Modifying Parent data from child in flutter

Question

How we can modify instance in child, created in parent widget and passed to child.

Do I have to use streams or call backs? Whats the easiest way to modify data on child while it should reflect on parents too.

Answer 1

I think you want something like ValueNotifier and ValueListenableBuilder Widgets. Like you said, if you put the data in parents to ValueNotifier Widget with its type. Then wrap everything that needs to change when data changes in ValueListenableBuilder Widget.

More Info:

• ValueListenableBuilder Widget
• ValueNotifier Widget

Look at this example:

  ValueNotifier<int> valueListener = ValueNotifier<int>(0);
  
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: ValueListenableBuilder(
        valueListenable: valueListener,
        builder: (BuildContext context, int value, Widget? child) {
          return Column(
            mainAxisAlignment: (value%2) == 0 ? MainAxisAlignment.start : MainAxisAlignment.end,
            children: [
              TextButton(
                onPressed: () => valueListener.value++,
                child: Center(
                  child: Text("$value"),
                ),
              ),
            ],
          );
        },
      ),
    }