Why validation ensures data quality in Flutter - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to add a simple validation that checks if the input is not empty.

Flutter

TextFormField(
  validator: (value) {
    if (value == null || value[1] '') {
      return 'Please enter some text';
    }
    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 validation to fail incorrectly.

Using comparison operators like '>' or '<' on strings causes errors.

The validator checks if the input value is equal to an empty string to ensure the user entered some text.

2fill in blank

medium

Complete the code to validate that the input length is at least 5 characters.

Flutter

TextFormField(
  validator: (value) {
    if (value != null && value.length [1] 5) {
      return 'Enter at least 5 characters';
    }
    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 '<' reverses the logic.

Using '>=' or '<=' includes 5, which is not the intended check.

The validator returns an error if the input length is less than 5 characters.

3fill in blank

hard

Fix the error in the validation that checks if the input is a valid email format.

Flutter

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

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

Acontains

Bmatch

ChasMatch

Dtest

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'match' or 'contains' causes errors because they are not RegExp methods.

Using 'test' is from other languages, not Dart.

The RegExp method 'hasMatch' checks if the input matches the email pattern.

4fill in blank

hard

Fill both blanks to create a validation that ensures the input is a number between 1 and 10.

Flutter

TextFormField(
  validator: (value) {
    final numValue = int.tryParse(value ?? '');
    if (numValue == null || numValue [1] 1 || numValue [2] 10) {
      return 'Enter a number between 1 and 10';
    }
    return null;
  },
)

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

A<

B>

C<=

D>=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<=' or '>=' includes boundary numbers incorrectly.

Reversing the operators changes the logic.

The validation checks if the number is less than 1 or greater than 10 to reject invalid inputs.

5fill in blank

hard

Fill all three blanks to create a validation that returns an error if the input is empty, less than 3 characters, or contains spaces.

Flutter

TextFormField(
  validator: (value) {
    if (value == null || value[1] '' || value.length [2] 3 || value.contains([3])) {
      return 'Invalid input';
    }
    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 '==' for empty check.

Using '>=' instead of '<' for length check.

Using wrong character for contains check.

The validation checks if the input is empty (== ''), shorter than 3 characters (< 3), or contains a space character (' ').