import 'package:flutter/material.dart';

/// create by 张风捷特烈 on 2020/9/21
/// contact me by email 1981462002@qq.com
/// 说明: 316 KeepAlive 保活 在懒加载的列表中，孩子的状态是否需要保活。是 AutomaticKeepAlive 的底层实现，一般不单独使用。
/// link 239
///
//    {
//      "widgetId": 316,
//      "name": 'KeepAlive 介绍',
//      "priority": 1,
//      "subtitle":
//          "【child】 : *子组件   【Widget】\n"
//          "【keepAlive】 : *是否保活   【bool】\n"
//          "在 flutter 框架层中，只用于 AutomaticKeepAlive 中，源码中也说很少单独使用它。该示例展示出 ListView 条目的状态保活。",
//    }

class KeepAliveDemo extends StatelessWidget {

  final List<Color> data = [
    Colors.purple[50],
    Colors.purple[100],
    Colors.purple[200],
    Colors.purple[300],
    Colors.purple[400],
    Colors.purple[500],
    Colors.purple[600],
    Colors.purple[700],
    Colors.purple[800],
    Colors.purple[900],
    Colors.red[50],
    Colors.red[100],
    Colors.red[200],
    Colors.red[300],
    Colors.red[400],
    Colors.red[500],
    Colors.red[600],
    Colors.red[700],
    Colors.red[800],
    Colors.red[900],
  ];

  @override
  Widget build(BuildContext context) {
    return Container(
      height: 300,
      child: ListView.builder(
        itemCount: data.length,
        itemBuilder: (_, index) => ColorBox(
          color: data[index],
          index: index,
        ),
      ),
    );
  }
}

class ColorBox extends StatefulWidget {
  final Color color;
  final int index;

  ColorBox({Key key, this.color, this.index}) : super(key: key);

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

class _ColorBoxState extends State<ColorBox> with AutomaticKeepAliveClientMixin {
  bool _checked = false;

  @override
  void initState() {
    super.initState();
    _checked = false;
    print('-----_ColorBoxState#initState---${widget.index}-------');
  }

  @override
  void dispose() {
    print('-----_ColorBoxState#dispose---${widget.index}-------');
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    super.build(context);

    return Container(
      alignment: Alignment.center,
      height: 50,
      color: widget.color,
      child: Row(
        children: [
          SizedBox(width: 60,),
          Checkbox(
            value: _checked,
            onChanged: (v) {
              setState(() {
                _checked = v;
              });
            },
          ),
          Text(
            "index ${widget.index}: ${colorString(widget.color)}",
            style: TextStyle(color: Colors.white, shadows: [
              Shadow(color: Colors.black, offset: Offset(.5, .5), blurRadius: 2)
            ]),
          ),
        ],
      ),
    );
  }

  String colorString(Color color) =>
      "#${color.value.toRadixString(16).padLeft(8, '0').toUpperCase()}";

  @override
  bool get wantKeepAlive => true;
}