CustomScrollView in Flutter - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a CustomScrollView with a single SliverList.

Flutter

CustomScrollView(
  slivers: [
    SliverList(
      delegate: SliverChildBuilderDelegate(
        (context, index) => Text('Item $index'),
        childCount: [1],
      ),
    ),
  ],
)

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

A10

Bitems

Cnull

Dfalse

Attempts:

3 left

💡 Hint

Common Mistakes

Using a variable name without defining it.

Passing null or false instead of a number.

The childCount property expects an integer to define how many items to build. Here, 10 means 10 items will be shown.

2fill in blank

medium

Complete the code to add a SliverAppBar inside CustomScrollView.

Flutter

CustomScrollView(
  slivers: [
    [1](
      title: Text('My AppBar'),
      floating: true,
    ),
  ],
)

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

ASliverList

BAppBar

CSliverAppBar

DSliverGrid

Attempts:

3 left

💡 Hint

Common Mistakes

Using AppBar directly inside slivers.

Using SliverList instead of SliverAppBar.

The SliverAppBar widget is used inside a CustomScrollView to create an app bar that scrolls with the content.

3fill in blank

hard

Fix the error in the code by completing the blank with the correct widget to create a grid inside CustomScrollView.

Flutter

CustomScrollView(
  slivers: [
    [1](
      gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(crossAxisCount: 2),
      delegate: SliverChildBuilderDelegate(
        (context, index) => Container(color: Colors.blue, height: 100),
        childCount: 6,
      ),
    ),
  ],
)

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

ASliverGrid

BSliverList

CGridView

DListView

Attempts:

3 left

💡 Hint

Common Mistakes

Using GridView inside slivers causes errors.

Using SliverList instead of SliverGrid for grids.

The SliverGrid widget is used to create grid layouts inside a CustomScrollView. GridView cannot be used directly inside slivers.

4fill in blank

hard

Fill both blanks to create a CustomScrollView with a SliverAppBar and a SliverList.

Flutter

CustomScrollView(
  slivers: [
    [1](
      title: Text('Header'),
      pinned: true,
    ),
    [2](
      delegate: SliverChildListDelegate([
        ListTile(title: Text('Item 1')),
        ListTile(title: Text('Item 2')),
      ]),
    ),
  ],
)

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

ASliverAppBar

BSliverGrid

CSliverList

DSliverPadding

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the widgets in the blanks.

Using SliverGrid instead of SliverList for the list.

The first blank should be SliverAppBar to create the header bar. The second blank should be SliverList to create a list of items.

5fill in blank

hard

Fill all three blanks to build a CustomScrollView with a pinned SliverAppBar, a SliverGrid, and a SliverList.

Flutter

CustomScrollView(
  slivers: [
    [1](
      title: Text('Gallery'),
      pinned: true,
    ),
    [2](
      gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(crossAxisCount: 3),
      delegate: SliverChildBuilderDelegate(
        (context, index) => Container(color: Colors.red, height: 100),
        childCount: 9,
      ),
    ),
    [3](
      delegate: SliverChildListDelegate([
        ListTile(title: Text('Footer Item 1')),
        ListTile(title: Text('Footer Item 2')),
      ]),
    ),
  ],
)

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

ASliverAppBar

BSliverChildBuilderDelegate

CSliverList

DSliverGrid

Attempts:

3 left

💡 Hint

Common Mistakes

Using SliverChildBuilderDelegate as a sliver widget.

Mixing up SliverGrid and SliverList positions.

The first blank is SliverAppBar for the pinned header. The second blank is SliverGrid to show a grid of items. The third blank is SliverList for the footer list.

Practice

1. What is the main purpose of a CustomScrollView in Flutter?

easy

A. To combine multiple scrollable widgets called slivers into one scrollable area.

B. To create a fixed header without scrolling.

C. To display only a single scrollable list.

D. To handle user input events like taps and swipes.

Solution

1. Step 1: Understand the role of CustomScrollView

   CustomScrollView allows combining different scrollable widgets called slivers into one scrollable area.

2. Step 2: Compare options with this understanding

   Only To combine multiple scrollable widgets called slivers into one scrollable area. correctly describes this purpose; others describe unrelated features.

3. Final Answer:

   To combine multiple scrollable widgets called slivers into one scrollable area. -> Option A

4. Quick Check:

   CustomScrollView = combine slivers [OK]

Hint: Remember: CustomScrollView = multiple slivers scrolling together [OK]

Common Mistakes:

• Thinking CustomScrollView only shows one list
• Confusing CustomScrollView with fixed headers
• Assuming it handles input events directly

2. Which of the following is the correct way to start a CustomScrollView with a sliver list in Flutter?

easy

A. CustomScrollView(children: [SliverList(delegate: SliverChildBuilderDelegate((context, index) => Text('Item $index'), childCount: 10))])

B. CustomScrollView(slivers: [SliverList(delegate: SliverChildBuilderDelegate((context, index) => Text('Item $index'), childCount: 10))])

C. CustomScrollView(children: [ListView.builder(itemCount: 10, itemBuilder: (context, index) => Text('Item $index'))])

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

Solution

1. Step 1: Check CustomScrollView property for slivers

   CustomScrollView uses the slivers property to accept sliver widgets, not children.

2. Step 2: Identify correct sliver list syntax

   SliverList requires a delegate like SliverChildBuilderDelegate to build items lazily.

3. Final Answer:

   CustomScrollView(slivers: [SliverList(delegate: SliverChildBuilderDelegate((context, index) => Text('Item $index'), childCount: 10))]) -> Option B

4. Quick Check:

   Use slivers property with SliverList [OK]

Hint: Use slivers: [] property, not children: [] for CustomScrollView [OK]

Common Mistakes:

• Using children instead of slivers property
• Putting ListView inside CustomScrollView slivers
• Not using SliverChildBuilderDelegate for SliverList

3. What will be the visible output when running this Flutter code snippet?

CustomScrollView(
  slivers: [
    SliverAppBar(
      expandedHeight: 100,
      flexibleSpace: FlexibleSpaceBar(title: Text('Header')),
      pinned: true,
    ),
    SliverList(
      delegate: SliverChildListDelegate([
        Container(height: 50, color: Colors.red),
        Container(height: 50, color: Colors.green),
        Container(height: 50, color: Colors.blue),
      ]),
    ),
  ],
)

medium

A. An error because SliverAppBar cannot be used inside CustomScrollView.

B. A static screen with only the header 'Header' visible and no scrolling.

C. A scrollable screen with three colored boxes but no header visible.

D. A scrollable screen with a pinned header titled 'Header' and three colored boxes stacked vertically.

Solution

1. Step 1: Understand SliverAppBar behavior

   SliverAppBar with pinned: true stays visible at top when scrolling.

2. Step 2: Analyze SliverList content

   SliverList shows three containers stacked vertically with specified colors and heights.

3. Final Answer:

   A scrollable screen with a pinned header titled 'Header' and three colored boxes stacked vertically. -> Option D

4. Quick Check:

   SliverAppBar pinned + SliverList visible = A scrollable screen with a pinned header titled 'Header' and three colored boxes stacked vertically. [OK]

Hint: Pinned SliverAppBar stays visible while scrolling content below [OK]

Common Mistakes:

• Thinking header disappears on scroll
• Assuming no scrolling because of pinned header
• Believing SliverAppBar causes error inside CustomScrollView

4. Identify the error in this Flutter code using CustomScrollView:

CustomScrollView(
  children: [
    SliverList(
      delegate: SliverChildBuilderDelegate(
        (context, index) => Text('Item $index'),
        childCount: 5,
      ),
    ),
  ],
)

medium

A. SliverList cannot be used inside CustomScrollView.

B. Missing itemCount in SliverChildBuilderDelegate.

C. Using children instead of slivers property in CustomScrollView.

D. Text widget cannot be used inside SliverChildBuilderDelegate.

Solution

1. Step 1: Check CustomScrollView properties

   CustomScrollView expects sliver widgets inside the slivers property, not children.

2. Step 2: Verify other parts

   SliverChildBuilderDelegate has childCount, SliverList is valid, and Text is allowed inside delegate.

3. Final Answer:

   Using children instead of slivers property in CustomScrollView. -> Option C

4. Quick Check:

   CustomScrollView uses slivers, not children [OK]

Hint: CustomScrollView needs slivers: [], not children: [] [OK]

Common Mistakes:

• Using children property instead of slivers
• Confusing SliverList with ListView
• Thinking Text widget is invalid inside SliverChildBuilderDelegate

5. You want to create a scrollable screen with a header that shrinks on scroll, a grid of images, and a list of text items below. Which combination of slivers inside a CustomScrollView will achieve this?

hard

A. SliverAppBar (with flexibleSpace), SliverGrid, SliverList

B. SliverPersistentHeader, ListView, GridView

C. AppBar, GridView.builder, ListView.builder

D. SliverToBoxAdapter, SliverFixedExtentList, SliverFillRemaining

Solution

1. Step 1: Identify slivers for header, grid, and list

   SliverAppBar with flexibleSpace creates a shrinking header. SliverGrid shows a grid of items. SliverList shows a scrollable list.

2. Step 2: Check options for correct sliver usage

   SliverAppBar (with flexibleSpace), SliverGrid, SliverList uses all correct slivers inside CustomScrollView. Others mix non-sliver widgets or incorrect combinations.

3. Final Answer:

   SliverAppBar (with flexibleSpace), SliverGrid, SliverList -> Option A

4. Quick Check:

   Header + grid + list = SliverAppBar + SliverGrid + SliverList [OK]

Hint: Use SliverAppBar for header, SliverGrid for grid, SliverList for list [OK]

Common Mistakes:

• Using ListView/GridView inside CustomScrollView slivers
• Not using SliverAppBar for shrinking header
• Confusing SliverPersistentHeader with SliverAppBar