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Is checking both `snapshot.hasData` and `snapshot.data != null` redundant in Flutter's FutureBuilder?

I’m working with Flutter’s FutureBuilder and came across a pattern where both snapshot.hasData and snapshot.data != null are checked before rendering a widget:

FutureBuilder(
  future: future,
  builder: (BuildContext context, AsyncSnapshot snapshot) {
    if (snapshot.hasData && snapshot.data != null) {
      return widgetToBuild;
    } else if (snapshot.hasError) {
      return Icon(Icons.error_outline);
    } else {
      return CircularProgressIndicator();
    }
  }
)

Upon examining the source code of AsyncSnapshot, I noticed that hasData is defined as true if data is not null:

bool get hasData => data != null;

Given this implementation, is it redundant to check both snapshot.hasData and snapshot.data != null? Wouldn’t snapshot.hasData suffice since it inherently checks if data is not null?

I am curious if there’s a scenario where both checks might be necessary, or if this is just a common misunderstanding in the usage of FutureBuilder that developers often mistaken.

Tags:

2

Answers


  1. 0

    Yes, it’s redundant, you are right: if you replace the AsyncSnapshot code in the first piece you posted, it would look like this

    if (snapshot.data != null && snapshot.data != null) {

    Regarding possible null results from a future, it happened once in some code of mine (due to an unexpected circumstance), and the FutureBuilder got stuck on the CircularProgressIndicator because the data was never detected.
    So, unless something changed, I think that null-returning futures are not to be used with FutureBuilder.

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  2. 0

    For an easy future handler I’d recommend doing this

    And yea, it is redundant casi the hasData getter already does that

    FutureBuilder(
  future: getValue(),
  builder: (BuildContext context, AsyncSnapshot snapshot) {
    // Check if is loading
    if (snapshot.connectionState == ConnectionState.waiting) {
      return const CircularProgressIndicator();
    }

    // When the builder has data
    if (snapshot.hasData) {
      // Here you can force no null without issues
      return Text(snapshot.data);
    }

    return const Icon(Icons.error_outline);
  },
)
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