Question 184859 in Flutter Question posted in
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How do I add ListView elements using FloatingActionButton in flutter?

I’m currently learning flutter and I’m having trouble managing states. I used this flutter guide as a reference: https://docs.flutter.dev/ui/interactive#managing-state.

I’m getting an exception thrown: "Lookup failed: addTiles in @methods in _MyTileState in package:app_recipes/main.dart"

This is my code:

import 'package:flutter/material.dart';

void main() => runApp(const MyApp());

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      home: MyHome(),
    );
  }
}

class MyHome extends StatelessWidget {
  const MyHome({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        centerTitle: true,
        title: const Text('My App'),
      ),
      body: const MyTile(),
    );
  }
}

class MyTile extends StatefulWidget {
  const MyTile({super.key});

  @override
  State<MyTile> createState() => _MyTileState();
}

class _MyTileState extends State<MyTile> {
  int _tileCount = 5;

  void _addTiles()
  {
    setState(() {
      _tileCount += 1;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: ListView.builder(
        itemCount: _MyTileState()._tileCount,
        itemBuilder: (BuildContext context, index)
        {
          return  ListTile(
            leading: const Icon(Icons.list),
            trailing: Text(
              'Tile $_tileCount'
            ),
          );
        }
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _addTiles,
        child: const Icon(Icons.add),
      ),
    );
  }
}
Tags:

4

Answers


  1. 0

    I solved it even tough I haven’t fully understood why this causes the problem.

    The trailing property of your list tiles displays not the current index of the tile but rather the count of the amount of tiles. This will show the same string for every tile but should not make a problem adding more tiles. Nevertheless, change Tile $_tileCount to Tile $index to fix it.

    return ListTile(
  leading: const Icon(Icons.list), 
  trailing: Text(
    'Tile $index'
  ),
);
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  2. 0

    You are accessing _tileCount via _MyTileState(), which is the Generic Object, not the current instance.

    You could use this._tileCount or just outright _tileCount.

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  3. 0

    You should use _tileCount instead of _MyTileState()._tileCount because u are creating new instace by calling constructor of class so it reverts to default.

    if you want to explicitly point for this class u should use this._tileCount it refers to current class.

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  4. 0

    Every Think fine but the way you accessed the _tileCount is not valid

    To access the _tileCount variable within the same class, you can directly refer to it by its name without mentioning the class, as they are both in the same scope.

    so I just replaced

    itemCount: _MyTileState()._tileCount,

    to

    itemCount: _tileCount,

    or

    itemCount: this._tileCount,

    Here is the final Code :

    import 'package:flutter/material.dart';

void main() => runApp(const MyApp());

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      home: MyHome(),
    );
  }
}

class MyHome extends StatelessWidget {
  const MyHome({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        centerTitle: true,
        title: const Text('My App'),
      ),
      body: const MyTile(),
    );
  }
}

class MyTile extends StatefulWidget {
  const MyTile({super.key});

  @override
  State<MyTile> createState() => _MyTileState();
}

class _MyTileState extends State<MyTile> {
  int _tileCount = 5;

  void _addTiles()
  {
    
    setState(() {
      _tileCount += 1;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: ListView.builder(
        itemCount: _tileCount,
        itemBuilder: (BuildContext context, index)
        {
          return  ListTile(
            leading: const Icon(Icons.list),
            trailing: Text(
              'Tile $index'
            ),
          );
        }
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _addTiles,
        child: const Icon(Icons.add),
      ),
    );
  }
}
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