When should I use a FutureBuilder?

I was wondering when I should use the future builder. For example, if I want to make an http request and show the results in a list view, as soon as you open the view, should I have to use the future builder or just build a ListViewBuilder like:

new ListView.builder(
        itemCount: _features.length,
        itemBuilder: (BuildContext context, int position) {
...stuff here...
}

Moreover, if I don't want to build a list view but some more complex stuff like circular charts, should I have to use the future builder?

Hope it's clear enough!

Solution

FutureBuilder removes boilerplate code.

Let's say you want to fetch some data from the backend on page launch and show a loader until data comes.

Tasks for ListBuilder:

Have two state variables, dataFromBackend and isLoadingFlag
On launch, set isLoadingFlag = true, and based on this, show loader.
Once data arrives, set data with what you get from backend and set isLoadingFlag = false (inside setState obviously)
We need to have a if-else in widget creation. If isLoadingFlag is true, show the loader else show the data. On failure, show error message.

Tasks for FutureBuilder:

Give the async task in future of Future Builder
Based on connectionState, show message (loading, active(streams), done)
Based on data(snapshot.hasError), show view

Pros of FutureBuilder

Does not use the two state variables and setState
Reactive programming (FutureBuilder will take care of updating the view on data arrival)

Example:

FutureBuilder<String>(
    future: _fetchNetworkCall, // async work
    builder: (BuildContext context, AsyncSnapshot<String> snapshot) {
       switch (snapshot.connectionState) {
         case ConnectionState.waiting: return Text('Loading....');
         default:
           if (snapshot.hasError)
              return Text('Error: ${snapshot.error}');
           else
          return Text('Result: ${snapshot.data}');
        }
      },
    )

Performance impact:

I just looked into the FutureBuilder code to understand the performance impact of using this.

FutureBuilder is just a StatefulWidget whose state variable is _snapshot
Initial state is _snapshot = AsyncSnapshot<T>.withData(ConnectionState.none, widget.initialData);
It is subscribing to future which we send via the constructor and update the state based on that.

Example:

widget.future.then<void>((T data) {
    if (_activeCallbackIdentity == callbackIdentity) {
      setState(() {
        _snapshot = AsyncSnapshot<T>.withData(ConnectionState.done, data);
      });
    }
}, onError: (Object error) {
  if (_activeCallbackIdentity == callbackIdentity) {
    setState(() {
      _snapshot = AsyncSnapshot<T>.withError(ConnectionState.done, error);
    });
  }
});

So the FutureBuilder is a wrapper/boilerplate of what we do typically, hence there should not be any performance impact.