UAReadAttribute Class

Visual Basic
C#
C++/CLI

'Declaration
 
<AttributeUsageAttribute(AttributeTargets.Class Or  _
    AttributeTargets.Event Or  _
    AttributeTargets.Field Or  _
    AttributeTargets.Method Or  _
    AttributeTargets.Property Or  _
    AttributeTargets.Struct)>
<ComVisibleAttribute(False)>
Public NotInheritable Class UAReadAttribute 
   Inherits System.Attribute
   Implements System.Runtime.InteropServices._Attribute

'Usage
 
Dim instance As UAReadAttribute

[AttributeUsage(AttributeTargets.Class | 
    AttributeTargets.Event | 
    AttributeTargets.Field | 
    AttributeTargets.Method | 
    AttributeTargets.Property | 
    AttributeTargets.Struct)]
[ComVisible(false)]
public sealed class UAReadAttribute : System.Attribute, System.Runtime.InteropServices._Attribute

[AttributeUsage(AttributeTargets.Class | 
    AttributeTargets.Event | 
    AttributeTargets.Field | 
    AttributeTargets.Method | 
    AttributeTargets.Property | 
    AttributeTargets.Struct)]
[ComVisible(false)]
public ref class UAReadAttribute sealed : public System.Attribute, System.Runtime.InteropServices._Attribute

By annotating your types and members by attributes, you provide information to the live mapping system about the correspondences between the source OPC system and the target .NET objects.

For example, using the combination of DANode and DAItem attributes on a property of your object, you denote that the property corresponds to a node in OPC-DA address space, specify the name of that node (if different from property name), and mark the node as OPC item, i.e. capable of reading, writing or subscriptions. Using other attributes, you can also specify parameters for these mapping operations (such as the requested update rate). In OPC-UA, you would use a similar combination of UANode and UAData attributes.

Attributes in .NET are classes that, by convention, are named so that they end in the word “Attribute”. Some languages, such as C#, allow you to omit the final Attribute word, when the attribute is specified. For example, in C#, you can write [DAItem] instead of [DAItemAttribute]. In this document, we will mostly use the “shortened” named of attribute classes. Remember that in some languages, you may have to use the full name of the attribute class, and therefore append the word “Attribute” to the attribute name listed here.

The following table shows the Live Mapping attributes common for OPC Classic and OPC-UA, and the type of elements they can be applied to.

Attribute	Purpose	on Class or Struct	on Property, Method, or Field	on Event
MappingTag	Member mapping		✔	✔
MetaMember	Member mapping		✔

The following table shows the attributes available for OPC Classic, and the type of elements they can be applied to.

Attribute	Purpose	on Class or Struct	on Property, Method, or Field	on Event
DAItem	Member mapping		✔	✔
DAItemIdTemplate	Propagated parameter	✔
DAMember	Member mapping		✔
DANode	Member mapping		✔	✔
DAProperty	Member mapping		✔
DARead	Propagated parameter	✔	✔	✔
DASubscription	Propagated parameter	✔	✔	✔
DAType	Type mapping	✔
Server	Propagated parameter		✔	✔

The following table shows the attributes available for OPC Unified Architecture, and the type of elements they can be applied to.

Attribute	Purpose	on Class or Struct	on Property, Method, or Field	on Event
UAData	Member mapping		✔	✔
UADataChangeFilter	Propagated parameter	✔	✔	✔
UAEndpoint	Propagated parameter		✔	✔
UAMember	Member mapping		✔
UAMonitoring	Propagated parameter	✔	✔	✔
UANamespace	Propagated parameter	✔
UANode	Member mapping		✔	✔
UANodeIdTemplate	Propagated parameter	✔
UARead	Propagated parameter	✔	✔	✔
UASubscription	Propagated parameter	✔	✔	✔
UAType	Type mapping	✔

The meaning of these attributes will be explained in subsequent chapters, and can be found in the reference documentation as well.

System.Object
System.Attribute
OpcLabs.EasyOpc.UA.LiveMapping.UAReadAttribute

Target Platforms: .NET Framework: Windows 10 (selected versions), Windows 11 (selected versions), Windows Server 2016, Windows Server 2022; .NET: Linux, macOS, Microsoft Windows

Reference

UAReadAttribute Members
OpcLabs.EasyOpc.UA.LiveMapping Namespace