Regex mask with two digit number validation using 'mask_text_input_formatter'

Question

I want to create a regexp for the month part in my input mask. This is what I have so far. But with this approach I can't write anything in the month part because it checks for only one digit ('m') and it expects to be two digits I think.

  MaskTextInputFormatter _birthdayFormatter = MaskTextInputFormatter(
    mask: 'dd/mm/yyyy',
    filter: {'d': RegExp(r'[0-9]'), 'm': RegExp(r'(^0?[1-9]$)|(^1[0-2]$)'), 'y': RegExp(r'[0-9]')}
  );

Is there a way to achieve this?

Answer 1

Mask and key

 final _formKey = GlobalKey<FormState>();

    MaskTextInputFormatter _birthdayFormatter = MaskTextInputFormatter(
      mask: '##/##/####',
      filter: {"#": RegExp(r'[0-9]')},
    );

Form

Form(
                        key: _formKey,
                        child: TextFormField(
                          inputFormatters: [_birthdayFormatter],
                          decoration: InputDecoration(
                            hintText: 'dd/mm/yyyy',
                          ),
                          validator: (value) {
                            if (value == null || value.isEmpty) {
                              return 'Please enter date';
                            }
                            List<String> dateParts = value.split('/');
                            if (dateParts.length != 3) {
                              return 'Date must be in dd/mm/yyyy format';
                            }

                            int? day = int.tryParse(dateParts[0]);
                            int? month = int.tryParse(dateParts[1]);
                            int? year = int.tryParse(dateParts[2]);

                            if (day == null || day < 1 || day > 31) {
                              return 'Day must be a number between 1 and 31';
                            }

                            if (month == null || month < 1 || month > 12) {
                              return 'Month must be a number between 1 and 12';
                            }

                            if (year == null || year < 1900 || year > 3000) {
                              return 'Year must be a number between 1900 and 3000';
                            }

                            // Create a DateTime to check if the date is correct.
                            DateTime? date =
                                DateTime.tryParse('$year-$month-$day');
                            if (date == null) {
                              return 'Invalid date';
                            }

                            return null;
                          },
                        ),
                      ),

Validator

if (_formKey.currentState!.validate()) {
                                    // If the form is valid, display a Snackbar.
                                    ScaffoldMessenger.of(context).showSnackBar(
                                        SnackBar(
                                            content: Text('Processing Data')));
                                  }