Flutter：Dismissible 小部件内的 SnackBar 无法正常工作

Question

My Home Screen is a Scaffold with a list of Dismissible widgets at its body. The child of each Dismissible is a custom widget I created, named Box . I have a FloatingActionButton that takes me to a new screen where I can add more Box es to the list. (Each Box receive a String as an argument, that is used as its title).

I want the method onDismissed to show a SnackBar with the text "(Title of the box) excluded". However, this is not working as expected. The problem is that it always displays the title of the last box included, and not the title of the one I just dismissed. For example, if I add a Box named "Box 1", and then a Box named "Box 2", and then I dismiss the "Box 1", the snackbar will say "Box 2 excluded".

What am I doing wrong?

Here is the relevant code:

import 'package:flutter/material.dart';
import 'box.dart';
import 'addCounter.dart';

class Home extends StatefulWidget {
  @override
  HomeState createState() => HomeState();
}

class HomeState extends State<Home> {

  List<String> lista;

  void incrementLista(String novoItem) {
    print('$lista');
    setState(() {
      lista.add(novoItem);
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Counters'),
        backgroundColor: Colors.black,
      ),
      body: ListView.builder(
        itemCount: lista.length,
        itemBuilder: (context, index) {
          return Dismissible(
              background: Container(color: Colors.grey[800], child: Icon(Icons.delete, color: Colors.grey[100])),
              key: Key(lista[index]),
              onDismissed: (direction) {
                setState(() {
                  lista.removeAt(index);
                });
                Scaffold.of(context).showSnackBar(
                    SnackBar(content: Text(lista[index] + ' excluded.')));
              },
              child: Box(lista[index]));
        },
      ),
      floatingActionButton: FloatingActionButton(
          backgroundColor: Colors.grey[1000],
          onPressed: () {
            //Navega para tela de adicionar tarefa
            Navigator.push(
                context,
                MaterialPageRoute(
                    builder: (context) => AddCounter(f: incrementLista)));
          },
          child: Icon(Icons.add, color: Colors.white)),
      floatingActionButtonLocation: FloatingActionButtonLocation.centerDocked,
      bottomNavigationBar: BottomNavigationBar(
        //backgroundColor: Colors.grey[50],
        unselectedItemColor: Colors.grey[700],
        items: const <BottomNavigationBarItem>[
          BottomNavigationBarItem(
            icon: Icon(Icons.list),
            title: Text('List'),
          ),
          BottomNavigationBarItem(
            icon: Icon(Icons.insert_chart),
            title: Text('Chart'),
          ),
        ],
        // currentIndex: _selectedIndex,
        selectedItemColor: Colors.blue,
        //onTap: _onItemTapped,
      ),
    );
  }
}

And here is the code of the addCounter.dart:

import 'package:flutter/material.dart';

class AddCounter extends StatefulWidget {
  final Function f;
  AddCounter({@required this.f});

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

class _AddCounterState extends State<AddCounter> {
  final myController = TextEditingController();

  @override
  void dispose() {
    myController.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text('Add a counter'),
          backgroundColor: Colors.blue,
        ),
        body: Column(children: [
          Padding(
            padding: EdgeInsets.all(15),
            child: TextField(
              controller: myController,
              decoration: InputDecoration(
                  enabledBorder: OutlineInputBorder(
                      borderSide: BorderSide(color: Colors.blue, width: 2)),
                  hintText: 'Type a name for the counter'),
            ),
          ),
          RaisedButton(
            color: Colors.green,
            onPressed: () {
              widget.f(myController.text);
              Navigator.pop(context);
            },
            child: Text(
              'Save',
              style: TextStyle(color: Colors.white),
            ),
          )
        ]));
  }
}

Answer 1

I think the problem is that you first remove the item of the list. When you show the SnackBar the item is already removed so you can't access it in the list. So I would suggest to first show the Snackbar and then remove the item.

Like this: (In your itemBuilder )

return Dismissible(
          background: Container(color: Colors.grey[800], child: Icon(Icons.delete, 
                          color: Colors.grey[100])),
          key: Key(lista[index]),
          onDismissed: (direction) {
            Scaffold.of(context).showSnackBar(
                SnackBar(content: Text(lista[index] + ' excluded.')));

            setState(() {
              lista.removeAt(index);
            });
          },
          child: Box(lista[index]));
    },