'Declaration<ExtensionAttribute()> <JetBrains.Annotations.CanBeNullAttribute()> Public Overloads Shared Function ReadItemValue( _ ByVal client As IEasyDAClient, _ ByVal machineName As String, _ ByVal serverClass As String, _ ByVal itemId As String, _ ByVal dataType As VarType _ ) As Object
'UsageDim client As IEasyDAClient Dim machineName As String Dim serverClass As String Dim itemId As String Dim dataType As VarType Dim value As Object value = IEasyDAClientExtension.ReadItemValue(client, machineName, serverClass, itemId, dataType)
[Extension()] [JetBrains.Annotations.CanBeNull()] public static object ReadItemValue( IEasyDAClient client, string machineName, string serverClass, string itemId, VarType dataType )
[Extension()] [JetBrains.Annotations.CanBeNull()] public: static Object^ ReadItemValue( IEasyDAClient^ client, String^ machineName, String^ serverClass, String^ itemId, VarType^ dataType )
Parameters
- client
- The client object that will perform the operation.
This is typically the EasyDAClient object.
The value of this parameter cannot be
null(Nothingin Visual Basic). - machineName
- Name of the machine. Determines the computer on which the OPC server is located. It may be an empty string, in which case the OPC server is assumed to exist on the local computer or at the computer specified for it by DCOM configuration.
The value represents a UNC or DNS computer name. Any string can be passed to this parameter (i.e. will not cause System.ArgumentException), but not all values make sense and will work when an operation using them is attempted. IPv6 addresses are normally enclosed between '[' and ']'.
The value of this parameter cannot be
null(Nothingin Visual Basic). - serverClass
- Contains ProgID of the OPC server to read from.
The value of this parameter cannot be
null(Nothingin Visual Basic). - itemId
- Contains OPC item identifier.
The value of this parameter cannot be
null(Nothingin Visual Basic). - dataType
- Specifies the data type requested. Passing OpcLabs.BaseLib.ComInterop.VarTypes.Empty will cause the value be returned in server's canonical data type.
Because the OpcLabs.BaseLib.ComInterop.VarType has an implicit conversion from System.Int32 and OpcLabs.BaseLib.ComInterop.VarTypes, in languages that support implicit conversion operators (such as C# or VB.NET), you can simply use an integer (representing the numerical value of the COM VARTYPE), or an element of the OpcLabs.BaseLib.ComInterop.VarTypes enumeration (or an allowed combination of OpcLabs.BaseLib.ComInterop.VarTypes flags) in place of this parameter, and the corresponding data type specification will be constructed automatically. When the implicit conversion operators are not supported (such as with Python.NET), you can use the OpcLabs.BaseLib.ComInterop.VarType.VarType Constructor(Int32) or OpcLabs.BaseLib.ComInterop.VarType.VarType Constructor(VarTypes) constructor instead.
The value of this parameter cannot be
null(Nothingin Visual Basic).
Return Value
This method can return null (Nothing in Visual Basic).