ReadMultipleItemValues(IEasyDAClient,DAItemArguments[],DAReadParameters) Method

Reads named items from an OPC-DA server or servers. Only the item values are returned (qualities and timestamps are not returned). Reads multiple named item values, using item arguments objects, and common read parameters.

Syntax

Visual Basic
C#
C++/CLI

'Declaration
 
<ExtensionAttribute()>
<NotNullAttribute()>
Public Overloads Shared Function ReadMultipleItemValues( _
   ByVal client As IEasyDAClient, _
   ByVal itemArgumentsArray() As DAItemArguments, _
   ByVal readParameters As DAReadParameters _
) As ValueResult()

'Usage
 
Dim client As IEasyDAClient
Dim itemArgumentsArray() As DAItemArguments
Dim readParameters As DAReadParameters
Dim value() As ValueResult
 
value = IEasyDAClientExtension.ReadMultipleItemValues(client, itemArgumentsArray, readParameters)

[Extension()]
[NotNull()]
public static ValueResult[] ReadMultipleItemValues( 
   IEasyDAClient client,
   DAItemArguments[] itemArgumentsArray,
   DAReadParameters readParameters
)

[Extension()]
[NotNull()]
public:
static array<ValueResult^>^ ReadMultipleItemValues( 
   IEasyDAClient^ client,
   array<DAItemArguments^>^ itemArgumentsArray,
   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).

itemArgumentsArray

Array of item arguments objects (determine the OPC server and an OPC-DA item).

The value of this parameter cannot be null (Nothing in Visual Basic).

The individual elements of the parameter value cannot be null (Nothing in Visual Basic).

readParameters

The read parameters (such as 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

The function returns an array of OpcLabs.EasyOpc.DataAccess.OperationModel.DAVtqResult objects. The indices of elements in the output array are the same as those in the input array, .

This method never returns null (Nothing in Visual Basic).

The individual elements of the returned value are never null (Nothing in Visual Basic).

Exceptions

Exception Description

Exception	Description
System.ArgumentNullException	A `null` reference (`Nothing` in Visual Basic) is passed to a method that does not accept it as a valid argument. This is a usage error, i.e. it will never occur (the exception will not be thrown) in a correctly written program. Your code should not catch this exception.

System.ArgumentNullException

A null reference (Nothing in Visual Basic) is passed to a method that does not accept it as a valid argument.

This is a usage error, i.e. it will never occur (the exception will not be thrown) in a correctly written program. Your code should not catch this exception.

Remarks

The ReadMultipleItemValues method requires that the quality is "good" for each item. The function performs all individual operations in parallel, but only returns after all individual operations are completed (or their timeouts elapse).

This method does not throw an exception in case of OPC operation failures. Instead, the eventual exception related to each item is returned in Exception property of each returned OpcLabs.EasyOpc.DataAccess.OperationModel.DAVtqResult element.

The server(s) can be local or can be remotely accessed via DCOM.

Optionally, a specific data type can be requested, or an access path can be specified (OPC DA 1.0 only).

The size of the input array will become the size of the output array. The element positions (indices) in the output array are the same as in the input array.

This is an extension method (info: C#, VB.NET). In languages that have support for extensions methods (such as C# and VB.NET), you can use the extension method as if it were a regular method on the object that is its first parameter. In other languages (such as with Python.NET), you will call the extension as a static method, and pass it the object on which it acts as its first parameter.

This is a multiple-operation method. In a properly written program, it does not throw any exceptions. You should therefore not put try/catch statements or similar constructs around calls to this method. The only exceptions thrown by this method are for usage errors, i.e. when your code violates the usage contract of the method, such as passing in invalid arguments or calling the method when the state of the object does not allow it. Any operation-related errors (i.e. errors that depend on external conditions that your code cannot reliably check) are indicated in the result objects returned by the method. For more information, see Multiple-operation Methods and Do not catch any exceptions with asynchronous or multiple-operation methods.

Requirements

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

Reference

IEasyDAClientExtension Class
IEasyDAClientExtension Members
Overload List

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