ValueQuery Methods
The ValueQuery object contains the following methods:
CancelValueFiltering
The CancelValueFiltering method terminates execution of the query thread, and waits for the specified number of seconds.
Syntax
CancelValueFiltering(TimeToWaitInSeconds As Integer) As Boolean
Parameters
| Parameter | Required | Description |
|---|---|---|
|
TimeToWaitInSeconds |
Yes |
The number of seconds to wait for the value query to terminate. This value must be within the range [1 - 100]. |
Remark
This method will hang for the specified number of seconds while the query thread terminates. If the query thread has not terminated by the time the interval has expired, this method will return false and the query thread will continue to attempt to terminate in the background. Call this method as part of the cleanup routine after querying is finished.
Example
The following example goes through the entire process of creating a filter, starting the query, retrieving a current value entry from a point tag, and cleaning up the query.
Sub
Dim bCreatedOk
bCreatedOk = ValueQuery.CreateValueFilter()
Dim bRunning
bRunning = ValueQuery.IsValueFilterRunning()
Dim bStarted
bStarted = ValueQuery.StartValueFiltering()
' retrieve the current value from a point tag (note that this
' query is designed to work with other queries that return lists
' of point tags, such as PointFacQuery)
Dim bRetrieved, pvValueInfoXml
bRetrieved = ValueQuery.GetValueEntryAsXml("CYGDEMO.UIS.00002109:MYPOINTTAG", pvValueInfoXml)
MsgBox pvValueInfoXml
ValueQuery.CancelValueFiltering(100)
End Sub
CreateValueFilter
The CreateValueFilter method creates a new value query thread.
Syntax
CreateValueFilter() As Boolean
Example
The following example goes through the entire process of creating a filter, starting the query, retrieving a current value entry from a point tag, and cleaning up the query.
Sub
Dim bCreatedOk
bCreatedOk = ValueQuery.CreateValueFilter()
Dim bRunning
bRunning = ValueQuery.IsValueFilterRunning()
Dim bStarted
bStarted = ValueQuery.StartValueFiltering()
' retrieve the current value from a point tag (note that this
' query is designed to work with other queries that return lists
' of point tags, such as PointFacQuery)
Dim bRetrieved, pvValueInfoXml
bRetrieved = ValueQuery.GetValueEntryAsXml("CYGDEMO.UIS.00002109:MYPOINTTAG", pvValueInfoXml)
MsgBox pvValueInfoXml
ValueQuery.CancelValueFiltering(100)
End Sub
GetValueEntryAsXml
The GetValueEntryAsXml method returns the current value entry for the given tag.
Syntax
GetValueEntryAsXml(Tag As String, ValueInfoXml As Variant) As Boolean
Parameters
| Parameter | Required | Description |
|---|---|---|
|
Tag |
Yes |
A fully qualified point tag. |
|
ValueInfoXml |
Yes |
The current value entry for the tag returned as an XML string. |
Example
The following example goes through the entire process of creating a filter, starting the query, retrieving a current value entry from a point tag, and cleaning up the query.
Sub
Dim bCreatedOk
bCreatedOk = ValueQuery.CreateValueFilter()
Dim bRunning
bRunning = ValueQuery.IsValueFilterRunning()
Dim bStarted
bStarted = ValueQuery.StartValueFiltering()
' retrieve the current value from a point tag (note that this
' query is designed to work with other queries that return lists
' of point tags, such as PointFacQuery)
Dim bRetrieved, pvValueInfoXml
bRetrieved = ValueQuery.GetValueEntryAsXml("CYGDEMO.UIS.00002109:MYPOINTTAG", pvValueInfoXml)
MsgBox pvValueInfoXml
ValueQuery.CancelValueFiltering(100)
End Sub
IsValueFilterRunning
The IsValueFilterRunning method returns true if the value query thread is running.
Syntax
IsValueFilterRunning() As Boolean
Remark
The value query thread is executed after a value filter is created; therefore, after a value filter is created, this method will only return false if the filter has been canceled using CancelValueFiltering.
Example
The following example creates a value filter, checks that it is running, destroys it, and checks that it is no longer running.
Sub
Dim bCreatedOk
bCreatedOk = ValueQuery.CreateValueFilter()
Dim bRunning
bRunning = ValueQuery.IsValueFilterRunning()
MsgBox bRunning 'should be "True"
ValueQuery.CancelValueFiltering(100)
bRunning = ValueQuery.IsValueFilterRunning()
MsgBox bRunning 'should be "False"
End Sub
StartValueFiltering
The StartValueFiltering method initiates value filtering on the background thread.
Syntax
StartValueFiltering() As Boolean
Remark
This method returns false if no value filter has been created.
Example
The following example goes through the entire process of creating a filter, starting the query, retrieving a current value entry from a point tag, and cleaning up the query.
Sub
Dim bCreatedOk
bCreatedOk = ValueQuery.CreateValueFilter()
Dim bRunning
bRunning = ValueQuery.IsValueFilterRunning()
Dim bStarted
bStarted = ValueQuery.StartValueFiltering()
' retrieve the current value from a point tag (note that this
' query is designed to work with other queries that return lists
' of point tags, such as PointFacQuery)
Dim bRetrieved, pvValueInfoXml
bRetrieved = ValueQuery.GetValueEntryAsXml("CYGDEMO.UIS.00002109:MYPOINTTAG", pvValueInfoXml)
MsgBox pvValueInfoXml
ValueQuery.CancelValueFiltering(100)
End Sub
