Expanded and Flexible in Flutter - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to make the child widget fill the available space horizontally using Expanded.

Flutter

Row(children: [Expanded(child: Container(color: Colors.blue, width: [1], height: 50))])

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

Anull

B100

Cdouble.infinity

D50

Attempts:

3 left

💡 Hint

Common Mistakes

Setting a fixed width like 100 prevents filling the space.

Using null width causes errors inside Expanded.

Using double.infinity for width inside Expanded makes the container fill all available horizontal space.

2fill in blank

medium

Complete the code to make the Flexible widget allow its child to shrink if needed.

Flutter

Flexible(flex: 2, fit: [1], child: Container(color: Colors.red, width: 100, height: 50))

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

AFlexFit.tight

BFlexFit.loose

CFlexFit.expand

DFlexFit.fill

Attempts:

3 left

💡 Hint

Common Mistakes

Using FlexFit.tight forces the child to fill all space, no shrinking.

FlexFit.expand is not a valid option.

FlexFit.loose lets the child be smaller than the available space, allowing it to shrink.

3fill in blank

hard

Fix the error in the code by choosing the correct widget to wrap the child for flexible space allocation.

Flutter

Row(children: [[1](child: Container(color: Colors.green, width: 50, height: 50))])

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

AFlexible

BExpanded

CContainer

DSizedBox

Attempts:

3 left

💡 Hint

Common Mistakes

Using Container or SizedBox does not provide flexible space behavior.

Expanded forces full expansion, which may cause layout issues.

Flexible allows flexible space allocation without forcing full expansion, suitable here.

4fill in blank

hard

Fill both blanks to create a Row where the first child takes twice the space of the second child using Expanded.

Flutter

Row(children: [Expanded(flex: [1], child: Container(color: Colors.orange, height: 50)), Expanded(flex: [2], child: Container(color: Colors.purple, height: 50))])

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

A2

B1

C3

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 flex causes the child to get no space.

Using equal flex values gives equal space, not twice.

The first Expanded has flex 2, the second has flex 1, so the first child gets twice the space.

5fill in blank

hard

Fill all three blanks to create a Column with Flexible children where the first child can shrink, the second fills tightly, and the third shrinks.

Flutter

Column(children: [Flexible(fit: [1], flex: [2], child: Container(color: Colors.yellow, height: 50)), Flexible(fit: [3], flex: 1, child: Container(color: Colors.blueGrey, height: 50)), Flexible(flex: 1, child: Container(color: Colors.teal, height: 50))])

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

AFlexFit.loose

B1

CFlexFit.tight

D2

Attempts:

3 left

💡 Hint

Common Mistakes

Using FlexFit.tight for all children forces all to fill space.

Not setting flex values properly changes space distribution.

The first Flexible uses FlexFit.loose and flex 2 to allow shrinking. The second uses FlexFit.tight and flex 1 to fill tightly.

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