Returning more than one widget using Dart 2.3's collection for

[Andrew Brogdon]

Not sure if anyone has run into this yet or not, but I'm attempting to do something like:

@override

Widget build(BuildContext context) {

  return Column(

    children: [

      AWidget(),

      SizedBox(height: 10),

      AnotherWidget(),

      for (final record in records) [

        SizedBox(height: 10),

        YetAnotherWidget(record),

      ],

      SizedBox(height: 10),

      FinalWidget(),

    ],

  );

}

The attempt to return an array in the for loop is making the analyzer angry when it tries to flatten everything. Obviously I can convert to use Padding instead of SizedBox in there and make it a single widget for each list record. Does anyone know a way to return two widgets in a Collection-For statement, though?

-Andrew

[Bob Nystrom]

On Friday, June 7, 2019 at 10:29:05 AM UTC-7, Andrew Brogdon wrote:

The attempt to return an array in the for loop is making the analyzer angry when it tries to flatten everything. Obviously I can convert to use Padding instead of SizedBox in there and make it a single widget for each list record. Does anyone know a way to return two widgets in a Collection-For statement, though?

You're almost there, you just need to use This One Trick Your Doctor Doesn't Want You To Know:

@override

Widget build(BuildContext context) {

  return Column(

    children: [

      AWidget(),

      SizedBox(height: 10),

      AnotherWidget(),

      for (final record in records) ...[

        SizedBox(height: 10),

        YetAnotherWidget(record),

      ],

      SizedBox(height: 10),

      FinalWidget(),

    ],

  );

}

Cheers!

– bob

[Andrew Brogdon]

Ah, got it. By itself, the for statement is returning a list of two-item lists (List<List<Widget>>), which can't be directly added into a List<Widget>.

Using the spread operator flattens the two-item lists returned by the for statement into one long List<Widget>, though, and it can then be combined with the rest of the outer List's contents.

Thanks! You just saved me some lines of code. :)

-Andrew

[Bob Nystrom]

On Fri, Jun 7, 2019 at 10:43 AM 'Andrew Brogdon' via Flutter Development (flutter-dev) <flutt...@googlegroups.com> wrote:

Ah, got it. By itself, the for statement is returning a list of two-item lists (List<List<Widget>>), which can't be directly added into a List<Widget>.

Exactly right. Because you might want to store a collection inside another collection, it doesn't automatically flatten. So you need to use a spread inside the for or if to tell it that's what you want.

Cheers!

– bob