Null safety in Flutter - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a nullable String variable.

Flutter

String? name[1]

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

A;

B:

C!

D=

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting the semicolon at the end.

Using an exclamation mark instead of a semicolon.

In Dart, to declare a nullable variable, you add a question mark after the type. The statement ends with a semicolon.

2fill in blank

medium

Complete the code to safely access the length of a nullable String variable.

Flutter

int? length = name[1].length;

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

A!

B??

C.

D?

Attempts:

3 left

💡 Hint

Common Mistakes

Using the dot operator directly on a nullable variable causes errors.

Using the exclamation mark forces non-null but can cause runtime errors.

The question mark before the dot safely accesses the property only if the variable is not null.

3fill in blank

hard

Fix the error in the code by forcing non-null access to the variable.

Flutter

int length = name[1].length;

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

A!

B?

C.

D??

Attempts:

3 left

💡 Hint

Common Mistakes

Using the safe access operator when the variable is expected to be non-null.

Forgetting to handle null values causing runtime errors.

The exclamation mark tells Dart you are sure the variable is not null, so it can access the property directly.

4fill in blank

hard

Fill both blanks to provide a default value if the nullable variable is null.

Flutter

String displayName = name[1] '' [2] 'Guest';

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

A??

B!

C+

D?

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong operator for null fallback.

Forgetting to concatenate strings properly.

The '??' operator returns the value on its left if not null, otherwise the right. The '+' concatenates strings.

5fill in blank

hard

Fill all three blanks to declare a nullable integer, assign a value, and force non-null access.

Flutter

int? count[1] 5;
int total = count[2] [3] 0;

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

A=

B!

C??

D;

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up assignment and comparison operators.

Not handling null values properly causing errors.

Use '=' to assign, '!' to assert non-null, and '??' to provide a default if null.