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React Nativemobile~20 mins

Cloud Storage in React Native - Mini App: Build & Ship

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Build: Cloud Storage Upload
This screen allows users to select an image from their device and upload it to cloud storage. It shows the upload progress and displays the uploaded image once done.
Target UI
-------------------------
| Cloud Storage Upload   |
|-----------------------|
| [Select Image Button]  |
|                       |
| [Upload Button]        |
|                       |
| Progress: 0%           |
|                       |
| [Uploaded Image Here]  |
-------------------------
A button to select an image from the device gallery
A button to upload the selected image to cloud storage
Show upload progress as a percentage
Display the uploaded image after successful upload
Handle permissions for accessing the gallery
Use React Native functional components and hooks
Starter Code
React Native
import React, { useState } from 'react';
import { View, Button, Image, Text, StyleSheet } from 'react-native';

export default function CloudStorageUpload() {
  const [imageUri, setImageUri] = useState(null);
  const [uploadProgress, setUploadProgress] = useState(0);
  const [uploadedImageUrl, setUploadedImageUrl] = useState(null);

  // TODO: Add function to select image from gallery

  // TODO: Add function to upload image to cloud storage

  return (
    <View style={styles.container}>
      <Button title="Select Image" onPress={() => { /* TODO */ }} />
      <View style={{ height: 20 }} />
      <Button title="Upload Image" onPress={() => { /* TODO */ }} disabled={!imageUri} />
      <View style={{ height: 20 }} />
      <Text>Progress: {uploadProgress}%</Text>
      {uploadedImageUrl && <Image source={{ uri: uploadedImageUrl }} style={styles.image} />}
    </View>
  );
}

const styles = StyleSheet.create({
  container: {
    flex: 1,
    padding: 20,
    justifyContent: 'center',
    alignItems: 'center'
  },
  image: {
    width: 200,
    height: 200,
    marginTop: 20
  }
});
Task 1
Task 2
Task 3
Solution
React Native
import React, { useState } from 'react';
import { View, Button, Image, Text, StyleSheet, Alert } from 'react-native';
import * as ImagePicker from 'expo-image-picker';
import { getStorage, ref, uploadBytesResumable, getDownloadURL } from 'firebase/storage';
import { initializeApp } from 'firebase/app';

const firebaseConfig = {
  apiKey: "YOUR_API_KEY",
  authDomain: "YOUR_AUTH_DOMAIN",
  projectId: "YOUR_PROJECT_ID",
  storageBucket: "YOUR_STORAGE_BUCKET",
  messagingSenderId: "YOUR_MESSAGING_SENDER_ID",
  appId: "YOUR_APP_ID"
};

const app = initializeApp(firebaseConfig);
const storage = getStorage(app);

export default function CloudStorageUpload() {
  const [imageUri, setImageUri] = useState(null);
  const [uploadProgress, setUploadProgress] = useState(0);
  const [uploadedImageUrl, setUploadedImageUrl] = useState(null);

  async function pickImage() {
    const permissionResult = await ImagePicker.requestMediaLibraryPermissionsAsync();
    if (permissionResult.granted === false) {
      Alert.alert('Permission required', 'Permission to access gallery is required!');
      return;
    }

    const pickerResult = await ImagePicker.launchImageLibraryAsync({
      mediaTypes: ImagePicker.MediaTypeOptions.Images,
      quality: 1
    });

    if (!pickerResult.cancelled) {
      setImageUri(pickerResult.uri);
      setUploadedImageUrl(null);
      setUploadProgress(0);
    }
  }

  async function uploadImage() {
    if (!imageUri) return;

    const response = await fetch(imageUri);
    const blob = await response.blob();

    const storageRef = ref(storage, `images/${Date.now()}.jpg`);
    const uploadTask = uploadBytesResumable(storageRef, blob);

    uploadTask.on('state_changed', (snapshot) => {
      const progress = Math.round((snapshot.bytesTransferred / snapshot.totalBytes) * 100);
      setUploadProgress(progress);
    }, (error) => {
      Alert.alert('Upload failed', error.message);
    }, () => {
      getDownloadURL(uploadTask.snapshot.ref).then((downloadURL) => {
        setUploadedImageUrl(downloadURL);
      });
    });
  }

  return (
    <View style={styles.container}>
      <Button title="Select Image" onPress={pickImage} />
      <View style={{ height: 20 }} />
      <Button title="Upload Image" onPress={uploadImage} disabled={!imageUri} />
      <View style={{ height: 20 }} />
      <Text>Progress: {uploadProgress}%</Text>
      {uploadedImageUrl && <Image source={{ uri: uploadedImageUrl }} style={styles.image} accessibilityLabel="Uploaded image" />}
    </View>
  );
}

const styles = StyleSheet.create({
  container: {
    flex: 1,
    padding: 20,
    justifyContent: 'center',
    alignItems: 'center'
  },
  image: {
    width: 200,
    height: 200,
    marginTop: 20
  }
});

This solution uses the expo-image-picker library to let the user select an image from their device gallery. It first asks for permission to access the gallery and shows an alert if permission is denied.

Once an image is selected, its URI is saved in state. The upload button becomes enabled.

When the user taps upload, the image file is fetched as a blob and uploaded to Firebase Storage using uploadBytesResumable. This method provides progress updates, which we use to update the progress percentage shown on screen.

After the upload completes, the download URL is retrieved and saved in state. The uploaded image is then displayed using an Image component.

This approach keeps the UI responsive and informs the user about the upload progress. Accessibility is considered by adding an accessibility label to the uploaded image.

Final Result
Completed Screen
-------------------------
| Cloud Storage Upload   |
|-----------------------|
| [Select Image Button]  |
|                       |
| [Upload Button]        |
|                       |
| Progress: 75%          |
|                       |
| [Uploaded Image Here]  |
-------------------------
Tap 'Select Image' opens device gallery to pick an image
After selection, 'Upload Image' button enables
Tap 'Upload Image' starts upload and progress updates from 0% to 100%
When upload finishes, the uploaded image appears below progress
Stretch Goal
Add a pull-to-refresh gesture to reset the screen to initial state
💡 Hint
Use React Native's RefreshControl with a ScrollView to implement pull-to-refresh that clears image and progress states

Practice

(1/5)
1.

What is the main purpose of Cloud Storage in a React Native app?

easy
A. To save and retrieve files online easily
B. To create user interfaces
C. To manage app navigation
D. To handle app state locally

Solution

  1. Step 1: Understand Cloud Storage role

    Cloud Storage is used to save and get files online, not for UI or navigation.
  2. Step 2: Match purpose with options

    Only To save and retrieve files online easily describes saving and retrieving files online.
  3. Final Answer:

    To save and retrieve files online easily -> Option A
  4. Quick Check:

    Cloud Storage = Save/Get files online [OK]
Hint: Cloud Storage is for files, not UI or navigation [OK]
Common Mistakes:
  • Confusing Cloud Storage with UI components
  • Thinking Cloud Storage manages app navigation
  • Assuming Cloud Storage handles local state
2.

Which of the following is the correct way to create a reference to a file named image.jpg in Cloud Storage?

const storage = getStorage();
const ref = ?
easy
A. getRef('image.jpg')
B. storage.ref('image.jpg')
C. ref(storage, 'image.jpg')
D. storage.getReference('image.jpg')

Solution

  1. Step 1: Recall correct syntax for reference

    In React Native Firebase, use ref(storage, 'filename') to create a reference.
  2. Step 2: Check options for correct function

    Only ref(storage, 'image.jpg') uses ref(storage, 'image.jpg') correctly.
  3. Final Answer:

    ref(storage, 'image.jpg') -> Option C
  4. Quick Check:

    Reference creation = ref(storage, 'filename') [OK]
Hint: Use ref(storage, 'filename') to create file reference [OK]
Common Mistakes:
  • Using storage.ref() which is not valid in React Native
  • Calling getRef() which does not exist
  • Using storage.getReference() which is incorrect
3.

What will the following code do?

const storage = getStorage();
const fileRef = ref(storage, 'docs/report.pdf');
await uploadBytes(fileRef, fileData);
const url = await getDownloadURL(fileRef);
console.log(url);
medium
A. Upload the file and print its download URL
B. Only upload the file without printing URL
C. Print the URL without uploading the file
D. Cause a syntax error due to missing await

Solution

  1. Step 1: Analyze uploadBytes usage

    The code uploads fileData to 'docs/report.pdf' using uploadBytes with await.
  2. Step 2: Analyze getDownloadURL usage

    After upload, it gets the file's URL and prints it with console.log.
  3. Final Answer:

    Upload the file and print its download URL -> Option A
  4. Quick Check:

    Upload + get URL = print URL [OK]
Hint: uploadBytes then getDownloadURL prints URL [OK]
Common Mistakes:
  • Thinking getDownloadURL works before upload
  • Missing await causing runtime errors
  • Assuming uploadBytes does not upload file
4.

Identify the error in this code snippet for uploading a file:

const storage = getStorage();
const fileRef = ref(storage, 'photos/pic.png');
uploadFile(fileRef, fileData);
const url = await getDownloadURL(fileRef);
console.log(url);
medium
A. ref function is used incorrectly
B. Missing await before uploadFile
C. getDownloadURL cannot be awaited
D. uploadFile is not a valid function

Solution

  1. Step 1: Check function names for uploading

    The correct function to upload is uploadBytes, not uploadFile.
  2. Step 2: Verify other code parts

    getDownloadURL can be awaited and ref usage is correct.
  3. Final Answer:

    uploadFile is not a valid function -> Option D
  4. Quick Check:

    uploadBytes is correct upload function [OK]
Hint: Use uploadBytes, not uploadFile [OK]
Common Mistakes:
  • Using uploadFile instead of uploadBytes
  • Forgetting to await uploadBytes
  • Misusing getDownloadURL without await
5.

You want to upload a profile picture and then immediately show it in your app. Which sequence of steps is correct?

  1. Get a reference to the file location
  2. Upload the file using uploadBytes
  3. Get the download URL using getDownloadURL
  4. Display the image using the URL
hard
A. 1 -> 3 -> 2 -> 4
B. 1 -> 2 -> 3 -> 4
C. 2 -> 1 -> 3 -> 4
D. 3 -> 1 -> 2 -> 4

Solution

  1. Step 1: Create file reference first

    You must first get a reference to where the file will be stored.
  2. Step 2: Upload file using uploadBytes

    Upload the file to that reference location.
  3. Step 3: Get download URL after upload

    Only after upload can you get the file's URL.
  4. Step 4: Display image using URL

    Use the URL to show the image in your app.
  5. Final Answer:

    1 -> 2 -> 3 -> 4 -> Option B
  6. Quick Check:

    Reference -> Upload -> URL -> Display [OK]
Hint: Reference, upload, get URL, then display [OK]
Common Mistakes:
  • Trying to get URL before uploading
  • Uploading before creating reference
  • Displaying image without URL
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10 questions~5 mineasy hard