How to use focus on RichText in flutter?

Question

I have a list of text span like this

var spans = [
TextSpan(text: content, style: style),
TextSpan(text: content, style: style) 
//and 100 more
]   

I am loading this inside SingleChildScrollView like this.

        SingleChildScrollView(
        controller: scrollController,
        child: Text.rich(
                  TextSpan(children: spans),
                       ),
                     )        

Now My question is how can I shift focus between the TextSpan list?. Say I want to load TextSpan at position 10 from spans list at top of screen without manually scrolling.

Answer 1

You could add a WidgetSpan next to each of your TextSpan, so you can assign it a key property which would be a GlobalKey so you can access its BuildContext to call the method Scrollable.ensureVisible().

Here's a code sample inspired by an answer to a similar question:

class ScrollToTextSpanPage extends StatefulWidget {
  const ScrollToTextSpanPage({Key? key}) : super(key: key);

  @override
  State<ScrollToTextSpanPage> createState() => _ScrollToTextSpanPageState();
}

class _ScrollToTextSpanPageState extends State<ScrollToTextSpanPage> {
  final _keys = List<GlobalKey>.generate(
    _kTextBlocks.length,
    (_) => GlobalKey(),
  );

  void _goToSpan(int spanIndex) {
    Scrollable.ensureVisible(
      _keys[spanIndex].currentContext!,
      alignment: 0.2,
      duration: const Duration(milliseconds: 300),
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Scroll to TextSpan'),
      ),
      floatingActionButton: FloatingActionButton.extended(
        onPressed: () => _goToSpan(8),
        label: const Text('Go to span 8'),
        icon: const Icon(Icons.navigate_next),
      ),
      body: SingleChildScrollView(
        padding: const EdgeInsets.all(16),
        child: Text.rich(
          TextSpan(
            children: [
              for (int i = 0; i < _kTextBlocks.length; i++) ...[
                WidgetSpan(child: SizedBox(key: _keys[i])),
                TextSpan(
                  text: 'Span $i\n',
                  style: const TextStyle(fontWeight: FontWeight.bold),
                  children: [
                    TextSpan(
                      text: '${_kTextBlocks[i]}\n\n',
                      style: const TextStyle(fontWeight: FontWeight.normal),
                    ),
                  ],
                ),
              ],
            ],
          ),
        ),
      ),
    );
  }
}

Try the sample on DartPad