在空值上使用空检查运算符与空安全冲突

如何解决在空值上使用空检查运算符与空安全冲突

我有空安全问题。

我想在我的类中创建函数 onFieldSubmitted 和 onChanged，如下所示

import 'package:Flutter/material.dart';
import 'package:Flutter/services.dart';
import 'package:rift/constants.dart';

class DateTextField extends StatelessWidget {

  final String dateComposition;
  final String dateCompositionHintText;
  final dynamic Function()? onFieldSubmitted;
  //onchanged function has to be determined if you want to automatically set the focus to another text field,see application on age_screen with the datetextfields
  final Function()? onChanged;
  //set the widget with its focusnode
  final FocusNode? focusNode;

并想将它们放入我的 textformfield

child: TextFormField(
            onFieldSubmitted: onFieldSubmitted!(),onChanged: onChanged!(),focusNode: focusNode!,

问题是我收到错误“在空值上使用了空检查运算符”，并且由于 onFieldSubmitted 和 onChanged 函数的 bang (!)。此错误会导致应用出现渲染问题 [1]：https://i.stack.imgur.com/7ALjp.png [Rederflex][1]。

另一方面，如果我删除 bang (!)，我会收到消息“无法无条件调用该函数，因为它可以为 'null'。尝试添加一个 null 检查 ('!')”>

基本上我现在处于循环中，不知道如何解决

我会很高兴得到一些帮助 最好 瑞德

完整代码：

import 'package:Flutter/material.dart';
import 'package:Flutter/services.dart';
import 'package:rift/constants.dart';

class DateTextField extends StatelessWidget {

  final String dateComposition;
  final String dateCompositionHintText;
  final dynamic Function()? onFieldSubmitted;
  //onchanged function has to be determined if you want to automatically set the focus to another text field,see application on age_screen with the datetextfields
  final Function()? onChanged;
  //set the widget with its focusnode
  final FocusNode? focusNode;

  DateTextField({required this.dateComposition,required this.dateCompositionHintText,this.onFieldSubmitted,this.onChanged,this.focusNode});

  //dateComposition can only have Day,Month,or Year as strings



  @override
  Widget build(BuildContext context) {
    return Column(
      mainAxisAlignment: MainAxisAlignment.center,crossAxisAlignment: CrossAxisAlignment.center,children: <Widget>[
        Text(
          dateComposition,style: TextStyle(fontSize: 18,fontWeight: FontWeight.w600),),SizedBox(height: 7),Container(
          margin: EdgeInsets.all(4),width: dateComposition == "Year"? 73: 55,child: TextFormField(
            onFieldSubmitted: onFieldSubmitted(),// onChanged: onChanged!(),textAlign: TextAlign.center,//Keyboardtype for numbers
            keyboardType: TextInputType.number,//only numbers can be typed in
            inputFormatters: <TextInputFormatter>[
              FilteringTextInputFormatter.digitsOnly,LengthLimitingTextInputFormatter(dateComposition=="Year"? 4 : 2),],autofocus: true,cursorColor: kPrimarymagentaColor,decoration: Inputdecoration(
              enabledBorder: OutlineInputBorder(
                borderSide: BorderSide(color: kTextIconColorDarkBlue),borderRadius: BorderRadius.circular(15),hintText: dateCompositionHintText,hintStyle: TextStyle(fontWeight: FontWeight.w600,fontSize: 18.0),contentPadding: EdgeInsets.only(
                left: 10,right: 10,top: 10,bottom: 10,focusedBorder: OutlineInputBorder(
                borderRadius: BorderRadius.circular(15),borderSide: BorderSide(
                  color: kPrimarymagentaColor,width: 1.5,);
  }
}

错误日志

═══════ Exception caught by widgets library ═══════════════════════════════════
The following _CastError was thrown building DateTextField(dirty):
Null check operator used on a null value

The relevant error-causing widget was
DateTextField
lib/…/age_screen/age_screen.dart:46
When the exception was thrown,this was the stack
#0      DateTextField.build
package:rift/…/age_screen/date_text_field.dart:36
#1      StatelessElement.build
package:Flutter/…/widgets/framework.dart:4648
#2      ComponentElement.performRebuild
package:Flutter/…/widgets/framework.dart:4574
#3      Element.rebuild
package:Flutter/…/widgets/framework.dart:4267
#4      ComponentElement._firstBuild
package:Flutter/…/widgets/framework.dart:4553
...
════════════════════════════════════════════════════════════════════════════════

════════ Exception caught by widgets library ═══════════════════════════════════
Null check operator used on a null value
The relevant error-causing widget was
DateTextField
lib/…/age_screen/age_screen.dart:57
════════════════════════════════════════════════════════════════════════════════

════════ Exception caught by widgets library ═══════════════════════════════════
Null check operator used on a null value
The relevant error-causing widget was
DateTextField
lib/…/age_screen/age_screen.dart:68
════════════════════════════════════════════════════════════════════════════════

════════ Exception caught by rendering library ═════════════════════════════════
A RenderFlex overflowed by 299572 pixels on the right.
The relevant error-causing widget was
Row
lib/…/age_screen/age_screen.dart:41
The specific RenderFlex in question is: RenderFlex#70b39 relayoutBoundary=up2 OVERFLOWING
════════════════════════════════════════════════════════════════════════════════

════════ Exception caught by rendering library ═════════════════════════════════
A RenderFlex overflowed by 99498 pixels on the bottom.
The relevant error-causing widget was
Column
lib/…/age_screen/age_screen.dart:25
════════════════════════════════════════════════════════════════════════════════