harmony 鸿蒙LazyForEach

2025-06-12
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LazyForEach

NOTE

The initial APIs of this module are supported since API version 7. Newly added APIs will be marked with a superscript to indicate their earliest API version.

For details about the development, see LazyForEach: Lazy Data Loading.

APIs

LazyForEach(dataSource: IDataSource,itemGenerator: (item: any, index: number) => void,keyGenerator?: (item: any, index: number) => string,)

LazyForEach iterates over provided data sources and creates corresponding components during each iteration. When LazyForEach is used in a scrolling container, the framework creates components as required within the visible area of the scrolling container. When a component is out of the visible area, the framework destroys and reclaims the component to reduce memory usage.

Atomic service API: This API can be used in atomic services since API version 11.

System capability: SystemCapability.ArkUI.ArkUI.Full

Parameters

Name	Type	Mandatory	Description
dataSource	IDataSource	Yes	LazyForEach data source. You need to implement related APIs.
itemGenerator	(item: Object, index: number) => void	Yes	Child component generation function, which generates a child component for each data item in the array. NOTE - item indicates the current data item, and index indicates the index of the data item. - The function body of itemGenerator must be included in braces {…}. - itemGenerator can and must generate only one child component for each iteration. - The if statement is allowed in itemGenerator, but you must ensure that each branch of the if statement creates a child component of the same type. - ForEach and LazyForEach statements are not allowed in itemGenerator.
keyGenerator	(item: Object, index: number) => string	No	ID generation function, which generates a unique and fixed ID for each data item in the data source. This ID must remain unchanged for the data item even when the item is relocated in the array. When the item is replaced by a new item, the ID of the new item must be different from that of the replaced item. This ID generation function is optional. However, for performance reasons, it is strongly recommended that the ID generation function be provided, so that the framework can better identify array changes. For example, if no ID generation function is provided, a reverse of an array will result in rebuilding of all nodes in LazyForEach. NOTE - item indicates the current data item, and index indicates the index of the data item. - The ID generated for each data item in the data source must be unique.

Name

Inherited from DynamicNode.

IDataSource¹⁰⁺

Atomic service API: This API can be used in atomic services since API version 11.

System capability: SystemCapability.ArkUI.ArkUI.Full

totalCount

totalCount(): number

Obtains the total number of data items.

Atomic service API: This API can be used in atomic services since API version 11.

System capability: SystemCapability.ArkUI.ArkUI.Full

getData

getData(index: number): Object

Obtains the data item that matches the specified index.

Atomic service API: This API can be used in atomic services since API version 11.

System capability: SystemCapability.ArkUI.ArkUI.Full

Parameters

Name	Type	Mandatory	Description
index	number	Yes	Index of the data record to obtain.

registerDataChangeListener

registerDataChangeListener(listener: DataChangeListener): void

Registers a listener for data changes.

Atomic service API: This API can be used in atomic services since API version 11.

System capability: SystemCapability.ArkUI.ArkUI.Full

Parameters

Name	Type	Mandatory	Description
listener	DataChangeListener	Yes	Listener for data changes.

unregisterDataChangeListener

unregisterDataChangeListener(listener: DataChangeListener): void

Unregisters the listener for data changes.

Atomic service API: This API can be used in atomic services since API version 11.

System capability: SystemCapability.ArkUI.ArkUI.Full

Parameters

Name	Type	Mandatory	Description
listener	DataChangeListener	Yes	Listener for data changes.

DataChangeListener¹⁰⁺

Listener for data changes.

NOTE

In APIs of DataChangeListener other than onDatasetChange, if the value of index is negative, the value is treated as 0 by default. In onDatasetChange, if the specified index in a DataOperation is outside the data source index range, the corresponding DataOperation does not take effect. (In DataAddOperation, the value of index can equal the data source length.)

Atomic service API: This API can be used in atomic services since API version 11.

System capability: SystemCapability.ArkUI.ArkUI.Full

onDataReloaded

onDataReloaded(): void

Invoked when all data is reloaded. For data items whose key remains unchanged, the original child component is used. For data items whose key changes, a new child component is created.

Atomic service API: This API can be used in atomic services since API version 11.

System capability: SystemCapability.ArkUI.ArkUI.Full

onDataAdded^(deprecated)

onDataAdded(index: number): void

Invoked when data is added to the position indicated by the specified index.

This API is deprecated since API version 8. You are advised to use onDataAdd instead.

System capability: SystemCapability.ArkUI.ArkUI.Full

Parameters

Name	Type	Mandatory	Description
index	number	Yes	Index of the position where data is added.

onDataMoved^(deprecated)

onDataMoved(from: number, to: number): void

Invoked when data is moved, that is, when data is swapped between the from and to positions.

This API is deprecated since API version 8. You are advised to use onDataMove instead.

NOTE

The ID must remain unchanged before and after data movement. If the ID changes, APIs for deleting and adding data must be called.

System capability: SystemCapability.ArkUI.ArkUI.Full

Parameters

Name	Type	Mandatory	Description
from	number	Yes	Original position of data.
to	number	Yes	Target position of data.

onDataDeleted^(deprecated)

onDataDeleted(index: number): void

Invoked when data is deleted from the position indicated by the specified index. LazyForEach will update the displayed content accordingly.

This API is deprecated since API version 8. You are advised to use onDataDelete instead.

System capability: SystemCapability.ArkUI.ArkUI.Full

Parameters

Name	Type	Mandatory	Description
index	number	Yes	Index of the position where data is deleted.

onDataChanged^(deprecated)

onDataChanged(index: number): void

Invoked when data in the position indicated by the specified index is changed.

This API is deprecated since API version 8. You are advised to use onDataChange instead.

System capability: SystemCapability.ArkUI.ArkUI.Full

Parameters

Name	Type	Mandatory	Description
index	number	Yes	Listener for data changes.

onDataAdd⁸⁺

onDataAdd(index: number): void

Invoked when data is added to the position indicated by the specified index.

Widget capability: This API can be used in ArkTS widgets since API version 10.

Atomic service API: This API can be used in atomic services since API version 11.

System capability: SystemCapability.ArkUI.ArkUI.Full

Parameters

Name	Type	Mandatory	Description
index	number	Yes	Index of the position where data is added.

onDataMove⁸⁺

onDataMove(from: number, to: number): void

Invoked when data is moved, that is, when data is swapped between the from and to positions.

NOTE

The ID must remain unchanged before and after data movement. If the ID changes, APIs for deleting and adding data must be called.

Atomic service API: This API can be used in atomic services since API version 11.

System capability: SystemCapability.ArkUI.ArkUI.Full

Parameters

Name	Type	Mandatory	Description
from	number	Yes	Original position of data.
to	number	Yes	Target position of data.

onDataDelete⁸⁺

onDataDelete(index: number): void

Invoked when data is deleted from the position indicated by the specified index. LazyForEach will update the displayed content accordingly.

NOTE

Before onDataDelete is called, ensure that the corresponding data in dataSource has been deleted. Otherwise, undefined behavior will occur during page rendering.

Atomic service API: This API can be used in atomic services since API version 11.

System capability: SystemCapability.ArkUI.ArkUI.Full

Parameters

Name	Type	Mandatory	Description
index	number	Yes	Index of the position where data is deleted.

onDataChange⁸⁺

onDataChange(index: number): void

Invoked when data in the position indicated by the specified index is changed.

Atomic service API: This API can be used in atomic services since API version 11.

System capability: SystemCapability.ArkUI.ArkUI.Full

Parameters

Name	Type	Mandatory	Description
index	number	Yes	Index of the position where data is changed.

onDatasetChange¹²⁺

onDatasetChange(dataOperations: DataOperation[]): void

Invoked when data is processed in batches to notify the component of refreshing.

NOTE

This API cannot be used together with other data operation APIs of DataChangeListener. For example, in the same LazyForEach, if you have called onDataAdd, do not call onDatasetChange; if you have called onDatasetChange, do not call onDataAdd or other data operation APIs. Different LazyForEach instances on the page do not affect each other.

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.ArkUI.ArkUI.Full

Parameters

Name	Type	Mandatory	Description
dataOperations	DataOperation[]	Yes	Array of data operations performed.

DataOperation¹²⁺

NOTE

The initial APIs of this module are supported since API version 12. Newly added APIs will be marked with a superscript to indicate their earliest API version.

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.ArkUI.ArkUI.Full

DataAddOperation

Represents an operation for adding data.

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.ArkUI.ArkUI.Full

Parameters

Name	Type	Mandatory	Description
type	DataOperationType.ADD	Yes	Type of data addition.
index	number	Yes	Index at which to insert the data record.
count	number	No	Number of data records to insert. Default value: 1.
key	string \|Array<string>	No	Keys to assign to the inserted data records.

DataDeleteOperation

Represents an operation for deleting data.

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.ArkUI.ArkUI.Full

Parameters

Name	Type	Mandatory	Description
type	DataOperationType.DELETE	Yes	Type of data deletion.
index	number	Yes	Index at which to start deleting data.
count	number	No	Number of data records to delete. Default value: 1.

DataChangeOperation

Represents an operation for changing data.

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.ArkUI.ArkUI.Full

Parameters

Name	Type	Mandatory	Description
type	DataOperationType.CHANGE	Yes	Type of data change.
index	number	Yes	Index of the data to be changed.
key	string	No	New key to assign to the changed data. The original key is used by default.

DataMoveOperation

Represents an operation for moving data.

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.ArkUI.ArkUI.Full

Parameters

Name	Type	Mandatory	Description
type	DataOperationType.MOVE	Yes	Type of data movement.
index	MoveIndex	Yes	Positions for the movement.
key	string	No	New key to assign to the moved data. The original key is used by default.

MoveIndex

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.ArkUI.ArkUI.Full

Parameters

Name	Type	Mandatory	Description
from	number	Yes	Start position for the movement.
to	number	Yes	End position for the movement.

DataExchangeOperation

Represents an operation for exchanging data.

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.ArkUI.ArkUI.Full

Parameters

Name	Type	Mandatory	Description
type	DataOperationType.EXCHANGE	Yes	Type of data exchange.
index	ExchangeIndex	Yes	Positions for the exchange.
key	ExchangeKey	No	New keys to assign to the exchanged data. The original keys are used by default.

ExchangeIndex

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.ArkUI.ArkUI.Full

Parameters

Name	Type	Mandatory	Description
start	number	Yes	First position for the exchange.
end	number	Yes	Second position for the exchange.

ExchangeKey

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.ArkUI.ArkUI.Full

Parameters

Name	Type	Mandatory	Description
start	string	Yes	New key to assign to the first position in the exchange. The original key is used by default.
end	string	Yes	New key to assign to the second position in the exchange. The original key is used by default.

DataReloadOperation

Represents an operation for reloading data. If the onDatasetChange event contains a DataOperationType.RELOAD operation, all other operations in the event are ineffective. In such cases, the framework will call keygenerator to perform a comparison of keys with their corresponding values.

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.ArkUI.ArkUI.Full

Parameters

Name	Type	Mandatory	Description
type	DataOperationType.RELOAD	Yes	Type of data reloading.

DataOperationType

Enumerates the data operation types.

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.ArkUI.ArkUI.Full

Name	Value	Description
ADD	add	Data addition.
DELETE	delete	Data deletion.
CHANGE	change	Data change.
MOVE	move	Data movement.
EXCHANGE	exchange	Data exchange.
RELOAD	reload	Data reloading.

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harmony 鸿蒙LazyForEach

LazyForEach

APIs

Name

IDataSource¹⁰⁺

totalCount

getData

registerDataChangeListener

unregisterDataChangeListener

DataChangeListener¹⁰⁺

onDataReloaded

onDataAdded^(deprecated)

onDataMoved^(deprecated)

onDataDeleted^(deprecated)

onDataChanged^(deprecated)

onDataAdd⁸⁺

onDataMove⁸⁺

onDataDelete⁸⁺

onDataChange⁸⁺

onDatasetChange¹²⁺

DataOperation¹²⁺

DataAddOperation

DataDeleteOperation

DataChangeOperation

DataMoveOperation

MoveIndex

DataExchangeOperation

ExchangeIndex

ExchangeKey

DataReloadOperation

DataOperationType

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本文目录

harmony 鸿蒙LazyForEach

LazyForEach

APIs

Name

IDataSource10+

totalCount

getData

registerDataChangeListener

unregisterDataChangeListener

DataChangeListener10+

onDataReloaded

onDataAdded(deprecated)

onDataMoved(deprecated)

onDataDeleted(deprecated)

onDataChanged(deprecated)

onDataAdd8+

onDataMove8+

onDataDelete8+

onDataChange8+

onDatasetChange12+

DataOperation12+

DataAddOperation

DataDeleteOperation

DataChangeOperation

DataMoveOperation

MoveIndex

DataExchangeOperation

ExchangeIndex

ExchangeKey

DataReloadOperation

DataOperationType

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标签云

最新文章

本文目录

IDataSource¹⁰⁺

DataChangeListener¹⁰⁺

onDataAdded^(deprecated)

onDataMoved^(deprecated)

onDataDeleted^(deprecated)

onDataChanged^(deprecated)

onDataAdd⁸⁺

onDataMove⁸⁺

onDataDelete⁸⁺

onDataChange⁸⁺

onDatasetChange¹²⁺

DataOperation¹²⁺