Passing parameters between screens in React Native - UI Render Trace

Component - Passing parameters between screens

This UI component demonstrates how to pass data (parameters) from one screen to another in a React Native app using navigation. It shows a simple flow where a button on the first screen sends a message to the second screen, which then displays it.

Widget Tree

HomeScreen, DetailsScreen

↓

Text, Button

The app uses a navigation container with a stack navigator managing two screens: HomeScreen and DetailsScreen. HomeScreen contains a View with a Text label and a Button. DetailsScreen contains a View with a Text that shows the passed parameter.

Render Trace - 4 Steps

Step 1: NavigationContainer

Step 2: HomeScreen > View

Step 3: HomeScreen > Button

Step 4: DetailsScreen > View

State Change - Re-render

Trigger:User taps the 'Go to Details' button on HomeScreen

Before

Current screen is HomeScreen, no parameters passed

→

After

Current screen changes to DetailsScreen with parameter { message: 'Hello from Home!' }

Re-renders:DetailsScreen and its children re-render to show the passed message

UI Quiz - 3 Questions

What happens when the button on HomeScreen is pressed?

A The app navigates to DetailsScreen and passes a message parameter

B The app reloads HomeScreen without changes

C The app closes

D The button text changes

Key Insight

Passing parameters between screens is a common way to share data in mobile apps. Using navigation libraries, you can send simple data like strings or objects when moving from one screen to another. The receiving screen can then use this data to update its UI, making the app interactive and dynamic.

Practice

1. What is the correct way to pass a parameter named userId with value 42 when navigating to a screen called Profile in React Native?

easy

A. navigation.move('Profile', { userId })

B. navigation.goTo('Profile', userId=42)

C. navigation.push('Profile', userId=42)

D. navigation.navigate('Profile', { userId: 42 })

Solution

1. Step 1: Understand navigation method

   To pass parameters, use navigation.navigate with the screen name and an object of params.

2. Step 2: Check parameter syntax

   The parameter must be inside an object like { userId: 42 } as the second argument.

3. Final Answer:

   navigation.navigate('Profile', { userId: 42 }) -> Option D

4. Quick Check:

   Pass params with navigate(screen, { params }) [OK]

Hint: Use navigate with screen name and params object [OK]

Common Mistakes:

• Using wrong method like goTo or move
• Passing params outside an object
• Forgetting to include params argument

2. Which of the following is the correct syntax to access a parameter named itemId inside a React Native screen component?

easy

A. const itemId = props.navigation.params.itemId;

B. const itemId = navigation.route.params.itemId;

C. const itemId = route.params.itemId;

D. const itemId = params.route.itemId;

Solution

1. Step 1: Identify how params are accessed

   In React Navigation, the screen receives a route prop containing params.

2. Step 2: Use correct property chain

   Access the parameter with route.params.itemId.

3. Final Answer:

   const itemId = route.params.itemId; -> Option C

4. Quick Check:

   Use route.params to get passed parameters [OK]

Hint: Use route.params to access passed data [OK]

Common Mistakes:

• Trying to get params from navigation instead of route
• Incorrect property order like navigation.route.params
• Using props.navigation.params which is invalid

3. Given this code snippet in a React Native app:

navigation.navigate('Details', { productId: 101 });

// In Details screen component:
const Details = ({ route }) => {
  return {route.params.productId};
};

What will be displayed on the screen?

medium

A. productId

B. 101

C. route.params.productId

D. undefined

Solution

1. Step 1: Understand parameter passing

   The productId with value 101 is passed to the Details screen via navigation.navigate.

2. Step 2: Check how parameter is used in Details

   The component accesses route.params.productId and displays it inside a Text component.

3. Final Answer:

   101 -> Option B

4. Quick Check:

   Passed param value is displayed [OK]

Hint: route.params contains passed values to display [OK]

Common Mistakes:

• Expecting param name string instead of value
• Using undefined or wrong property to access param
• Not passing params correctly in navigate

4. What is wrong with this code snippet that tries to pass a parameter name to a screen called Welcome?

navigation.navigate('Welcome', name: 'Alice');

medium

A. Parameters must be passed inside an object as the second argument.

B. The screen name should be lowercase.

C. The parameter name cannot be a string.

D. navigate method does not accept parameters.

Solution

1. Step 1: Check navigate method syntax

   The second argument to navigate must be an object containing parameters.

2. Step 2: Identify error in parameter passing

   The code passes name: 'Alice' without wrapping it in curly braces, which is invalid syntax.

3. Final Answer:

   Parameters must be passed inside an object as the second argument. -> Option A

4. Quick Check:

   Params go inside an object in navigate [OK]

Hint: Always wrap params in an object when navigating [OK]

Common Mistakes:

• Passing params without curly braces
• Using wrong syntax for navigate arguments
• Assuming screen names must be lowercase

5. You want to navigate from a Home screen to a Profile screen and pass both userId and userName. How should you write the navigation call to pass these parameters correctly?

hard

A. navigation.navigate('Profile', { userId: 5, userName: 'John' })

B. navigation.navigate('Profile', userId=5, userName='John')

C. navigation.navigate('Profile', ['userId', 5, 'userName', 'John'])

D. navigation.navigate('Profile', { 'userId': 5 }, { 'userName': 'John' })

Solution

1. Step 1: Understand parameter object structure

   Multiple parameters must be passed inside a single object with key-value pairs.

2. Step 2: Check each option's syntax

   navigation.navigate('Profile', { userId: 5, userName: 'John' }) correctly passes both userId and userName inside one object.

3. Final Answer:

   navigation.navigate('Profile', { userId: 5, userName: 'John' }) -> Option A

4. Quick Check:

   Pass multiple params inside one object [OK]

Hint: Put all params inside one object in navigate call [OK]

Common Mistakes:

• Passing params as separate arguments
• Using array instead of object for params
• Splitting params into multiple objects