Stack and Positioned in Flutter - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a Stack widget.

Flutter

Stack(children: [
  Container(width: 100, height: 100, color: Colors.blue),
  [1](left: 10, top: 10, child: Icon(Icons.star, color: Colors.white))
])

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

APositioned

BAlign

CPadding

DCenter

Attempts:

3 left

💡 Hint

Common Mistakes

Using Align instead of Positioned inside Stack for exact positioning.

Forgetting to use Positioned when specifying left and top.

The Positioned widget is used inside a Stack to place a child at a specific position.

2fill in blank

medium

Complete the code to position a red square 20 pixels from the bottom and right inside a Stack.

Flutter

Stack(children: [
  Container(width: 150, height: 150, color: Colors.grey),
  [1](bottom: 20, right: 20, child: Container(width: 50, height: 50, color: Colors.red))
])

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

APositioned

BPadding

CAlign

DCenter

Attempts:

3 left

💡 Hint

Common Mistakes

Using Align which positions relative to the Stack but does not accept bottom and right properties.

Using Padding which only adds space around a widget.

Positioned is used to place the red square 20 pixels from the bottom and right edges inside the Stack.

3fill in blank

hard

Fix the error in the code to correctly position the text inside the Stack.

Flutter

Stack(children: [
  Container(width: 200, height: 200, color: Colors.yellow),
  Positioned(left: 30, top: 30, child: [1]('Hello'))
])

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

AText('Hello')

BContainer('Hello')

CText

DTextWidget('Hello')

Attempts:

3 left

💡 Hint

Common Mistakes

Putting the widget call inside the child property as a string.

Using a non-existent widget like TextWidget.

The child property expects a widget instance. Text is a widget class, so it should be called with parentheses outside the Positioned widget, not inside the child property as a string.

4fill in blank

hard

Fill both blanks to create a Stack with a blue box and a green box positioned 15 pixels from the top and left.

Flutter

Stack(children: [
  Container(width: 120, height: 120, color: [1]),
  Positioned(top: 15, left: 15, child: Container(width: 60, height: 60, color: [2]))
])

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

AColors.blue

BColors.red

CColors.green

DColors.yellow

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up the colors for the containers.

Using colors not in the options.

The first container is blue, and the positioned container is green as specified.

5fill in blank

hard

Fill all three blanks to create a Stack with a yellow background, a centered icon, and a positioned text 10 pixels from the bottom and right.

Flutter

Stack(children: [
  Container(color: [1]),
  Center(child: Icon(Icons.favorite, color: [2])),
  Positioned(bottom: 10, right: 10, child: Text([3]))
])

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

AColors.yellow

BColors.red

C'Love'

DColors.blue

Attempts:

3 left

💡 Hint

Common Mistakes

Using color names incorrectly.

Forgetting quotes around the text string.

The background container is yellow, the icon is red, and the positioned text shows 'Love'.

Practice

1. What does the Stack widget do in Flutter?

easy

A. It layers widgets on top of each other.

B. It arranges widgets in a vertical list.

C. It creates a scrollable grid of widgets.

D. It displays widgets side by side horizontally.

Solution

1. Step 1: Understand Stack widget purpose

   The Stack widget allows placing widgets on top of each other in layers.

2. Step 2: Compare with other layout widgets

   Other widgets like Column or Row arrange widgets vertically or horizontally, not layered.

3. Final Answer:

   It layers widgets on top of each other. -> Option A

4. Quick Check:

   Stack = layering widgets [OK]

Hint: Stack means layering widgets over each other [OK]

Common Mistakes:

• Confusing Stack with Column or Row
• Thinking Stack scrolls content
• Assuming Stack arranges widgets side by side

2. Which of the following is the correct syntax to position a widget 10 pixels from the top and 20 pixels from the left inside a Stack?

easy

A. Positioned(left: 10, top: 20, child: Text('Hello'))

B. Positioned(top: 10, left: 20, child: Text('Hello'))

C. Positioned(bottom: 10, right: 20, child: Text('Hello'))

D. Positioned(10, 20, child: Text('Hello'))

Solution

1. Step 1: Check parameter order and values

   Positioned requires named parameters; order doesn't matter but values must match position.

2. Step 2: Verify correct top and left values

   Positioned(top: 10, left: 20, child: Text('Hello')) correctly sets top: 10 and left: 20 with child widget.

3. Final Answer:

   Positioned(top: 10, left: 20, child: Text('Hello')) -> Option B

4. Quick Check:

   top=10 and left=20 in Positioned [OK]

Hint: Use named parameters top and left with correct values [OK]

Common Mistakes:

• Swapping top and left values
• Placing child before position parameters
• Using bottom and right instead of top and left

3. What will be the visual result of this Flutter code?

Stack(
  children: [
    Container(width: 100, height: 100, color: Colors.red),
    Positioned(top: 20, left: 20, child: Container(width: 50, height: 50, color: Colors.blue))
  ]
)

medium

A. Only a blue square visible at top-left corner.

B. Two squares side by side, red on left and blue on right.

C. A red square with a smaller blue square overlapping near the top-left corner.

D. A blue square behind a red square, both fully visible.

Solution

1. Step 1: Understand Stack layering

   The red container is the base layer sized 100x100 pixels.

2. Step 2: Analyze Positioned child

   The blue container is 50x50 pixels placed 20 pixels from top and left, overlapping the red.

3. Final Answer:

   A red square with a smaller blue square overlapping near the top-left corner. -> Option C

4. Quick Check:

   Stack layers with Positioned overlap [OK]

Hint: Positioned child overlaps base widget at given offset [OK]

Common Mistakes:

• Thinking widgets appear side by side
• Assuming blue is behind red
• Ignoring Positioned offsets

4. Identify the error in this Flutter code snippet:

Stack(
  children: [
    Positioned(top: 10, child: Text('Hello')),
    Positioned(left: 20, child: Text('World'))
  ]
)

medium

A. Both Positioned widgets must have both top and left properties.

B. Positioned widgets cannot be direct children of Stack.

C. Positioned widgets must have at least two positioning properties (top, left, bottom, right).

D. Positioned widgets can have only one property; this code is correct.

Solution

1. Step 1: Review Positioned requirements

   Positioned widgets can use zero, one, or more positioning properties (top, left, bottom, right). Partial constraints are allowed (unspecified directions default to 0).

2. Step 2: Check given Positioned widgets

   The first uses top: 10 (Hello positioned 10px from top, left=0). The second uses left: 20 (World positioned 20px from left, top=0). No errors; valid code.

3. Final Answer:

   Positioned widgets can have only one property; this code is correct. -> Option D

4. Quick Check:

   Positioned allows partial properties [OK]

Hint: Positioned supports partial positioning properties [OK]

Common Mistakes:

• Thinking Positioned requires at least two properties
• Believing partial positioning is invalid
• Confusing Positioned requirements

5. You want to create a Stack where a small green circle is always centered over a larger yellow square, regardless of screen size. Which code snippet achieves this correctly?

hard

A. Stack(
children: [
Container(width: 200, height: 200, color: Colors.yellow),
Positioned.fill(child: Align(alignment: Alignment.center, child: Container(width: 50, height: 50, decoration: BoxDecoration(color: Colors.green, shape: BoxShape.circle))))
]
)

B. Stack(
alignment: Alignment.topLeft,
children: [
Container(width: 200, height: 200, color: Colors.yellow),
Container(width: 50, height: 50, decoration: BoxDecoration(color: Colors.green, shape: BoxShape.circle))
]
)

C. Stack(
children: [
Container(width: 200, height: 200, color: Colors.yellow),
Positioned(top: 75, left: 75, child: Container(width: 50, height: 50, decoration: BoxDecoration(color: Colors.green, shape: BoxShape.circle)))
]
)

D. Stack(
children: [
Container(width: 200, height: 200, color: Colors.yellow),
Positioned(bottom: 75, right: 75, child: Container(width: 50, height: 50, decoration: BoxDecoration(color: Colors.green, shape: BoxShape.circle)))
]
)

Solution

1. Step 1: Understand centering in Stack

   Using Positioned.fill with Align centers the child relative to the Stack size.

2. Step 2: Analyze each option

   Stack(
     children: [
       Container(width: 200, height: 200, color: Colors.yellow),
       Positioned.fill(child: Align(alignment: Alignment.center, child: Container(width: 50, height: 50, decoration: BoxDecoration(color: Colors.green, shape: BoxShape.circle))))
     ]
   )

   uses Positioned.fill and Align with Alignment.center, ensuring the green circle stays centered regardless of screen size.

3. Final Answer:

   Stack with Positioned.fill and Align to center the circle. -> Option A

4. Quick Check:

   Use Positioned.fill + Align for responsive centering [OK]

Hint: Use Positioned.fill with Align to center inside Stack [OK]

Common Mistakes:

• Hardcoding top and left offsets (Option A)
• Missing Positioned for precise control (Option B)
• Using bottom and right offsets incorrectly (Option D)