Expanded and Flexible in Flutter - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the Expanded widget do in Flutter?

The Expanded widget tells its child to fill the available space in the main axis of a Row, Column, or Flex. It expands the child to use all leftover space.

intermediate

How does the Flexible widget differ from Expanded?

Flexible lets its child be smaller than the available space if it wants, while Expanded forces the child to fill all the available space. Flexible gives more control over child's size.

beginner

What is the role of the flex property in Expanded and Flexible?

The flex property is a number that tells how much space this widget should take relative to its siblings. For example, flex: 2 means twice as much space as flex: 1.

intermediate

Can Flexible widget shrink its child smaller than its intrinsic size?

Yes, Flexible can shrink its child smaller than its intrinsic size if the child allows it. This helps when you want flexible but not forced expansion.

beginner

Why use Expanded or Flexible inside a Row or Column?

They help control how children share space. Without them, children take only the space they need. With them, you can make children grow or shrink to fill or share leftover space nicely.

What happens if you wrap a widget with Expanded inside a Row?

A The widget fills all remaining horizontal space.

B The widget shrinks to its minimum size.

C The widget disappears.

D The widget fills all vertical space.

Expanded makes the child fill all leftover space along the main axis, which is horizontal in a Row.

Which widget allows its child to be smaller than the available space if it wants?

A Flexible

B Expanded

C Container

D SizedBox

Flexible lets the child be smaller or bigger, depending on child's size and constraints.

If two Expanded widgets have flex values 1 and 3, how is space divided?

A 3/4 for first, 1/4 for second

B Equal space for both

C 1/4 for first, 3/4 for second

D Only the first gets space

The space is divided in ratio 1:3, so first gets 1/4 and second gets 3/4 of leftover space.

Which widget forces its child to fill all available space?

A Flexible

B Expanded

C Padding

D Align

Expanded forces the child to fill all available space along the main axis.

What is the main axis in a Column?

A Horizontal

B Diagonal

C None

D Vertical

The main axis of a Column is vertical, so Expanded expands vertically.

Explain the difference between Expanded and Flexible widgets in Flutter.

Think about how much space the child widget takes inside a Row or Column.

Describe a real-life scenario where you would use Expanded inside a Row.

Imagine a toolbar with a search box that should grow to fill space.

Practice

1. What does the Expanded widget do inside a Row or Column in Flutter?

easy

A. It makes the child widget scrollable.

B. It makes the child widget ignore available space and keep its size.

C. It makes the child widget fill all the available space tightly.

D. It adds padding around the child widget.

Solution

1. Step 1: Understand Expanded behavior

   The Expanded widget forces its child to fill the available space tightly inside a Row or Column.

2. Step 2: Compare with other options

   Other options describe unrelated behaviors like padding or scrolling, which Expanded does not do.

3. Final Answer:

   It makes the child widget fill all the available space tightly. -> Option C

4. Quick Check:

   Expanded = fills space tightly [OK]

Hint: Expanded fills space tightly inside Row or Column [OK]

Common Mistakes:

• Confusing Expanded with Flexible
• Thinking Expanded adds padding
• Assuming Expanded makes widget scrollable

2. Which of the following is the correct syntax to use Flexible with a child widget in Flutter?

easy

A. Flexible(child: Text('Hello'))

B. Flexible(Text('Hello'))

C. Flexible = Text('Hello')

D. Flexible: Text('Hello')

Solution

1. Step 1: Recall Flexible widget syntax

   The correct syntax requires the child widget passed as a named parameter: Flexible(child: ...).

2. Step 2: Identify incorrect syntax

   Options B, C, and D miss the named parameter or use invalid assignment syntax.

3. Final Answer:

   Flexible(child: Text('Hello')) -> Option A

4. Quick Check:

   Flexible uses child: parameter [OK]

Hint: Flexible requires child: parameter for its widget [OK]

Common Mistakes:

• Omitting child: label
• Using assignment instead of constructor
• Passing child without parentheses

3. Consider this Flutter code inside a Row:

Row(
  children: [
    Expanded(child: Container(width: 50, color: Colors.red)),
    Expanded(flex: 2, child: Container(width: 50, color: Colors.blue)),
  ],
)

What will be the relative widths of the red and blue containers on screen?

medium

A. Red fills 1/3, blue fills 2/3 of the row width

B. Red fills half the row, blue fills the other half

C. Red and blue both have fixed width 50 pixels

D. Red fills all space, blue is ignored

Solution

1. Step 1: Understand Expanded and Expanded with flex

   Expanded takes available space tightly with default flex=1. Expanded(flex:2) takes twice the space tightly.

2. Step 2: Calculate relative widths

   Total flex = 1 (first Expanded) + 2 (second Expanded) = 3. Red gets 1/3, blue gets 2/3 of the row width. The width: 50 is overridden by the tight constraints.

3. Final Answer:

   Red fills 1/3, blue fills 2/3 of the row width -> Option A

4. Quick Check:

   Flex ratio 1:2 means widths 1/3 and 2/3 [OK]

Hint: Sum flex values, divide space proportionally [OK]

Common Mistakes:

• Ignoring flex values
• Thinking width property overrides flex
• Assuming equal widths without flex

4. This Flutter code throws an error. What is the problem?

Row(
  children: [
    Flexible(flex: 1),
    Container(color: Colors.green),
  ],
)

medium

A. flex property must be greater than 1.

B. Container cannot be inside a Row.

C. Row requires at least three children.

D. Flexible widget is missing a child widget.

Solution

1. Step 1: Check Flexible widget usage

   Flexible requires a child widget to display. Here, it is missing.

2. Step 2: Validate other options

   Container can be inside Row, flex can be 1, and Row can have any number of children.

3. Final Answer:

   Flexible widget is missing a child widget. -> Option D

4. Quick Check:

   Flexible must have child [OK]

Hint: Flexible always needs a child widget [OK]

Common Mistakes:

• Omitting child in Flexible
• Thinking flex must be >1
• Assuming Row needs 3 children

5. You want two buttons side by side in a Row. The first button should take 1/4 of the width, the second button 3/4. Which Flutter widget setup achieves this best?

hard

A. Row(children: [Expanded(child: Button1), Expanded(child: Button2)])

B. Row(children: [Flexible(flex: 1, child: Button1), Flexible(flex: 3, child: Button2)])

C. Row(children: [Button1, Button2]) with fixed widths

D. Column(children: [Flexible(flex: 1, child: Button1), Flexible(flex: 3, child: Button2)])

Solution

1. Step 1: Understand flex distribution in Row

   Using Flexible with flex values 1 and 3 divides the Row width into 4 parts, assigning 1/4 and 3/4 respectively.

2. Step 2: Evaluate other options

   Row(children: [Expanded(child: Button1), Expanded(child: Button2)]) gives equal widths (1/2 each). Row(children: [Button1, Button2]) with fixed widths is less flexible. Column(children: [Flexible(flex: 1, child: Button1), Flexible(flex: 3, child: Button2)]) uses Column, which stacks vertically, not side by side.

3. Final Answer:

   Row(children: [Flexible(flex: 1, child: Button1), Flexible(flex: 3, child: Button2)]) -> Option B

4. Quick Check:

   Flexible flex ratio 1:3 divides width correctly [OK]

Hint: Use Flexible with flex ratio matching desired width parts [OK]

Common Mistakes:

• Using Expanded for unequal widths
• Using Column instead of Row
• Setting fixed widths instead of flex