XML-DA method to poll subscribed items from either an XML-DA or OPC-DA server.
Syntax
| C# | |
|---|
[SoapDocumentMethodAttribute(Action="http://opcfoundation.org/webservices/XMLDA/1.0/SubscriptionPolledRefresh",
RequestNamespace="http://opcfoundation.org/webservices/XMLDA/1.0/",
ResponseNamespace="http://opcfoundation.org/webservices/XMLDA/1.0/",
Use=SoapBindingUse.Literal,
ParameterStyle=SoapParameterStyle.Wrapped)]
public ReplyBase SubscriptionPolledRefresh(
RequestOptions Options,
string[] ServerSubHandles,
DateTime HoldTime,
bool HoldTimeSpecified,
int WaitTime,
bool ReturnAllItems,
out string[] InvalidServerSubHandles,
out SubscribePolledRefreshReplyItemList[] RItemList,
out OPCError[] Errors,
out bool DataBufferOverflow
) |
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 - InvalidServerSubHandles
- The server will identify 0 or more ServerSubHandles that were invalid.
- RItemList
- One RItemList for each subscription of which items have to be returned.
A RItemList for each polled (and valid) subscription handle is sent if the client requested them with “ReturnAllItems”. If “ReturnAllItems” is FALSE, the server only returns Items which had changed. Each RItemList contains the SubscriptionHandle. Within each list the Items will be returned in a relative order based on their relative order in the original Subscribe even if some of the Items are missing because the values have not changed. If there are no values which have changed, the server will respond with a response without any RItemList.
If EnableBuffering = False then the server will send only the latest value that it is maintaining for those changed items.
If EnableBuffering = True then the server will send all value changes (Last Changed Value and any buffered values) for those changed items since the last SubscriptionPolledRefresh. - Errors
- An array of OPCError elements with the description of the errors occured in this server call.
Errors are only present if Items contain result codes.
- DataBufferOverflow
- individual items occurred, but not all of these changes could be buffered due to resource
limitations. The server is required to provide at least the most recent change for each item that changed since the last update.
The individual items will indicate whether they were impacted by this resource limitation.
For more details on buffering see the section on Buffered Data and the OPC DA Custom Specification for additional details
on this topic.
Return Value
Container of information that represents the basic information for most responses.
Example
| Visual Basic |  Copy Code |
|---|
Public Sub PollThread()
Dim Srv As XmlServer = New XmlServer(cbURL.Text)
While Not pollTermiateRequest ' periodic refresh loop
' request the refresh in Sync mode
Dim rOpt As RequestOptions = New RequestOptions
Dim SubscrHnds(0) As String
SubscrHnds(0) = srvHandle
Dim invalidHandles As String()
Dim rslt As SubscribePolledRefreshReplyItemList()
Dim Err As OPCError()
Dim overflow As Boolean
Dim rep As ReplyBase
Try
rep = Srv.SubscriptionPolledRefresh(rOpt, SubscrHnds, DateTime.MinValue, False, 5000, True, _
invalidHandles, rslt, Err, overflow)
If Not Err Is Nothing Then
If Err.Length > 0 Then
MessageBox.Show(Err(0).Text, "Exception in Poll")
Return ' abort thread
End If
End If
Dim rItem As ItemValue
For Each rItem In rslt(0).Items ' for simplicity only one subscription
' handle the item value
Next
Catch ex As Exception
MessageBox.Show(ex.Message, "Exception in Poll")
Return ' abort thread
End Try
Thread.Sleep(2000)
End While
End Sub |
| C# | Copy Code |
|---|
public void PollThread( )
{
XmlServer Srv = new XmlServer( cbURL.Text );
while( ! pollTermiateRequest ) // periodic refresh loop
{
// request the refresh in Sync mode
RequestOptions rOpt = new RequestOptions();
string[] SubscrHnds = new string[ 1 ] ;
SubscrHnds[0] = srvHandle ;
string[] invalidHandles;
SubscribePolledRefreshReplyItemList[] rslt ;
OPCError[] err ;
bool overflow ;
ReplyBase rep;
try
{
rep = Srv.SubscriptionPolledRefresh( rOpt, SubscrHnds, DateTime.MinValue, false, 5000, true,
out invalidHandles, out rslt, out err, out overflow );
if( (err != null) && (err.Length>0) )
{
MessageBox.Show( err[0].Text, "Exception in Poll" );
return ; // abort thread
}
foreach( ItemValue rItem in rslt[0].Items ) // for simplicity only one subscription
{
// handle the item values
}
}
catch( Exception ex )
{
MessageBox.Show( ex.Message, "Exception in Poll" );
return ; // abort thread
}
Thread.Sleep( 2000 );
}
} |
Requirements
Target Platforms:Windows XP Professional, Windows Server 2003 family, Windows Vista, Windows 7, Windows Server 2008 family
>
See Also
