GetX 关于报错 Null check operator used on a null value的解决

import 'package:flutter/material.dart';
import 'package:get/get.dart';
import 'logic.dart';

class GetIndexPage extends StatefulWidget {
  int count;
  GetIndexPage({required this.count, Key? key}) : super(key: key);
  @override
  State<GetIndexPage> createState() => _GetIndexPageState();
}

class _GetIndexPageState extends State<GetIndexPage> {
  late GetIndexLogic logic;
  @override
  void initState() {
    super.initState();
    logic = Get.put(GetIndexLogic(widget.count));
  }

  @override
  Widget build(BuildContext context) {
    return GetBuilder<GetIndexLogic>(builder: (_) {
      return Scaffold(
        body: Container(
          child: Column(
            children: [
              Text('测试数据:'),
              Expanded(child: _body),
            ],
          ),
        ),
      );
    });
  }

  get _body {
    if (logic.state.list.isEmpty) {
      return Container(
        child: Text('暂无数据'),
        alignment: Alignment.center,
      );
    }
    return GetBuilder<GetIndexLogic>(
        builder: (_) {
      return ListView.builder(
        itemBuilder: (c, index) {
          return Container(
            child: Text(logic.state.list[index]),
            alignment: Alignment.center,
            height: 70,
          );
        },
        itemCount: logic.state.list.length,
      );
    });
  }

  @override
  void dispose() {
    // TODO: implement dispose
    Get.delete<GetIndexLogic>();
    super.dispose();
  }
}

import 'dart:math';
import 'package:get/get.dart';
import 'state.dart';

class GetIndexLogic extends GetxController {
  int count = 0;
  GetIndexLogic(this.count);
  final GetIndexState state = GetIndexState();

  @override
  void onInit() {
    refreshData();
    print("lw----onInit:$count");
    super.onInit();
  }

  refreshData() {
    state.list.clear();
　　/// 模拟网络请求
    Future.delayed(const Duration(milliseconds: 100), () {
      bool res = Random().nextBool();
      if (true) {
        state.list.add('jack');
        state.list.add('rose');
        state.list.add(count.toString());
      }
      print("lw----res:$res--state.list:${state.list}");
      update();
    });
  }

  @override
  void onClose() {
    print("lw----onClose:$count");
    super.onClose();
  }
}

class GetIndexState {
  List<String> list = [];

  GetIndexState() {
    ///Initialize variables
  }
}

以上是所有代码，也是使用getx 的常见场景。正常操作是不会有任何问题的。

但是如果网络数据响应时间变长，而且快速的进出页面，就会报错Null check operator used on a null value。

具体报错原因：由于快速的进出页面，当数据返回时，get内部已经delete了logic,  然后再重新创建新的

GetBuilder<GetIndexLogic>(
        builder: (_) {
      return ListView.builder(
        itemBuilder: (c, index) {
          return Container(
            child: Text(logic.state.list[index]),
            alignment: Alignment.center,
            height: 70,
          );
        },
        itemCount: logic.state.list.length,
      );
    });

getx内部，由于controller已经被释放，
执行 GetInstance().put<T>(controller!, tag: widget.tag); 的时候就会报错；

解决方式：
新创建GetBuilder的时候，

 return GetBuilder<GetIndexLogic>(
      init: logic,
        builder: (_) {
      return ListView.builder(
        itemBuilder: (c, index) {
          return Container(
            child: Text(logic.state.list[index]),
            alignment: Alignment.center,
            height: 70,
          );
        },
        itemCount: logic.state.list.length,
      );
    });

总结：
只要不是在初始化时就创建出的GetBuilder，就需要加上init: logic,但是logic应该是当前页面持有的logic，才能保持数据的准确性，