XML-DA method to asynchronously poll subscribed items from either an XML-DA or OPC-DA server.
Syntax
| Visual Basic (Usage) |  Copy Code |
|---|
Dim instance As OpcXmlDA
Dim Options As RequestOptions
Dim ServerSubHandles() As String
Dim HoldTime As Date
Dim HoldTimeSpecified As Boolean
Dim WaitTime As Integer
Dim ReturnAllItems As Boolean
Dim callback As AsyncCallback
Dim asyncState As Object
Dim value As IAsyncResult
value = instance.BeginSubscriptionPolledRefresh(Options, ServerSubHandles, HoldTime, HoldTimeSpecified, WaitTime, ReturnAllItems, callback, asyncState) |
Parameters
- Options
- Container with options used in most server calls.
- ServerSubHandles
- Supplied by the Server in the SubscribeResponse, it is used by the server to identify the
Subscription to be polled. Multiple ServerSubHandles may be supplied. The server will respond with the changes in data
associated with all supplied ServerSubHandles. The Server will maintain the order of Items within each polled subscription list,
and for subscriptions in the response (relative to the ServerSubHandles) – even if some subscriptions or some items in the
subscriptions are missing.
- HoldTime
- Instructs the server to hold off returning from the refresh service call until the absolute time of
the server is equal or greater than this value.
- HoldTimeSpecified
- If FALSE then the HoldTime argument is ignored.
- WaitTime
- Instructs the server to wait the specified number of milliseconds after HoldTime before returning if
there are no changes to report. A change in one of the subscribed items, during this wait period, will result in the service
returning immediately rather than completing the wait time.
- ReturnAllItems
- If set to FALSE, then the server will return only the changed Items between this SubscriptionPolledRefresh request and the previous request.
If TRUE the server will return all Items specified by the original Subscribe. The server will wait the HoldTime but then return with all current values (and any buffered values if EnableBuffering) ignoring the change status of the items. That is the WaitTime is not considered under this condition - 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
>
See Also
