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React Native Academy · レッスン

expo-cameraによるカメラアクセス

カメラの権限をリクエストし、シャッターボタン付きのCameraコンポーネントを描画して写真を撮影し、撮影した画像のURIをImageコンポーネントに表示します

「expo-cameraによるカメラアクセス」はCoddyKit上の無料React Native Academyレッスンです。 これはレッスン1/4です。 下記で完全なレッスンを無料で読むことができます。その後、ブラウザ内の組み込みコードエディタと24時間対応のAIチューターでハンズオン演習できます。 これはReact Native Academy学習パスの一部であり、ウェブとCoddyKitアプリ全体で進捗が同期されます。 React Native Academyコースには全4レッスンが含まれています。

このレッスンの一部はまだ翻訳されておらず、英語で表示されています。

Why Use expo-camera?

expo-camera provides a React Native component that renders a live camera preview and lets users capture photos and videos. It works in both iOS and Android and integrates cleanly with Expo's managed workflow. Using expo-camera you can build features like profile photo capture, document scanning, QR code reading, and real-time image capture without writing any native code.

Installing expo-camera

Install expo-camera with the Expo install command so Expo picks the SDK-compatible version. After installation, expo-camera's native modules are linked automatically in an Expo managed project. In a bare workflow project you must also run pod install for iOS after installing.

npx expo install expo-camera

Requesting Camera Permission

Before showing the camera, you must request the user's permission. Use Camera.requestCameraPermissionsAsync() and check the returned status field. If the status is not 'granted', the camera cannot be shown. Always request permission in response to a user action (like tapping a button) so the OS permission dialog appears at a natural moment.

import { Camera } from 'expo-camera';

const [permission, requestPermission] = Camera.useCameraPermissions();

if (!permission) {
  return <ActivityIndicator />;
}

if (!permission.granted) {
  return (
    <View>
      <Text>Camera access is required to take photos.</Text>
      <Button title='Grant Permission' onPress={requestPermission} />
    </View>
  );
}

Rendering the Camera Component

Once permission is granted, render the CameraView component from expo-camera. Give it a style with defined dimensions — it will not render if it has no size. The camera preview fills the allocated space. Use facing to set the initial lens: 'back' for the rear camera or 'front' for the selfie camera.

import { CameraView } from 'expo-camera';
import { StyleSheet } from 'react-native';

export default function CameraScreen() {
  const [permission, requestPermission] = Camera.useCameraPermissions();
  const cameraRef = React.useRef(null);

  if (!permission?.granted) return <PermissionPrompt onPress={requestPermission} />;

  return (
    <View style={styles.container}>
      <CameraView style={styles.camera} facing='back' ref={cameraRef} />
    </View>
  );
}

const styles = StyleSheet.create({
  container: { flex: 1 },
  camera: { flex: 1 },
});

Capturing a Photo

Attach a ref to the CameraView component and call ref.current.takePictureAsync() to capture a photo. This returns a CameraCapturedPicture object with a uri property pointing to the captured image on the device's temporary file system. Display the captured image using React Native's Image component.

const [photo, setPhoto] = React.useState(null);

async function takePicture() {
  if (cameraRef.current) {
    const captured = await cameraRef.current.takePictureAsync({
      quality: 0.8,     // 0 to 1, lower = smaller file
      base64: false,    // true to include base64 string in result
    });
    setPhoto(captured.uri);
  }
}

Displaying the Captured Image

Once a photo URI is captured, switch the view from the camera preview to an Image component showing the captured photo. Provide 'Retake' and 'Use Photo' buttons so the user can confirm or discard the capture. This preview-before-confirm pattern is standard in camera apps and prevents accidental bad photos.

if (photo) {
  return (
    <View style={styles.container}>
      <Image source={{ uri: photo }} style={styles.camera} />
      <View style={styles.buttonRow}>
        <Button title='Retake' onPress={() => setPhoto(null)} />
        <Button title='Use Photo' onPress={() => onPhotoSelected(photo)} />
      </View>
    </View>
  );
}

Toggling Between Front and Back Camera

Allow users to switch between the front and back camera by toggling a state variable. Pass the state to the facing prop of CameraView. React Native handles the camera switch automatically when the prop changes. Add a flip button in the UI overlay for intuitive UX.

const [facing, setFacing] = React.useState<'back' | 'front'>('back');

function toggleCamera() {
  setFacing((current) => (current === 'back' ? 'front' : 'back'));
}

<CameraView style={styles.camera} facing={facing} ref={cameraRef}>
  <TouchableOpacity onPress={toggleCamera} style={styles.flipButton}>
    <Ionicons name='camera-reverse' size={32} color='white' />
  </TouchableOpacity>
  <TouchableOpacity onPress={takePicture} style={styles.shutterButton} />
</CameraView>

Scanning QR Codes

CameraView also supports barcode scanning, including QR codes. Set the onBarcodeScanned prop to a callback function. The callback fires with a result object containing the barcode type and data (the decoded string). Pause scanning after the first result to avoid handling the same code multiple times.

const [scanned, setScanned] = React.useState(false);

function handleBarcodeScan({ type, data }) {
  if (!scanned) {
    setScanned(true);
    Alert.alert('Scanned!', 'Type: ' + type + '\nData: ' + data, [
      { text: 'Scan Again', onPress: () => setScanned(false) },
    ]);
  }
}

<CameraView
  style={styles.camera}
  onBarcodeScanned={scanned ? undefined : handleBarcodeScan}
  barcodeScannerSettings={{ barcodeTypes: ['qr', 'ean13'] }}
/>

Adjusting Camera Quality

The pictureSize prop lets you control the resolution of captured images. Use Camera.getAvailablePictureSizesAsync to query the device's supported sizes and let users choose. Higher resolution photos are better quality but produce larger files. For user-facing profile photos, a medium resolution (around 1080p) is usually the right balance.

const photo = await cameraRef.current.takePictureAsync({
  quality: 0.7,
  exif: false,      // skip EXIF metadata to reduce file size
  skipProcessing: true, // faster capture on Android
});
console.log('Photo size:', photo.width, 'x', photo.height);

Saving to the Media Library

A captured photo's uri points to a temporary location. To save it permanently to the device's photo gallery, use expo-media-library. Call MediaLibrary.saveToLibraryAsync(photo.uri) after capture. Remember to request MediaLibrary permission separately in addition to the camera permission.

import * as MediaLibrary from 'expo-media-library';

async function savePhoto(uri: string) {
  const { status } = await MediaLibrary.requestPermissionsAsync();
  if (status === 'granted') {
    await MediaLibrary.saveToLibraryAsync(uri);
    Alert.alert('Saved!', 'Photo saved to your gallery.');
  }
}

Camera Overlay UI Tips

The CameraView component can render child components on top of the camera preview, acting as a UI overlay. Place shutter buttons, flash toggles, and crop guides as absolute-positioned children inside CameraView. Use a StyleSheet with position: 'absolute' and bottom / top coordinates to position overlay controls intuitively over the live preview.

Quick Check

Test your understanding of React Native Mobile Development concepts from this lesson.

Lesson Recap

In this lesson you learned: Camera.useCameraPermissions handles requesting and checking camera permission before rendering the viewfinder, CameraView with a ref lets you call takePictureAsync to capture a photo and get its URI, and onBarcodeScanned enables QR code reading with the same camera component. Next up we explore reading GPS location with expo-location.

よくある質問

「expo-cameraによるカメラアクセス」レッスンは無料ですか？

はい。「expo-cameraによるカメラアクセス」の完全なテキストはこのウェブで無料で読めます。インタラクティブに演習し（組み込みコードエディタと24時間対応のAIチューター）、React Native Academyコースの残りをアンロックするには、CoddyKit PROにアップグレードしてください。 React Native Academyコースには全4レッスンが含まれています。

「expo-cameraによるカメラアクセス」で何を学びますか？

カメラの権限をリクエストし、シャッターボタン付きのCameraコンポーネントを描画して写真を撮影し、撮影した画像のURIをImageコンポーネントに表示します ブラウザで直接実行するハンズオンコードでReact Native Academyを演習し、24時間対応のAIチューターがレッスンを進める中での質問に答えます。

React Native Academyを始めるのに経験は必要ですか？

事前経験は必要ありません。CoddyKitのReact Native Academyは初級者から上級者向けに構成されているため、ここから始めるか最初から始めて、自分のペースで進むことができます。 これはレッスン1/4です。

「expo-cameraによるカメラアクセス」レッスンにはどのくらい時間がかかりますか？

ほとんどのCoddyKitレッスンは約5～10分かかります。各レッスンはコンパクトでインタラクティブなので、着実に進歩し、ウェブとアプリ全体で正確に前回の場所から再開できます。

このReact Native Academyレッスンでコードを書いて実行できますか？

はい。すべてのReact Native Academyレッスンに組み込みコードエディタが含まれているため、ブラウザでリアルコードを書いて実行し、即座のAIフィードバックを取得できます。ローカル設定は不要です。

このコースのすべてのレッスン

  1. expo-cameraによるカメラアクセス
  2. expo-locationによるGPS位置情報の取得
  3. ローカル通知のスケジュール設定
  4. 権限の適切な処理
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