Question 75234 in Flutter Question posted in
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How to change text color with textTheme – Flutter

I’m trying to make an android application using flutter from the tutorial, and when I want to change the color of the text according to the tutorial by means of :

children: [
  text(
    'Hi Yoikers!',
    style: Theme.of(context).textTheme.headlineSmall.copyWith(color: Colors.white),
  ),
],

The program error :

The method 'copyWith' can't be unconditionally invoked because the receiver can be 'null'.
Try making the call conditional (using '?.') or adding a null check to the target ('!').

Can you guys help me with this code, thanks.

Tags:

4

Answers


  1. 0

    Try with null check:

    style: Theme.of(context).textTheme.headlineSmall!.copyWith(color: Colors.white),
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  2. 0

    An Addition to the above answer try using ‘?’

    style: Theme.of(context).textTheme.headlineSmall?.copyWith(color: Colors.white),
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  3. 0

    Try with code I modified for you (I am also begenner with ethics)

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

  @override
  _TextWidgetState createState() => _TextWidgetState();
}

class _TextWidgetState extends State<TextWidget> {
  final _textController = TextEditingController();
  late final FocusNode _focusNode;
  TextSelection? _textSelection;

  @override
  void initState() {
    super.initState();
    _focusNode = FocusNode();
    _textController.text = '-> No issue if I remove SelectionContainer.disabled <-';
  }

  @override
  void dispose() {
    _focusNode.dispose();
    _textController.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    final textSpans = <InlineSpan>[
      const TextSpan(text: 'Hey 123 456 789'),
      WidgetSpan(
        child: SelectionContainer(
          child: TextField(
            controller: _textController,
            focusNode: _focusNode,
            style: Theme.of(context)
                .textTheme
                .bodyMedium!
                .copyWith(color: Colors.transparent),
            decoration: InputDecoration(
              border: InputBorder.none,
              isDense: true,
            ),
            onTap: () {
              if (_textSelection != null) {
                _textSelection = null;
                setState(() {});
              }
            },
            onSelectionChanged: (textSelection, _) {
              _textSelection = textSelection;
            },
          ),
        ),
      ),
    ];

    if (_textSelection != null) {
      _focusNode.requestFocus();
      _textController.selection = _textSelection!;
    }

    return Text.rich(TextSpan(children: textSpans));
  }
}

    The TextWidget keeps track of the selected text by storing the TextSelection object in the _textSelection variable.
    The TextField calls the onSelectionChanged callback every time the text selection changes, and the TextWidget updates the _textSelection variable accordingly.

    In the build() method, the TextWidget checks if there is a selected text and sets the selection on the TextField widget using the TextEditingController.selection property.

    The TextField is focused using the FocusNode.requestFocus() method, and the _textSelection variable is set to null to clear the selection when the TextField is tapped.

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  4. 0

    I’d like to address 2 issues here (possible solutions too).

    1. Theme

    That usually happens when you haven’t explicitly provided theme / darkTheme in MaterialApp.

    You can optionally provide Theme() widget wrapped around the Text widget you have in your code right now. Also make sure you have a Scaffold. Remember this theme would be scoped to the Text widget only.

        Theme(
      data: ThemeData(
        textTheme: const TextTheme(
              /// define the ones you will invoke 
               headlineSmall: TextStyle(
                  color: Colors.white,
                   )
                ),
            ),
       child: Text(
                'Hi Yoikers!',
                  style: Theme.of(context).textTheme.headlineSmall,
                ),
      ),
    1. Null aware

    To avoid getting run-time errors add ? before invoking copyWith() as suggested by an other answer (and Flutter in console). This would mean it copies your specified values only if there exists a definition to copy with. In other words it would ignore your specs and use defaults without throwing errors.

    For more clarifications, provide more code, and add a comment!

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