Custom tab bars in React Native - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a custom tab bar in React Native?

A custom tab bar is a user-designed navigation bar that replaces the default tab bar to provide unique styles or behaviors in a React Native app.

beginner

Which React Navigation component is commonly customized to create a custom tab bar?

The component's tabBar option allows you to provide a custom tab bar component.

intermediate

How do you receive navigation state and descriptors in a custom tab bar component?

The custom tab bar component receives props like state, descriptors, and navigation to control tab selection and rendering.

beginner

Why might you want to create a custom tab bar instead of using the default one?

To match a unique design, add animations, change layout, or include extra buttons not supported by the default tab bar.

beginner

What React Native component is often used inside a custom tab bar to make tabs touchable?

TouchableOpacity or Pressable components are used to make tab buttons respond to user taps.

Which prop provides the current active tab index in a custom tab bar?

A descriptors.active

B navigation.activeTab

C state.index

D tabBar.activeIndex

The state prop contains the navigation state, and state.index gives the active tab index.

What is the purpose of the descriptors prop in a custom tab bar?

A To store user data

B To describe each tab's options and render functions

C To handle gestures

D To manage app state

Descriptors contain options and render functions for each tab screen.

Which React Native component is best for making a tab button respond to taps?

A TouchableOpacity

B Text

C View

D ScrollView

TouchableOpacity provides a touchable area with feedback for taps.

How do you tell React Navigation to use your custom tab bar?

A Pass it to tabBar prop in Tab.Navigator

B Replace Tab.Screen with CustomTab

C Use a different navigator

D Set customTabBar=true

You pass your custom component to the tabBar prop inside Tab.Navigator.

What is a common reason to create a custom tab bar?

A To increase loading speed

B To reduce app size

C To disable navigation

D To add unique styles or animations

Custom tab bars allow unique styles and animations beyond the default.

Explain how to create and use a custom tab bar in React Native with React Navigation.

Think about how the default tab bar works and how you can replace it.

Describe why and when you might want to customize the tab bar in a mobile app.

Consider user interface and user experience needs.

Practice

1. What is the main purpose of a custom tab bar in React Native navigation?

easy

A. To replace the entire navigation stack with a new one

B. To disable navigation between screens

C. To create a personalized look and behavior for the bottom navigation tabs

D. To automatically fetch data for each tab

Solution

1. Step 1: Understand what a tab bar does

   A tab bar shows navigation options at the bottom of the screen for switching between views.

2. Step 2: Identify the role of a custom tab bar

   A custom tab bar lets you change how these tabs look and behave, instead of using the default style.

3. Final Answer:

   To create a personalized look and behavior for the bottom navigation tabs -> Option C

4. Quick Check:

   Custom tab bar = personalized navigation UI [OK]

Hint: Custom tab bars change appearance and interaction of bottom tabs [OK]

Common Mistakes:

• Thinking it replaces navigation logic entirely
• Assuming it disables navigation
• Confusing it with data fetching

2. Which React Native component is commonly used to make a tab clickable in a custom tab bar?

easy

A. View

B. TouchableOpacity

C. TextInput

D. ScrollView

Solution

1. Step 1: Identify clickable components

   TouchableOpacity is designed to respond to touch events and provide feedback.

2. Step 2: Match with tab interaction needs

   Tabs need to be clickable to switch screens, so TouchableOpacity is the right choice.

3. Final Answer:

   TouchableOpacity -> Option B

4. Quick Check:

   Clickable tab = TouchableOpacity [OK]

Hint: Use TouchableOpacity for clickable tabs in React Native [OK]

Common Mistakes:

• Using View which is not clickable by default
• Choosing TextInput which is for text input
• Using ScrollView which is for scrolling content

3. Given this snippet inside a custom tab bar component:

state.index === 1 ? 'blue' : 'gray'

What does this expression do?

medium

A. Causes a syntax error because of missing parentheses

B. Always sets the tab color to gray

C. Changes the tab color to blue when the app starts

D. Sets the tab color to blue if it is the active tab, otherwise gray

Solution

1. Step 1: Understand the ternary expression

   The expression checks if state.index equals 1; if true, it returns 'blue', else 'gray'.

2. Step 2: Relate to tab color logic

   This means the tab at index 1 is highlighted blue when active, others are gray.

3. Final Answer:

   Sets the tab color to blue if it is the active tab, otherwise gray -> Option D

4. Quick Check:

   state.index === 1 ? 'blue' : 'gray' = active tab color logic [OK]

Hint: Ternary ? : chooses color based on active tab index [OK]

Common Mistakes:

• Thinking it always returns gray
• Assuming it causes syntax error
• Confusing the condition with app start

4. Identify the error in this custom tab bar code snippet:

const CustomTabBar = ({ state, navigation }) => {
  return (
    <View>
      {state.routes.map((route, index) => (
        <TouchableOpacity
          key={index}
          onPress={() => navigation.navigate(route.name)}
        >
          <Text>{route.name}</Text>
        </TouchableOpacity>
      ))}
    </View>
  );
};

medium

A. Missing accessibility props for TouchableOpacity

B. Using index as key causes navigation errors

C. Incorrect use of navigation.navigate inside onPress

D. No error, code works correctly

Solution

1. Step 1: Review accessibility best practices

   TouchableOpacity should have accessibilityRole and accessibilityState for screen readers.

2. Step 2: Check other parts of code

   Using index as key is not ideal but won't cause navigation errors; navigation.navigate usage is correct.

3. Final Answer:

   Missing accessibility props for TouchableOpacity -> Option A

4. Quick Check:

   Accessibility props missing = error [OK]

Hint: Always add accessibilityRole and accessibilityState to touchables [OK]

Common Mistakes:

• Ignoring accessibility props
• Thinking index key breaks navigation
• Assuming navigation.navigate is wrong here

5. You want to create a custom tab bar that highlights the active tab with a bold label and changes the icon color. Which approach correctly uses state and navigation to achieve this?

hard

A. Use state.index to check active tab, and navigation.navigate(route.name) on press; style label bold if active

B. Use navigation.state.index to check active tab, and state.navigate(route.name) on press; style label bold if active

C. Use state.activeTab to check active tab, and navigation.goBack() on press; style label bold if active

D. Use state.index to check active tab, and navigation.push(route.key) on press; style label bold if active

Solution

1. Step 1: Identify correct state usage

   The active tab index is in state.index, not navigation.state or state.activeTab.

2. Step 2: Identify correct navigation method

   navigation.navigate(route.name) is used to switch tabs; goBack or push are not appropriate here.

3. Step 3: Apply styling based on active tab

   Compare current index with tab index to apply bold style and change icon color.

4. Final Answer:

   Use state.index to check active tab, and navigation.navigate(route.name) on press; style label bold if active -> Option A

5. Quick Check:

   state.index + navigation.navigate = correct tab control [OK]

Hint: Use state.index for active tab and navigation.navigate for switching [OK]

Common Mistakes:

• Using wrong property like navigation.state.index
• Using navigation.goBack instead of navigate
• Using state.activeTab which doesn't exist