Hello Dear Friends,
Today, I am going to talk on the event handling new mechanism introduced in AX 2012. You could do event handling in earlier versions too but in AX 2012, event handling is better than previous version. Now it uses the concepts of delegates, event handlers etc...
Everybody must have seen that there are very few customers that use out of the box AX without any customizations. I would say not even a single customer. All customers are required to customize AX to fulfill their business needs. Sometimes, customizations become so large that it becomes difficult to upgrade when Microsoft does make changes in the lower layer. Finally, it becomes cost/budget issue so event handling mechanism in AX 2012 will help to lower the cost of developing customizations and then upgrading these customizations.
AX 2012 events are based on .NET eventing concepts.
Event: An action that needs to be triggered
Event Payload: Information that can go along with event.
Delegate: Definition that is passed to trigger an event. Basically, communicator between producer and consumer
Now, let me show you how to use events in AX 2012.
1. Let’s create a class Consumer to create EventHandler (sendEmailToCustomer). This will be called once order is shipped so that email can be sent to customer to notify. It has to be static method.
2. Now let’s create Producer class where
this event (sendEmailToCustomer) is called using Delegates. Add delegate by
right clicking on Producer class > New > Delegate.
4. Now drag and drop
sendEmailToCustomer method from Consumer class to delegateEmail.
5. Look at properties of EventHandler. You will notice it is pointing to
Class Consumer and method sendEmailToCustomer
6. If order is not
shipped, I am creating another event handler (errorLog) in Consumer class to
log error into error log.
7. Create another
delegate method (delegateErrorLog) in Producer class to call this event handler
(errorLog)
8. Drag and drop event handler (errorLog) in delegate method
(delegateErrorLog) similar to step 4.
9. Now let’s create main method in Producer class to ship order and let’s see how delegates can be used to trigger event handlers.
10. Suppose shipOrder method returns true. Now, if I run this main method,
it should go into delegateEmail method and should trigger method
sendEmailToCustomer. Let’s run and see the result. 11. Here is the result and it is as expected so it did trigger method
sendEmailToCustomer.
12. Let’s suppose
shipOrder method returns false. Now, if I run this main method, it should go
into delegateErrorLog method and should trigger method errorLog. Let’s run and
see the result.
13. Here is the result and it is as expected so it did trigger method
errorLog.
14. Handlers can also be
added/removed in x++.
15. Now, let’s use
addStaticHandler in main method. If you see the code, it is calling
addStaticHandler before calling delegate method. If we run it and see the
result, it should send 2 emails.
16. Here is the result as expected.
17. Similarly if we use removeStaticHandler method instead of addStaticHandler before calling delegate method then it will remove handler and will not send any email.
With use of events, it has opened so many doors and possibilities. Model architecture and events can be integrated which can help if multiple vendors are doing customizations in different models so that it doesn’t impact customizations of other models/vendors. Use of pre and post handlers is so powerful that it can be used without changing a single line of code in original method. Pre or Post handlers can be just dropped in the original method and will be called automatically before (pre handler method) or after (post handler method) original method.
Today, I am going to talk on the event handling new mechanism introduced in AX 2012. You could do event handling in earlier versions too but in AX 2012, event handling is better than previous version. Now it uses the concepts of delegates, event handlers etc...
Everybody must have seen that there are very few customers that use out of the box AX without any customizations. I would say not even a single customer. All customers are required to customize AX to fulfill their business needs. Sometimes, customizations become so large that it becomes difficult to upgrade when Microsoft does make changes in the lower layer. Finally, it becomes cost/budget issue so event handling mechanism in AX 2012 will help to lower the cost of developing customizations and then upgrading these customizations.
Events are simple and powerful concept. In daily life, we encounter with so many events. Events can be used to support these programming paradigms.
- Observation: Generate alerts to see exceptional behavior.
- Information dissemination: To convey information to right people at right time.
- Decoupling: Consumer doesn’t need to know about producer. Producer and Consumer can be sitting in totally different applications.
AX 2012 events are based on .NET eventing concepts.
Producer: Object to trigger the event.
Consumer: Object to consume the event and process logic based on the event triggered.Event: An action that needs to be triggered
Event Payload: Information that can go along with event.
Delegate: Definition that is passed to trigger an event. Basically, communicator between producer and consumer
Things to remember while using Events in AX2012
- Delegate keyword to use in delegate method.
- Public or any other accessibility specifier is not allowed in a delegate method.
- Delegate Method return type must be void.
- Delegate Method body must be empty.
- A delegate declaration can have the same type of parameters as a method.
- Event handlers can run only on the same tier as the publisher class of the delegate runs on.
- Handler can be implemented either in X++ or in managed code.
- Only static methods are allowed to be event handlers.
- Delegate method can’t be called outside class. Basically, events can’t be raised outside class in which event is defined.
- Event handlers for host methods can use one of two parameter signatures:
- One parameter of the type XppPrePostArgs. Go through all the methods available in XppPrePostArgs.
- The same parameters that are on the host method that the event handler subscribes to.
Now, let me show you how to use events in AX 2012.
1. Let’s create a class Consumer to create EventHandler (sendEmailToCustomer). This will be called once order is shipped so that email can be sent to customer to notify. It has to be static method.
3. Change its name to delegateEmail (you can
have any name). Parameter should be same as event handler method
(sendEmailToCustomer) i.e. of type Email. Notice it has no body and is a blank
method.
9. Now let’s create main method in Producer class to ship order and let’s see how delegates can be used to trigger event handlers.
Add Handler: It uses += sign.
Remove Handler: It uses -= sign.
17. Similarly if we use removeStaticHandler method instead of addStaticHandler before calling delegate method then it will remove handler and will not send any email.
So, you can see that with the
use of delegates and event handlers, it is so easy to trigger events. Also, it
will be easy and less time consuming to upgrade it. Suppose if delegates are
called from standard methods while doing customizations then it will be so easy
to upgrade if standard methods are changed in next release because only 1 liner
code of calling delegate method needs to be rearranged and no changes will be
required in event handler methods.
Use of Pre and Post event
handlers
In AX 2012, any event handler
method can dropped in other method. If the property “CalledWhen” is set to
“Pre” then it becomes pre event handler. If it is set to “Post” then it becomes
post event handler. Pre event handler is called before the method under which
it is dropped and Post event handler is called after method ends. These are so
powerful that event handler method can be created in new class and can be
dropped in any standard or any other method without changing a single line of
code and can be set as pre or post event handler as per business need. Suppose,
before creating a customer in AX, business need is to do some business logic
then logic can be written in pre event handler and can be dropped in insert
method of CustTable. Similarly, if there is post logic to be written after
customer is created then post event handler can be created and dropped in
insert method of CustTable.
Let’s see how pre and post
event handler methods can be created and used.
1. Let’s take same example. I added 2 event
handler methods in Consumer class.
2. Drag and drop both
these event handlers in method sendEmailToCustomer
3. Set property “CalledWhen” to Pre for EventHandler1 and Post for
EventHandler2.
4. Now let’s run main method of Producer class again and see the results.
It should call EventHandler1 and then sendEmailToCustomer and then
EventHandler2.
5. Here is the result as
expected.
With use of events, it has opened so many doors and possibilities. Model architecture and events can be integrated which can help if multiple vendors are doing customizations in different models so that it doesn’t impact customizations of other models/vendors. Use of pre and post handlers is so powerful that it can be used without changing a single line of code in original method. Pre or Post handlers can be just dropped in the original method and will be called automatically before (pre handler method) or after (post handler method) original method.
Stay tuned for more on
events. I am still exploring the possibilities using events in AX 2012.
