Subscription class

Class representing a Subscription to be submitted to a Lightstreamer Server.

It contains subscription details and the listeners needed to process the real-time data.
After the creation, a Subscription object is in the "inactive" state. When a Subscription object is subscribed to on a LightstreamerClient object, through the LightstreamerClient.subscribe method, its state becomes "active". This means that the client activates a subscription to the required items through Lightstreamer Server and the Subscription object begins to receive real-time events.
A Subscription can be configured to use either an Item Group or an Item List to specify the items to be subscribed to and using either a Field Schema or Field List to specify the fields.
"Item Group" and "Item List" are defined as follows:

• "Item Group": an Item Group is a String identifier representing a list of items. Such Item Group has to be expanded into a list of items by the getItems method of the MetadataProvider of the associated Adapter Set. When using an Item Group, items in the subscription are identified by their 1-based index within the group.
  It is possible to configure the Subscription to use an "Item Group" using the [setItemGroup] method.
• "Item List": an Item List is an array of Strings each one representing an item. For the Item List to be correctly interpreted a LiteralBasedProvider or a MetadataProvider with a compatible implementation of getItems has to be configured in the associated Adapter Set.
  Note that no item in the list can be empty, can contain spaces or can be a number.
  When using an Item List, items in the subscription are identified by their name or by their 1-based index within the list.
  It is possible to configure the Subscription to use an "Item List" using the [setItems] method or by specifying it in the constructor.

"Field Schema" and "Field List" are defined as follows:

• "Field Schema": a Field Schema is a String identifier representing a list of fields. Such Field Schema has to be expanded into a list of fields by the getFields method of the MetadataProvider of the associated Adapter Set. When using a Field Schema, fields in the subscription are identified by their 1-based index within the schema.
  It is possible to configure the Subscription to use a "Field Schema" using the [setFieldSchema] method.
• "Field List": a Field List is an array of Strings each one representing a field. For the Field List to be correctly interpreted a LiteralBasedProvider or a MetadataProvider with a compatible implementation of getFields has to be configured in the associated Adapter Set.
  Note that no field in the list can be empty or can contain spaces.
  When using a Field List, fields in the subscription are identified by their name or by their 1-based index within the list.
  It is possible to configure the Subscription to use a "Field List" using the [setFields] method or by specifying it in the constructor.

Constructors

Subscription(String mode, [List<String>? items, List<String>? fields])

Creates an object to be used to describe a Subscription that is going to be subscribed to through Lightstreamer Server.

Properties

hashCode → int

The hash code for this object.

no setter, inherited

runtimeType → Type

A representation of the runtime type of the object.

no setter, inherited

Methods

addListener(SubscriptionListener listener) → void

Adds a listener that will receive events from the Subscription instance.

getCommandPosition() → int?

Returns the position of the "command" field in a COMMAND Subscription.

getCommandSecondLevelDataAdapter() → String?

Inquiry method that can be used to read the second-level Data Adapter name configured through setCommandSecondLevelDataAdapter.

getCommandSecondLevelFields() → List<String>?

Inquiry method that can be used to read the "Field List" specified for second-level Subscriptions.

getCommandSecondLevelFieldSchema() → String?

Inquiry method that can be used to read the "Field Schema" specified for second-level Subscriptions.

getCommandValue(String itemNameOrPosition, String keyValue, String fieldNameOrPosition) → Future<String?>

Returns the latest value received for the specified item/key/field combination.

getDataAdapter() → String?

Inquiry method that can be used to read the name of the Data Adapter specified for this Subscription through setDataAdapter.

getFields() → List<String>?

Inquiry method that can be used to read the "Field List" specified for this Subscription.

getFieldSchema() → String?

Inquiry method that can be used to read the field schema specified for this Subscription.

getItemGroup() → String?

Inquiry method that can be used to read the item group specified for this Subscription.

getItems() → List<String>?

Inquiry method that can be used to read the "Item List" specified for this Subscription.

getKeyPosition() → int?

Returns the position of the "key" field in a COMMAND Subscription.

getListeners() → List<SubscriptionListener>

Returns a list containing the SubscriptionListener instances that were added to this client.

getMode() → String

Inquiry method that can be used to read the mode specified for this Subscription.

getRequestedBufferSize() → String?

Inquiry method that can be used to read the buffer size, configured though setRequestedBufferSize, to be requested to the Server for this Subscription.

getRequestedMaxFrequency() → String?

Inquiry method that can be used to read the max frequency, configured through setRequestedMaxFrequency, to be requested to the Server for this Subscription.

getRequestedSnapshot() → String?

Inquiry method that can be used to read the snapshot preferences, configured through setRequestedSnapshot, to be requested to the Server for this Subscription.

getSelector() → String?

Inquiry method that can be used to read the selector name
specified for this Subscription through setSelector.

getValue(String itemNameOrPosition, String fieldNameOrPosition) → Future<String?>

Returns the latest value received for the specified item/field pair.

isActive() → bool

Inquiry method that checks if the Subscription is currently "active" or not.

isSubscribed() → bool

Inquiry method that checks if the Subscription is currently subscribed to through the server or not.

noSuchMethod(Invocation invocation) → dynamic

Invoked when a nonexistent method or property is accessed.

inherited

removeListener(SubscriptionListener listener) → void

Removes a listener from the Subscription instance so that it will not receive events anymore.

setCommandSecondLevelDataAdapter(String? dataAdapter) → void

Setter method that sets the name of the second-level Data Adapter (within the Adapter Set used by the current session) that supplies all the second-level items.

setCommandSecondLevelFields(List<String>? fields) → void

Setter method that sets the "Field List" to be subscribed to through Lightstreamer Server for the second-level items.

setCommandSecondLevelFieldSchema(String? schemaName) → void

Setter method that sets the "Field Schema" to be subscribed to through Lightstreamer Server for the second-level items.

setDataAdapter(String? dataAdapter) → void

Setter method that sets the name of the Data Adapter (within the Adapter Set used by the current session) that supplies all the items for this Subscription.

setFields(List<String>? fields) → void

Setter method that sets the "Field List" to be subscribed to through Lightstreamer Server.

setFieldSchema(String? schemaName) → void

Setter method that sets the "Field Schema" to be subscribed to through Lightstreamer Server.

setItemGroup(String? groupName) → void

Setter method that sets the "Item Group" to be subscribed to through Lightstreamer Server.

setItems(List<String>? items) → void

Setter method that sets the "Item List" to be subscribed to through Lightstreamer Server.

setRequestedBufferSize(String? size) → void

Setter method that sets the length to be requested to Lightstreamer Server for the internal queuing buffers for the items in the Subscription.

setRequestedMaxFrequency(String? freq) → Future<void>

Setter method that sets the maximum update frequency to be requested to Lightstreamer Server for all the items in the Subscription.

setRequestedSnapshot(String? isRequired) → void

Setter method that enables/disables snapshot delivery request for the items in the Subscription.

setSelector(String? selector) → void

Setter method that sets the selector name for all the items in the Subscription. The selector is a filter on the updates received.

toString() → String

A string representation of this object.

inherited

Operators

operator ==(Object other) → bool

The equality operator.

inherited