CODEWITHSUNDEEP
c#com.net-3.5
dior001
dior001

Reputation: 761

How to check if a COM property or method exists without generating an exception?

I'm working on some legacy code that creates a list of strings containing property and/or method names and then attempts to apply those properties or methods to a COM object. The property or method for the COM object is not guaranteed to exist and it could be either a property or a method I don't know which.

At the moment if a property or method doesn't exist it's caught as a COM exception. This results in poor performance. I am trying to find a way to check if a property or method exists in a COM object without generating an exception so that I can check for its existence before attempting to apply it.

Using GetType returns type System.com_object. Using GetProperty on System.com_object doesn't work as this is the exact runtime type not the type it's derived from. Instead I have to InvokeMember which creates an exception if the member doesn't exist. Does anyone have a better way of doing this?

I'm working in .NET 3.5 at the moment. Migration to .NET 4 is not an option at present but I'd still be interested in solutions in .NET 4 if the new language features provide a better way of solving the problem.

public static bool CheckIfComPropertyOrMethodExists<T1>(T1 objectToCheck, string propertyOrMethodName)
{
    if (CheckIfComPropertyExists(objectToCheck, propertyOrMethodName) == false & CheckIfComMethodExists(objectToCheck, propertyOrMethodName) == false) {
        return false;
    }
    {
        return true;
    }
}

public static bool CheckIfComPropertyExists<T1>(T1 objectToCheck, string propertyName)
{
    return objectToCheck.GetType().InvokeMember(propertyName, BindingFlags.GetProperty, null, objectToCheck, null) != null;
}

public static bool CheckIfComMethodExists<T1>(T1 objectToCheck, string methodName)
{
    return objectToCheck.GetType().GetMethod(methodName, BindingFlags.Public | BindingFlags.Instance) != null;
}

Helpful articles so far

How to check whether an object has certain method/property?

Calling a member of IDispatch COM interface from C#

http://msdn.microsoft.com/en-us/library/aa909091.aspx

Implementing IDispatch in c#

http://msdn.microsoft.com/en-us/magazine/dd347981.aspx

http://blogs.msdn.com/b/lucian/archive/2008/10/06/reflection-on-com-objects.aspx

Upvotes: 4

Views: 2610

Answers (1)

Wiktor Zychla
Wiktor Zychla

Reputation: 48240

Most probably the COM class implements also the IDispatch interface. You could then use its GetIDsOfNames to check whether a member exists in the class.

Here someone calls it from C#:

Calling a member of IDispatch COM interface from C#

Upvotes: 1

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