I made a Delphi example for specifying the type explicitly. In COM, you need to use WriteMultipleValues instead of WriteValue (but you can use it with just one value if you need to).
// This example shows how to write values into 3 nodes at once, specifying a type code explicitly. It tests for success of
// each write and displays the exception message in case of failure.
//
// Reasons for specifying the type explicitly might be:
// - The data type in the server has subtypes, and the client therefore needs to pick the subtype to be written.
// - The data type that the reports is incorrect.
// - Writing with an explicitly specified type is more efficient.
//
// Alternative ways of specifying the type are using the ValueType or ValueTypeFullName properties.
class procedure WriteMultipleValues.ValueTypeCode;
var
Arguments: OleVariant;
Client: TEasyUAClient;
I: Cardinal;
WriteResult: _UAWriteResult;
WriteValueArguments1, WriteValueArguments2, WriteValueArguments3: _UAWriteValueArguments;
Results: OleVariant;
begin
WriteValueArguments1 := CoUAWriteValueArguments.Create;
WriteValueArguments1.EndpointDescriptor.UrlString := 'http://opcua.demo-this.com:51211/UA/SampleServer';
WriteValueArguments1.NodeDescriptor.NodeId.ExpandedText := 'nsu=http://test.org/UA/Data/;i=10221';
WriteValueArguments1.Value := 23456;
WriteValueArguments1.ValueTypeCode := TypeCode_Int32; // here is the type explicitly specified
WriteValueArguments2 := CoUAWriteValueArguments.Create;
WriteValueArguments2.EndpointDescriptor.UrlString := 'http://opcua.demo-this.com:51211/UA/SampleServer';
WriteValueArguments2.NodeDescriptor.NodeId.ExpandedText := 'nsu=http://test.org/UA/Data/;i=10226';
WriteValueArguments2.Value := 'This string cannot be converted to Double';
WriteValueArguments2.ValueTypeCode := TypeCode_Double; // here is the type explicitly specified
WriteValueArguments3 := CoUAWriteValueArguments.Create;
WriteValueArguments3.EndpointDescriptor.UrlString := 'http://opcua.demo-this.com:51211/UA/SampleServer';
WriteValueArguments3.NodeDescriptor.NodeId.ExpandedText := 'nsu=http://test.org/UA/Data/;s=UnknownNode';
WriteValueArguments3.Value := 'ABC';
WriteValueArguments3.ValueTypeCode := TypeCode_String; // here is the type explicitly specified
Arguments := VarArrayCreate([0, 2], varVariant);
Arguments[0] := WriteValueArguments1;
Arguments[1] := WriteValueArguments2;
Arguments[2] := WriteValueArguments3;
// Instantiate the client object
Client := TEasyUAClient.Create(nil);
// Modify values of nodes
TVarData(Results).VType := varArray or varVariant;
TVarData(Results).VArray := PVarArray(Client.WriteMultipleValues(
PSafeArray(TVarData(Arguments).VArray)));
// Display results
for I := VarArrayLowBound(Results, 1) to VarArrayHighBound(Results, 1) do
begin
WriteResult := IInterface(Results[I]) as _UAWriteResult;
if WriteResult.Succeeded then
WriteLn('Result ', I, ' success')
else
WriteLn('Result ', I, ': ', WriteResult.Exception.GetBaseException.Message);
end;
end;
This example works for set of basic types covered by the TypeCode enumeration. I suppose it will be sufficient for your application. There is also an option to specify other types, using the ValueTypeFullName property. If you end up needing that, let me know.
Best regards
