Question

我有一个ListView，其中包含StateFull Widgets，每个Tiles代表一个列表中的一个对象。问题是，当我尝试从该列表中删除对象时，仅最后一个Tile会在屏幕上被删除。对于删除项目，我使用对每个_deleteItem(_HomeItem item)的适当方法（Tile）的引用。我怀疑这是我使用的Keys的问题，但不确定。我已经尝试使用其他键（即ObjectKey(item)和GlobalKey<_TileState>()）代替，但这并没有改变任何内容。

我仅发现一个有关我的问题here的问题。但是那里的解决方案不起作用，或者我没有正确地遵循它们。

这是我尝试做的一个最小的工作示例：

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Slidable Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Slidable Demo'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  final List<_HomeItem> items = List.generate(
    5,
    (i) => _HomeItem(
      i,
      'Tile n°$i',
    ),
  );

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: _buildList(context),
      ),
    );
  }

  Widget _buildList(BuildContext context) {
    return ListView.builder(
      itemBuilder: (context, index) {
        return Tile(items[index], _deleteItem);
      },
      itemCount: items.length,
    );
  }

  void _deleteItem(_HomeItem item) {
    setState(() {
      print(context);
      print("remove: $item");
      print("Number of items before: ${items.length}");
      items.remove(item);
      print("Number of items after delete: ${items.length}");
    });
  }
}

class Tile extends StatefulWidget {
  final _HomeItem item;
  final Function delete;

  Tile(this.item, this.delete);

  @override
  State<StatefulWidget> createState() => _TileState(item, delete);
}

class _TileState extends State<Tile> {
  final _HomeItem item;
  final Function delete;

  _TileState(this.item, this.delete);

  @override
  Widget build(BuildContext context) {
    return ListTile(
      key: ValueKey(item.index),
      title: Text("${item.title}"),
      subtitle: Text("${item.index}"),
      onTap: () => delete(item),
    );
  }
}

class _HomeItem {
  const _HomeItem(
    this.index,
    this.title,
  );

  final int index;
  final String title;
}

由于这会引起误解，因此列表中的每个项目现在都在这里：

/*
  privacyIDEA Authenticator

  Authors: Timo Sturm <timo.sturm@netknights.it>

  Copyright (c) 2017-2019 NetKnights GmbH

  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
  You may obtain a copy of the License at

  http://www.apache.org/licenses/LICENSE-2.0

  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.
*/

import 'dart:developer';

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'package:flutter_slidable/flutter_slidable.dart';
import 'package:privacyidea_authenticator/model/tokens.dart';
import 'package:privacyidea_authenticator/utils/storageUtils.dart';
import 'package:privacyidea_authenticator/utils/util.dart';

class TokenWidget extends StatefulWidget {
  final Token _token;
  final Function _delete;

  TokenWidget(this._token, this._delete);

  @override
  State<StatefulWidget> createState() {
    if (_token is HOTPToken) {
      return _HotpWidgetState(_token, _delete);
    } else if (_token is TOTPToken) {
      return _TotpWidgetState(_token, _delete);
    } else {
      throw ArgumentError.value(_token, "token",
          "The token [$_token] is of unknown type and not supported.");
    }
  }
}

abstract class _TokenWidgetState extends State<TokenWidget> {
  final Token _token;
  static final SlidableController _slidableController = SlidableController();
  String _otpValue;
  String _label;

  final Function _delete;

  _TokenWidgetState(this._token, this._delete) {
    _otpValue = calculateOtpValue(_token);
    _saveThisToken();
    _label = _token.label;
  }

  @override
  Widget build(BuildContext context) {
    return Slidable(
      key: ValueKey(_token.serial),
      // This is used to only let one Slidable be open at a time.
      controller: _slidableController,
      actionPane: SlidableDrawerActionPane(),
      actionExtentRatio: 0.25,
      child: Container(
        color: Colors.white,
        child: _buildTile(),
      ),
      secondaryActions: <Widget>[
        IconSlideAction(
          caption: 'Delete',
          color: Colors.red,
          icon: Icons.delete,
          onTap: () => _deleteTokenDialog(),
        ),
        IconSlideAction(
          caption: 'Rename',
          color: Colors.blue,
          icon: Icons.edit,
          onTap: () => _renameTokenDialog(),
        ),
      ],
    );
  }

  // TODO Test this behaviour with integration testing.
  void _renameTokenDialog() {
    final _nameInputKey = GlobalKey<FormFieldState>();
    String _selectedName;

    showDialog(
        context: context,
        builder: (BuildContext context) {
          return AlertDialog(
            title: Text("Rename token"),
            titleTextStyle: Theme.of(context).textTheme.subhead,
            content: TextFormField(
              autofocus: true,
              initialValue: _label,
              key: _nameInputKey,
              onChanged: (value) => this.setState(() => _selectedName = value),
              decoration: InputDecoration(labelText: "Name"),
              validator: (value) {
                if (value.isEmpty) {
                  return 'Please enter a name for this token.';
                }
                return null;
              },
            ),
            actions: <Widget>[
              FlatButton(
                child: Text("Rename"),
                onPressed: () {
                  if (_nameInputKey.currentState.validate()) {
                    _renameToken(_selectedName);
                    Navigator.of(context).pop();
                  }
                },
              ),
              FlatButton(
                child: Text("Cancel"),
                onPressed: () => Navigator.of(context).pop(),
              ),
            ],
          );
        });
  }

  void _renameToken(String newLabel) {
    _saveThisToken();
    log(
      "Renamed token:",
      name: "token_widgets.dart",
      error: "\"${_token.label}\" changed to \"$newLabel\"",
    );
    _token.label = newLabel;

    setState(() {
      _label = _token.label;
    });
  }

  void _deleteTokenDialog() {
    showDialog(
        context: context,
        builder: (BuildContext context) {
          return AlertDialog(
            title: Text("Confirm deletion"),
            titleTextStyle: Theme.of(context).textTheme.subhead,
            content: RichText(
              text: TextSpan(
                  style: TextStyle(
                    color: Colors.black,
                  ),
                  children: [
                    TextSpan(
                      text: "Are you sure you want to delete ",
                    ),
                    TextSpan(
                        text: "\'$_label\'?",
                        style: TextStyle(
                          fontStyle: FontStyle.italic,
                        ))
                  ]),
            ),
            actions: <Widget>[
              FlatButton(
                onPressed: () => {
                  _delete(_token),
                  Navigator.of(context).pop(),
                },
                child: Text("Yes!"),
              ),
              FlatButton(
                onPressed: () => Navigator.of(context).pop(),
                child: Text("No, take me back!"),
              ),
            ],
          );
        });
  }

  void _saveThisToken() {
    StorageUtil.saveOrReplaceToken(this._token);
  }

  void _updateOtpValue();

  Widget _buildTile();
}

class _HotpWidgetState extends _TokenWidgetState {
  _HotpWidgetState(Token token, Function delete) : super(token, delete);

  @override
  void _updateOtpValue() {
    setState(() {
      (_token as HOTPToken).incrementCounter();
      _otpValue = calculateOtpValue(_token);
    });
  }

  @override
  Widget _buildTile() {
    return Stack(
      children: <Widget>[
        ListTile(
          title: Center(
            child: Text(
              insertCharAt(_otpValue, " ", _otpValue.length ~/ 2),
              textScaleFactor: 2.5,
            ),
          ),
          subtitle: Center(
            child: Text(
              _label,
              textScaleFactor: 2.0,
            ),
          ),
        ),
        Align(
          alignment: Alignment.centerRight,
          child: RaisedButton(
            onPressed: () => _updateOtpValue(),
            child: Text(
              "Next",
              textScaleFactor: 1.5,
            ),
          ),
        ),
      ],
    );
  }
}

class _TotpWidgetState extends _TokenWidgetState
    with SingleTickerProviderStateMixin {
  AnimationController
      controller; // Controller for animating the LinearProgressAnimator

  _TotpWidgetState(Token token, Function delete) : super(token, delete);

  @override
  void _updateOtpValue() {
    setState(() {
      _otpValue = calculateOtpValue(_token);
    });
  }

  @override
  void initState() {
    super.initState();

    controller = AnimationController(
      duration: Duration(seconds: (_token as TOTPToken).period),
      // Animate the progress for the duration of the tokens period.
      vsync:
          this, // By extending SingleTickerProviderStateMixin we can use this object as vsync, this prevents offscreen animations.
    )
      ..addListener(() {
        // Adding a listener to update the view for the animation steps.
        setState(() => {
              // The state that has changed here is the animation object’s value.
            });
      })
      ..addStatusListener((status) {
        // Add listener to restart the animation after the period, also updates the otp value.
        if (status == AnimationStatus.completed) {
          controller.forward(from: 0.0);
          _updateOtpValue();
        }
      })
      ..forward(); // Start the animation.

    // Update the otp value when the android app resumes, this prevents outdated otp values
    // ignore: missing_return
    SystemChannels.lifecycle.setMessageHandler((msg) {
      log(
        "SystemChannels:",
        name: "totpwidget.dart",
        error: msg,
      );
      if (msg == AppLifecycleState.resumed.toString()) {
        _updateOtpValue();
      }
    });
  }

  @override
  void dispose() {
    controller.dispose(); // Dispose the controller to prevent memory leak.
    super.dispose();
  }

  @override
  Widget _buildTile() {
    return Column(
      children: <Widget>[
        ListTile(
          title: Center(
            child: Text(
              insertCharAt(_otpValue, " ", _otpValue.length ~/ 2),
              textScaleFactor: 2.5,
            ),
          ),
          subtitle: Center(
            child: Text(
              _label,
              textScaleFactor: 2.0,
            ),
          ),
        ),
        LinearProgressIndicator(
          value: controller.value,
        ),
      ],
    );
  }
}

计划是将来在列表中添加不同种类的项目，每种项目可能呈现出完全不同的方式，并且还需要不同的逻辑。有关完整项目，请参阅github。尽管我确信这是为列表创建不同Widget的正确方法，但我愿意采用不同的方法来做到这一点。

Answer 1

嗨，您应该为每个图块设置Key。您可以观看此Flutter Tutorial来了解代码中正在发生的事情。

我在以下代码中使用了ObjectKey。

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Slidable Demo',
      home: MyListPage(),
    );
  }
}

class MyListPage extends StatefulWidget {
  MyListPage({Key key}) : super(key: key);

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

class _MyListPageState extends State<MyListPage> {
  final List<Item> items = [
    Item("ItemName_1", "ItemType_1"),
    Item("ItemName_2", "ItemType_2"),
    Item("ItemName_3", "ItemType_1"),
  ];

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("Flutter Slidable Demo"),
      ),
      body: _buildList(context),
    );
  }

  Widget _buildList(BuildContext context) {
    return ListView.builder(
      itemCount: items.length,
      itemBuilder: (context, index) {
        final item = items[index];
        return MyTile(
          key: ObjectKey(item),
          item: items[index],
          onDeleteClicked: () => _deleteItem(item),
        );
      },
    );
  }

  void _deleteItem(Item item) {
    items.remove(item);
    setState(() {});
  }
}

class Item {
  String itemName;
  String itemType;

  Item(this.itemName, this.itemType);
}

class MyTile extends StatefulWidget {
  final Item item;
  final VoidCallback onDeleteClicked;

  const MyTile({Key key, this.item, this.onDeleteClicked}) : super(key: key);

  @override
  _MyTileState createState() {
    if (item.itemType == "ItemType_1")
      return TileStateType1();
    else if (item.itemType == "ItemType_2")
      return TileStateType2();
    else
      throw ArgumentError.value("Unknown Item type and not supported.");
  }
}

abstract class _MyTileState extends State<MyTile> {
  void _renameItem() {
    final txtCtrl = TextEditingController(text: widget.item.itemName);
    showDialog(
      context: context,
      builder: (BuildContext context) {
        return AlertDialog(
          title: Text("Rename"),
          content: TextField(
            controller: txtCtrl,
          ),
          actions: <Widget>[
            RaisedButton(
              color: Colors.green,
              child: Text("Confirm", style: TextStyle(color: Colors.white)),
              onPressed: () {
                setState(() {
                  widget.item.itemName = txtCtrl.text;
                });
                Navigator.pop(context);
              },
            ),
            RaisedButton(
              color: Colors.red,
              child: Text("Cancel", style: TextStyle(color: Colors.white)),
              onPressed: () => Navigator.pop(context),
            ),
          ],
        );
      },
    );
  }

  void _deleteItem() {
    showDialog(
        context: context,
        builder: (BuildContext context) {
          return AlertDialog(
            title: Text("Delete"),
            content: Text("Are you sure?"),
            actions: <Widget>[
              RaisedButton(
                color: Colors.green,
                child: Text("Confirm", style: TextStyle(color: Colors.white)),
                onPressed: () {
                  widget.onDeleteClicked();
                  Navigator.pop(context);
                },
              ),
              RaisedButton(
                color: Colors.red,
                child: Text("Cancel", style: TextStyle(color: Colors.white)),
                onPressed: () => Navigator.pop(context),
              ),
            ],
          );
        });
  }

  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: const EdgeInsets.all(8.0),
      child: Material(
        elevation: 3.0,
        color: Colors.white,
        child: Row(
          children: <Widget>[
            Expanded(
              child: InkWell(
                onTap: _doDifferently,
                child: Padding(
                  padding: const EdgeInsets.all(8.0),
                  child: _buildDifferently(),
                ),
              ),
            ),
            IconButton(
              icon: Icon(Icons.edit),
              onPressed: _renameItem,
            ),
            IconButton(
              icon: Icon(Icons.delete),
              onPressed: _deleteItem,
            ),
          ],
        ),
      ),
    );
  }

  Widget _buildDifferently();

  void _doDifferently();
}

class TileStateType1 extends _MyTileState {
  @override
  Widget _buildDifferently() {
    return Row(
      children: <Widget>[
        Text(
          widget.item.itemName,
          style: TextStyle(color: Colors.red, fontWeight: FontWeight.bold),
        ),
        Material(
          color: Colors.blue,
          child: Padding(
            padding: const EdgeInsets.all(5.0),
            child: Text(
              widget.item.itemType,
              style: TextStyle(fontSize: 12, color: Colors.white),
            ),
          ),
        )
      ],
    );
  }

  @override
  void _doDifferently() {
    Scaffold.of(context).showSnackBar(SnackBar(
      content: Text("I am type 1"),
    ));
  }
}

class TileStateType2 extends _MyTileState {
  @override
  Widget _buildDifferently() {
    return Row(
      children: <Widget>[
        Icon(Icons.security),
        Text(
          widget.item.itemName,
          style: TextStyle(color: Colors.green, fontStyle: FontStyle.italic),
        ),
        Material(
          color: Colors.red,
          shape: StadiumBorder(),
          child: Padding(
            padding: const EdgeInsets.all(5.0),
            child: Text(
              widget.item.itemType,
              style: TextStyle(fontSize: 12, color: Colors.white),
            ),
          ),
        ),
      ],
    );
  }

  @override
  void _doDifferently() {
    showDialog(
        context: context,
        builder: (BuildContext context) {
          return AlertDialog(
            title: Text("Message"),
            content: Text("I am type 2"),
          );
        });
  }
}

希望这会有所帮助

Answer 2

尝试一下：



import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Slidable Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Slidable Demo'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  final List<_HomeItem> items = List.generate(
    5,
    (i) => _HomeItem(
      i,
      'Tile n°$i',
    ),
  );

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: _buildList(context),
      ),
    );
  }

  Widget _buildList(BuildContext context) {
    return ListView.builder(
      itemBuilder: (BuildContext context, int i) {
        _HomeItem item = items[i];
          return ListTile(

            title: Text(item.index.toString()),
            subtitle: Text(item.title.toString()),
            onTap: () {
              setState(() {
                items.removeAt(i);
              });
            },

          );
      },
      itemCount: items.length,
    );
  }
}



class _HomeItem {
  const _HomeItem(
    this.index,
    this.title,
  );

  final int index;
  final String title;
}

其他解决方案：-


import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Slidable Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Slidable Demo'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);
  final String title;
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
   List<_HomeItem> items = [];

   @override
  void initState() {
    for(int i=0; i<5; i++) {
      items.add(_HomeItem(i, 'Title $i', Key(i.toString())));
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: _buildList(context),
      ),
    );
  }

  Widget _buildList(BuildContext context) {
    return ListView.builder(
      itemBuilder: (context, index) {
        return tiles(items[index], _deleteItem);
      },
      itemCount: items.length,
    );
  }

  Widget tiles(_HomeItem item, Function detete) {
    return ListTile(
            key: item.key,
            title: Text("${item.title}"),
            subtitle: Text("${item.index}"),
            onTap: () => detete(item),
      );
  } 
    void _deleteItem(_HomeItem itemtoDelete,) {
    for(int i =0; i <items.length; i++) {
        if(items[i].key == itemtoDelete.key) {
          setState(() {
            items.removeWhere((item) => item.key == itemtoDelete.key);
          });
        }else {
        }
    }
    }
  }

class _HomeItem {
  const _HomeItem(
    this.index,
    this.title,
    this.key,
  );

  final int index;
  final String title;
   final Key key;

}

从Flutters ListView删除项目仅删除最后一个小部件

2 个答案: