'Declaration
<ExtensionAttribute()> <NotNullAttribute()> Public Overloads Shared Function ReadItem( _ ByVal client As IEasyDAClient, _ ByVal serverDescriptor As ServerDescriptor, _ ByVal itemDescriptor As DAItemDescriptor, _ ByVal readParameters As DAReadParameters _ ) As DAVtq
'Usage
Dim client As IEasyDAClient Dim serverDescriptor As ServerDescriptor Dim itemDescriptor As DAItemDescriptor Dim readParameters As DAReadParameters Dim value As DAVtq value = IEasyDAClientExtension.ReadItem(client, serverDescriptor, itemDescriptor, readParameters)
[Extension()] [NotNull()] public static DAVtq ReadItem( IEasyDAClient client, ServerDescriptor serverDescriptor, DAItemDescriptor itemDescriptor, DAReadParameters readParameters )
[Extension()] [NotNull()] public: static DAVtq^ ReadItem( IEasyDAClient^ client, ServerDescriptor^ serverDescriptor, DAItemDescriptor^ itemDescriptor, DAReadParameters^ readParameters )
Parameters
- client
- The client object that will perform the operation.
This is typically the EasyDAClient object.
The value of this parameter cannot be
null
(Nothing
in Visual Basic). - serverDescriptor
- The OPC server involved in the operation.
Because the OpcLabs.EasyOpc.ServerDescriptor has an implicit conversion from System.Guid, System.String and OpcLabs.EasyOpc.ServerElement, in languages that support implicit conversion operators (such as C# or VB.NET), you can simply use a GUID (representing the CLSID of the server), a string (representing the so-called OPC server descriptor string, such as a ProgID or the URL of the server), or a OpcLabs.EasyOpc.ServerElement object (result from OPC browsing), in place of this parameter, and the corresponding OPC server descriptor will be constructed automatically. When the implicit conversion operators are not supported (such as with Python.NET), you can use the FromGuid, FromString or FromServerElement static method instead.
The value of this parameter cannot be
null
(Nothing
in Visual Basic). - itemDescriptor
- The OPC item involved in the operation.
Because the DAItemDescriptor has an implicit conversion from System.String and OpcLabs.EasyOpc.DataAccess.AddressSpace.DANodeElement, in languages that support implicit conversion operators (such as C# or VB.NET), you can simply use a string (representing the qualified name of the node), or a OpcLabs.EasyOpc.DataAccess.AddressSpace.DANodeElement object (result from OPC browsing), in place of this parameter, and the corresponding OPC DA item descriptor will be constructed automatically. When the implicit conversion operators are not supported (such as with Python.NET), you can use the FromString or FromDANodeElement static method instead.
The value of this parameter cannot be
null
(Nothing
in Visual Basic). - readParameters
- Read parameters, such as the data source or value age.
Because the DAReadParameters has an implicit conversion from System.Int32 and DADataSource, in languages that support implicit conversion operators (such as C# or VB.NET), you can simply use an integer (representing the value age in milliseconds), or an element of the DADataSource enumeration in place of this parameter, and the corresponding OPC DA read parameters object will be constructed automatically. When the implicit conversion operators are not supported (such as with Python.NET), you can use the DAReadParameters Constructor(Int32) or DAReadParameters Constructor(DADataSource) constructor instead.
The value of this parameter cannot be
null
(Nothing
in Visual Basic).
Return Value
This method never returns null
(Nothing
in Visual Basic).