Slider widget in Flutter - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a basic Slider widget with a value of 0.5.

Flutter

Slider(value: [1], onChanged: (newValue) {})

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

Anull

B1

Ctrue

D0.5

Attempts:

3 left

💡 Hint

Common Mistakes

Using an integer like 1 without decimal point

Setting value to null or boolean

Omitting the value property

The value property of Slider must be a double between 0.0 and 1.0. Here, 0.5 sets the slider in the middle.

2fill in blank

medium

Complete the code to update the slider's value when the user moves it.

Flutter

Slider(value: sliderValue, onChanged: ([1]) { setState(() { sliderValue = [1]; }); })

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

Avalue

BnewValue

Cindex

Dcontext

Attempts:

3 left

💡 Hint

Common Mistakes

Using a parameter name that is not used inside the callback

Forgetting to update the state inside setState

The onChanged callback receives the new slider value as a parameter. Naming it newValue is common and clear.

3fill in blank

hard

Fix the error in the Slider widget by completing the missing property for minimum value.

Flutter

Slider(value: sliderVal, min: [1], max: 10, onChanged: (val) { setState(() { sliderVal = val; }); })

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

A0

B1

C-1

Dnull

Attempts:

3 left

💡 Hint

Common Mistakes

Setting min to null or a value greater than max

Using a negative number when not intended

The min property sets the slider's minimum value. It must be a double or int. Usually, 0 is the start.

4fill in blank

hard

Fill both blanks to create a Slider that only allows integer steps from 0 to 5.

Flutter

Slider(value: sliderVal.toDouble(), min: [1], max: [2], divisions: 5, onChanged: (val) { setState(() { sliderVal = val.toInt(); }); })

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

A0

B5

C10

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Setting max less than min

Not matching divisions with max-min range

Setting min to 0 and max to 5 with divisions: 5 creates steps of 1 between 0 and 5.

5fill in blank

hard

Fill all three blanks to create a Slider with a label showing the current value rounded to an integer.

Flutter

Slider(value: sliderVal, min: 0, max: 100, divisions: 100, label: sliderVal.[1]().toString(), onChanged: (val) { setState(() { sliderVal = val; }); })

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

Around

Bfloor

Cceil

DtoInt

Attempts:

3 left

💡 Hint

Common Mistakes

Using floor or ceil which always round down or up

Using toInt which truncates without rounding

The round() method rounds the double to the nearest integer, which is then converted to string for the label.

Practice

1. What is the main purpose of the Slider widget in Flutter?

easy

A. To display a list of items vertically

B. To let users select a value by sliding a thumb along a line

C. To create a button that changes color when pressed

D. To show an image with zoom controls

Solution

1. Step 1: Understand the Slider widget function

   The Slider widget allows users to pick a numeric value by moving a thumb along a horizontal line.

2. Step 2: Compare with other widget purposes

   Other options describe different widgets: lists, buttons, images, which are unrelated to Slider.

3. Final Answer:

   To let users select a value by sliding a thumb along a line -> Option B

4. Quick Check:

   Slider = select value by sliding [OK]

Hint: Slider is for picking values by sliding [OK]

Common Mistakes:

• Confusing Slider with ListView or Button widgets
• Thinking Slider is for displaying images
• Assuming Slider is a static display widget

2. Which of the following is the correct way to create a basic Slider with a value of 0.5, minimum 0, maximum 1, and a simple onChanged callback?

easy

A. Slider(value: 0.5, min: 0, max: 1, onChanged: (v) => print(v))

B. Slider(value: 0.5, minimum: 0, maximum: 1, onChange: (v) => print(v))

C. Slider(val: 0.5, min: 0, max: 1, onChanged: (v) => print(v))

D. Slider(value: 0.5, min: 0, max: 1)

Solution

1. Step 1: Check property names

   The Slider widget uses value, min, max, and onChanged properties exactly as in Slider(value: 0.5, min: 0, max: 1, onChanged: (v) => print(v)).

2. Step 2: Validate callback presence

   Slider(value: 0.5, min: 0, max: 1, onChanged: (v) => print(v)) includes a valid onChanged callback. Slider(value: 0.5, min: 0, max: 1) misses it, causing an error.

3. Final Answer:

   Slider(value: 0.5, min: 0, max: 1, onChanged: (v) => print(v)) -> Option A

4. Quick Check:

   Correct property names and onChanged callback = Slider(value: 0.5, min: 0, max: 1, onChanged: (v) => print(v)) [OK]

Hint: Use exact property names: value, min, max, onChanged [OK]

Common Mistakes:

• Using wrong property names like minimum or onChange
• Omitting onChanged callback causing errors
• Using val instead of value

3. What will be printed when the user moves the slider thumb to the middle position in this code?

double sliderValue = 0.0;
Slider(
  value: sliderValue,
  min: 0,
  max: 10,
  divisions: 10,
  label: (value) => value.round().toString(),
  onChanged: (double value) {
    print(value);
  },
)

medium

A. 5.0

B. 0.5

C. 10.0

D. 1.0

Solution

1. Step 1: Understand slider range and divisions

   The slider ranges from 0 to 10 with 10 divisions, so each step is 1 unit.

2. Step 2: Calculate middle position value

   The middle position is halfway, so value = (max + min) / 2 = (10 + 0) / 2 = 5.0.

3. Final Answer:

   5.0 -> Option A

4. Quick Check:

   Middle of 0 to 10 with 10 steps = 5.0 [OK]

Hint: Middle value = (min + max) / 2 with divisions [OK]

Common Mistakes:

• Confusing divisions with decimal steps
• Using 0.5 instead of 5.0 for middle
• Ignoring divisions and assuming continuous values

4. Identify the error in this Slider code snippet:

Slider(
  value: 5,
  min: 0,
  max: 10,
  onChanged: null,
)

medium

A. min must be greater than max

B. value must be a string, not a number

C. onChanged is null, making the slider non-interactive

D. Slider requires a label property

Solution

1. Step 1: Check onChanged property requirement

   The Slider widget requires a non-null onChanged callback to be interactive. Setting it to null disables the slider.

2. Step 2: Validate other properties

   Value is correctly a number within min and max. Label is optional.

3. Final Answer:

   onChanged is null, making the slider non-interactive -> Option C

4. Quick Check:

   onChanged null = disabled slider [OK]

Hint: Always provide a non-null onChanged callback [OK]

Common Mistakes:

• Setting onChanged to null disables slider
• Confusing value type as string
• Thinking label is mandatory

5. You want a Slider that lets users pick only whole numbers from 1 to 5 and shows the current value as a label. Which code snippet correctly implements this?

hard

A. Slider(value: 3, min: 1, max: 5, label: (v) => v.round().toString(), onChanged: (v) => print(v))

B. Slider(value: 3, min: 1, max: 5, divisions: 5, label: (v) => v.round().toString(), onChanged: (v) => print(v))

C. Slider(value: 3, min: 0, max: 5, divisions: 5, label: (v) => v.round().toString(), onChanged: (v) => print(v))

D. Slider(value: 3, min: 1, max: 5, divisions: 4, label: (v) => v.round().toString(), onChanged: (v) => print(v))

Solution

1. Step 1: Set min, max, and divisions for whole numbers

   To allow whole numbers from 1 to 5, min=1, max=5, and divisions=4 (steps between 1 and 5) are correct.

2. Step 2: Include label and onChanged callback

   Label shows current value, and onChanged is required for interactivity.

3. Final Answer:

   Slider(value: 3, min: 1, max: 5, divisions: 4, label: (v) => v.round().toString(), onChanged: (v) => print(v)) -> Option D

4. Quick Check:

   Divisions = max - min = 4 for whole steps [OK]

Hint: Divisions = max - min for whole number steps [OK]

Common Mistakes:

• Setting divisions equal to max instead of max-min
• Omitting divisions for discrete steps
• Setting min to 0 when range starts at 1