Class Subscription

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 subscribe(Subscription) 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" leveraging the ItemGroup property.
  • "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" leveraging the Items property 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" leveraging the FieldSchema property.
  • "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" leveraging the Fields property or by specifying it in the constructor.
Inheritance
System.Object
Subscription
Inherited Members
System.Object.Equals(System.Object)
System.Object.Equals(System.Object, System.Object)
System.Object.GetHashCode()
System.Object.GetType()
System.Object.MemberwiseClone()
System.Object.ReferenceEquals(System.Object, System.Object)
System.Object.ToString()
Namespace: com.lightstreamer.client
Assembly: Lightstreamer_DotNet_Client_Unified.dll
Syntax
public class Subscription

Constructors

Subscription(String)

Creates an object to be used to describe a Subscription that is going to be subscribed to through Lightstreamer Server. The object can be supplied to subscribe(Subscription) and unsubscribe(Subscription), in order to bring the Subscription to "active" or back to "inactive" state.
Note that all of the methods used to describe the subscription to the server can only be called while the instance is in the "inactive" state; the only exception is RequestedMaxFrequency.

Declaration
public Subscription(string subscriptionMode)
Parameters
Type Name Description
System.String subscriptionMode

the subscription mode for the items, required by Lightstreamer Server. Permitted values are:

  • MERGE
  • DISTINCT
  • RAW
  • COMMAND

Subscription(String, String, String[])

Creates an object to be used to describe a Subscription that is going to be subscribed to through Lightstreamer Server. The object can be supplied to subscribe(Subscription) and unsubscribe(Subscription), in order to bring the Subscription to "active" or back to "inactive" state.
Note that all of the methods used to describe the subscription to the server can only be called while the instance is in the "inactive" state; the only exception is RequestedMaxFrequency.

Declaration
public Subscription(string subscriptionMode, string item, string[] fields)
Parameters
Type Name Description
System.String subscriptionMode

the subscription mode for the items, required by Lightstreamer Server. Permitted values are:

  • MERGE
  • DISTINCT
  • RAW
  • COMMAND
System.String item

the item name to be subscribed to through Lightstreamer Server.
System.String[] fields

an array of fields for the items to be subscribed to through Lightstreamer Server.
It is also possible to specify the "Field List" or "Field Schema" later through Fields and FieldSchema.

Subscription(String, String[], String[])

Creates an object to be used to describe a Subscription that is going to be subscribed to through Lightstreamer Server. The object can be supplied to subscribe(Subscription) and unsubscribe(Subscription), in order to bring the Subscription to "active" or back to "inactive" state.
Note that all of the methods used to describe the subscription to the server can only be called while the instance is in the "inactive" state; the only exception is RequestedMaxFrequency.

Declaration
public Subscription(string subscriptionMode, string[] items, string[] fields)
Parameters
Type Name Description
System.String subscriptionMode

the subscription mode for the items, required by Lightstreamer Server. Permitted values are:

  • MERGE
  • DISTINCT
  • RAW
  • COMMAND
System.String[] items

an array of items to be subscribed to through Lightstreamer server.
It is also possible specify the "Item List" or "Item Group" later through Items and ItemGroup.
System.String[] fields

an array of fields for the items to be subscribed to through Lightstreamer Server.
It is also possible to specify the "Field List" or "Field Schema" later through Fields and FieldSchema.

Properties

Active

Declaration
public virtual bool Active { get; }
Property Value
Type Description
System.Boolean

Read-only property Active checks if the Subscription is currently "active" or not. Most of the Subscription properties cannot be modified if a Subscription is "active".
The status of a Subscription is changed to "active" through the
subscribe(Subscription) method and back to "inactive" through the unsubscribe(Subscription) one.
Returns true/false if the Subscription is "active" or not.

Lifecycle: This method can be called at any time.
See Also

CommandPosition

Declaration
public virtual int CommandPosition { get; }
Property Value
Type Description
System.Int32

Read-only property CommandPosition represents the "command" field in a COMMAND Subscription.
This method can only be used if the Subscription mode is COMMAND and the Subscription was initialized using a "Field Schema".
The value is the 1-based position of the "command" field within the "Field Schema".

Lifecycle: This method can be called at any time after the first onSubscription() event.

CommandSecondLevelDataAdapter

Declaration
public virtual string CommandSecondLevelDataAdapter { get; set; }
Property Value
Type Description
System.String

Property CommandSecondLevelDataAdapter represents the name of the second-level Data Adapter (within the Adapter Set used by the current session) that supplies all the second-level items.
All the possible second-level items should be supplied in "MERGE" mode with snapshot available.
The Data Adapter name is configured on the server side through the "name" attribute of the data_provider element, in the "adapters.xml" file that defines the Adapter Set (a missing attribute configures the "DEFAULT" name).
A null value is equivalent to the "DEFAULT" name.
See also: CommandSecondLevelFields, CommandSecondLevelFieldSchema

Lifecycle: This method can only be called while the Subscription instance is in its "inactive" state.

Default value: The default Data Adapter for the Adapter Set, configured as "DEFAULT" on the Server.

CommandSecondLevelFields

Declaration
public virtual string[] CommandSecondLevelFields { get; set; }
Property Value
Type Description
System.String[]

Property CommandSecondLevelFields represents the "Field List" to be subscribed to through Lightstreamer Server for the second-level items. It can only be used on COMMAND Subscriptions.
Any call to this method will override any "Field List" or "Field Schema" previously specified for the second-level.
Calling this method enables the two-level behavior: in synthesis, each time a new key is received on the COMMAND Subscription, the key value is treated as an Item name and an underlying Subscription for this Item is created and subscribed to automatically, to feed fields specified by this method. This mono-item Subscription is specified through an "Item List" containing only the Item name received. As a consequence, all the conditions provided for subscriptions through Item Lists have to be satisfied. The item is subscribed to in "MERGE" mode, with snapshot request and with the same maximum frequency setting as for the first-level items (including the "unfiltered" case). All other Subscription properties are left as the default. When the key is deleted by a DELETE command on the first-level Subscription, the associated second-level Subscription is also unsubscribed from.
Specifying null as parameter will disable the two-level behavior.
Ensure that no name conflict is generated between first-level and second-level fields. In case of conflict, the second-level field will not be accessible by name, but only by position.
See also: CommandSecondLevelFieldSchema

Lifecycle: This method can only be called while the Subscription instance is in its "inactive" state.

CommandSecondLevelFieldSchema

Declaration
public virtual string CommandSecondLevelFieldSchema { get; set; }
Property Value
Type Description
System.String

Property CommandSecondLevelFieldSchema represents the "Field Schema" to be subscribed to through Lightstreamer Server for the second-level items. It can only be used on COMMAND Subscriptions.
Any call to this method will override any "Field List" or "Field Schema" previously specified for the second-level.
Calling this method enables the two-level behavior: in synthesis, each time a new key is received on the COMMAND Subscription, the key value is treated as an Item name and an underlying Subscription for this Item is created and subscribed to automatically, to feed fields specified by this method. This mono-item Subscription is specified through an "Item List" containing only the Item name received. As a consequence, all the conditions provided for subscriptions through Item Lists have to be satisfied. The item is subscribed to in "MERGE" mode, with snapshot request and with the same maximum frequency setting as for the first-level items (including the "unfiltered" case). All other Subscription properties are left as the default. When the key is deleted by a DELETE command on the first-level Subscription, the associated second-level Subscription is also unsubscribed from.
Specify null as parameter will disable the two-level behavior.
See also: CommandSecondLevelFields

Lifecycle: This method can only be called while the Subscription instance is in its "inactive" state.

DataAdapter

Declaration
public virtual string DataAdapter { get; set; }
Property Value
Type Description
System.String

Property DataAdapter represents the name of the Data Adapter (within the Adapter Set used by the current session) that supplies all the items for this Subscription.
The Data Adapter name is configured on the server side through the "name" attribute of the "data_provider" element, in the "adapters.xml" file that defines the Adapter Set (a missing attribute configures the "DEFAULT" name).
Note that if more than one Data Adapter is needed to supply all the items in a set of items, then it is not possible to group all the items of the set in a single Subscription. Multiple Subscriptions have to be defined.

Lifecycle: This method can only be called while the Subscription instance is in its "inactive" state.

Default value: The default Data Adapter for the Adapter Set, configured as "DEFAULT" on the Server.

Fields

Declaration
public virtual string[] Fields { get; set; }
Property Value
Type Description
System.String[]

Property Fields represents the "Field List" to be subscribed to through Lightstreamer Server. Any call to set this property will override any "Field List" or "Field Schema" previously specified.

Lifecycle: This property can be set only while the Subscription instance is in its "inactive" state.

FieldSchema

Declaration
public virtual string FieldSchema { get; set; }
Property Value
Type Description
System.String

Property FieldSchema represents the "Field Schema" to be subscribed to through Lightstreamer Server. Any call to set this property will override any "Field List" or "Field Schema" previously specified.

Lifecycle: This property can be set only while the Subscription instance is in its "inactive" state.

ItemGroup

Declaration
public virtual string ItemGroup { get; set; }
Property Value
Type Description
System.String

Property ItemGroup represents the the "Item Group" to be subscribed to through Lightstreamer Server. Any call to set this property will override any "Item List" or "Item Group" previously specified.

Lifecycle: This method can only be called if the Subscription has been initialized using an "Item Group".

Items

Declaration
public virtual string[] Items { get; set; }
Property Value
Type Description
System.String[]

Property Items represents the "Item List" to be subscribed to through Lightstreamer Server. Any call to set this property will override any "Item List" or "Item Group" previously specified. Note that if the single-item-constructor was used, this method will return an array of length 1 containing such item.

Lifecycle: This method can only be called if the Subscription has been initialized with an "Item List".

KeyPosition

Declaration
public virtual int KeyPosition { get; }
Property Value
Type Description
System.Int32

Read-only property KeyPosition represents the position of the "key" field in a COMMAND Subscription.
This method can only be used if the Subscription mode is COMMAND and the Subscription was initialized using a "Field Schema".
The value is the 1-based position of the "key" field within the "Field Schema".

Lifecycle: This method can be called at any time.

Listeners

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

Declaration
public virtual IList<SubscriptionListener> Listeners { get; }
Property Value
Type Description
System.Collections.Generic.IList<SubscriptionListener>

a list containing the listeners that were added to this client.
See Also

Mode

Declaration
public virtual string Mode { get; }
Property Value
Type Description
System.String

Read-only property Mode represents the mode specified in the constructor for this Subscription.

Lifecycle: This method can be called at any time.

RequestedBufferSize

Declaration
public virtual string RequestedBufferSize { get; set; }
Property Value
Type Description
System.String

Property RequestedBufferSize represents the length to be requested to Lightstreamer Server for the internal queuing buffers for the items in the Subscription. A Queuing buffer is used by the Server to accumulate a burst of updates for an item, so that they can all be sent to the client, despite of bandwidth or frequency limits. It can be used only when the subscription mode is MERGE or DISTINCT and unfiltered dispatching has not been requested. Note that the Server may pose an upper limit on the size of its internal buffers.
The value of this property is integer number, representing the length of the internal queuing buffers to be used in the Server. If the string "unlimited" is supplied, then no buffer size limit is requested (the check is case insensitive). It is also possible to supply a null value to stick to the Server default (which currently depends on the subscription mode).

Lifecycle: This method can only be called while the Subscription instance is in its "inactive" state.

Default value: null, meaning to lean on the Server default based on the subscription mode. This means that the buffer size will be 1 for MERGE subscriptions and "unlimited" for DISTINCT subscriptions. See the "General Concepts" document for further details.

RequestedMaxFrequency

Declaration
public virtual string RequestedMaxFrequency { get; set; }
Property Value
Type Description
System.String

Property RequestedMaxFrequency represents the maximum update frequency to be requested to Lightstreamer Server for all the items in the Subscription. It can be used only if the Subscription mode is MERGE, DISTINCT or COMMAND (in the latter case, the frequency limitation applies to the UPDATE events for each single key). For Subscriptions with two-level behavior (see CommandSecondLevelFields and CommandSecondLevelFieldSchema, the specified frequency limit applies to both first-level and second-level items.
Note that frequency limits on the items can also be set on the server side and this request can only be issued in order to furtherly reduce the frequency, not to rise it beyond these limits.
This method can also be used to request unfiltered dispatching for the items in the Subscription. However, unfiltered dispatching requests may be refused if any frequency limit is posed on the server side for some item.
The value can be a decimal number, representing the maximum update frequency (expressed in updates per second) for each item in the Subscription; for instance, with a setting of 0.5, for each single item, no more than one update every 2 seconds will be received. If the string "unlimited" is supplied, then no frequency limit is requested. It is also possible to supply the string "unfiltered", to ask for unfiltered dispatching, if it is allowed for the items, or a null value to stick to the Server default (which currently corresponds to "unlimited"). The check for the string constants is case insensitive.

Edition Note: A further global frequency limit could also be imposed by the Server, depending on Edition and License Type; this specific limit also applies to RAW mode and to unfiltered dispatching. To know what features are enabled by your license, please see the License tab of the Monitoring Dashboard (by default, available at /dashboard).

Lifecycle: This method can can be called at any time with some differences based on the Subscription status:

  • If the Subscription instance is in its "inactive" state then this method can be called at will.
  • If the Subscription instance is in its "active" state then the method can still be called unless the current value is "unfiltered" or the supplied value is "unfiltered" or null. If the Subscription instance is in its "active" state and the connection to the server is currently open, then a request to change the frequency of the Subscription on the fly is sent to the server.

Default value: null, meaning to lean on the Server default based on the subscription mode. This consists, for all modes, in not applying any frequency limit to the subscription (the same as "unlimited"); see the "General Concepts" document for further details.

RequestedSnapshot

Declaration
public virtual string RequestedSnapshot { get; set; }
Property Value
Type Description
System.String

Property RequestedSnapshot enables/disables snapshot delivery request for the items in the Subscription. The snapshot can be requested only if the Subscription mode is MERGE, DISTINCT or COMMAND. The value can be "yes"/"no" to request/not request snapshot delivery (the check is case insensitive). If the Subscription mode is DISTINCT, instead of "yes", it is also possible to supply an integer number, to specify the requested length of the snapshot (though the length of the received snapshot may be less than requested, because of insufficient data or server side limits); passing "yes" means that the snapshot length should be determined only by the Server. Null is also a valid value; if specified, no snapshot preference will be sent to the server that will decide itself whether or not to send any snapshot.

Lifecycle: This method can only be called while the Subscription instance is in its "inactive" state.

Default value: "yes" if the Subscription mode is not "RAW", null otherwise.

Selector

Declaration
public virtual string Selector { get; set; }
Property Value
Type Description
System.String

Property Selector represents the selector name for all the items in the Subscription. The selector is a filter on the updates received. It is executed on the Server and implemented by the Metadata Adapter.
The name of a selector should be recognized by the Metadata Adapter, or can be null to unset the selector.

Lifecycle: This method can only be called while the Subscription instance is in its "inactive" state.

Default value: null (no selector).

Subscribed

Declaration
public virtual bool Subscribed { get; }
Property Value
Type Description
System.Boolean

Read-only property Subscribed thtat checks if the Subscription is currently subscribed to through the server or not.
This flag is switched to true by server sent Subscription events, and back to false in case of client disconnection, unsubscribe(Subscription) calls and server sent unsubscription events.
Returns true/false if the Subscription is subscribed to through the server or not.

Lifecycle: This method can be called at any time.

Methods

addListener(SubscriptionListener)

Adds a listener that will receive events from the Subscription instance.
The same listener can be added to several different Subscription instances.

Lifecycle: A listener can be added at any time. A call to add a listener already present will be ignored.

Declaration
public virtual void addListener(SubscriptionListener listener)
Parameters
Type Name Description
SubscriptionListener listener

An object that will receive the events as documented in the SubscriptionListener interface.
See Also

getCommandValue(Int32, String, Int32)

Returns the latest value received for the specified item/key/field combination. This method can only be used if the Subscription mode is COMMAND. Subscriptions with two-level behavior (see CommandSecondLevelFields and CommandSecondLevelFieldSchema) are also supported, hence the specified field can be either a first-level or a second-level one.
It is suggested to consume real-time data by implementing and adding a proper SubscriptionListener rather than probing this method.
Note that internal data is cleared when the Subscription is unsubscribed from.

Declaration
public virtual string getCommandValue(int itemPos, string keyValue, int fieldPos)
Parameters
Type Name Description
System.Int32 itemPos

the 1-based position of an item within the configured "Item Group" or "Item List"
System.String keyValue

the value of a key received on the COMMAND subscription.
System.Int32 fieldPos

the 1-based position of a field within the configured "Field Schema" or "Field List"
Returns
Type Description
System.String

the current value for the specified field of the specified key within the specified item (possibly null), or null if the specified key has not been added yet (note that it might have been added and then deleted).

getCommandValue(Int32, String, String)

Returns the latest value received for the specified item/key/field combination. This method can only be used if the Subscription mode is COMMAND. Subscriptions with two-level behavior (see CommandSecondLevelFields and CommandSecondLevelFieldSchema) are also supported, hence the specified field can be either a first-level or a second-level one.
It is suggested to consume real-time data by implementing and adding a proper SubscriptionListener rather than probing this method.
Note that internal data is cleared when the Subscription is unsubscribed from.

Declaration
public virtual string getCommandValue(int itemPos, string keyValue, string fieldName)
Parameters
Type Name Description
System.Int32 itemPos

the 1-based position of an item within the configured "Item Group" or "Item List"
System.String keyValue

the value of a key received on the COMMAND subscription.
System.String fieldName

a field in the configured "Field List"
Returns
Type Description
System.String

the current value for the specified field of the specified key within the specified item (possibly null), or null if the specified key has not been added yet (note that it might have been added and then deleted).

getCommandValue(String, String, Int32)

Returns the latest value received for the specified item/key/field combination. This method can only be used if the Subscription mode is COMMAND. Subscriptions with two-level behavior (see CommandSecondLevelFields and CommandSecondLevelFieldSchema) are also supported, hence the specified field can be either a first-level or a second-level one.
It is suggested to consume real-time data by implementing and adding a proper SubscriptionListener rather than probing this method.
Note that internal data is cleared when the Subscription is unsubscribed from.

Declaration
public virtual string getCommandValue(string itemName, string keyValue, int fieldPos)
Parameters
Type Name Description
System.String itemName

an item in the configured "Item List"
System.String keyValue

the value of a key received on the COMMAND subscription.
System.Int32 fieldPos

the 1-based position of a field within the configured "Field Schema" or "Field List"
Returns
Type Description
System.String

the current value for the specified field of the specified key within the specified item (possibly null), or null if the specified key has not been added yet (note that it might have been added and then deleted).

getCommandValue(String, String, String)

Returns the latest value received for the specified item/key/field combination. This method can only be used if the Subscription mode is COMMAND. Subscriptions with two-level behavior are also supported, hence the specified field (see CommandSecondLevelFields and CommandSecondLevelFieldSchema) can be either a first-level or a second-level one.
It is suggested to consume real-time data by implementing and adding a proper SubscriptionListener rather than probing this method.
Note that internal data is cleared when the Subscription is unsubscribed from.

Declaration
public virtual string getCommandValue(string itemName, string keyValue, string fieldName)
Parameters
Type Name Description
System.String itemName

an item in the configured "Item List"
System.String keyValue

the value of a key received on the COMMAND subscription.
System.String fieldName

a field in the configured "Field List"
Returns
Type Description
System.String

the current value for the specified field of the specified key within the specified item (possibly null), or null if the specified key has not been added yet (note that it might have been added and then deleted).

getValue(Int32, Int32)

Returns the latest value received for the specified item/field pair.
It is suggested to consume real-time data by implementing and adding a proper SubscriptionListener rather than probing this method.
In case of COMMAND Subscriptions, the value returned by this method may be misleading, as in COMMAND mode all the keys received, being part of the same item, will overwrite each other; for COMMAND Subscriptions, use getCommandValue(Int32, String, Int32) instead.
Note that internal data is cleared when the Subscription is unsubscribed from.
Returns null if no value has been received yet for the specified item/field pair.

Lifecycle: This method can be called at any time; if called to retrieve a value that has not been received yet, then it will return null.

Declaration
public virtual string getValue(int itemPos, int fieldPos)
Parameters
Type Name Description
System.Int32 itemPos

the 1-based position of an item within the configured "Item Group" or "Item List"
System.Int32 fieldPos

the 1-based position of a field within the configured "Field Schema" or "Field List"
Returns
Type Description
System.String

the current value for the specified field of the specified item (possibly null), or null if no value has been received yet.

getValue(Int32, String)

Returns the latest value received for the specified item/field pair.
It is suggested to consume real-time data by implementing and adding a proper SubscriptionListener rather than probing this method.
In case of COMMAND Subscriptions, the value returned by this method may be misleading, as in COMMAND mode all the keys received, being part of the same item, will overwrite each other; for COMMAND Subscriptions, use getCommandValue(Int32, String, String) instead.
Note that internal data is cleared when the Subscription is unsubscribed from.

Lifecycle: This method can be called at any time; if called to retrieve a value that has not been received yet, then it will return null.

Declaration
public virtual string getValue(int itemPos, string fieldName)
Parameters
Type Name Description
System.Int32 itemPos

the 1-based position of an item within the configured "Item Group" or "Item List"
System.String fieldName

a field in the configured "Field List"
Returns
Type Description
System.String

the current value for the specified field of the specified item (possibly null), or null if no value has been received yet.

getValue(String, Int32)

Returns the latest value received for the specified item/field pair.
It is suggested to consume real-time data by implementing and adding a proper SubscriptionListener rather than probing this method.
In case of COMMAND Subscriptions, the value returned by this method may be misleading, as in COMMAND mode all the keys received, being part of the same item, will overwrite each other; for COMMAND Subscriptions, use getCommandValue(String, String, Int32) instead.
Note that internal data is cleared when the Subscription is unsubscribed from.

Lifecycle: This method can be called at any time; if called to retrieve a value that has not been received yet, then it will return null.

Declaration
public virtual string getValue(string itemName, int fieldPos)
Parameters
Type Name Description
System.String itemName

an item in the configured "Item List"
System.Int32 fieldPos

the 1-based position of a field within the configured "Field Schema" or "Field List"
Returns
Type Description
System.String

the current value for the specified field of the specified item (possibly null), or null if no value has been received yet.

getValue(String, String)

Returns the latest value received for the specified item/field pair.
It is suggested to consume real-time data by implementing and adding a proper SubscriptionListener rather than probing this method.
In case of COMMAND Subscriptions, the value returned by this method may be misleading, as in COMMAND mode all the keys received, being part of the same item, will overwrite each other; for COMMAND Subscriptions, use getCommandValue(String, String, String) instead.
Note that internal data is cleared when the Subscription is unsubscribed from.

Lifecycle: This method can be called at any time; if called to retrieve a value that has not been received yet, then it will return null.

Declaration
public virtual string getValue(string itemName, string fieldName)
Parameters
Type Name Description
System.String itemName

an item in the configured "Item List"
System.String fieldName

a field in the configured "Field List"
Returns
Type Description
System.String

the current value for the specified field of the specified item (possibly null), or null if no value has been received yet.

removeListener(SubscriptionListener)

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

Lifecycle: a listener can be removed at any time.

Declaration
public virtual void removeListener(SubscriptionListener listener)
Parameters
Type Name Description
SubscriptionListener listener

The listener to be removed.
See Also