Switch and checkbox patterns in React Native - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

Toggle Switch State Update

What will be the value of isEnabled after toggling the switch once in this React Native component?

React Native

import React, { useState } from 'react';
import { Switch, View, Text } from 'react-native';

export default function App() {
  const [isEnabled, setIsEnabled] = useState(false);
  const toggleSwitch = () => setIsEnabled(previousState => !previousState);

  return (
    <View>
      <Switch onValueChange={toggleSwitch} value={isEnabled} />
      <Text>{isEnabled ? 'On' : 'Off'}</Text>
    </View>
  );
}

A false

B true

C undefined

D null

💡 Hint

The toggleSwitch function flips the current boolean state.

The initial state is false. Toggling once flips it to true, so the switch value becomes true.

📝 Syntax

intermediate

Correct Checkbox State Handling

Which option correctly updates the checkbox state when the user taps it in React Native?

React Native

import React, { useState } from 'react';
import { CheckBox, View } from 'react-native';

export default function App() {
  const [checked, setChecked] = useState(false);

  return (
    <View>
      <CheckBox
        value={checked}
        onValueChange={/* Which option here? */}
      />
    </View>
  );
}

A (newValue) => setChecked(newValue)

B () => setChecked(undefined)

C () => setChecked(checked)

D () => setChecked(!checked)

💡 Hint

The onValueChange handler receives the new boolean value.

The onValueChange callback provides the new checked value. Using it directly updates state correctly.

❓ lifecycle

advanced

Switch State Persistence on Re-render

Given this component, what will be the displayed text after pressing the switch twice?

React Native

import React, { useState } from 'react';
import { Switch, View, Text } from 'react-native';

export default function App() {
  const [isOn, setIsOn] = useState(false);

  const toggle = () => {
    setIsOn(!isOn);
  };

  return (
    <View>
      <Switch value={isOn} onValueChange={toggle} />
      <Text>{isOn ? 'Enabled' : 'Disabled'}</Text>
    </View>
  );
}

A Disabled

B Enabled

C undefined

D Error

💡 Hint

Each toggle flips the boolean state.

Starting false, first toggle sets true, second toggle sets false again, so text shows 'Disabled'.

❓ navigation

advanced

Checkbox State and Navigation Behavior

In a React Native app using React Navigation, if a checkbox state is stored locally in a screen component, what happens to the checkbox state when navigating away and back to that screen?

A The checkbox state causes a navigation error on return.

B The checkbox state persists automatically without extra code.

C The checkbox state is shared across all screens automatically.

D The checkbox state resets to its initial value each time the screen is visited.

💡 Hint

Local state in a component resets when the component unmounts and remounts.

When navigating away, the screen unmounts by default, so local state resets on return unless stored globally or persisted.

🔧 Debug

expert

Why does this Switch not toggle visually?

This React Native Switch component does not visually toggle when pressed. What is the cause?

React Native

import React, { useState } from 'react';
import { Switch, View } from 'react-native';

export default function App() {
  const [enabled, setEnabled] = useState(false);

  return (
    <View>
      <Switch
        value={enabled}
        onValueChange={() => setEnabled(enabled)}
      />
    </View>
  );
}

A The useState hook is missing an initial value.

B The Switch component requires a different prop name than value.

C The onValueChange handler sets the state to the current value, so no change occurs.

D The Switch component must be wrapped in a TouchableOpacity.

💡 Hint

Check what value is passed to setEnabled inside onValueChange.

The handler sets state to the same value, so the state never changes and the switch never visually toggles.

Practice

1. What is the main purpose of a Switch component in React Native?

easy

A. To toggle between two states like ON and OFF

B. To select multiple options from a list

C. To input text from the user

D. To display images in a gallery

Solution

1. Step 1: Understand the Switch component

   A Switch is a UI element that lets users toggle between two states, usually ON or OFF.

2. Step 2: Compare with other components

   Checkboxes allow multiple selections, text inputs accept text, and image galleries display images, so these do not match the Switch's purpose.

3. Final Answer:

   To toggle between two states like ON and OFF -> Option A

4. Quick Check:

   Switch toggles states = B [OK]

Hint: Switch means ON/OFF toggle, not multiple selections [OK]

Common Mistakes:

• Confusing Switch with Checkbox
• Thinking Switch accepts text input
• Assuming Switch displays images

2. Which of the following is the correct way to declare a controlled Switch component in React Native?

easy

A. setIsOn(!isOn)} />

B. setIsOn(!isOn)} />

C. setIsOn(!isOn)} />

D. setIsOn(!isOn)} />

Solution

1. Step 1: Recall Switch props in React Native

   The Switch component uses value to set its state and onValueChange as the event handler for toggling.

2. Step 2: Identify correct syntax

   Options using checked or onChange are incorrect because React Native Switch does not use these props.

3. Final Answer:

   <Switch value={isOn} onValueChange={() => setIsOn(!isOn)} /> -> Option D

4. Quick Check:

   Switch uses value and onValueChange = C [OK]

Hint: Switch uses value and onValueChange props [OK]

Common Mistakes:

• Using checked instead of value
• Using onChange instead of onValueChange
• Mixing HTML input props with React Native Switch

3. What will be the output on the screen after running this React Native code snippet?

const [checked, setChecked] = React.useState(false);

return (
  <CheckBox
    value={checked}
    onValueChange={() => setChecked(!checked)}
  />
);

If the user taps the checkbox once, what is the new value of checked?

medium

A. false

B. true

C. undefined

D. null

Solution

1. Step 1: Initial state value

   The state variable checked starts as false.

2. Step 2: Effect of tapping checkbox

   The onValueChange toggles checked to its opposite, so it becomes true after one tap.

3. Final Answer:

   true -> Option B

4. Quick Check:

   Toggle false once = true [OK]

Hint: Tapping toggles boolean state from false to true [OK]

Common Mistakes:

• Assuming state stays false after tap
• Confusing value prop with event
• Thinking onValueChange returns new value

4. Identify the error in this React Native code for a controlled Switch:

const [isEnabled, setIsEnabled] = React.useState(false);

return (
  <Switch
    value={isEnabled}
    onChange={() => setIsEnabled(!isEnabled)}
  />
);

medium

A. Using value instead of checked

B. Missing initial state declaration

C. Using onChange instead of onValueChange

D. Not importing React

Solution

1. Step 1: Check event handler prop

   The Switch component uses onValueChange to handle toggle events, not onChange.

2. Step 2: Verify other parts

   The initial state is declared, value is correct, and React import is assumed correct.

3. Final Answer:

   Using onChange instead of onValueChange -> Option C

4. Quick Check:

   Switch needs onValueChange, not onChange [OK]

Hint: Switch uses onValueChange, not onChange [OK]

Common Mistakes:

• Using onChange event instead of onValueChange
• Confusing value and checked props
• Forgetting to declare state

5. You want to create a list of three checkboxes in React Native where only one can be selected at a time (like radio buttons). Which approach correctly implements this behavior?

hard

A. Use three CheckBox components sharing one state variable that stores the selected option

B. Use one CheckBox component and change its label dynamically

C. Use three CheckBox components each with its own boolean state variable

D. Use three Switch components each with independent state variables

Solution

1. Step 1: Understand single selection requirement

   Only one checkbox can be selected at a time, so all must share one state that tracks which is selected.

2. Step 2: Evaluate options

   Use three CheckBox components sharing one state variable that stores the selected option. This uses one state variable to store the selected option and updates it on selection, ensuring only one is selected. Options A and C use independent states allowing multiple selections. Use one CheckBox component and change its label dynamically uses only one checkbox, which cannot represent three options.

3. Final Answer:

   Use three CheckBox components sharing one state variable that stores the selected option -> Option A

4. Quick Check:

   Single selection needs shared state = D [OK]

Hint: Single selection means one state tracks selected checkbox [OK]

Common Mistakes:

• Giving each checkbox its own state allowing multiple selections
• Using Switch instead of CheckBox for selection list
• Trying to reuse one checkbox for multiple options