useState hook in React Native - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the useState hook from React.

React Native

import React, { [1] } from 'react';

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

AuseEffect

BuseState

CuseContext

DuseRef

Attempts:

3 left

💡 Hint

Common Mistakes

Importing useEffect instead of useState

Forgetting to import useState

Using useContext or useRef by mistake

The useState hook is imported from React to manage state in functional components.

2fill in blank

medium

Complete the code to declare a state variable called count with initial value 0.

React Native

const [count, [1]] = useState(0);

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

AsetCount

BgetCount

CcountSetter

DupdateCount

Attempts:

3 left

💡 Hint

Common Mistakes

Using getCount instead of setCount

Naming the setter function incorrectly

Confusing the order of the array destructuring

The second element returned by useState is the setter function to update the state variable.

3fill in blank

hard

Fix the error in the code to update the count state by adding 1.

React Native

setCount([1] + 1);

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

Acount()

BCount

CsetCount

Dcount

Attempts:

3 left

💡 Hint

Common Mistakes

Calling count as a function like count()

Using setCount inside itself incorrectly

Using wrong capitalization like Count

To update the state, use the current state variable count plus 1 inside the setter function.

4fill in blank

hard

Fill both blanks to create a button that increases count when pressed.

React Native

<Button title="Increase" onPress={() => [1]([2] + 1)} />

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

AsetCount

Bcount

Cincrement

DupdateCount

Attempts:

3 left

💡 Hint

Common Mistakes

Using increment or updateCount which are not defined

Swapping the setter and state variable

Forgetting to add 1 to count

The onPress handler calls setCount with the current count plus 1 to increase the count.

5fill in blank

hard

Fill all three blanks to create a functional component that shows count and a button to increase it.

React Native

function Counter() {
  const [[1], [2]] = useState(0);
  return (
    <View>
      <Text>{ [1] }</Text>
      <Button title="Add" onPress={() => [2]([1] + 1)} />
    </View>
  );
}

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

Acount

BsetCount

CupdateCount

Dcounter

Attempts:

3 left

💡 Hint

Common Mistakes

Using undefined names like updateCount or counter

Mixing up the order of state and setter

Not using the state variable inside the Text component

The state variable is count, the setter is setCount, and the displayed value is count.

Practice

1. What does the useState hook do in a React Native component?

easy

A. It fetches data from an external API automatically.

B. It styles the component with CSS properties.

C. It allows the component to remember and update values over time.

D. It creates a new screen in the app navigation.

Solution

1. Step 1: Understand the purpose of useState

   The useState hook is designed to let components keep track of values that can change, like user input or toggles.

2. Step 2: Compare options with useState's role

   Only It allows the component to remember and update values over time. correctly describes this behavior. Styling, fetching data, or navigation are handled by other tools.

3. Final Answer:

   It allows the component to remember and update values over time. -> Option C

4. Quick Check:

   useState manages state = A [OK]

Hint: Remember: useState stores and updates values inside components [OK]

Common Mistakes:

• Confusing useState with styling or navigation
• Thinking useState fetches data automatically
• Believing useState creates new screens

2. Which of the following is the correct way to declare a state variable called count with initial value 0 using useState?

easy

A. const [count, setCount] = useState;

B. const [count, setCount] = useState(0);

C. const count, setCount = useState(0);

D. const count = useState(0);

Solution

1. Step 1: Recall useState syntax

   The correct syntax uses array destructuring: const [state, setState] = useState(initialValue);

2. Step 2: Check each option

   const [count, setCount] = useState(0); matches the correct syntax. const count = useState(0); misses destructuring, C uses comma incorrectly, and A misses parentheses.

3. Final Answer:

   const [count, setCount] = useState(0); -> Option B

4. Quick Check:

   useState syntax = D [OK]

Hint: Use array destructuring with useState and provide initial value [OK]

Common Mistakes:

• Not using array destructuring
• Forgetting parentheses after useState
• Using commas instead of brackets

3. What will be displayed on the screen after the button is pressed twice in this React Native component?

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

export default function Counter() {
  const [count, setCount] = useState(0);
  return (
    
      {count}
       setCount(count + 1)} />
    
  );
}

medium

A. 2

B. 0

C. 1

D. Error: setCount is not a function

Solution

1. Step 1: Understand initial state and button action

   The initial count is 0. Each button press calls setCount(count + 1), increasing count by 1.

2. Step 2: Calculate count after two presses

   After first press: count = 1. After second press: count = 2. The displayed text updates accordingly.

3. Final Answer:

   2 -> Option A

4. Quick Check:

   Two increments from 0 = 2 [OK]

Hint: Each press adds 1 to count starting from 0 [OK]

Common Mistakes:

• Thinking count stays 0 without update
• Confusing initial value with updated value
• Expecting error due to misunderstanding setCount

4. Identify the error in this React Native code using useState:

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

export default function Example() {
  const [value, setValue] = useState;
  return (
    
      {value}
       setValue('Hello')} />
    
  );
}

medium

A. useState is missing parentheses to call it as a function.

B. The setter function name should be getValue, not setValue.

C. The initial state value must be a number, not undefined.

D. The Button component cannot have an onPress prop.

Solution

1. Step 1: Check useState declaration

   The code uses useState without parentheses, so it does not call the function to get state and setter.

2. Step 2: Understand consequences

   Without calling useState(), value and setValue are undefined, causing errors when used.

3. Final Answer:

   useState is missing parentheses to call it as a function. -> Option A

4. Quick Check:

   useState() must be called with () [OK]

Hint: Always call useState with parentheses: useState() [OK]

Common Mistakes:

• Forgetting parentheses after useState
• Misnaming setter function
• Assuming Button lacks onPress prop

5. You want to toggle a boolean state isVisible between true and false each time a button is pressed. Which is the best way to update the state using useState to ensure the toggle works correctly even if updates happen quickly?

const [isVisible, setIsVisible] = useState(false);

hard

A. setIsVisible(!isVisible);

B. setIsVisible(true);

C. setIsVisible(false);

D. setIsVisible(prev => !prev);

Solution

1. Step 1: Understand state updates with previous value

   When toggling, using the previous state ensures correct flipping even if updates queue quickly.

2. Step 2: Compare update methods

   setIsVisible(prev => !prev); uses a function to get previous state and invert it, which is reliable. setIsVisible(!isVisible); uses current state which may be stale. Options B and D set fixed values, not toggling.

3. Final Answer:

   setIsVisible(prev => !prev); -> Option D

4. Quick Check:

   Use functional update for toggling state [OK]

Hint: Use functional update: setState(prev => !prev) for toggles [OK]

Common Mistakes:

• Using current state directly causing stale updates
• Setting fixed true or false instead of toggling
• Not using functional update for quick repeated changes