com.vaadin.flow.component.combobox.dataview

Class ComboBoxLazyDataView<T>

java.lang.Object

com.vaadin.flow.data.provider.AbstractDataView<T>

com.vaadin.flow.data.provider.AbstractLazyDataView<T>

com.vaadin.flow.component.combobox.dataview.ComboBoxLazyDataView<T>

Type Parameters:

T - the type of the items in ComboBox

All Implemented Interfaces:

DataView<T>, LazyDataView<T>, Serializable

public class ComboBoxLazyDataView<T>
extends AbstractLazyDataView<T>

Data view implementation for ComboBox with lazy data fetching. Provides information on the data and allows operations on it.

See Also:

Serialized Form

Field Summary

Fields inherited from class com.vaadin.flow.data.provider.AbstractDataView

component, dataProviderSupplier, NULL_IDENTIFIER_ERROR_MESSAGE, NULL_ITEM_ERROR_MESSAGE

Constructor Summary

Constructors

Constructor and Description
ComboBoxLazyDataView(DataCommunicator<T> dataCommunicator, Component component) Creates a new lazy data view for ComboBox and verifies the passed data provider is compatible with this data view implementation.

Method Summary

Modifier and Type	Method and Description
Registration	addItemCountChangeListener(ComponentEventListener<ItemCountChangeEvent<?>> listener) Add an item count change listener that is fired when the item count changes.
T	getItem(int index) Gets the item at the given index from the data available in the ComboBox's server-side.
Stream<T>	getItems() Gets the items available on the ComboBox's server-side.
void	setItemCountCallback(CallbackDataProvider.CountCallback<T,String> callback) Sets a callback that the combo box uses to get the exact item count in the backend.
void	setItemCountEstimate(int itemCountEstimate) Sets the estimated item count for the component.
void	setItemCountFromDataProvider() Switches the component to get the exact item count from the data provider's DataProvider.size(Query).
void	setItemCountUnknown() Switches the component to automatically extend the number of items as the previous end is almost reached.

Methods inherited from class com.vaadin.flow.data.provider.AbstractLazyDataView

getDataCommunicator, getItemCountEstimate, getItemCountEstimateIncrease, getSupportedDataProviderType, setItemCountEstimateIncrease

Methods inherited from class com.vaadin.flow.data.provider.AbstractDataView

equals, getIdentifierProvider, refreshAll, refreshItem, setIdentifierProvider, verifyDataProviderType

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface com.vaadin.flow.data.provider.DataView

refreshAll, refreshItem, setIdentifierProvider

Constructor Detail

ComboBoxLazyDataView

public ComboBoxLazyDataView(DataCommunicator<T> dataCommunicator,
                            Component component)

Creates a new lazy data view for ComboBox and verifies the passed data provider is compatible with this data view implementation.

Parameters:

dataCommunicator - the data communicator of the component

component - the ComboBox

Method Detail

setItemCountCallback

public void setItemCountCallback(CallbackDataProvider.CountCallback<T,String> callback)

Sets a callback that the combo box uses to get the exact item count in the backend. Use this when it is cheap to get the exact item count and it is desired that the user sees the "full scrollbar size".

The given callback will be queried for the count instead of the data provider DataProvider.size(Query) method when the component has a distinct data provider set with HasLazyDataView.setItems(BackEndDataProvider).

Parameters:

callback - the callback to use for determining item count in the backend, not null

See Also:

setItemCountFromDataProvider(), setItemCountUnknown()

setItemCountFromDataProvider

public void setItemCountFromDataProvider()

Description copied from interface: LazyDataView

Switches the component to get the exact item count from the data provider's DataProvider.size(Query). Use this when it is cheap to get the exact item count and it is desired that the user sees the "full scrollbar size".

Specified by:

setItemCountFromDataProvider in interface LazyDataView<T>

Overrides:

setItemCountFromDataProvider in class AbstractLazyDataView<T>

setItemCountEstimate

public void setItemCountEstimate(int itemCountEstimate)

Sets the estimated item count for the component. The component will automatically fetch more items once the estimate is reached or adjust the count if the backend runs out of items before the end. Use this when the backend will have a lot more items than shown by default and it should be shown to the user.

The given estimate is discarded if it is less than the currently shown range or if the actual number of items has been determined. The estimate shouldn't be less than two pages (see setPageSize(int) in the component) or it causes unnecessary backend requests.

Calling this method will clear any previously set count callback setItemCountCallback(CallbackDataProvider.CountCallback).

Specified by:

setItemCountEstimate in interface LazyDataView<T>

Overrides:

setItemCountEstimate in class AbstractLazyDataView<T>

Parameters:

itemCountEstimate - estimated item count of the backend

See Also:

LazyDataView.setItemCountUnknown(), LazyDataView.setItemCountEstimateIncrease(int)

setItemCountUnknown

public void setItemCountUnknown()

Switches the component to automatically extend the number of items as the previous end is almost reached. The component stops increasing the number of items once the backend has run out of items. Not getting the exact size of the backend upfront can improve performance with large sets of data.

The default initial item count and how much the item count is increased depends on the component. These values can be customized with LazyDataView.setItemCountEstimate(int) and LazyDataView.setItemCountEstimateIncrease(int) when the backend has a lot of items and faster scrolling down is desired.

Calling this method will clear any previously set count callback setItemCountCallback(CallbackDataProvider.CountCallback).

Specified by:

setItemCountUnknown in interface LazyDataView<T>

Overrides:

setItemCountUnknown in class AbstractLazyDataView<T>

addItemCountChangeListener

public Registration addItemCountChangeListener(ComponentEventListener<ItemCountChangeEvent<?>> listener)

Add an item count change listener that is fired when the item count changes. This can happen for instance when filtering the items.

Item count change listener is bound to the component and will be retained even if the data changes by setting of a new items or DataProvider to component.

NOTE: when the component supports lazy loading (implements HasLazyDataView) and a count callback has not been provided, an estimate of the item count is used and increased until the actual count has been reached. When the estimate is used, the event is fired with the ItemCountChangeEvent.isItemCountEstimated() returning true.

Combo box fires ItemCountChangeEvent and notifies all the listeners added by this method, if the items count changed, for instance, due to fetching more items while scrolling with unknown item count.

ComboBox's client-side filter change won't fire ItemCountChangeEvent, since it doesn't change the item count on the server-side, but only makes it easier for users to search through the items in the UI.

Specified by:

addItemCountChangeListener in interface DataView<T>

Overrides:

addItemCountChangeListener in class AbstractDataView<T>

Parameters:

listener - item count change listener to register

Returns:

registration for removing the listener

getItem

public T getItem(int index)

Gets the item at the given index from the data available in the ComboBox's server-side.

This method does not take into account the ComboBox client-side filtering, since it doesn't change the item count on the server-side, but only makes it easier for users to search through the items in the UI.

Specified by:

getItem in interface DataView<T>

Overrides:

getItem in class AbstractLazyDataView<T>

Parameters:

index - item index number

Returns:

item on index

Throws:

IndexOutOfBoundsException - requested index is outside of the data set

getItems

public Stream<T> getItems()

Gets the items available on the ComboBox's server-side.

This method does not take into account the ComboBox client-filtering, since it doesn't change the item count on the server-side, but only makes it easier for users to search through the items in the UI.

Specified by:

getItems in interface DataView<T>

Overrides:

getItems in class AbstractLazyDataView<T>

Returns:

items available on the server-side