XMLDA.NET Reference
BeginSubscribe Method
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xmldanet.xmlda Namespace > OpcXmlDA Class : BeginSubscribe Method

Visual Basic (Usage)
C#

Options: Container with options used in most server calls.

ItemList: The container for the individual Items. It is expected that there are one or more Items per ItemList.

ReturnValuesOnReply: If TRUE the server will return item values which are readily available for inclusion in the SubscribeResponse. Depending on when the SubscriptionPolledRefresh is requested, these items may or may not be updated in the first SubscriptionPolledRefresh.
If FALSE the server must not deliver any item values in the SubscribeResponse.

SubscriptionPingRate: The SubscriptionPingRate is the requested rate in milliseconds that the server should reevaluate the existence of the client. If the client has not had any communication in the specified period, then the Server is free to clean up all resources associated with that client for this Subscription.
The server should attempt to honor the client’s request, but it may reevaluate the existence of the client at a rate faster than the SubscriptionPingRate based on its own implementation, and resource constraints. If the SubscriptionPingRate is 0, then the server will use its own algorithm to reevaluate the existence of the client. It is highly recommended that clients always specify a non-zero ping rate since specifying zero will allow the server to choose a ping rate that the client will not have knowledge of and may be inappropriate.

callback: Delegate of the method to be called when the asynchronous operation is completed.

asyncState: A user-provided object that distinguishes this particular asynchronous request from other requests.

XML-DA method to asynchronously subscribe a set of item values with either an XML-DA or OPC-DA server.

Syntax

Visual Basic (Usage)	Copy Code
Dim instance As OpcXmlDA Dim Options As RequestOptions Dim ItemList As SubscribeRequestItemList Dim ReturnValuesOnReply As Boolean Dim SubscriptionPingRate As Integer Dim callback As AsyncCallback Dim asyncState As Object Dim value As IAsyncResult value = instance.BeginSubscribe(Options, ItemList, ReturnValuesOnReply, SubscriptionPingRate, callback, asyncState)

Visual Basic (Usage)

Copy Code

Dim instance As OpcXmlDA
Dim Options As RequestOptions
Dim ItemList As SubscribeRequestItemList
Dim ReturnValuesOnReply As Boolean
Dim SubscriptionPingRate As Integer
Dim callback As AsyncCallback
Dim asyncState As Object
Dim value As IAsyncResult
 
value = instance.BeginSubscribe(Options, ItemList, ReturnValuesOnReply, SubscriptionPingRate, callback, asyncState)

C#
public IAsyncResult BeginSubscribe( RequestOptions Options, SubscribeRequestItemList ItemList, bool ReturnValuesOnReply, int SubscriptionPingRate, AsyncCallback callback, object asyncState )

public IAsyncResult BeginSubscribe( 
   RequestOptions Options,
   SubscribeRequestItemList ItemList,
   bool ReturnValuesOnReply,
   int SubscriptionPingRate,
   AsyncCallback callback,
   object asyncState
)

Parameters

Options: Container with options used in most server calls.
ItemList: The container for the individual Items. It is expected that there are one or more Items per ItemList.
ReturnValuesOnReply: If TRUE the server will return item values which are readily available for inclusion in the SubscribeResponse. Depending on when the SubscriptionPolledRefresh is requested, these items may or may not be updated in the first SubscriptionPolledRefresh.
If FALSE the server must not deliver any item values in the SubscribeResponse.
SubscriptionPingRate: The SubscriptionPingRate is the requested rate in milliseconds that the server should reevaluate the existence of the client. If the client has not had any communication in the specified period, then the Server is free to clean up all resources associated with that client for this Subscription.
The server should attempt to honor the client’s request, but it may reevaluate the existence of the client at a rate faster than the SubscriptionPingRate based on its own implementation, and resource constraints. If the SubscriptionPingRate is 0, then the server will use its own algorithm to reevaluate the existence of the client. It is highly recommended that clients always specify a non-zero ping rate since specifying zero will allow the server to choose a ping rate that the client will not have knowledge of and may be inappropriate.
callback: Delegate of the method to be called when the asynchronous operation is completed.
asyncState: A user-provided object that distinguishes this particular asynchronous request from other requests.

Return Value

An object that supports the IAsyncResult interface stores state information for an asynchronous operation, and provides a synchronization object to allow threads to be signaled when the operation

Requirements

Target Platforms:Windows XP Professional, Windows Server 2003 family, Windows Vista, Windows 7, Windows Server 2008 family

Syntax

Parameters

Return Value

Requirements

See Also

Reference