The Second FutureBuilder Gives Anomalous Behaviour, But Why?

Are you tired of dealing with the mysterious anomalies that arise from using the second FutureBuilder in your Flutter application? Do you find yourself scratching your head, wondering why your code isn’t behaving as expected? Fear not, dear developer, for we’re about to dive into the depths of this enigmatic issue and emerge with a profound understanding of what’s going on.

What is FutureBuilder, and why do we need it?

Before we delve into the anomaly, let’s take a step back and revisit the fundamentals. A FutureBuilder is a widget that builds itself based on the latest snapshot of interaction with a Future. It’s a powerful tool that allows us to asynchronously load data, handle errors, and manage the state of our application. In essence, it’s a bridge that connects our UI to the future (pun intended).

FutureBuilder<String>(
  future: _loadString(), // a Future that loads a string
  builder: (context, snapshot) {
    if (snapshot.hasData) {
      return Text(snapshot.data); // display the data
    } else if (snapshot.hasError) {
      return Text('Error: ${snapshot.error}'); // display the error
    } else {
      return CircularProgressIndicator(); // display a loading indicator
    }
  },
)

The Anomaly: Second FutureBuilder Malfunction

Now, let’s create a scenario where we have two FutureBuilders, one nested inside the other. Sounds simple, right? But what happens when we try to use the second FutureBuilder? Unexpected behaviour, that’s what! The second FutureBuilder seems to malfunction, ignoring the Futures it’s supposed to build upon. It’s as if the second FutureBuilder is living in a parallel universe, oblivious to the changes happening around it.

FutureBuilder<String>(
  future: _loadString1(), // a Future that loads a string
  builder: (context, snapshot) {
    if (snapshot.hasData) {
      return FutureBuilder<int>(
        future: _loadInt(), // a Future that loads an integer
        builder: (context, snapshot) {
          if (snapshot.hasData) {
            return Text(' Loaded: ${snapshot.data}'); // this never gets called
          } else {
            return Text('Error: ${snapshot.error}'); // this never gets called either
          }
        },
      );
    } else {
      return CircularProgressIndicator(); // this is all we see
    }
  },
)

Why Does This Happen?

The culprit behind this anomaly is the way Flutter handles the build process. When a FutureBuilder is rebuilt, it cancels the previous Future and starts a new one. However, when we nest FutureBuilders, the inner FutureBuilder is rebuilt every time the outer FutureBuilder rebuilds. This causes the inner FutureBuilder to cancel and restart its Future repeatedly, resulting in the anomalous behaviour we observe.

Flutter’s Build Process Explained

To understand why this happens, let’s take a step back and examine the build process in Flutter:

1. The widget tree is built from the top down.
2. Each widget is given a chance to build itself.
3. If a widget depends on a Future, it will wait for the Future to complete before building.
4. When the Future completes, the widget will rebuild itself with the new data.
5. If the widget is rebuilt, it will cancel any existing Futures and start new ones.

In our case, the outer FutureBuilder rebuilds itself when the inner FutureBuilder completes. This causes the inner FutureBuilder to cancel and restart its Future, resulting in the anomalous behaviour.

Solutions to the Anomaly

Now that we understand the root cause of the anomaly, let’s explore some solutions to this problem:

1. Use a Single FutureBuilder

One straightforward solution is to use a single FutureBuilder that loads both the string and the integer. This eliminates the need for nested FutureBuilders and avoids the anomaly altogether.

FutureBuilder<Map>(
  future: _loadData(), // a Future that loads a map with string and integer
  builder: (context, snapshot) {
    if (snapshot.hasData) {
      return Text('Loaded: ${snapshot.data['string']} and ${snapshot.data['integer']}');
    } else {
      return CircularProgressIndicator();
    }
  },
)

2. Use a State Management Solution

Another solution is to use a state management solution like Provider or Riverpod to manage the state of your application. This allows you to load the data independently of the UI and then use the loaded data to build your widgets.

class DataLoader with ChangeNotifier {
  String _string;
  int _integer;

  Future _loadData() async {
    _string = await _loadString();
    _integer = await _loadInt();
    notifyListeners();
  }

  String get string => _string;
  int get integer => _integer;
}

FutureBuilder(
  future: dataLoader._loadData(),
  builder: (context, snapshot) {
    if (snapshot.connectionState == ConnectionState.done) {
      return Text('Loaded: ${dataLoader.string} and ${dataLoader.integer}');
    } else {
      return CircularProgressIndicator();
    }
  },
)

3. Use a Custom Solution

If neither of the above solutions appeals to you, you can create a custom solution that suits your specific needs. For example, you can create a FutureBuilder that takes a list of Futures and waits for all of them to complete before building itself.

class MultiFutureBuilder extends StatefulWidget {
  @override
  _MultiFutureBuilderState createState() => _MultiFutureBuilderState();
}

class _MultiFutureBuilderState extends State<MultiFutureBuilder> {
  List<Future> _futures;

  @override
  Widget build(BuildContext context) {
    return FutureBuilder(
      future: Future.wait(_futures),
      builder: (context, snapshot) {
        if (snapshot.hasData) {
          return Text('Loaded: ${snapshot.data[0]} and ${snapshot.data[1]}');
        } else {
          return CircularProgressIndicator();
        }
      },
    );
  }
}

Conclusion

In conclusion, the second FutureBuilder gives anomalous behaviour because of the way Flutter handles the build process. By understanding the root cause of the anomaly, we can find solutions to this problem, such as using a single FutureBuilder, a state management solution, or a custom solution. Remember, in the world of Flutter, anomalies are just opportunities to learn and grow.

Solution	Pros	Cons
Single FutureBuilder	Easy to implement, avoids anomaly	Limited flexibility, may not be suitable for complex scenarios
State Management Solution	Provides a scalable architecture, easy to maintain	Requires additional setup and boilerplate code
Custom Solution	Highly customizable, suitable for complex scenarios	Requires advanced knowledge of Flutter and Futures

We hope this article has shed light on the mysterious anomaly of the second FutureBuilder. Remember to always keep learning, and never be afraid to dive into the depths of a problem to find the solution.

Frequently Asked Question

Are you scratching your head wondering why the second futurebuilder gives anomalous behaviour? You’re not alone! Here are some answers to the most frequently asked questions about this mysterious phenomenon.