harmony 鸿蒙Practices for Camera Recovery from the Background (ArkTS)

2025-06-12
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Practices for Camera Recovery from the Background (ArkTS)

This sample demonstrates the complete process for transitioning a camera application from the background to the foreground, providing you with a clear understanding of the entire sequence of API calls.

The state changes during the camera application’s transition between foreground and background are as follows: - When the camera application transitions to the background, it is forcibly disconnected due to security policies, and the camera status callback returns the camera available state, indicating that the camera device is now idle. - When the camera application returns to the foreground, the camera status callback returns the camera unavailable state, indicating that the camera device is now busy. - Upon transitioning from the background to the foreground, the camera application must restart the preview stream, photo stream, and camera session management accordingly.

Before referring to the sample code, you are advised to read Camera Device Management, Device Input Management, Camera Session Management, and other related topics in Camera Development (ArkTS).

Development Process

The figure below shows the process of transitioning a camera application from the background to the foreground.

Camera Background recovery processing

Sample

For details about how to obtain the context, see Obtaining the Context of UIAbility.

During the transition of the camera application from the background to the foreground, call the onPageShow callback function to re-initialize the camera device.

   import { camera } from '@kit.CameraKit';
   import { BusinessError } from '@kit.BasicServicesKit';
   import { common } from '@kit.AbilityKit';
   
   let context: common.BaseContext;
   let surfaceId: string = '';
   async function onPageShow(): Promise<void> {
      // Reinitialize the camera when the application transitions from the background to the foreground.
      await initCamera(context, surfaceId);
   }
   
   async function initCamera(baseContext: common.BaseContext, surfaceId: string): Promise<void> {
      console.info('onForeGround recovery begin.');
      let cameraManager: camera.CameraManager = camera.getCameraManager(context);
      if (!cameraManager) {
        console.error("camera.getCameraManager error");
        return;
      }
      // Listen for camera status changes.
      cameraManager.on('cameraStatus', (err: BusinessError, cameraStatusInfo: camera.CameraStatusInfo) => {
          if (err !== undefined && err.code !== 0) {
            console.error('cameraStatus with errorCode = ' + err.code);
            return;
          }
          console.info(`camera : ${cameraStatusInfo.camera.cameraId}`);
          console.info(`status: ${cameraStatusInfo.status}`);
        });

      // Obtain the camera list.
      let cameraArray: Array<camera.CameraDevice> = cameraManager.getSupportedCameras();
      if (cameraArray.length <= 0) {
        console.error("cameraManager.getSupportedCameras error");
        return;
      }

      for (let index = 0; index < cameraArray.length; index++) {
        console.info('cameraId : ' + cameraArray[index].cameraId);                       // Obtain the camera ID.
        console.info('cameraPosition : ' + cameraArray[index].cameraPosition);           // Obtain the camera position.
        console.info('cameraType : ' + cameraArray[index].cameraType);                   // Obtain the camera type.
        console.info('connectionType : ' + cameraArray[index].connectionType);           // Obtain the camera connection type.
      }

      // Create a camera input stream.
      let cameraInput: camera.CameraInput|undefined = undefined;
      try {
        cameraInput = cameraManager.createCameraInput(cameraArray[0]);
      } catch (error) {
          let err = error as BusinessError;
          console.error('Failed to createCameraInput errorCode = ' + err.code);
      }
      if (cameraInput === undefined) {
        return;
      }

      // Listen for camera input errors.
      let cameraDevice: camera.CameraDevice = cameraArray[0];
        cameraInput.on('error', cameraDevice, (error: BusinessError) => {
        console.error(`Camera input error code: ${error.code}`);
      });

      // Open the camera.
      await cameraInput.open();

      // Obtain the supported modes.
      let sceneModes: Array<camera.SceneMode> = cameraManager.getSupportedSceneModes(cameraArray[0]);
      let isSupportPhotoMode: boolean = sceneModes.indexOf(camera.SceneMode.NORMAL_PHOTO) >= 0;
      if (!isSupportPhotoMode) {
        console.error('photo mode not support');
        return;
      }
      // Obtain the output stream capability supported by the camera.
      let cameraOutputCap: camera.CameraOutputCapability = cameraManager.getSupportedOutputCapability(cameraArray[0], camera.SceneMode.NORMAL_PHOTO);
      if (!cameraOutputCap) {
        console.error("cameraManager.getSupportedOutputCapability error");
        return;
      }
      console.info("outputCapability: " + JSON.stringify(cameraOutputCap));

      let previewProfilesArray: Array<camera.Profile> = cameraOutputCap.previewProfiles;
      if (!previewProfilesArray) {
        console.error("createOutput previewProfilesArray == null||undefined");
      }

      let photoProfilesArray: Array<camera.Profile> = cameraOutputCap.photoProfiles;
      if (!photoProfilesArray) {
        console.error("createOutput photoProfilesArray == null||undefined");
      }

      // Create a preview output stream. For details about the surfaceId parameter, see the XComponent. The preview stream uses the surface provided by the XComponent.
      let previewOutput: camera.PreviewOutput|undefined = undefined;
      try {
        previewOutput = cameraManager.createPreviewOutput(previewProfilesArray[0], surfaceId);
      } catch (error) {
        let err = error as BusinessError;
        console.error(`Failed to create the PreviewOutput instance. error code: ${err.code}`);
      }
      if (previewOutput === undefined) {
        return;
      }
      // Listen for preview output errors.
      previewOutput.on('error', (error: BusinessError) => {
        console.error(`Preview output error code: ${error.code}`);
      });

      // Create a photo output stream.
      let photoOutput: camera.PhotoOutput|undefined = undefined;
      try {
        photoOutput = cameraManager.createPhotoOutput(photoProfilesArray[0]);
      } catch (error) {
          let err = error as BusinessError;
          console.error('Failed to createPhotoOutput errorCode = ' + err.code);
      }
      if (photoOutput === undefined) {
        return;
      }

      // Create a session.
      let photoSession: camera.PhotoSession|undefined = undefined;
      try {
        photoSession = cameraManager.createSession(camera.SceneMode.NORMAL_PHOTO) as camera.PhotoSession;
      } catch (error) {
          let err = error as BusinessError;
          console.error('Failed to create the session instance. errorCode = ' + err.code);
      }
      if (photoSession === undefined) {
        return;
      }
      // Listen for session errors.
      photoSession.on('error', (error: BusinessError) => {
        console.error(`Capture session error code: ${error.code}`);
      });

      // Start configuration for the session.
      try {
        photoSession.beginConfig();
      } catch (error) {
          let err = error as BusinessError;
          console.error('Failed to beginConfig. errorCode = ' + err.code);
      }

      // Add the camera input stream to the session.
      try {
        photoSession.addInput(cameraInput);
      } catch (error) {
          let err = error as BusinessError;
          console.error('Failed to addInput. errorCode = ' + err.code);
      }

      // Add the preview output stream to the session.
      try {
        photoSession.addOutput(previewOutput);
      } catch (error) {
          let err = error as BusinessError;
          console.error('Failed to addOutput(previewOutput). errorCode = ' + err.code);
      }

      // Add the photo output stream to the session.
      try {
        photoSession.addOutput(photoOutput);
      } catch (error) {
          let err = error as BusinessError;
          console.error('Failed to addOutput(photoOutput). errorCode = ' + err.code);
      }

      // Commit the session configuration.
      await photoSession.commitConfig();

      // Start the session.
      await photoSession.start().then(() => {
        console.info('Promise returned to indicate the session start success.');
      });
      // Check whether the camera has flash.
      let flashStatus: boolean = false;
        try {
          flashStatus = photoSession.hasFlash();
      } catch (error) {
          let err = error as BusinessError;
          console.error('Failed to hasFlash. errorCode = ' + err.code);
      }
      console.info('Returned with the flash light support status:' + flashStatus);

      if (flashStatus) {
        // Check whether the auto flash mode is supported.
        let flashModeStatus: boolean = false;
        try {
          let status: boolean = photoSession.isFlashModeSupported(camera.FlashMode.FLASH_MODE_AUTO);
          flashModeStatus = status;
        } catch (error) {
            let err = error as BusinessError;
            console.error('Failed to check whether the flash mode is supported. errorCode = ' + err.code);
        }
        if(flashModeStatus) {
          // Set the flash mode to auto.
          try {
            photoSession.setFlashMode(camera.FlashMode.FLASH_MODE_AUTO);
          } catch (error) {
              let err = error as BusinessError;
              console.error('Failed to set the flash mode. errorCode = ' + err.code);
          }
        }
      }

      // Check whether the continuous auto focus is supported.
      let focusModeStatus: boolean = false;
      try {
        let status: boolean = photoSession.isFocusModeSupported(camera.FocusMode.FOCUS_MODE_CONTINUOUS_AUTO);
        focusModeStatus = status;
      } catch (error) {
          let err = error as BusinessError;
          console.error('Failed to check whether the focus mode is supported. errorCode = ' + err.code);
      }

      if (focusModeStatus) {
        // Set the focus mode to continuous auto focus.
        try {
          photoSession.setFocusMode(camera.FocusMode.FOCUS_MODE_CONTINUOUS_AUTO);
        } catch (error) {
            let err = error as BusinessError;
            console.error('Failed to set the focus mode. errorCode = ' + err.code);
        }
      }

      // Obtain the zoom ratio range supported by the camera.
      let zoomRatioRange: Array<number> = [];
      try {
        zoomRatioRange = photoSession.getZoomRatioRange();
      } catch (error) {
          let err = error as BusinessError;
          console.error('Failed to get the zoom ratio range. errorCode = ' + err.code);
      }
      if (zoomRatioRange.length <= 0) {
        return;
      }
      // Set a zoom ratio.
      try {
        photoSession.setZoomRatio(zoomRatioRange[0]);
      } catch (error) {
          let err = error as BusinessError;
          console.error('Failed to set the zoom ratio value. errorCode = ' + err.code);
      }
      let photoCaptureSetting: camera.PhotoCaptureSetting = {
        quality: camera.QualityLevel.QUALITY_LEVEL_HIGH, // Set the photo quality to high.
        rotation: camera.ImageRotation.ROTATION_0 // Set the rotation angle of the photo to 0.
      }
      // Use the current photo capture settings to take photos.
      photoOutput.capture(photoCaptureSetting, (err: BusinessError) => {
        if (err) {
          console.error(`Failed to capture the photo ${err.message}`);
          return;
        }
        console.info('Callback invoked to indicate the photo capture request success.');
      });

      console.info('onForeGround recovery end.');
   }