Props passing in React Native

Introduction

Props let you send information from one part of your app to another. This helps different parts work together and show the right data.

You want to show a user's name inside a greeting message component.

You need to reuse a button component but with different labels.

You want to pass a color choice to a box component to change its background.

You want to send a number to a counter component to start counting from that number.

Syntax

React Native

function ChildComponent(props) {
  return <Text>{props.message}</Text>;
}

function ParentComponent() {
  return <ChildComponent message="Hello!" />;
}

Props are like function arguments but for components.

You can pass any data type as props: text, numbers, functions, or objects.

Examples

This sends the name "Anna" to the Greeting component, which shows "Hello, Anna!".

React Native

function Greeting(props) {
  return <Text>Hello, {props.name}!</Text>;
}

<Greeting name="Anna" />

The ColorBox uses the color prop to set its background color.

React Native

function ColorBox(props) {
  return <View style={{backgroundColor: props.color, width: 100, height: 100}} />;
}

<ColorBox color="blue" />

This button shows "Click me" and runs a function when pressed.

React Native

function Button(props) {
  return <TouchableOpacity onPress={props.onPress}>
    <Text>{props.label}</Text>
  </TouchableOpacity>;
}

<Button label="Click me" onPress={() => Alert.alert('Pressed!')} />

Sample App

This app shows a welcome message using a prop called username. It also has a button that shows an alert when pressed.

React Native

import React from 'react';
import { Text, View, TouchableOpacity, Alert } from 'react-native';

function WelcomeMessage(props) {
  return <Text style={{fontSize: 20}}>Welcome, {props.username}!</Text>;
}

export default function App() {
  return (
    <View style={{flex: 1, justifyContent: 'center', alignItems: 'center'}}>
      <WelcomeMessage username="Sam" />
      <TouchableOpacity
        onPress={() => Alert.alert('Button pressed!')}
        style={{marginTop: 20, backgroundColor: '#4CAF50', padding: 10, borderRadius: 5}}
        accessibilityLabel="Press this button"
      >
        <Text style={{color: 'white'}}>Press me</Text>
      </TouchableOpacity>
    </View>
  );
}

Important Notes

Props are read-only. You cannot change them inside the child component.

Always name props clearly so others understand what data is expected.

Use accessibilityLabel on touchable elements for better accessibility.

Summary

Props pass data from parent to child components.

They help make components reusable and dynamic.

Props are like inputs that components use to show or do different things.

Practice

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

easy

A. To style components with CSS

B. To store internal state of a component

C. To pass data from a parent component to a child component

D. To handle user input events

Solution

1. Step 1: Understand the role of props

   Props are used to send data from a parent component down to its children, allowing dynamic content.

2. Step 2: Differentiate props from state and styling

   State holds internal data, styling is separate, and event handling is done via callbacks, not props alone.

3. Final Answer:

   To pass data from a parent component to a child component -> Option C

4. Quick Check:

   Props = Data passing from parent to child [OK]

Hint: Props always flow from parent to child components [OK]

Common Mistakes:

• Confusing props with state
• Thinking props handle styling
• Assuming props manage events directly

2. Which of the following is the correct way to pass a prop named title with value "Hello" to a component Greeting?

easy

A.

B.

C.

D.

Solution

1. Step 1: Recognize JSX prop syntax

   Props with string values must be passed inside quotes like title="Hello".

2. Step 2: Identify incorrect syntax

   Using curly braces without quotes expects a variable, missing quotes or equals sign is invalid.

3. Final Answer:

   <Greeting title="Hello" /> -> Option A

4. Quick Check:

   String props need quotes in JSX [OK]

Hint: Use quotes for string props in JSX [OK]

Common Mistakes:

• Omitting quotes around string values
• Using curly braces for plain strings
• Missing equals sign between prop and value

3. What will be displayed on the screen when this code runs?

function Welcome(props) {
  return {props.message};
}

export default function App() {
  return ;
}

medium

A. props.message

B. Error: message not defined

C. Welcome

D. Hi there!

Solution

1. Step 1: Identify prop usage in Welcome component

   The Welcome component receives message prop and displays it inside Text.

2. Step 2: Check what prop value is passed

   The App component passes message="Hi there!" to Welcome.

3. Final Answer:

   Hi there! -> Option D

4. Quick Check:

   Props value shown in child component [OK]

Hint: Props values appear where used inside child components [OK]

Common Mistakes:

• Printing the prop name instead of its value
• Expecting component name to display
• Assuming missing prop causes error

4. Identify the error in this code snippet:

function Button(props) {
  return {props.label};
}

export default function App() {
  return ;
}

medium

A. Missing quotes around string prop value

B. Incorrect component name

C. Text component cannot display props

D. Props cannot be passed to functional components

Solution

1. Step 1: Check prop syntax in App component

   The prop label is passed as label=ClickMe without quotes, which is invalid for strings.

2. Step 2: Understand correct JSX prop passing

   String values must be in quotes like label="ClickMe" or in curly braces if variable.

3. Final Answer:

   Missing quotes around string prop value -> Option A

4. Quick Check:

   String props need quotes in JSX [OK]

Hint: Always quote string props in JSX [OK]

Common Mistakes:

• Forgetting quotes around string props
• Thinking props can't be passed to functions
• Misunderstanding Text component usage

5. You want to create a reusable Profile component that shows a user's name and age. Which of these is the best way to pass props to make it flexible?

hard

A.

B.

C.

D.

Solution

1. Step 1: Check prop value types and syntax

   Strings like name should be in quotes; numbers like age should be passed as JavaScript expressions using curly braces.

2. Step 2: Evaluate each option

   <Profile name="Alice" age={30} /> correctly passes name as string and age as number. <Profile name={"Alice"} age="30" /> passes age as string which is less ideal. <Profile name=Alice age=30 /> misses quotes and braces. <Profile name={Alice} age={30} /> uses undefined variable Alice.

3. Final Answer:

   <Profile name="Alice" age={30} /> -> Option B

4. Quick Check:

   Strings in quotes, numbers in braces [OK]

Hint: Use quotes for strings, braces for numbers in props [OK]

Common Mistakes:

• Passing numbers as strings
• Omitting quotes for strings
• Using undefined variables without quotes