Reads a named item using individual parameters specifying its location, and using server's canonical data type.
Syntax
'Declaration
<NotNullAttribute()>
Function ReadItem( _
ByVal As String, _
ByVal As String, _
ByVal As String _
) As DAVtq
'Usage
Dim instance As _EasyDAClient
Dim machineName As String
Dim serverClass As String
Dim itemId As String
Dim value As DAVtq
value = instance.ReadItem(machineName, serverClass, itemId)
Parameters
- machineName
- Name of the machine. Determines the computer on which the OPC server is located. 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.
- serverClass
- Contains ProgID of the OPC server to read from.
- itemId
- Contains OPC item identifier.
Return Value
If successful, the function returns a
OpcLabs.EasyOpc.DataAccess.DAVtq object. The object contains the value, timestamp and quality of the OPC item requested.
Exceptions
| Exception | Description |
|---|
| System.Exception | An error has occurred during application execution. |
Example
COM
// This example shows how to read a single item, and display its value, timestamp and quality.
var Client = new ActiveXObject("OpcLabs.EasyOpc.DataAccess.EasyDAClient");
var VTQ = Client.ReadItem("", "OPCLabs.KitServer.2", "Simulation.Random");
WScript.Echo("VTQ.ToString(): " + VTQ.ToString());
// This example shows how to read a single item, and display its value, timestamp and quality.
class procedure ReadItem.Main;
var
Client: OpcLabs_EasyOpcClassic_TLB._EasyDAClient;
Vtq: _DAVtq;
begin
// Instantiate the client object
Client := CoEasyDAClient.Create;
try
Vtq := Client.ReadItem('', 'OPCLabs.KitServer.2', 'Simulation.Random');
except
on E: EOleException do
begin
WriteLn(Format('*** Failure: %s', [E.GetBaseException.Message]));
Exit;
end;
end;
// Display results
WriteLn('Vtq: ', Vtq.ToString);
end;
// This example shows how to read a single item, and display its value, timestamp and quality.
$Client = new COM("OpcLabs.EasyOpc.DataAccess.EasyDAClient");
try
{
$Vtq = $Client->ReadItem("", "OPCLabs.KitServer.2", "Simulation.Random");
}
catch (com_exception $e)
{
printf("*** Failure: %s\n", $e->getMessage());
Exit();
}
printf("Vtq: %s\n", $Vtq);
// This example shows how to read a single item, and display its value, timestamp and quality.
mle_outputtext.Text = ""
// Instantiate the client object
OLEObject client
client = CREATE OLEObject
client.ConnectToNewObject("OpcLabs.EasyOpc.DataAccess.EasyDAClient")
// Obtain value/timestamp/quality
OLEObject vtq
TRY
vtq = client.ReadItem("", "OPCLabs.KitServer.2", "Demo.Ramp")
CATCH (OLERuntimeError oleRuntimeError)
mle_outputtext.Text = mle_outputtext.Text + "*** Failure: " + oleRuntimeError.Description + "~r~n"
RETURN
END TRY
// Display results
mle_outputtext.Text = mle_outputtext.Text + "Vtq: " + vtq.DisplayString + "~r~n"
Rem This example shows how to read a single item, and display its value, timestamp and quality.
Private Sub ReadItem_Main_Command_Click()
OutputText = ""
' Instantiate the client object
Dim client As New EasyDAClient
On Error Resume Next
Dim vtq As DAVtq
Set vtq = client.ReadItem("", "OPCLabs.KitServer.2", "Simulation.Random")
If Err.Number <> 0 Then
OutputText = OutputText & "*** Failure: " & Err.Source & ": " & Err.Description & vbCrLf
Exit Sub
End If
On Error GoTo 0
' Display results
OutputText = OutputText & "Vtq: " & vtq & vbCrLf
End Sub
Rem This example shows how to read a single item, and display its value, timestamp and quality.
Option Explicit
Dim Client: Set Client = CreateObject("OpcLabs.EasyOpc.DataAccess.EasyDAClient")
On Error Resume Next
Dim Vtq: Set Vtq = Client.ReadItem("", "OPCLabs.KitServer.2", "Simulation.Random")
If Err.Number <> 0 Then
WScript.Echo "*** Failure: " & Err.Source & ": " & Err.Description
WScript.Quit
End If
On Error Goto 0
WScript.Echo "Vtq: " & Vtq
Requirements
Target Platforms: .NET Framework: Windows 10 (selected versions), Windows 11 (selected versions), Windows Server 2016, Windows Server 2022; .NET: Linux, macOS, Microsoft Windows
See Also
