Callback props in React Native - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a callback prop in React Native?

A callback prop is a function passed from a parent component to a child component. The child calls this function to send data or notify the parent about events.

beginner

Why do we use callback props in React Native?

We use callback props to let child components communicate with their parents, especially to send data or trigger actions in the parent.

beginner

How do you define a callback prop in a parent component?

You define a function in the parent and pass it as a prop to the child component, like <Child onPress={handlePress} />.

beginner

How does a child component use a callback prop?

The child calls the function received as a prop, for example props.onPress(), to notify or send data back to the parent.

intermediate

What happens if a callback prop is not passed to a child component?

If the child tries to call the callback but it is not passed, it can cause an error. It's good to check if the prop exists before calling it.

What is the main purpose of a callback prop in React Native?

A To allow child components to send data to parent components

B To style components dynamically

C To fetch data from the internet

D To create new components

Callback props let child components communicate with parents by sending data or events.

How do you pass a callback prop from a parent to a child component?

A <Child style={functionName} />

B <Child data={functionName} />

C <Child callback={functionName} />

D <Child onClick={functionName} />

You pass the function as a prop, often named to describe the event, like callback or onPress.

In the child component, how do you call the callback prop named onPress?

A this.onPress()

B props.onPress()

C call.onPress()

D onPress()

The child calls the function from props using props.onPress() to notify the parent.

What should you do before calling a callback prop in a child component?

A Delete the callback prop

B Change the callback prop

C Ignore the callback prop

D Check if the callback prop exists

Checking if the callback exists prevents errors if the parent did not pass it.

Which of these is NOT a reason to use callback props?

A To pass styling information

B To send data from child to parent

C To notify parent of user actions

D To update parent state from child

Styling is usually passed as style props, not callback functions.

Explain how callback props enable communication between parent and child components in React Native.

Think about how a child tells the parent something happened.

Describe the steps to safely use a callback prop in a child component.

Avoid errors by verifying the callback before calling.

Practice

1. What is the main purpose of using callback props in React Native components?

easy

A. To manage component state internally

B. To style components dynamically

C. To allow child components to communicate events back to parent components

D. To fetch data from an API

Solution

1. Step 1: Understand callback props role

   Callback props are functions passed from parent to child to notify the parent about events.

2. Step 2: Identify communication direction

   They let children send information or events back to parents, enabling communication.

3. Final Answer:

   To allow child components to communicate events back to parent components -> Option C

4. Quick Check:

   Callback props = child-to-parent communication [OK]

Hint: Callback props let children tell parents about events [OK]

Common Mistakes:

• Thinking callback props manage styling
• Confusing callback props with state management
• Assuming callback props fetch data

2. Which of the following is the correct way to pass a callback prop named onPress from a parent to a child component in React Native?

easy

A.

B.

C. handlePress />

D.

Solution

1. Step 1: Recall JSX prop syntax

   Props are passed as attributes with values inside curly braces for functions.

2. Step 2: Match correct syntax

   uses onPress={handlePress}, which is valid JSX syntax.

3. Final Answer:

   <ChildComponent onPress={handlePress} /> -> Option A

4. Quick Check:

   JSX props use = and curly braces for functions [OK]

Hint: Use = and curly braces to pass functions as props [OK]

Common Mistakes:

• Using colon : instead of =
• Using arrow => inside prop
• Adding parentheses () in prop name

3. Given the code below, what will be logged when the button is pressed?

function Parent() {
  const handleClick = () => console.log('Clicked!');
  return <Child onPress={handleClick} />;
}

function Child({ onPress }) {
  return <Button title="Press me" onPress={onPress} />;
}

medium

A. Nothing happens

B. Clicked!

C. Error: onPress is not a function

D. Button title is logged

Solution

1. Step 1: Trace callback prop usage

   The Parent passes handleClick as onPress prop to Child.

2. Step 2: Check Child button onPress

   The Child uses onPress prop as the button's onPress handler, so pressing calls handleClick.

3. Final Answer:

   Clicked! -> Option B

4. Quick Check:

   Button press triggers parent's callback [OK]

Hint: Child calls parent's function on event [OK]

Common Mistakes:

• Assuming onPress is undefined
• Thinking button title logs
• Ignoring callback function call

4. Identify the error in this React Native code snippet:

function Parent() {
  const handlePress = () => alert('Pressed');
  return <Child onPress={handlePress()} />;
}

function Child({ onPress }) {
  return <Button title="Click" onPress={onPress} />;
}

medium

A. alert cannot be used in React Native

B. Child component is missing props destructuring

C. Button component does not support onPress

D. handlePress is called immediately instead of passed as a function

Solution

1. Step 1: Analyze prop passing

   In onPress={handlePress()}, the function is called immediately, passing its result (undefined) instead of the function.

2. Step 2: Understand correct usage

   We should pass the function itself without calling it: onPress={handlePress}.

3. Final Answer:

   handlePress is called immediately instead of passed as a function -> Option D

4. Quick Check:

   Pass function reference, not call it [OK]

Hint: Pass function, don't call it when passing as prop [OK]

Common Mistakes:

• Calling function instead of passing reference
• Thinking alert is invalid in React Native
• Ignoring destructuring in Child

5. You want a child component to notify the parent when a text input changes, but only if the input length is more than 3 characters. How should you implement the callback prop pattern to achieve this?

hard

A. Pass a callback prop from parent; child calls it only when input length > 3

B. Child manages input state and updates parent state directly

C. Parent listens to child's internal state without callback

D. Use a global variable to share input value between components

Solution

1. Step 1: Understand callback prop usage for conditional events

   The parent passes a function as a prop to the child to receive input changes.

2. Step 2: Implement conditional call in child

   The child calls the callback only if the input length is more than 3, controlling when to notify the parent.

3. Final Answer:

   Pass a callback prop from parent; child calls it only when input length > 3 -> Option A

4. Quick Check:

   Child controls event call; parent receives updates [OK]

Hint: Child calls parent callback only when condition meets [OK]

Common Mistakes:

• Letting child update parent state directly
• Ignoring conditional logic in child
• Using global variables for communication