Interface (MetadataOutput)

MetadataOutput implements metadata streams. It inherits from CameraOutput.

NOTE

The initial APIs of this module are supported since API version 10. Newly added APIs will be marked with a superscript to indicate their earliest API version.

Modules to Import

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

start

start(callback: AsyncCallback<void>): void

Starts to output metadata. This API uses an asynchronous callback to return the result.

Atomic service API: This API can be used in atomic services since API version 19.

System capability: SystemCapability.Multimedia.Camera.Core

Parameters

Name	Type	Mandatory	Description
callback	AsyncCallback<void>	Yes	Callback used to return the result. If the metadata output starts successfully, err is undefined; otherwise, err is an error object with an error code defined in CameraErrorCode.

Error codes

For details about the error codes, see Camera Error Codes.

ID	Error Message
7400103	Session not config.
7400201	Camera service fatal error.

Example

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

function startMetadataOutput(metadataOutput: camera.MetadataOutput): void {
  metadataOutput.start((err: BusinessError) => {
    if (err) {
      console.error(`Failed to start metadata output, error code: ${err.code}.`);
      return;
    }
    console.info('Callback returned with metadata output started.');
  });
}

start

start(): Promise<void>

Starts to output metadata. This API uses a promise to return the result.

Atomic service API: This API can be used in atomic services since API version 19.

System capability: SystemCapability.Multimedia.Camera.Core

Return value

Type	Description
Promise<void>	Promise that returns no value.

Error codes

For details about the error codes, see Camera Error Codes.

ID	Error Message
7400103	Session not config.
7400201	Camera service fatal error.

Example

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

function startMetadataOutput(metadataOutput: camera.MetadataOutput): void {
  metadataOutput.start().then(() => {
    console.info('Callback returned with metadata output started.');
  }).catch((error: BusinessError) => {
    console.error(`Failed to metadata output start, error code: ${error.code}`);
  });
}

stop

stop(callback: AsyncCallback<void>): void

Stops outputting metadata. This API uses an asynchronous callback to return the result.

Atomic service API: This API can be used in atomic services since API version 19.

System capability: SystemCapability.Multimedia.Camera.Core

Parameters

Name	Type	Mandatory	Description
callback	AsyncCallback<void>	Yes	Callback used to return the result. If the metadata output stops successfully, err is undefined; otherwise, err is an error object.

Example

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

function stopMetadataOutput(metadataOutput: camera.MetadataOutput): void {
  metadataOutput.stop((err: BusinessError) => {
    if (err) {
      console.error(`Failed to stop the metadata output, error code: ${err.code}.`);
      return;
    }
    console.info('Callback returned with metadata output stopped.');
  })
}

stop

stop(): Promise<void>

Stops outputting metadata. This API uses a promise to return the result.

Atomic service API: This API can be used in atomic services since API version 19.

System capability: SystemCapability.Multimedia.Camera.Core

Return value

Type	Description
Promise<void>	Promise that returns no value.

Example

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

function stopMetadataOutput(metadataOutput: camera.MetadataOutput): void {
  metadataOutput.stop().then(() => {
    console.info('Callback returned with metadata output stopped.');
  }).catch((error: BusinessError) => {
    console.error(`Failed to metadata output stop, error code: ${error.code}`);
  });
}

on('metadataObjectsAvailable')

on(type: 'metadataObjectsAvailable', callback: AsyncCallback<Array<MetadataObject>>): void

Subscribes to events indicating available metadata objects. This API uses an asynchronous callback to return the result.

NOTE

Currently, you cannot use off() to unregister the callback in the callback method of on().

Atomic service API: This API can be used in atomic services since API version 19.

System capability: SystemCapability.Multimedia.Camera.Core

Parameters

Name	Type	Mandatory	Description
type	string	Yes	Event type. The value is fixed at 'metadataObjectsAvailable'. The event can be listened for when a metadataOutput instance is created. This event is triggered and the corresponding metadata is returned when valid metadata is detected. If the input field is incorrect, no valid listening will be created.
callback	AsyncCallback<Array<MetadataObject>>	Yes	Callback used to return the metadata.

Example

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

function callback(err: BusinessError, metadataObjectArr: Array<camera.MetadataObject>): void {
  if (err !== undefined && err.code !== 0) {
    console.error(`Callback Error, errorCode: ${err.code}`);
    return;
  }
  console.info('metadata output metadataObjectsAvailable');
}

function registerMetadataObjectsAvailable(metadataOutput: camera.MetadataOutput): void {
  metadataOutput.on('metadataObjectsAvailable', callback);
}

off('metadataObjectsAvailable')

off(type: 'metadataObjectsAvailable', callback?: AsyncCallback<Array<MetadataObject>>): void

Unsubscribes from events indicating available metadata objects.

Atomic service API: This API can be used in atomic services since API version 19.

System capability: SystemCapability.Multimedia.Camera.Core

Parameters

Name	Type	Mandatory	Description
type	string	Yes	Event type. The value is fixed at 'metadataObjectsAvailable'. The event can be listened for when a metadataOutput instance is created.
callback	AsyncCallback<Array<MetadataObject>>	No	Callback used to return the result. If this parameter is specified, the subscription to the specified event with the specified callback is canceled. (The callback object cannot be an anonymous function.) Otherwise, the subscriptions to the specified event with all the callbacks are canceled.

Example

function unregisterMetadataObjectsAvailable(metadataOutput: camera.MetadataOutput): void {
  metadataOutput.off('metadataObjectsAvailable');
}

on('error')

on(type: 'error', callback: ErrorCallback): void

Subscribes to metadata error events. This API uses an asynchronous callback to return the result.

NOTE

Currently, you cannot use off() to unregister the callback in the callback method of on().

Atomic service API: This API can be used in atomic services since API version 19.

System capability: SystemCapability.Multimedia.Camera.Core

Parameters

Name	Type	Mandatory	Description
type	string	Yes	Event type. The value is fixed at 'error'. The event can be listened for when a metadataOutput instance is created. This event is triggered and the corresponding error message is returned when an error occurs during the use of a metadata-related API such as start or CameraOutput.release.
callback	ErrorCallback	Yes	Callback used to return an error code defined in CameraErrorCode.

Example

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

function callback(metadataOutputError: BusinessError): void {
  console.error(`Metadata output error code: ${metadataOutputError.code}`);
}

function registerMetadataOutputError(metadataOutput: camera.MetadataOutput): void {
  metadataOutput.on('error', callback);
}

off('error')

off(type: 'error', callback?: ErrorCallback): void

Unsubscribes from metadata error events.

Atomic service API: This API can be used in atomic services since API version 19.

System capability: SystemCapability.Multimedia.Camera.Core

Parameters

Name	Type	Mandatory	Description
type	string	Yes	Event type. The value is fixed at 'error'. The event can be listened for when a metadataOutput instance is created.
callback	ErrorCallback	No	Callback used to return the result. If this parameter is specified, the subscription to the specified event with the specified callback is canceled. (The callback object cannot be an anonymous function.) Otherwise, the subscriptions to the specified event with all the callbacks are canceled.

Example

function unregisterMetadataOutputError(metadataOutput: camera.MetadataOutput): void {
  metadataOutput.off('error');
}

addMetadataObjectTypes²³⁺

addMetadataObjectTypes(types: Array<MetadataObjectType>): void

Adds the types of metadata objects to be detected.

Atomic service API: This API can be used in atomic services since API version 23.

System capability: SystemCapability.Multimedia.Camera.Core

Parameters

Name	Type	Mandatory	Description
types	Array<MetadataObjectType>	Yes	Metadata object types, which are obtained through getSupportedOutputCapability.

Error codes

For details about the error codes, see Camera Error Codes.

ID	Error Message
7400101	Parameter missing or parameter type incorrect.
7400103	Session not config.
7400201	Camera service fatal error.

Example

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

function addMetadataObjectTypes(metadataOutput: camera.MetadataOutput, types: Array<camera.MetadataObjectType>): void {
  try {
    metadataOutput.addMetadataObjectTypes(types);
  } catch (error) {
    // If the operation fails, error.code is returned and processed.
    let err = error as BusinessError;
    console.error(`addMetadataObjectTypes error. error code: ${err.code}`);
  }
}

removeMetadataObjectTypes²³⁺

removeMetadataObjectTypes(types: Array<MetadataObjectType>): void

Removes the types of metadata objects to be detected.

Atomic service API: This API can be used in atomic services since API version 23.

System capability: SystemCapability.Multimedia.Camera.Core

Parameters

Name	Type	Mandatory	Description
types	Array<MetadataObjectType>	Yes	Metadata object types, which are obtained through getSupportedOutputCapability.

Error codes

For details about the error codes, see Camera Error Codes.

ID	Error Message
7400101	Parameter missing or parameter type incorrect.
7400103	Session not config.
7400201	Camera service fatal error.

Example

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

function removeMetadataObjectTypes(metadataOutput: camera.MetadataOutput, types: Array<camera.MetadataObjectType>): void {
  try {
    metadataOutput.removeMetadataObjectTypes(types);
  } catch (error) {
    // If the operation fails, error.code is returned and processed.
    let err = error as BusinessError;
    console.error(`removeMetadataObjectTypes error. error code: ${err.code}`);
  }
}