updated or not.

In the specific case of FutureBuilder, you can use the initialData parameter to provide an initial value for the snapshot. This can help to avoid triggering another HTTP request when the widget is rebuilt. You can also use one of the strategies mentioned above to prevent the widget from being rebuilt unnecessarily.