Flutter

Question

我正在构建一个学生选择视图，但是当我滚动网格视图时，数据丢失了

视频示例：https://drive.google.com/file/d/1oB3VQHSfZzZjANC8dNnd4p4TmTIePqBC/view?usp=sharing

我准备使用 addAutomaticKeepAlives 和 addRepaintBoundaries 属性

class StudentCellGridView extends StatelessWidget {
  const StudentCellGridView({
    Key? key,
    this.crossAxisCount = 4,
  }) : super(key: key);

  final int crossAxisCount;

  @override
  Widget build(BuildContext context) {
    return GridView.builder(
      addAutomaticKeepAlives: false,
      addRepaintBoundaries: false,
      padding: EdgeInsets.only(bottom: defaultPadding),
      itemCount: 30,
      gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
        crossAxisCount: crossAxisCount,
        mainAxisSpacing: defaultPadding,
      ),
      itemBuilder: (context, index) => StudentCell(),
    );
  }
}

class _StudentCellState extends State<StudentCell> {
  var color = Colors.grey;

  @override
  Widget build(BuildContext context) {
    return Stack(
      children: [
        TextButton(
            style: ButtonStyle(
              overlayColor: MaterialStateColor.resolveWith(
                  (states) => Colors.transparent),
            ),
            onPressed: () {
              setState(() {
                this.color =
                    this.color == Colors.grey ? Colors.green : Colors.grey;
              });
            },
            child: Padding(
              padding: const EdgeInsets.symmetric(horizontal: defaultPadding),
              child: Column(
                children: [
                  SizedBox(
                    height: 80,
                    child: ClipRRect(
                      borderRadius: BorderRadius.circular(8.0),
                      child: Image.asset("assets/images/Foto.png"),
                    ),
                  ),
                  Expanded(
                    child: Container(
                      child: Center(
                        child: Text(
                          "Child name",
                          maxLines: 3,
                          style: TextStyle(color: Colors.black),
                          overflow: TextOverflow.ellipsis,
                        ),
                      ),
                    ),
                  ),
                ],
              ),
            )),
        Row(
          mainAxisAlignment: MainAxisAlignment.end,
          children: [
            Container(
              width: 20,
              height: 20,
              decoration: new BoxDecoration(
                color: this.color,
                shape: BoxShape.circle,
              ),
            ),
            SizedBox(
              width: defaultPadding,
            )
          ],
        ),
      ],
    );
  }
}

如何在名单很长的情况下保留选中的学生

Answer 1

首先你的 GridView.builder() 小部件应该有 addAutomaticKeepAlives: true.

然后将 AutomaticKeepAliveClientMixin 添加到您的 _StudentCellState 小部件，如下所示：

class _StudentCellState extends State<StudentCell> with AutomaticKeepAliveClientMixin {
  
  var color = Colors.grey;

  @override
  bool get wantKeepAlive => true;

  @override
  Widget build(BuildContext context) {
    super.build(context);
    return Stack(
      children: [
        //the rest of your code
      ],
    );
  }
}

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