ListView.builder in Flutter - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a ListView using ListView.builder.

Flutter

ListView.builder(
  itemCount: 10,
  itemBuilder: (context, index) {
    return Text('Item ${index}');
  },
  [1]: true,
)

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

Aprimary

BscrollDirection

Creverse

DshrinkWrap

Attempts:

3 left

💡 Hint

Common Mistakes

Using scrollDirection instead of shrinkWrap here.

Forgetting to set shrinkWrap when nesting ListView.

The shrinkWrap property tells the ListView to size itself based on its children. Setting it to true is common when ListView is inside another scrollable widget.

2fill in blank

medium

Complete the code to set the scroll direction of the ListView to horizontal.

Flutter

ListView.builder(
  itemCount: 5,
  itemBuilder: (context, index) => Text('Item ${index}'),
  [1]: Axis.horizontal,
)

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

AscrollDirection

Breverse

CshrinkWrap

Dprimary

Attempts:

3 left

💡 Hint

Common Mistakes

Using reverse instead of scrollDirection to change scroll direction.

Not importing Axis enum.

The scrollDirection property controls the direction in which the ListView scrolls. Setting it to Axis.horizontal makes the list scroll sideways.

3fill in blank

hard

Fix the error in the itemBuilder function to correctly return a ListTile widget.

Flutter

ListView.builder(
  itemCount: 3,
  itemBuilder: (context, index) {
    return [1](
      title: Text('Title ${index}'),
    );
  },
)

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

ATextField

BContainer

CListTile

DColumn

Attempts:

3 left

💡 Hint

Common Mistakes

Returning a Container without child widgets.

Using TextField which is for input, not list items.

The itemBuilder must return a widget. Here, ListTile is the correct widget to display a title in a list.

4fill in blank

hard

Fill both blanks to create a ListView.builder that shows 4 items with a blue background color.

Flutter

ListView.builder(
  itemCount: [1],
  itemBuilder: (context, index) {
    return Container(
      color: [2],
      child: Text('Item ${index}'),
    );
  },
)

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

A4

BColors.red

CColors.blue

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Setting itemCount to 5 instead of 4.

Using red color instead of blue.

The itemCount should be 4 to show four items. The color property is set to Colors.blue to give a blue background.

5fill in blank

hard

Fill all three blanks to create a ListView.builder that shows uppercase item titles with 6 items and a green background.

Flutter

ListView.builder(
  itemCount: [1],
  itemBuilder: (context, index) {
    return Container(
      color: [2],
      child: Text('Item ${index}'.[3]()),
    );
  },
)

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

A6

BColors.green

CtoUpperCase

DtoLowerCase

Attempts:

3 left

💡 Hint

Common Mistakes

Using toLowerCase instead of toUpperCase.

Setting itemCount to wrong number.

Set itemCount to 6 to show six items. The container color is Colors.green. The text is converted to uppercase using toUpperCase().

Practice

1. What does ListView.builder do in Flutter?

easy

A. Creates list items only when they are visible on screen for better performance.

B. Creates all list items at once when the list is built.

C. Creates a fixed number of buttons instead of list items.

D. Creates a grid layout instead of a list.

Solution

1. Step 1: Understand ListView.builder purpose

   ListView.builder creates list items lazily, meaning it builds only those items visible on screen.

2. Step 2: Compare with other list types

   Other list types like ListView create all items at once, which can be slow for large lists.

3. Final Answer:

   Creates list items only when they are visible on screen for better performance. -> Option A

4. Quick Check:

   ListView.builder = lazy item creation [OK]

Hint: ListView.builder builds items on demand, not all at once [OK]

Common Mistakes:

• Thinking ListView.builder creates all items immediately
• Confusing ListView.builder with GridView
• Assuming ListView.builder creates buttons instead of list items

2. Which of the following is the correct syntax to create a ListView.builder with 10 items?

easy

A. ListView.builder(items: 10, buildItem: (context, index) => Text('Item $index'))

B. ListView.builder(count: 10, builder: (context, index) => Text('Item $index'))

C. ListView.builder(length: 10, itemBuilder: (context, i) => Text('Item $i'))

D. ListView.builder(itemCount: 10, itemBuilder: (context, index) => Text('Item $index'))

Solution

1. Step 1: Identify correct parameter names

   The correct parameters are itemCount for number of items and itemBuilder for building each item.

2. Step 2: Check syntax correctness

   ListView.builder(itemCount: 10, itemBuilder: (context, index) => Text('Item $index')) uses correct parameter names and syntax with itemCount: 10 and itemBuilder function.

3. Final Answer:

   ListView.builder(itemCount: 10, itemBuilder: (context, index) => Text('Item $index')) -> Option D

4. Quick Check:

   Correct parameters = ListView.builder(itemCount: 10, itemBuilder: (context, index) => Text('Item $index')) [OK]

Hint: Use itemCount and itemBuilder parameters exactly [OK]

Common Mistakes:

• Using wrong parameter names like count or length
• Using buildItem instead of itemBuilder
• Missing itemCount parameter

3. What will be displayed by this Flutter code snippet?

ListView.builder(
  itemCount: 3,
  itemBuilder: (context, index) {
    return Text('Number: $index');
  },
)

medium

A. An empty list with no items

B. A list showing: Number: 0, Number: 1, Number: 2

C. A list showing: Number: 1, Number: 2, Number: 3

D. A runtime error because index is not defined

Solution

1. Step 1: Understand itemCount and index values

   itemCount is 3, so index goes from 0 to 2.

2. Step 2: Check itemBuilder output

   Each item shows text 'Number: ' followed by the index value, so items are 'Number: 0', 'Number: 1', 'Number: 2'.

3. Final Answer:

   A list showing: Number: 0, Number: 1, Number: 2 -> Option B

4. Quick Check:

   Index starts at 0, so output matches A list showing: Number: 0, Number: 1, Number: 2 [OK]

Hint: Index starts at 0 up to itemCount - 1 [OK]

Common Mistakes:

• Assuming index starts at 1
• Expecting 3 items with index 1 to 3
• Thinking it causes an error due to index

4. Identify the error in this ListView.builder code:

ListView.builder(
  itemCount: 5,
  itemBuilder: (context, index) {
    return Text('Item');
  },
  itemCount: 10,
)

medium

A. Duplicate itemCount parameter causes a syntax error.

B. Missing return statement inside itemBuilder.

C. itemBuilder function has wrong parameters.

D. No error; code runs fine.

Solution

1. Step 1: Check parameters in ListView.builder

   There are two itemCount parameters, which is not allowed and causes a syntax error.

2. Step 2: Verify other parts

   The itemBuilder returns a Text widget correctly, and parameters are correct.

3. Final Answer:

   Duplicate itemCount parameter causes a syntax error. -> Option A

4. Quick Check:

   Duplicate keys in widget constructor cause errors [OK]

Hint: Check for duplicate parameters in widget constructors [OK]

Common Mistakes:

• Ignoring duplicate parameters
• Thinking missing return causes error here
• Assuming itemBuilder parameters are wrong

5. You want to display a list of user names from a list users = ['Anna', 'Bob', 'Cara'] using ListView.builder. Which code correctly shows each name with its position number starting from 1?

hard

A. ListView.builder(itemCount: users.length, itemBuilder: (context, index) => Text('${index}. ${users[index + 1]}'))

B. ListView.builder(itemCount: users.length, itemBuilder: (context, index) => Text('$index. $users[index]'))

C. ListView.builder(itemCount: users.length, itemBuilder: (context, index) => Text('${index + 1}. ${users[index]}'))

D. ListView.builder(itemCount: users.length, itemBuilder: (context, i) => Text('${i}. ${users[i]}'))

Solution

1. Step 1: Adjust index to start numbering from 1

   Since index starts at 0, add 1 to show position starting from 1.

2. Step 2: Access user names correctly

   Use users[index] to get the correct user name for each index.

3. Final Answer:

   ListView.builder(itemCount: users.length, itemBuilder: (context, index) => Text('${index + 1}. ${users[index]}')) -> Option C

4. Quick Check:

   Index + 1 for numbering, users[index] for names [OK]

Hint: Add 1 to index for numbering, use users[index] for names [OK]

Common Mistakes:

• Using index without +1 for numbering
• Accessing users[index + 1] causing out-of-range error
• Using wrong variable name like i without declaration