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折叠设备形态各异，在相机应用的开发过程中需要统一的摄像头切换方案，以确保用户在拍照、录像过程中获得更好的体验。

一台可折叠设备在不同折叠状态下，可使用不同的相机。系统会标识所有摄像头，每个摄像头与一个折叠状态相对应，表示该摄像头可在对应的折叠状态下使用。应用可调用CameraManager.on('foldStatusChange')或display.on('foldStatusChange')监听设备的折叠状态变化，并调用CameraManager.getSupportedCameras获取当前状态下可用相机，完成相应适配，确保应用在折叠状态变更时的用户体验。

不同折叠设备在不同折叠状态下支持的摄像头数量不同。

例如，折叠设备拥有三颗摄像头：后置摄像头A、前置摄像头B和前置摄像头C。在展开状态下，通过CameraManager.getSupportedCameras接口可获取到后置摄像头A和前置摄像头B；在折叠状态下，可获取到后置摄像头A和前置摄像头C。不同的折叠状态获取到的镜头不同，因此，在折叠状态变化时，需要重新获取镜头信息。

详细的API说明请参考@ohos.multimedia.camera (相机管理)。

Context获取方式请参考：获取UIAbility的上下文信息。

在开发相机应用时，需要先申请相机相关权限，请参考申请相关权限。

创建XComponent

使用两个XComponent分别展示折叠态和展开态，防止切换折叠屏状态亮屏的时候上一个相机还未关闭，残留上一个相机的画面。

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 @Entry
 @Component
 struct Index {
   @State reloadXComponentFlag: boolean = false;
   @StorageLink('foldStatus') @Watch('reloadXComponent') foldStatus: number = 0;
   private mXComponentController: XComponentController = new XComponentController();
   private mXComponentOptions: XComponentOptions = {
     type: XComponentType.SURFACE,
     controller: this.mXComponentController
   }

   reloadXComponent() {
     this.reloadXComponentFlag = !this.reloadXComponentFlag;
   }

   async loadXComponent() {
     // 初始化XComponent。
   }

   build() {
     Stack() {
       if (this.reloadXComponentFlag) {
         XComponent(this.mXComponentOptions)
           .onLoad(async () => {
             await this.loadXComponent();
           })
           .width(this.getUIContext().px2vp(1080))
           .height(this.getUIContext().px2vp(1920))
       } else {
         XComponent(this.mXComponentOptions)
           .onLoad(async () => {
             await this.loadXComponent();
           })
           .width(this.getUIContext().px2vp(1080))
           .height(this.getUIContext().px2vp(1920))
       }
     }
     .size({ width: '100%', height: '100%' })
     .backgroundColor(Color.Black)
   }
 }

获取设备折叠状态

此处提供两种方案供开发者选择。

方案一：使用相机框架提供的CameraManager.on('foldStatusChange')监听设备折叠态变化。

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import { camera } from '@kit.CameraKit';
import { BusinessError } from '@kit.BasicServicesKit';

function registerFoldStatusChanged(err: BusinessError, foldStatusInfo: camera.FoldStatusInfo) {
  // foldStatus 变量用来控制显示XComponent组件。
  AppStorage.setOrCreate<number>('foldStatus', foldStatusInfo.foldStatus);
}

function onFoldStatusChange(cameraManager: camera.CameraManager) {
  cameraManager.on('foldStatusChange', registerFoldStatusChanged);
}

function offFoldStatusChange(cameraManager: camera.CameraManager) {
  cameraManager.off('foldStatusChange', registerFoldStatusChanged);
}

方案二：使用图形图像的display.on('foldStatusChange')监听设备折叠态变化。

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import { display } from '@kit.ArkUI';

function getFoldStatus(): display.FoldStatus {
  let curFoldStatus: display.FoldStatus = display.FoldStatus.FOLD_STATUS_UNKNOWN;
  try {
    curFoldStatus = display.getFoldStatus();
  } catch (error) {
    console.error('getFoldStatus call failed');
  }
  return curFoldStatus;
}

let preFoldStatus: display.FoldStatus = getFoldStatus();
display.on('foldStatusChange', (foldStatus: display.FoldStatus) => {
  // 从半折叠态（FOLD_STATUS_HALF_FOLDED）到展开态（FOLD_STATUS_EXPANDED），相机框架返回所支持的相机是一致的，所以从半折叠态到展开态不需要重新配流，从展开态到半折叠态也是一样的。
  if ((preFoldStatus === display.FoldStatus.FOLD_STATUS_HALF_FOLDED &&
    foldStatus === display.FoldStatus.FOLD_STATUS_EXPANDED) ||
    (preFoldStatus === display.FoldStatus.FOLD_STATUS_EXPANDED &&
      foldStatus === display.FoldStatus.FOLD_STATUS_HALF_FOLDED)) {
    preFoldStatus = foldStatus;
    return;
  }
  preFoldStatus = foldStatus;
  // foldStatus 变量用来控制显示XComponent组件。
  AppStorage.setOrCreate<number>('foldStatus', foldStatus);
})

判断是否存在对应位置摄像头

通过CameraManager.getSupportedCameras接口可获取到当前设备折叠状态下支持的所有镜头，遍历获取到的结果，通过CameraPosition判断镜头是否存在。

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import { camera } from '@kit.CameraKit';

// connectionType默认为camera.ConnectionType.CAMERA_CONNECTION_BUILT_IN，表示设备的内置镜头。
function hasCameraAt(cameraManager: camera.CameraManager, cameraPosition: camera.CameraPosition,
  connectionType: camera.ConnectionType = camera.ConnectionType.CAMERA_CONNECTION_BUILT_IN): boolean {
  let cameraArray: Array<camera.CameraDevice> = cameraManager.getSupportedCameras();
  if (cameraArray.length <= 0) {
    console.error('cameraManager.getSupportedCameras error');
    return false;
  }
  for (let index = 0; index < cameraArray.length; index++) {
    if (cameraArray[index].cameraPosition === cameraPosition &&
      cameraArray[index].connectionType === connectionType) {
      return true;
    }
  }
  return false;
}

摄像头切换逻辑

在监听到折叠状态发生变化时通过设置被@StorageLink修饰的foldStatus变量改变，触发reloadXComponent方法重新加载XComponent组件，从而实现相机的切换逻辑。

完整示例

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import { camera } from '@kit.CameraKit';
import { BusinessError } from '@kit.BasicServicesKit';
import { abilityAccessCtrl } from '@kit.AbilityKit';
import { display } from '@kit.ArkUI';

const TAG = 'FoldScreenCameraAdaptationDemo ';

@Entry
@Component
struct Index {
  @State isShow: boolean = false;
  @State reloadXComponentFlag: boolean = false;
  @StorageLink('foldStatus') @Watch('reloadXComponent') foldStatus: number = 0;
  private mXComponentController: XComponentController = new XComponentController();
  private mXComponentOptions: XComponentOptions = {
    type: XComponentType.SURFACE,
    controller: this.mXComponentController
  }
  private mSurfaceId: string = '';
  private mCameraPosition: camera.CameraPosition = camera.CameraPosition.CAMERA_POSITION_BACK;
  private mCameraManager: camera.CameraManager | undefined = undefined;
  // surface宽高根据需要自行选择。
  private surfaceRect: SurfaceRect = {
    surfaceWidth: 1080,
    surfaceHeight: 1920
  };
  private curCameraDevice: camera.CameraDevice | undefined = undefined;
  private mCameraInput: camera.CameraInput | undefined = undefined;
  private mPreviewOutput: camera.PreviewOutput | undefined = undefined;
  private mPhotoSession: camera.PhotoSession | undefined = undefined;
  // 请根据实际业务诉求选择符合需求场景的预览流Profile，此处以分辨率1080P，CameraFormat：1003为例。
  private previewProfileObj: camera.Profile = {
    format: 1003,
    size: {
      width: 1920,
      height: 1080
    }
  };
  private mContext: Context | undefined = undefined;

  private preFoldStatus: display.FoldStatus = this.getFoldStatus();
  // 监听折叠屏状态，可以使用cameraManager.on(type: 'foldStatusChange', callback: AsyncCallback<FoldStatusInfo>): void;
  // 也可以使用display.on(type: 'foldStatusChange', callback: Callback<FoldStatus>): void;
  private foldStatusCallback =
    (err: BusinessError, info: camera.FoldStatusInfo): void => this.registerFoldStatusChanged(err, info);
  private displayFoldStatusCallback =
    (foldStatus: display.FoldStatus): void => this.onDisplayFoldStatusChange(foldStatus);

  getFoldStatus(): display.FoldStatus {
    let curFoldStatus: display.FoldStatus = display.FoldStatus.FOLD_STATUS_UNKNOWN;
    try {
      curFoldStatus = display.getFoldStatus();
    } catch (error) {
      console.info(`${TAG} getFoldStatus call failed, error: ${error.code}`);
    }
    return curFoldStatus;
  }

  registerFoldStatusChanged(err: BusinessError, foldStatusInfo: camera.FoldStatusInfo) {
    if (err !== undefined && err.code !== 0) {
      console.info(`${TAG} registerFoldStatusChanged call failed, error: ${err.code}`);
      return;
    }
    console.info(TAG + 'foldStatusChanged foldStatus: ' + foldStatusInfo.foldStatus);
    for (let i = 0; i < foldStatusInfo.supportedCameras.length; i++) {
      console.info(TAG +
        `foldStatusChanged camera[${i}]: ${foldStatusInfo.supportedCameras[i].cameraId},cameraPosition: ${foldStatusInfo.supportedCameras[i].cameraPosition}`);
    }
    AppStorage.setOrCreate<number>('foldStatus', foldStatusInfo.foldStatus);
  }

  onDisplayFoldStatusChange(foldStatus: display.FoldStatus): void {
    console.info(TAG + `onDisplayFoldStatusChange foldStatus: ${foldStatus}`);
    if ((this.preFoldStatus === display.FoldStatus.FOLD_STATUS_HALF_FOLDED &&
      foldStatus === display.FoldStatus.FOLD_STATUS_EXPANDED) ||
      (this.preFoldStatus === display.FoldStatus.FOLD_STATUS_EXPANDED &&
        foldStatus === display.FoldStatus.FOLD_STATUS_HALF_FOLDED)) {
      this.preFoldStatus = foldStatus;
      return;
    }
    this.preFoldStatus = foldStatus;
    if (!this.curCameraDevice) {
      return;
    }
    // foldStatus 变量用来控制显示XComponent组件。
    AppStorage.setOrCreate<number>('foldStatus', foldStatus);
  }

  requestPermissionsFn(): void {
    let atManager = abilityAccessCtrl.createAtManager();
    atManager.requestPermissionsFromUser(this.mContext, [
      'ohos.permission.CAMERA'
    ]).then((): void => {
      this.isShow = true;
    }).catch((error: BusinessError): void => {
      console.error(`${TAG} requestPermissionsFromUser call failed, error: ${error.code}`);
    });
  }

  initContext(): void {
    let uiContext = this.getUIContext();
    this.mContext = uiContext.getHostContext();
  }

  initCameraManager(): void {
    try {
      this.mCameraManager = camera.getCameraManager(this.mContext);
    } catch (error) {
      console.error(`${TAG} getCameraManager call failed, error: ${error.code}`);
    }
  }

  aboutToAppear(): void {
    console.info(TAG + 'aboutToAppear is called');
    this.initContext();
    this.initCameraManager();
    this.requestPermissionsFn();
    this.onFoldStatusChange();
  }

  async aboutToDisappear(): Promise<void> {
    await this.releaseCamera();
    // 解注册。
    this.offFoldStatusChange();
  }

  async onPageShow(): Promise<void> {
    await this.initCamera(this.mSurfaceId, this.mCameraPosition);
  }

  async releaseCamera(): Promise<void> {
    // 停止当前会话。
    try {
      await this.mPhotoSession?.stop();
    } catch (error) {
      let err = error as BusinessError;
      console.error(TAG + 'Failed to stop session, errorCode = ' + err.code);
    }

    // 释放相机输入流。
    try {
      await this.mCameraInput?.close();
    } catch (error) {
      let err = error as BusinessError;
      console.error(TAG + 'Failed to close device, errorCode = ' + err.code);
    }

    // 释放预览输出流。
    try {
      await this.mPreviewOutput?.release();
    } catch (error) {
      let err = error as BusinessError;
      console.error(TAG + 'Failed to release previewOutput, errorCode = ' + err.code);
    }

    this.mPreviewOutput = undefined;

    // 释放会话。
    try {
      await this.mPhotoSession?.release();
    } catch (error) {
      let err = error as BusinessError;
      console.error(TAG + 'Failed to release photoSession, errorCode = ' + err.code);
    }

    // 会话置空。
    this.mPhotoSession = undefined;
  }

  onFoldStatusChange(): void {
    this.mCameraManager?.on('foldStatusChange', this.foldStatusCallback);
    // display.on('foldStatusChange', this.displayFoldStatusCallback);
  }

  offFoldStatusChange(): void {
    this.mCameraManager?.off('foldStatusChange', this.foldStatusCallback);
    // display.off('foldStatusChange', this.displayFoldStatusCallback);
  }

  reloadXComponent(): void {
    this.reloadXComponentFlag = !this.reloadXComponentFlag;
  }

  async loadXComponent(): Promise<void> {
    if (!this.mXComponentController) {
      console.error(TAG + 'mXComponentController is null');
      return;
    }
    this.mSurfaceId = this.mXComponentController.getXComponentSurfaceId();
    this.mXComponentController.setXComponentSurfaceRect(this.surfaceRect);
    console.info(TAG + `mCameraPosition: ${this.mCameraPosition}`)
    await this.initCamera(this.mSurfaceId, this.mCameraPosition);
  }

  getPreviewProfile(cameraOutputCapability: camera.CameraOutputCapability): camera.Profile | undefined {
    let previewProfiles = cameraOutputCapability.previewProfiles;
    if (previewProfiles.length < 1) {
      return undefined;
    }
    let index = previewProfiles.findIndex((previewProfile: camera.Profile) => {
      return previewProfile.size.width === this.previewProfileObj.size.width &&
        previewProfile.size.height === this.previewProfileObj.size.height &&
        previewProfile.format === this.previewProfileObj.format;
    })
    if (index === -1) {
      return undefined;
    }
    return previewProfiles[index];
  }

  async initCamera(surfaceId: string, cameraPosition: camera.CameraPosition,
    connectionType: camera.ConnectionType = camera.ConnectionType.CAMERA_CONNECTION_BUILT_IN): Promise<void> {
    await this.releaseCamera();
    // 创建CameraManager对象。
    if (!this.mCameraManager) {
      console.error(TAG + 'camera.getCameraManager error');
      return;
    }

    // 获取相机列表。
    let cameraArray: Array<camera.CameraDevice> = this.mCameraManager.getSupportedCameras();
    if (!cameraArray || cameraArray.length == 0) {
      console.error(TAG + 'cameraManager.getSupportedCameras error');
      return;
    }

    for (let index = 0; index < cameraArray.length; index++) {
      console.info(TAG + 'cameraId : ' + cameraArray[index].cameraId); // 获取相机ID。
      console.info(TAG + 'cameraPosition : ' + cameraArray[index].cameraPosition); // 获取相机位置。
      console.info(TAG + 'cameraType : ' + cameraArray[index].cameraType); // 获取相机类型。
      console.info(TAG + 'connectionType : ' + cameraArray[index].connectionType); // 获取相机连接类型。
    }

    let deviceIndex = cameraArray.findIndex((cameraDevice: camera.CameraDevice) => {
      return cameraDevice.cameraPosition === cameraPosition && cameraDevice.connectionType === connectionType;
    })
    // 没有找到对应位置的摄像头，可选择其他摄像头，具体场景具体对待。
    if (deviceIndex === -1) {
      deviceIndex = 0;
      console.error(TAG + 'not found camera');
    }
    this.curCameraDevice = cameraArray[deviceIndex];

    // 创建相机输入流。
    try {
      this.mCameraInput = this.mCameraManager.createCameraInput(this.curCameraDevice);
    } catch (error) {
      let err = error as BusinessError;
      console.error(TAG + 'Failed to createCameraInput errorCode = ' + err.code);
    }
    if (this.mCameraInput === undefined) {
      return;
    }

    // 打开相机。
    try {
      await this.mCameraInput.open();
    } catch (error) {
      let err = error as BusinessError;
      console.error(TAG + 'Failed to open device, errorCode = ' + err.code);
    }

    // 获取支持的模式类型。
    let sceneModes: Array<camera.SceneMode> = this.mCameraManager.getSupportedSceneModes(this.curCameraDevice);
    let isSupportPhotoMode: boolean = sceneModes.indexOf(camera.SceneMode.NORMAL_PHOTO) >= 0;
    if (!isSupportPhotoMode) {
      console.error(TAG + 'photo mode not support');
      await this.releaseCamera();
      return;
    }

    // 获取相机设备支持的输出流能力。
    let cameraOutputCapability: camera.CameraOutputCapability =
      this.mCameraManager.getSupportedOutputCapability(this.curCameraDevice, camera.SceneMode.NORMAL_PHOTO);
    if (!cameraOutputCapability) {
      console.error(TAG + 'cameraManager.getSupportedOutputCapability error');
      return;
    }
    console.info(TAG + 'outputCapability: ' + JSON.stringify(cameraOutputCapability));
    let previewProfile = this.getPreviewProfile(cameraOutputCapability);
    if (!previewProfile) {
      console.error(TAG + 'The resolution of the current preview stream is not supported.');
      await this.releaseCamera();
      return;
    }
    this.previewProfileObj = previewProfile;

    // 创建预览输出流,其中参数 surfaceId 参考上文 XComponent 组件，预览流为XComponent组件提供的surface。
    try {
      this.mPreviewOutput = this.mCameraManager.createPreviewOutput(this.previewProfileObj, surfaceId);
    } catch (error) {
      let err = error as BusinessError;
      console.error(TAG + `Failed to create the PreviewOutput instance. error code: ${err.code}`);
    }
    if (!this.mPreviewOutput) {
      await this.releaseCamera();
      return;
    }

    // 创建会话。
    try {
      let session = this.mCameraManager.createSession(camera.SceneMode.NORMAL_PHOTO);
      if (!session) {
        await this.releaseCamera();
        return;
      }
      this.mPhotoSession = session as camera.PhotoSession;
    } catch (error) {
      let err = error as BusinessError;
      console.error(TAG + 'Failed to create the session instance. errorCode = ' + err.code);
    }

    if (!this.mPhotoSession) {
      await this.releaseCamera();
      return;
    }

    // 开始配置会话。
    try {
      this.mPhotoSession.beginConfig();
    } catch (error) {
      let err = error as BusinessError;
      console.error(TAG + 'Failed to beginConfig. errorCode = ' + err.code);
    }

    // 向会话中添加相机输入流。
    try {
      this.mPhotoSession.addInput(this.mCameraInput);
    } catch (error) {
      let err = error as BusinessError;
      console.error(TAG + 'Failed to addInput. errorCode = ' + err.code);
    }

    // 向会话中添加预览输出流。
    try {
      this.mPhotoSession.addOutput(this.mPreviewOutput);
    } catch (error) {
      let err = error as BusinessError;
      console.error(TAG + 'Failed to addOutput(previewOutput). errorCode = ' + err.code);
    }

    // 提交会话配置。
    try {
      await this.mPhotoSession.commitConfig();
    } catch (error) {
      let err = error as BusinessError;
      console.error(TAG + 'Failed to commit session configuration, errorCode = ' + err.code);
    }

    // 启动会话。
    try {
      await this.mPhotoSession.start()
    } catch (error) {
      let err = error as BusinessError;
      console.error(TAG + 'Failed to start session. errorCode = ' + err.code);
    }
  }

  build() {
    if (this.isShow) {
      Stack() {
        if (this.reloadXComponentFlag) {
          XComponent(this.mXComponentOptions)
            .onLoad(async () => {
              await this.loadXComponent();
            })
            .width(this.getUIContext().px2vp(1080))
            .height(this.getUIContext().px2vp(1920))
        } else {
          XComponent(this.mXComponentOptions)
            .onLoad(async () => {
              await this.loadXComponent();
            })
            .width(this.getUIContext().px2vp(1080))
            .height(this.getUIContext().px2vp(1920))
        }
        Text('切换相机')
          .size({ width: 80, height: 48 })
          .position({ x: 1, y: 1 })
          .backgroundColor(Color.White)
          .textAlign(TextAlign.Center)
          .borderRadius(24)
          .onClick(async () => {
            this.mCameraPosition = this.mCameraPosition === camera.CameraPosition.CAMERA_POSITION_BACK ?
              camera.CameraPosition.CAMERA_POSITION_FRONT : camera.CameraPosition.CAMERA_POSITION_BACK;
            this.reloadXComponentFlag = !this.reloadXComponentFlag;
          })
      }
      .size({ width: '100%', height: '100%' })
      .backgroundColor(Color.Black)
    }
  }
}

常见问题

折叠状态改变时，如何处理相机画面可能出现的拉伸变形问题

折叠状态发生变化导致镜头切换后，可能出现图像分辨率与XComponent的宽高比不匹配的情况。应用可通过Window.on('windowSizeChange')监听窗口的变化，根据屏幕旋转角度（Display.rotation）与相机镜头角度（CameraDevice.cameraOrientation）之间的关系来确定布局的宽高比，以确保XComponent的宽高比能跟随窗口实时调整。

详细代码可参考：指定XComponent的大小，防止旋转后图像拉伸变形。