D365 FinOps: Accessing private or protected class methods and members from extension code

 All class member variables are protected by default in AX 7, so it is impossible to access them from extensions. It becomes a real problem when you try to extend classes like SalesLineType.

For example, we want to add custom logic on sales line insert event. Call to super() is commented out so we cannot create pre or post event handlers. We may try to create event handlers for SalesLineType.insert() mehtod, but we won’t get access to salesLine buffer because this variable is protected.

There are two options: use overlaying or use reflection.

Overlaying is preferable approach, but today we will talk about reflection to explain this option.

Reflection is usually used for unit testing in case you need to cover protected or private code and it is hard to call this code using public API.

It has bunch of disadvantages:

• It breaches entire basis of OO programming.
• Slow performance.
• Possible issues with future updates. Private methods could be changed at any time.

However, once you may get into situation where it could be the only option so it’s better to know about this possibility.

Let’s try to change some fields on sales line insert using reflection.

Create new event handler class for SalesLineType and subscribe to post insert:

using System.Reflection;

/// 

/// Handles events raised by SalesLineTypeEventHandler class.
/// 
public class SalesLineTypeEventHandler
{
    [PostHandlerFor(classStr(SalesLineType), methodStr(SalesLineType, insert))]
    public static void SalesLineType_Post_insert(XppPrePostArgs _args)
    {
        SalesLineType salesLineType = _args.getThis();

        var bindFlags = BindingFlags::Instance | BindingFlags::NonPublic;

        var field = salesLineType.GetType().GetField("salesLine", bindFlags);

        SalesLine salesLine = field.GetValue(salesLineType);

        if (salesLine)
        {
            salesLine.MyNewField = 42;
            salesLine.doUpdate();
        }
    }
}

Also we can call private or protected method:

var bindFlags = BindingFlags::Instance | BindingFlags::NonPublic;

var methodInfo = salesLineType.GetType().GetMethod(methodStr(SalesLineType, checkQuantityUpdate), bindFlags);

if (methodInfo)
{
    methodInfo.Invoke(salesLineType,  new System.Object[0]());
}

You can read more about reflection on msdn