参数\'hintText\'因其类型的原因不能有\'null\'的值，但隐含的默认值为\'null\'

Answer 1

在构造函数中，它必须被标记为 final 或传递一个值给它，比如

CustomTextFormField(
      {required this.hintText,  required this.verticalPadding, required this.value, required this.suffixIcon, this.showLabel = true});

显示标签有一个默认值，如果你注意到并且所有其他都是必需的

Answer 2

首先尝试了解 Dart 中的 null 安全性：https://dart.dev/null-safety

要指示参数可能具有 null 值，只需添加 ?对其类型声明：

final String? hintText;
final double? verticalPadding;
final String? value;
final Icon? suffixIcon;
final bool? showLabel;

CustomTextFormField(
      {this.hintText,  this.verticalPadding, this.value, this.suffixIcon, this.showLabel = true});

在数据类型之后添加 (?) 可空运算符意味着您的参数可以为空 & 是可选的，当您调用 CommonTextFormField() 时，它们不需要传递任何值。

如果在数据类型之后不添加 (?) 可为空，则构造函数参数中需要所有字段

像这样：

final String hintText;
final double verticalPadding;
final String value;
final Icon suffixIcon;
final bool showLabel;

CustomTextFormField(
      {required this.hintText,  required this.verticalPadding,required this.value,required this.suffixIcon,required this.showLabel});

命名参数是可选的，除非它们被明确标记为必需。

试试这个代码（包括密码、手机、电子邮件验证）：

class CommonTextFormField extends StatelessWidget {
  const CommonTextFormField(
      {Key? key,
      this.focusNode,
      this.height,
      this.maxLength,
      this.maxLines,
      this.textInputAction,
      required this.hintText,
      this.controller,
      this.readOnly,
      this.isImportantStarLabelRequired,
      this.obscureText,
      this.isFixedlabel,
      this.isDense,
      this.onSubmittedRequired,
      this.autofocus,
      this.isSuffixIconRequired,
      this.keyboardType,
      this.onChanged,
      this.onTap,
      this.suffixIcon,
      this.labelHeading,
      this.inputFormatters,
      this.errorText,
      this.isfilled = false,
      this.textAlign,
      this.textAlignVertical,
      this.hintStyle,
      this.customDateError,
      this.isMobileValidationRequired,
      this.isEmailValidationRequired,
      this.isPasswordValidationRequired,
      this.compareWithcontroller,
      this.compareWithPrevious = false,
      this.compareErrorText})
      : super(key: key);

  final FocusNode? focusNode;
  final TextAlign? textAlign;
  final TextAlignVertical? textAlignVertical;
  final TextStyle? hintStyle;
  final double? height;
  final int? maxLength;
  final int? maxLines;
  final TextInputAction? textInputAction;
  final String hintText;
  final String? errorText;
  final String? compareErrorText;
  final TextEditingController? controller;
  final TextEditingController? compareWithcontroller;
  final bool? readOnly;
  final bool? isImportantStarLabelRequired;
  final bool? obscureText;
  final bool? isFixedlabel;
  final bool? isDense;
  final bool? onSubmittedRequired;
  final bool? isfilled;
  final bool? isMobileValidationRequired;
  final bool? isEmailValidationRequired;
  final bool? isPasswordValidationRequired;
  final bool? customDateError;

  final bool? autofocus;
  final bool? compareWithPrevious;
  final bool? isSuffixIconRequired;
  final TextInputType? keyboardType;
  final void Function(String)? onChanged;
  final void Function()? onTap;
  final Widget? suffixIcon;

  final String? labelHeading;

  final List<TextInputFormatter>? inputFormatters;

  @override
  Widget build(BuildContext context) {
    final themeViewModel = context.watch<ThemeViewModel>();
    final baseTextTheme = themeViewModel.baseTextTheme;
    final baseColorTheme = themeViewModel.colors;
    bool error = false;
    return TextFormField(
      autovalidateMode: AutovalidateMode.onUserInteraction,
      autofocus: autofocus ?? false,
      focusNode: focusNode,
      maxLength: maxLength,
      maxLines: maxLines ?? 1,
      readOnly: readOnly ?? false,
      onTap: onTap,
      keyboardType: keyboardType ?? TextInputType.text,
      textInputAction: textInputAction ?? TextInputAction.next,
      controller: controller,
      obscureText: obscureText ?? false,
      inputFormatters: inputFormatters,
      onChanged: onChanged,
      onFieldSubmitted: onSubmittedRequired == true
          ? (_) => FocusScope.of(context).nextFocus()
          : null,
      style: baseTextTheme.hintValueTextStyle,
      textCapitalization: TextCapitalization.sentences,
      textAlign: textAlign ?? TextAlign.start,
      textAlignVertical: textAlignVertical,
      decoration: InputDecoration(
          // fillColor: baseColorTheme.primaryColor,
          // focusColor:  Colors.white,
          errorMaxLines: 2,
          contentPadding:
              const EdgeInsets.symmetric(horizontal: 10, vertical: 12),
          suffixIcon: isSuffixIconRequired == true ? suffixIcon : null,
          suffixIconConstraints:
              const BoxConstraints(minWidth: 20, minHeight: 20),
          // helperText: " ",
          // helperStyle: const TextStyle(fontSize: 0),

          isDense: true,
          hintText: hintText,
          hintStyle: hintStyle ?? baseTextTheme.loginTextFieldHintTextStyle,
          errorStyle: TextStyle(
              fontSize: 13,
              fontFamily: 'Avenir',
              color: baseColorTheme.textFieldFloatingLabelStarColor),

          // errorStyle: focusNode.hasFocus
          //     ? const TextStyle(fontSize: 0, height: 0)
          //     : TextStyle(
          //         fontSize: 13,
          //         fontFamily: 'Avenir',
          //         color: baseColorTheme.textFieldFloatingLabelStarColor),

          floatingLabelBehavior:
              isFixedlabel == true ? FloatingLabelBehavior.always : null,
          label: labelHeading != null
              ? RichText(
                  text: TextSpan(children: [
                  TextSpan(
                    text: labelHeading,
                    style: baseTextTheme.loginTextFieldFloatingLabelTextStyle,
                  ),
                  if (isImportantStarLabelRequired == true)
                    TextSpan(
                        text: " *",
                        style: baseTextTheme
                            .loginTextFieldFloatingLabelStarTextStyle),
                ]))
              : null,
          focusedErrorBorder: OutlineInputBorder(
              borderSide: BorderSide(
                  color: baseColorTheme.textFieldFloatingLabelStarColor)),
          errorBorder: (controller != null && controller!.text.isNotEmpty)
              ? null
              : OutlineInputBorder(
                  borderSide: BorderSide(
                      color: baseColorTheme.textFieldFloatingLabelStarColor)),
          focusedBorder: const OutlineInputBorder(
              borderSide: BorderSide(color: Colors.black)),
          enabledBorder: OutlineInputBorder(
              borderSide:
                  BorderSide(color: baseColorTheme.textfieldInputBorderColor)),
          border: OutlineInputBorder(
              borderSide:
                  BorderSide(color: baseColorTheme.textfieldInputBorderColor))),
      validator: (value) {
        value!.trim().isNotEmpty ? error = !error : error = error;
        if (customDateError == true) {
          if (value.toLowerCase() == hintText.toLowerCase()) {
            return errorText;
          }
        }
        if (value.isEmpty) {
          return errorText;
        }
        if (compareWithPrevious == true) {
          if (compareWithcontroller != null) {
            if (value != compareWithcontroller!.text) {
              return compareErrorText ??
                  'Make sure your field matches with above';
            }
          }
        }
        if (isMobileValidationRequired == true) {
          if (value.length > 10 || value.length < 10) {
            return "Please Enter Valid Mobile Number";
          }
        }

        if (isEmailValidationRequired == true) {
          if (!RegExp(
                  r'^(([^<>()[\]\\.,;:\s@\"]+(\.[^<>()[\]\\.,;:\s@\"]+)*)|(\".+\"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$')
              .hasMatch(value)) {
            return "Please Enter Valid Email ID";
          }
        }
        if (isPasswordValidationRequired == true) {
          if (!RegExp(
                  r'^(?=.*?[A-Z])(?=.*?[a-z])(?=.*?[0-9])(?=.*?[!@#\$&*~]).{6,}$')
              .hasMatch(value)) {
            return "Please enter a strong password of atleast 6 characters ( for eg. Name@1234 )";
          }
        }
        return null;
      },
    );
  }
}