Flutter-GetX Error: The parameter 'index' can't have a value of 'null' because of its type, but the implicit default value is 'null'

Question

1 我是 Dart 的新手，一般来说是编码。我在观看 YouTube 上的教程后制作了这段代码。大多数情况下，我已经能够自己解决大部分问题，但我无法找出最近的错误。当我尝试在无状态小部件中调整变量时，出现以下错误。

The parameter 'index' can't have a value of 'null' because of its type, but the implicit default value is 'null'.

密码是：

class TodoScreen extends StatelessWidget {

final TodoController todoController = Get.find();
int index;
TodoScreen({this.index});



@override
Widget build(BuildContext context) {
String? text ='';
if(this.index != null){

  text = todoController.todos[index].text;

}
TextEditingController textEditingController = TextEditingController();
return Scaffold(
  body: Container(
    padding: const EdgeInsets.all(20.0),
    child: Column(
      children: [
        Expanded(
          child: TextField(
            controller: textEditingController,
            autofocus: true,
            decoration: const InputDecoration(
                hintText: 'What do you want to accomplish',
                border: InputBorder.none,
                focusedBorder: InputBorder.none),
            style: TextStyle(fontSize: 25.0),
            keyboardType: TextInputType.multiline,
            maxLines: 999,
          ),
        ),
        Row(
          mainAxisAlignment: MainAxisAlignment.spaceBetween,
          children: [
            ElevatedButton(
              onPressed: () {Get.back();},
              child: const Text("Cancle"),
              style: ButtonStyle(
                backgroundColor: MaterialStateProperty.all(Colors.red),
              ),
            ),
            ElevatedButton(
              onPressed: () {
                todoController.todos.add(Todo(text: textEditingController.text), ); Get.back();

              },
              child: const Text("Add"),
              style: ButtonStyle(
                backgroundColor: MaterialStateProperty.all(Colors.green),
              ),
            )
          ],
        ),
      ],
    ),
  ),
);
}
[![enter image description here][1]][1]}

当我改变时

final TodoController todoController = Get.find();
int? index;
TodoScreen({this.index});

constructor 现在很好但是

text = todoController.todos[index].text;

必须遵循错误

The argument type 'int?' can't be assigned to the parameter type 'int'.

有人能找出这里有什么问题吗？

Answer 1

您的代码

class TodoScreen extends StatelessWidget {

final TodoController todoController = Get.find();
int index;
TodoScreen({this.index});



@override
Widget build(BuildContext context) {
String? text ='';
if(this.index != null){

  text = todoController.todos[index].text;

}

更新代码

class TodoScreen extends StatelessWidget {
    
    final TodoController todoController = Get.find();
    int? index;
    TodoScreen({this.index});
    
    
    
    @override
    Widget build(BuildContext context) {
    String? text ='';
    if(this.index != null){
    
      text = todoController.todos[index].text;
    
    }

Answer 2

出现这个错误是因为null_safety想告诉你这个int可以为null，但是在你想使用它的地方是绝对必要的，这意味着：int必须有一个值

您可以通过输入 '!' 来解决问题在索引名称后

text = todoController.todos[index!].text;

Flutter-GetX Error: The parameter 'index' can't have a value of 'null' because of its type, but the implicit default value is 'null'

Flutter-GetX Error: The parameter 'index' can't have a value of 'null' because of its type, but the implicit default value is 'null'

flutter

dart

flutter-getx