如何正确关闭释放相机流

问题现象

在自定义相机开发中，由于开发者未能正确关闭或释放相机流，经常会出现各种错误，如关闭相机阻塞、日志报错、拍照回调不触发或者获取数据为空等。

背景知识

相机拍照流程一般分为获取相机管理器和相机设备、创建相机输入流、获取相机输出能力、创建相机预览输出流、创建拍照输出流、设置拍照回调、创建并配置相机会话、启动相机会话、触发拍照、保存图片、释放资源等流程，流程之间存在依赖关系，具体开发流程可参考拍照（ArkTS）。

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解决方案

若相机错误码为7400109，表示相机设备被抢占导致无法使用相机，可能原因是由于之前的相机流未能正确关闭或释放导致同时打开2个相同摄像头。需要在创建CameraManager对象前对之前的相机流进行释放，参考代码如下：

// 释放相机。
async releaseCamera(): Promise<void> {
  console.info('start releaseCamera');
  // 停止当前会话。
  await this.session?.stop().catch((e: BusinessError) => {
    console.error('Failed to stop session: ', e);
  });
  // 释放相机输入流。
  await this.cameraInput?.close().catch((e: BusinessError) => {
    console.error('Failed to close the camera: ', e);
  });
  // 释放预览输出流。
  await this.previewOutput?.release().catch((e: BusinessError) => {
    console.error('Failed to stop the preview stream: ', e);
  });
  // 释放会话。
  await this.session?.release().then(() => {
    this.session = undefined;
  }).catch((e: BusinessError) => {
    console.error('Failed to release session: ', e);
  });
  console.info('end releaseCamera.');
}

若相机应用首次打开应用黑屏，或退到后台后再切到前台预览画面停止，则需要检查是否在页面的各生命周期正确释放相机流或初始化相机，核心代码如下：

async requestPermissionsFn(): Promise<void> {
  let atManager = abilityAccessCtrl.createAtManager();
  if (this.context) {
    let res = await atManager.requestPermissionsFromUser(this.context, [this.cameraPermission]);
    for (let i = 0; i < res.permissions.length; i++) {
      if (this.cameraPermission.toString() === res.permissions[i] &&
        res.authResults[i] === abilityAccessCtrl.GrantStatus.PERMISSION_GRANTED) {
        this.isShow = true;
      }
    }
  }
}

aboutToAppear(): void {
  this.requestPermissionsFn();
}

onPageShow(): void {
  console.info('onPageShow');
  if (this.xComponentSurfaceId !== '') {
    this.initCamera();
  }
}

onPageHide(): void {
  console.info('onPageHide');
  this.releaseCamera();
}

在不同相机镜头进行切换时，也需要释放相机流：

async changeCameraPosition() {
  await this.releaseCamera();
  this.cameraPosition = this.cameraPosition === camera.CameraPosition.CAMERA_POSITION_BACK ?
    camera.CameraPosition.CAMERA_POSITION_FRONT : camera.CameraPosition.CAMERA_POSITION_BACK;
  this.initCamera();
}

若拍照回调不触发或者获取数据为空，可以在拍照执行后等待回调发生再停止会话，或者通过定时器setInterval延时异步调用会话停止使得会话可以先处理拍照响应数据，再关闭会话，避免会话因为当前任务被挂起导致无法监听到拍照回调事件。

完整示例代码如下：

参考声明权限文档，需要先在module.json5文件中声明ohos.permission.CAMERA权限。

import { camera } from '@kit.CameraKit';
import { BusinessError } from '@kit.BasicServicesKit';
import { abilityAccessCtrl, Permissions } from '@kit.AbilityKit';

@Entry
@Component
struct Index {
  private xComponentCtl: XComponentController = new XComponentController();
  private xComponentSurfaceId: string = '';
  @State imageWidth: number = 1920;
  @State imageHeight: number = 1080;
  private cameraManager: camera.CameraManager | undefined = undefined;
  private cameras: Array<camera.CameraDevice> | Array<camera.CameraDevice> = [];
  private cameraInput: camera.CameraInput | undefined = undefined;
  private previewOutput: camera.PreviewOutput | undefined = undefined;
  private session: camera.VideoSession | undefined = undefined;
  private uiContext: UIContext = this.getUIContext();
  private context: Context | undefined = this.uiContext.getHostContext();
  private cameraPermission: Permissions = 'ohos.permission.CAMERA';
  @State isShow: boolean = false;
  @State cameraPosition: camera.CameraPosition = camera.CameraPosition.CAMERA_POSITION_BACK; // 默认使用后置摄像头

  async requestPermissionsFn(): Promise<void> {
    let atManager = abilityAccessCtrl.createAtManager();
    if (this.context) {
      let res = await atManager.requestPermissionsFromUser(this.context, [this.cameraPermission]);
      for (let i = 0; i < res.permissions.length; i++) {
        if (this.cameraPermission.toString() === res.permissions[i] &&
          res.authResults[i] === abilityAccessCtrl.GrantStatus.PERMISSION_GRANTED) {
          this.isShow = true;
        }
      }
    }
  }

  aboutToAppear(): void {
    this.requestPermissionsFn();
  }

  onPageShow(): void {
    console.info('onPageShow');
    if (this.xComponentSurfaceId !== '') {
      this.initCamera();
    }
  }

  onPageHide(): void {
    console.info('onPageHide');
    this.releaseCamera();
  }

  async requestPermissions(): Promise<void> {
    let atManager = abilityAccessCtrl.createAtManager();
    if (this.context) {
      let res = await atManager.requestPermissionOnSetting(this.context, [this.cameraPermission]);
      for (let i = 0; i < res.length; i++) {
        if (res[i] === abilityAccessCtrl.GrantStatus.PERMISSION_GRANTED) {
          this.isShow = true;
        } else {
          this.isShow = false;
        }
      }
    }
  }

  build() {
    Column({ space: 20 }) {
      if (this.isShow) {
        XComponent({
          id: 'componentId',
          type: XComponentType.SURFACE,
          controller: this.xComponentCtl
        })
          .onLoad(async () => {
            console.info('onLoad is called');
            this.xComponentSurfaceId = this.xComponentCtl.getXComponentSurfaceId(); // 获取组件surfaceId。
            // 初始化相机，组件实时渲染每帧预览流数据。
            this.initCamera();
          })
          .width(300)
          .height(this.imageWidth / this.imageHeight * 300);

        Button('切换摄像头')
          .type(ButtonType.ROUNDED_RECTANGLE)
          .backgroundColor('#0a59f7')
          .onClick(async () => {
            await this.changeCameraPosition();
          });
      } else {
        Button('请先授予相机权限')
          .type(ButtonType.ROUNDED_RECTANGLE)
          .backgroundColor('#0a59f7')
          .onClick(() => {
            this.requestPermissions();
          });
      }
    }
    .justifyContent(FlexAlign.Center)
    .height('100%')
    .width('100%');
  }

  async changeCameraPosition() {
    await this.releaseCamera();
    this.cameraPosition = this.cameraPosition === camera.CameraPosition.CAMERA_POSITION_BACK ?
      camera.CameraPosition.CAMERA_POSITION_FRONT : camera.CameraPosition.CAMERA_POSITION_BACK;
    this.initCamera();
  }

  // 初始化相机。
  async initCamera(): Promise<void> {
    console.info(`initCamera previewOutput xComponentSurfaceId:${this.xComponentSurfaceId}`);
    try {
      // 获取相机管理器实例。
      this.cameraManager = camera.getCameraManager(this.context);
      if (!this.cameraManager) {
        console.error('initCamera getCameraManager');
        return;
      }
      // 获取当前设备支持的相机device列表。
      this.cameras = this.cameraManager.getSupportedCameras();
      if (!this.cameras) {
        console.error('initCamera getSupportedCameras');
      }
      // 选择一个相机device，创建cameraInput输出对象。
      let curCamera = this.cameras[0];
      for (let index = 0; index < this.cameras.length; index++) {
        const tempCamera = this.cameras[index];
        if (this.cameraPosition == tempCamera.cameraPosition) {
          curCamera = tempCamera;
          break;
        }
      }
      this.cameraInput = this.cameraManager.createCameraInput(curCamera);
      if (!this.cameraInput) {
        console.error('initCamera createCameraInput');
        return;
      }
      // 打开相机。
      await this.cameraInput.open();
      // 获取相机device支持的profile。
      let capability: camera.CameraOutputCapability =
        this.cameraManager.getSupportedOutputCapability(curCamera, camera.SceneMode.NORMAL_VIDEO);
      if (!capability || capability.previewProfiles.length === 0) {
        console.error('capability is null || []');
        this.releaseCamera();
        return;
      }
      let minRatioDiff: number = 0.1;
      let surfaceRatio: number = this.imageWidth / this.imageHeight; // 最接近16:9宽高比。
      let previewProfile: camera.Profile = capability.previewProfiles[0];
      // 应用开发者根据实际业务需求选择一个支持的预览流previewProfile。
      // 此处以选择CAMERA_FORMAT_YUV_420_SP（NV21）格式、满足限定条件分辨率的预览流previewProfile为例。
      for (let index = 0; index < capability.previewProfiles.length; index++) {
        const tempProfile = capability.previewProfiles[index];
        let tempRatio = tempProfile.size.width >= tempProfile.size.height ?
          tempProfile.size.width / tempProfile.size.height : tempProfile.size.height / tempProfile.size.width;
        let currentRatio = Math.abs(tempRatio - surfaceRatio);
        if (currentRatio <= minRatioDiff && tempProfile.format == camera.CameraFormat.CAMERA_FORMAT_YUV_420_SP) {
          previewProfile = tempProfile;
          break;
        }
      }
      this.imageWidth = previewProfile.size.width; // 更新xComponent组件的宽。
      this.imageHeight = previewProfile.size.height; // 更新xComponent组件的高。
      console.info(`initCamera imageWidth:${this.imageWidth} imageHeight:${this.imageHeight}`);

      // 使用xComponentSurfaceId创建预览。
      this.previewOutput = this.cameraManager.createPreviewOutput(previewProfile, this.xComponentSurfaceId);
      if (!this.previewOutput) {
        console.error('initCamera createPreviewOutput');
        this.releaseCamera();
        return;
      }
      // 创建录像模式相机会话。
      let session = this.cameraManager.createSession(camera.SceneMode.NORMAL_VIDEO);
      if (!session) {
        console.error('session is null');
        this.releaseCamera();
        return;
      }
      this.session = session as camera.VideoSession;
      // 开始配置会话。
      this.session.beginConfig();
      // 添加相机设备输入。
      this.session.addInput(this.cameraInput);
      // 添加预览流输出。
      this.session.addOutput(this.previewOutput);
      // 提交会话配置。
      await this.session.commitConfig();
      // 开始启动已配置的输入输出流。
      await this.session.start();
    } catch (error) {
      let err = error as BusinessError;
      console.error(`initCamera fail, err.code: ${err.code}, err.message: ${err.message}.`);
      this.releaseCamera();
    }
  }

  // 释放相机。
  async releaseCamera(): Promise<void> {
    console.info('start releaseCamera');
    // 停止当前会话。
    await this.session?.stop().catch((e: BusinessError) => {
      console.error('Failed to stop session: ', e);
    });
    // 释放相机输入流。
    await this.cameraInput?.close().catch((e: BusinessError) => {
      console.error('Failed to close the camera: ', e);
    });
    // 释放预览输出流。
    await this.previewOutput?.release().catch((e: BusinessError) => {
      console.error('Failed to stop the preview stream: ', e);
    });
    // 释放会话。
    await this.session?.release().then(() => {
      this.session = undefined;
    }).catch((e: BusinessError) => {
      console.error('Failed to release session: ', e);
    });
    console.info('end releaseCamera.');
  }
}

目录

如何正确关闭释放相机流

问题现象

背景知识

解决方案