Loading and error states in React Native

Introduction

Loading and error states help users know what is happening in the app. They show when data is loading or if something went wrong.

When fetching data from the internet and waiting for a response.

When submitting a form and waiting for confirmation.

When loading images or files that take time to appear.

When an app cannot connect to the server and needs to show an error.

When a process takes time and you want to keep the user informed.

Syntax

React Native

function MyComponent() {
  const [loading, setLoading] = React.useState(false);
  const [error, setError] = React.useState(null);

  if (loading) {
    return <Text>Loading...</Text>;
  }

  if (error) {
    return <Text>Error: {error}</Text>;
  }

  return <Text>Data loaded successfully!</Text>;
}

Use loading state to show a spinner or message while waiting.

Use error state to show a friendly message if something goes wrong.

Examples

Show a loading message while data is being fetched.

React Native

const [loading, setLoading] = React.useState(true);

if (loading) {
  return <Text>Loading data...</Text>;
}

Show an error message if there is a problem.

React Native

const [error, setError] = React.useState('Network error');

if (error) {
  return <Text>Error: {error}</Text>;
}

Use a spinner to show loading visually.

React Native

if (loading) {
  return <ActivityIndicator size="large" color="#0000ff" />;
}

Sample App

This app shows a button to load data. When pressed, it shows a spinner for 2 seconds. Then it randomly shows data or an error message.

React Native

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

export default function LoadingErrorExample() {
  const [loading, setLoading] = React.useState(false);
  const [error, setError] = React.useState(null);
  const [data, setData] = React.useState(null);

  const fetchData = () => {
    setLoading(true);
    setError(null);
    setData(null);

    setTimeout(() => {
      const success = Math.random() > 0.5;
      if (success) {
        setData('Here is your data!');
        setLoading(false);
      } else {
        setError('Failed to load data.');
        setLoading(false);
      }
    }, 2000);
  };

  return (
    <View style={{ flex: 1, justifyContent: 'center', alignItems: 'center' }}>
      {loading && <ActivityIndicator size="large" color="#0000ff" />}
      {error && <Text style={{ color: 'red', marginBottom: 10 }}>{error}</Text>}
      {data && <Text style={{ marginBottom: 10 }}>{data}</Text>}
      {!loading && !data && !error && <Text>Press the button to load data.</Text>}
      <Button title="Load Data" onPress={fetchData} />
    </View>
  );
}

Important Notes

Always give users feedback when waiting or when errors happen.

Use clear and simple messages for errors.

Spinners or progress bars help users understand the app is working.

Summary

Loading states show when the app is busy getting data.

Error states show when something goes wrong.

Use states in React Native to control what the user sees.

Practice

1. What is the main purpose of a loading state in a React Native app?

easy

A. To display an error message when something goes wrong

B. To show the user that data is being fetched or processed

C. To permanently hide content from the user

D. To restart the app automatically

Solution

1. Step 1: Understand loading state role

   Loading states inform users that the app is busy fetching or processing data.

2. Step 2: Differentiate from error state

   Error states show problems, not loading progress.

3. Final Answer:

   To show the user that data is being fetched or processed -> Option B

4. Quick Check:

   Loading state = show progress [OK]

Hint: Loading means waiting for data, not errors [OK]

Common Mistakes:

• Confusing loading with error states
• Thinking loading hides content permanently
• Assuming loading restarts the app

2. Which of the following is the correct way to declare a loading state using React Native's useState hook?

easy

A. const loading = useState(false);

B. let loading = useState(true);

C. var loading = useState(false);

D. const [loading, setLoading] = useState(false);

Solution

1. Step 1: Recall useState syntax

   useState returns an array with current value and setter function, usually destructured.

2. Step 2: Check options for correct destructuring

   const [loading, setLoading] = useState(false); correctly uses array destructuring with const and initial value false.

3. Final Answer:

   const [loading, setLoading] = useState(false); -> Option D

4. Quick Check:

   useState destructuring = const [loading, setLoading] = useState(false); [OK]

Hint: useState returns [value, setter], destructure with const [a,b] [OK]

Common Mistakes:

• Not destructuring the array from useState
• Using let or var instead of const
• Assigning useState directly to a variable without destructuring

3. Given this React Native snippet, what will be displayed when loading is true?

const [loading, setLoading] = useState(true);
return (
  loading ? Loading... : Data loaded
);

medium

A. Loading...

B. Nothing is displayed

C. Data loaded

D. Error message

Solution

1. Step 1: Check the value of loading

   loading is true initially.

2. Step 2: Evaluate the ternary expression

   If loading is true, Loading... is returned and shown.

3. Final Answer:

   Loading... -> Option A

4. Quick Check:

   loading true shows loading text [OK]

Hint: Ternary shows first option if condition true [OK]

Common Mistakes:

• Confusing true and false branches
• Thinking nothing shows when loading is true
• Assuming error message shows automatically

4. Identify the error in this React Native code handling loading and error states:

const [loading, setLoading] = useState(false);
const [error, setError] = useState(null);

if (loading) {
  return Loading...;
} else if (error) {
  return Error occurred;
}
return Data loaded;

medium

A. Error state should be a boolean, not null

B. The if-else logic is reversed

C. Loading state should be true initially to show loading

D. No error, code works fine

Solution

1. Step 1: Check initial loading state

   Loading is false initially, so loading screen never shows on start.

2. Step 2: Understand typical loading flow

   Loading should start as true while fetching data, then false after.

3. Final Answer:

   Loading state should be true initially to show loading -> Option C

4. Quick Check:

   Initial loading true needed to show loading [OK]

Hint: Loading usually starts true before data fetch [OK]

Common Mistakes:

• Setting loading false initially hides loading screen
• Thinking error must be boolean
• Assuming if-else order is wrong

5. You want to show a loading spinner while fetching data, then show an error message if fetch fails, or the data if successful. Which React Native pattern correctly handles these states?

hard

A. Use separate states: loading (boolean), error (string|null), data (object|null), and conditionally render based on these

B. Only use a loading state and ignore errors

C. Use a single state variable for all three states with strings 'loading', 'error', 'data'

D. Render data immediately without any loading or error checks

Solution

1. Step 1: Understand state separation

   Separate states for loading, error, and data allow clear control of UI for each condition.

2. Step 2: Evaluate options

   Use separate states: loading (boolean), error (string|null), data (object|null), and conditionally render based on these uses best practice: boolean loading, error message or null, and data object or null.

3. Final Answer:

   Use separate states: loading (boolean), error (string|null), data (object|null), and conditionally render based on these -> Option A

4. Quick Check:

   Separate states for clarity and control [OK]

Hint: Use separate states for loading, error, and data [OK]

Common Mistakes:

• Ignoring error handling
• Using one string state for all conditions
• Rendering data without waiting for fetch