一个包含一个文本字段的表单字段。这是一个方便的小部件，它将一个文本字段小部件 Package 在一个表单字段中。

static formField({
    required String label,
    String? initialValue,
    FormFieldSetter? onSaved,
    ValueChanged? onChanged,
    Icon? icon,
    int? maxLines,
    TextEditingController? controller,
    TextInputType? keyboard,
  }) {
    return Padding(
      padding: const EdgeInsets.symmetric(vertical: 10, horizontal: 8),
      child: TextFormField(
        validator: (value) {
          if (value!.isEmpty) {
            return 'please type the $label above';
          }
        },
        initialValue: initialValue,
        controller: controller,
        maxLines: maxLines,
        onChanged: onChanged,
        onSaved: onSaved,
        keyboardType: keyboard,
        decoration: InputDecoration(
          label: Text(label),
          prefixIcon: icon,
          hintText: 'Type $label here',
          border: const OutlineInputBorder(),
        ),
      ),
    );
  }