ReadMultipleItems Method (IEasyDAClientExtension)

Reads data of multiple OPC-DA items.

The ReadMultipleItems method reads the data (values, timestamps and qualities) of multiple items from one or more OPC-DA servers. It uses the first available data from the server for each item; it does not wait until the quality becomes "uncertain" or "good". 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).

This method operates on multiple items at once. If you only have one item, you can use the ReadItem(IEasyDAClient,DAReadItemArguments) method instead.

Overload List

Overload	Description
ReadMultipleItems(IEasyDAClient,DAItemArguments[],DAReadParameters)	Reads multiple named items from a single OPC server, using item arguments objects, and common read parameters. Values, qualities and timestamps are returned.
ReadMultipleItems(IEasyDAClient,ServerDescriptor,DAItemDescriptor[])	Reads multiple named items from a single OPC server, using descriptor objects for the OPC server and OPC-DA items. Values, qualities and timestamps are returned.
ReadMultipleItems(IEasyDAClient,ServerDescriptor,DAItemDescriptor[],DAReadParameters)	Reads multiple named items from a single OPC server, using descriptor objects for the OPC server and OPC-DA items, and specifying read operation parameters. Values, qualities and timestamps are returned.

Remarks

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

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