Custom validators in Flutter - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a simple validator that checks if the input is empty.

Flutter

String? validateNotEmpty(String? value) {
  if (value == null || value[1] '') {
    return 'Field cannot be empty';
  }
  return null;
}

Drag options to blanks, or click blank then click option'

A!=

B==

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using != instead of == causes the validator to fail when the field is empty.

Using > or < operators on strings causes errors.

The validator returns an error message if the input is null or equals an empty string. The operator == checks for equality.

2fill in blank

medium

Complete the code to create a validator that checks if the input length is at least 6 characters.

Flutter

String? validateMinLength(String? value) {
  if (value == null || value.length [1] 6) {
    return 'Minimum 6 characters required';
  }
  return null;
}

Drag options to blanks, or click blank then click option'

A<

B>

C<=

D>=

Attempts:

3 left

💡 Hint

Common Mistakes

Using > or >= will allow shorter inputs incorrectly.

Using <= includes length 6 as invalid, which is wrong.

The validator returns an error if the input length is less than 6. The operator < checks this condition.

3fill in blank

hard

Fix the error in the validator that checks if the input contains only digits.

Flutter

String? validateDigitsOnly(String? value) {
  final regex = RegExp(r'^[0-9]+$');
  if (value == null || !regex.[1](value)) {
    return 'Only digits allowed';
  }
  return null;
}

Drag options to blanks, or click blank then click option'

Amatch

Bcontains

ChasMatch

DstartsWith

Attempts:

3 left

💡 Hint

Common Mistakes

Using match causes a runtime error because it does not exist.

Using contains or startsWith only checks part of the string.

The hasMatch method checks if the entire string matches the pattern. Using match or others causes errors or wrong checks.

4fill in blank

hard

Fill both blanks to create a validator that checks if the input is a valid email format.

Flutter

String? validateEmail(String? value) {
  final emailRegex = RegExp(r'^[\w-\.]+@([\w-]+\.)+[\w-]{2,4}$');
  if (value == null || !emailRegex.[1](value)) {
    return 'Enter a valid email';
  }
  return [2];
}

Drag options to blanks, or click blank then click option'

AhasMatch

Bmatch

Cnull

Dvalue

Attempts:

3 left

💡 Hint

Common Mistakes

Returning the input value instead of null causes the form to think there is an error.

Using match causes errors.

The hasMatch method checks if the input matches the email pattern. The validator returns null when the input is valid, meaning no error.

5fill in blank

hard

Fill all three blanks to create a validator that checks if the input password has at least 8 characters, contains a digit, and returns null if valid.

Flutter

String? validatePassword(String? value) {
  final digitRegex = RegExp(r'\d');
  if (value == null || value.length [1] 8 || !digitRegex.[2](value)) {
    return 'Password must be 8+ chars and include a digit';
  }
  return [3];
}

Drag options to blanks, or click blank then click option'

A<

BhasMatch

Cnull

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using > instead of < for length check allows short passwords.

Using wrong regex method causes errors.

Returning value instead of null causes validation failure.

The validator checks if the password length is less than 8 and if it does not contain a digit using hasMatch. It returns null when valid.