How to check if value in ExpressionEdit is an expression or a literal string?

[Nesh]

I am making an Edit Step dialog for a custom step type, Multiple String Value Test. The step type is set up like String Value Test only that it has a Measurement array like Multiple Numeric Limit Test. The measurement type has, among other properties, String, StringExpr, and UseStringExpr just like Limits in StringValueTest.

In the Edit Step dialog I use an ExpressionEdit ActiveX control to enter the string limit, either an expression that evaluates to a string or a literal string. When the text in the ExpressionEdit is an expression I want to set the value to StringExpr property on the measurement type and set UseStringExpr to True. When the text in the ExpressionEdit is a string I want to set the value to String property on the measurement type and set UseStringExpr to False, just like String Value Test does.

How do I differentiate between an expression and a string in an ExpressionEdit?

See attached images if you are unsure what I mean.

[James_Grey · Accepted solution]

I think you are looking for Expression.GetConstantValue.

[Nesh]

Thank you, it looks like Expression has what I need.

If Text is empty it is not an expression,

if Text has more than 1 token or it is not a constant value (GetConstantValue returns null) it is an expression,

else it is not an expression.