Slivers (SliverList, SliverGrid, SliverAppBar) in Flutter - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a basic SliverAppBar with a title.

Flutter

SliverAppBar(
  pinned: true,
  expandedHeight: 150.0,
  flexibleSpace: FlexibleSpaceBar(
    title: Text([1]),
  ),
)

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

AMyApp

B"My App"

Ctitle

DAppBar

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting quotes around the title string.

Passing a widget instead of a string.

The title property expects a Text widget with a string. "My App" is the correct string literal.

2fill in blank

medium

Complete the code to create a SliverList with 5 Text widgets.

Flutter

SliverList(
  delegate: SliverChildBuilderDelegate(
    (BuildContext context, int index) {
      return Text('Item ${index + 1}');
    },
    childCount: [1],
  ),
)

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

A5

B1

C10

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Setting childCount to 0 results in no items.

Using a number larger than needed.

childCount defines how many children the SliverList builds. To create 5 items, use 5.

3fill in blank

hard

Fix the error in the SliverGrid delegate to use the correct grid delegate.

Flutter

SliverGrid(
  gridDelegate: [1](
    crossAxisCount: 3,
    mainAxisSpacing: 10.0,
    crossAxisSpacing: 10.0,
  ),
  delegate: SliverChildBuilderDelegate(
    (BuildContext context, int index) {
      return Container(color: Colors.blue, height: 50.0);
    },
    childCount: 6,
  ),
)

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

ASliverGridDelegateFixedCrossAxisCount

BSliverGridDelegate

CGridDelegateWithFixedCrossAxisCount

DSliverGridDelegateWithFixedCrossAxisCount

Attempts:

3 left

💡 Hint

Common Mistakes

Using a non-existent class name.

Omitting 'With' in the class name.

The correct class for fixed cross axis count grid delegate is SliverGridDelegateWithFixedCrossAxisCount.

4fill in blank

hard

Fill both blanks to create a SliverAppBar that floats and snaps.

Flutter

SliverAppBar(
  floating: [1],
  snap: [2],
  title: Text('Floating AppBar'),
)

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

Atrue

Bfalse

Cnull

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Setting snap to true but floating to false causes error.

Using non-boolean values.

To enable floating and snapping behavior, both floating and snap must be true.

5fill in blank

hard

Fill all three blanks to create a SliverGrid with 2 columns, 8 items, and 8.0 spacing.

Flutter

SliverGrid(
  gridDelegate: [1](
    crossAxisCount: [2],
    mainAxisSpacing: [3],
    crossAxisSpacing: [3],
  ),
  delegate: SliverChildBuilderDelegate(
    (context, index) => Container(color: Colors.red),
    childCount: 8,
  ),
)

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

ASliverGridDelegateWithFixedCrossAxisCount

B2

C8.0

DSliverGridDelegateWithMaxCrossAxisExtent

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong delegate class.

Setting spacing as integer instead of double.

Use SliverGridDelegateWithFixedCrossAxisCount for fixed columns, set crossAxisCount to 2, and spacing to 8.0.

Practice

1. What is the main purpose of using SliverAppBar in a Flutter app?

easy

A. To replace the default app bar with a static title

B. To display a fixed footer at the bottom of the screen

C. To create a grid layout inside a scrollable area

D. To create a header that can expand, collapse, and stay visible when scrolling

Solution

1. Step 1: Understand SliverAppBar role

   SliverAppBar is designed to create headers that can expand and collapse as the user scrolls.

2. Step 2: Compare options with SliverAppBar behavior

   Only To create a header that can expand, collapse, and stay visible when scrolling describes the expandable and pinned header behavior of SliverAppBar.

3. Final Answer:

   To create a header that can expand, collapse, and stay visible when scrolling -> Option D

4. Quick Check:

   SliverAppBar = expandable header [OK]

Hint: Remember: SliverAppBar controls flexible headers [OK]

Common Mistakes:

• Confusing SliverAppBar with fixed AppBar
• Thinking SliverAppBar creates grids or lists
• Assuming SliverAppBar is a footer widget

2. Which of the following is the correct way to create a SliverList inside a CustomScrollView?

easy

A. SliverList(items: List.generate(5, (index) => Text('Item $index')))

B. SliverList(delegate: SliverChildBuilderDelegate((context, index) => Text('Item $index')))

C. SliverList(itemBuilder: (context, index) => Text('Item $index'))

D. SliverList(children: [Text('Item 1'), Text('Item 2')])

Solution

1. Step 1: Recall SliverList constructor

   SliverList requires a delegate parameter, usually SliverChildBuilderDelegate or SliverChildListDelegate.

2. Step 2: Check each option's syntax

   SliverList(delegate: SliverChildBuilderDelegate((context, index) => Text('Item $index'))) correctly uses delegate: SliverChildBuilderDelegate. Options A, B, and C use invalid parameters or properties.

3. Final Answer:

   SliverList(delegate: SliverChildBuilderDelegate((context, index) => Text('Item $index'))) -> Option B

4. Quick Check:

   SliverList needs delegate = SliverList(delegate: SliverChildBuilderDelegate((context, index) => Text('Item $index'))) [OK]

Hint: SliverList always needs a delegate parameter [OK]

Common Mistakes:

• Using children instead of delegate
• Using itemBuilder directly on SliverList
• Passing items instead of delegate

3. Given the code snippet below, what will be displayed on the screen?

CustomScrollView(
  slivers: [
    SliverAppBar(
      expandedHeight: 100,
      pinned: true,
      flexibleSpace: FlexibleSpaceBar(title: Text('Hello')),
    ),
    SliverList(
      delegate: SliverChildBuilderDelegate(
        (context, index) => ListTile(title: Text('Item $index')),
        childCount: 3,
      ),
    ),
  ],
)

medium

A. A scrollable view with a pinned app bar titled 'Hello' and 3 list items labeled Item 0 to Item 2

B. A static app bar with title 'Hello' and 3 buttons labeled Item 1 to Item 3

C. An error because SliverAppBar cannot be pinned

D. A scrollable grid with 3 items and no app bar

Solution

1. Step 1: Analyze SliverAppBar properties

   The app bar is pinned and has a flexible space with title 'Hello', so it stays visible when scrolling.

2. Step 2: Analyze SliverList delegate

   The list builds 3 items labeled 'Item 0', 'Item 1', and 'Item 2'.

3. Final Answer:

   A scrollable view with a pinned app bar titled 'Hello' and 3 list items labeled Item 0 to Item 2 -> Option A

4. Quick Check:

   Pinned SliverAppBar + SliverList with 3 items = A scrollable view with a pinned app bar titled 'Hello' and 3 list items labeled Item 0 to Item 2 [OK]

Hint: Pinned SliverAppBar stays visible; SliverList shows items lazily [OK]

Common Mistakes:

• Thinking pinned means static, not scrollable
• Confusing list items count or labels
• Assuming SliverAppBar cannot be pinned

4. Identify the error in the following Flutter code snippet using slivers:

CustomScrollView(
  slivers: [
    SliverGrid(
      gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(crossAxisCount: 2),
      children: List.generate(4, (index) => Container(color: Colors.blue)),
    ),
  ],
)

medium

A. List.generate cannot be used inside SliverGrid

B. SliverGridDelegateWithFixedCrossAxisCount is not a valid class

C. SliverGrid requires a delegate, not a children parameter

D. CustomScrollView cannot contain SliverGrid

Solution

1. Step 1: Check SliverGrid constructor requirements

   SliverGrid requires a delegate parameter, not children.

2. Step 2: Validate other parts

   SliverGridDelegateWithFixedCrossAxisCount is valid, and List.generate can be used inside a delegate.

3. Final Answer:

   SliverGrid requires a delegate, not a children parameter -> Option C

4. Quick Check:

   SliverGrid needs delegate, not children [OK]

Hint: SliverGrid uses delegate, not children, for lazy loading [OK]

Common Mistakes:

• Using children instead of delegate in SliverGrid
• Confusing SliverGridDelegateWithFixedCrossAxisCount as invalid
• Thinking CustomScrollView disallows SliverGrid

5. You want to create a scrollable screen with a header that expands and pins, followed by a grid of images with 3 columns, and then a list of text items. Which of the following is the best way to structure your Flutter widget tree?

hard

A. CustomScrollView(slivers: [SliverAppBar(pinned: true, expandedHeight: 200, flexibleSpace: FlexibleSpaceBar(title: Text('Gallery'))), SliverGrid(delegate: SliverChildBuilderDelegate((c, i) => Image.network(urls[i]), childCount: urls.length), gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(crossAxisCount: 3)), SliverList(delegate: SliverChildBuilderDelegate((c, i) => ListTile(title: Text(items[i])), childCount: items.length))])

B. ListView(children: [AppBar(title: Text('Gallery')), GridView.count(crossAxisCount: 3, children: images), ListView(children: texts)])

C. CustomScrollView(children: [SliverAppBar(), SliverGrid(), SliverList()])

D. Column(children: [SliverAppBar(), SliverGrid(), SliverList()])

Solution

1. Step 1: Identify correct widget for scrollable slivers

   CustomScrollView with slivers parameter is needed to combine SliverAppBar, SliverGrid, and SliverList.

2. Step 2: Check each option's structure

   CustomScrollView(slivers: [SliverAppBar(pinned: true, expandedHeight: 200, flexibleSpace: FlexibleSpaceBar(title: Text('Gallery'))), SliverGrid(delegate: SliverChildBuilderDelegate((c, i) => Image.network(urls[i]), childCount: urls.length), gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(crossAxisCount: 3)), SliverList(delegate: SliverChildBuilderDelegate((c, i) => ListTile(title: Text(items[i])), childCount: items.length))]) correctly uses CustomScrollView with slivers and proper delegates. ListView(children: [AppBar(title: Text('Gallery')), GridView.count(crossAxisCount: 3, children: images), ListView(children: texts)]) uses nested scrollables incorrectly. CustomScrollView(children: [SliverAppBar(), SliverGrid(), SliverList()]) uses children instead of slivers. Column(children: [SliverAppBar(), SliverGrid(), SliverList()]) uses Column which cannot host slivers.

3. Final Answer:

   CustomScrollView with SliverAppBar, SliverGrid, and SliverList using delegates -> Option A

4. Quick Check:

   Use CustomScrollView with slivers and delegates = CustomScrollView(slivers: [SliverAppBar(pinned: true, expandedHeight: 200, flexibleSpace: FlexibleSpaceBar(title: Text('Gallery'))), SliverGrid(delegate: SliverChildBuilderDelegate((c, i) => Image.network(urls[i]), childCount: urls.length), gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(crossAxisCount: 3)), SliverList(delegate: SliverChildBuilderDelegate((c, i) => ListTile(title: Text(items[i])), childCount: items.length))]) [OK]

Hint: Use CustomScrollView with slivers and delegates for mixed scroll content [OK]

Common Mistakes:

• Using ListView or Column instead of CustomScrollView for slivers
• Passing slivers as children instead of slivers parameter
• Not using delegates for SliverGrid and SliverList