Walkthrough: Publishing, Raising, and Subcribing to an Event in Microsoft Dynamics NAV

This walkthrough uses a simple example scenario to demonstrate how to program events in the application.

About This Walkthrough

The walkthrough illustrates the following tasks:

• Creating an event publisher function to publish an event.

• Adding code to application to raise the published event.

• Creating an event subscriber function to subscribe to a published event.

• Adding code to the event subscriber function to handle the raised event

Prerequisites

To complete this walkthrough, you will need:

• Microsoft Dynamics NAV 2018 with a developer license.

• CRONUS International Ltd. demonstration database.

Story

When users change the address of a customer, you want to check that the address does not include invalid characters, which in this walkthrough is a plus sign (+). To accomplish this, you will publish an event that is raised when the Address field on page 21 Customer Card is changed. To handle the event when it is raised, you will add an event subscriber function that includes logic that checks the address value and returns a message to the user if it contains a plus sign.

Note

Most of the tasks are performed from the Microsoft Dynamics NAV Development Environment.

Publishing the Event

To publish an event, you create a C/AL function that is set up to be an event publisher. An event publisher function can be added in any object, such as a codeunit, page, or table. This procedure will add the event publisher function to a new codeunit, in which you can potentially add more event publisher functions for other events later. Because you might want to change this event implementation in the future, you decide to create an integration event type. The event publisher requires a single text parameter for handling the address of the customer.

To create a new codeunit

1. Open the development environment, and then connect to the CRONUS International Ltd. company.

   For more information, see How to: Open Databases.

2. On the Tools menu, choose Object Designer, choose Codeunit, and then choose New.

   The C/AL Editor opens.

3. On the File menu, choose Save.

4. On the Save window, enter 50000 in the ID field and enter My Publishers in the Name field.

5. Make sure the Compiled check box is selected, and then choose the OK button.

   The codeunit for the event publisher is created. Keep the C/AL editor open for the next task. You can now add the event publisher function to publish the event.

To create the event publisher function to publisher the event

1. On the View menu, choose C/AL Globals.

2. In the C/AL Globals window, choose the Functions tab.

3. In a blank row, in the Name field, enter OnAddressLineChanged.

4. To open the properties for the OnAddressLineChanged function, select the function, and then in the View menu, choose Properties. Set the properties as follows:

   1. Set the Local property to No.

      Setting this property makes the function available to be called from the other objects. For more information about this property, see Local Property.

   2. Set the Event property to Publisher. This makes the function an event publisher.

      For more information, see Event Property.

   3. Set the EventType property to Integration.

      For more information, see EventType Property.

   4. Close the Properties window.

5. Add a local parameter to the function for the address of the customer as described in the following steps:

   1. On the Functions tab, select the OnAddressLineChanged function, and then choose the Locals button.

      The C/AL Locals window opens.

   2. On the Parameters tab, in the Name field, enter line.

   3. Set the DataType field to Text.

   4. Set the Length field to 100.

      Important

      An event publisher function cannot have a return value, variables, or text constants; otherwise you will not be able to compile the function.

   5. Close the C/AL Locals window.

6. Close the C/AL Globals window.

   The new function appears in the C/AL Editor with the following signature:

   [IntegrationEvent] OnAddressLineChanged(line : Text[100])

   You can now raise the event in the application.

Raising the Event

After you create the event publisher function to publish the event, you can add code to the application to raise the event where it is required. In this case, you want to raise the event when the Address field is changed on the page 21 Customer Card. Therefore, you will add code to the Address - OnValidate() trigger in C/AL code of the page. Raising an event basically involves calling the event publisher function that publishes the event.

To raise the event

1. In the development environment, open page 21 Customer Card as follows:

   1. On the Tools menu, choose Object Designer, and then choose Page.

   2. Select page 21 Customer Card, and then choose the Design button.

2. Add a C/AL variable that specifies the object that publishes the event. In this case, the event publisher object is codeunit 50000 My Publishers, which contains the event publisher function OnAddressLineChanged that you created in the previous procedure.

   1. On the View menu, choose C/AL Globals.

   2. On a blank row, in the Name field, enter Publisher.

   3. Set the DataType field to Codeunit.

   4. In the Subtype field, select codeunit 50000 My Publishers.

   5. Close the C/AL Globals window.

3. In C/AL code, add the following code on the Address - OnValidate() trigger to raise the event:

   Publisher.OnAddressLineChanged(Address);  
   

   This calls the event publisher function to raise the event.

4. On the File menu, choose Save to save and compile the changes to the page.

   The event can now be subscribed to and handled.

Subscribing to and Handling an Event

Once an event has been published you can add code to the application that subscribes to and handles the event when it is raised. For example, in this walkthrough, when a user changes the address of a customer (the event), you want code that checks that the value does not contain a plus sign. Subscribing to and handling an event is accomplished by creating a C/AL function that is set up as an event subscriber and subscribes to a specific event (defined by an event publisher function). The event subscription function contains the application logic for handling the raised event. For this walkthrough, you will create an event subscriber function that subscribes to the OnAddressLineChanged function in codeunit 50000 My Publishers.

Unlike an event publisher function, an event subscriber function can only reside in a codeunit object. This procedure will add the event subscriber function to a new codeunit, in which you can potentially add more event subscriber functions for other events later.

To create a new codeunit

• In the development environment, create a new codeunit that has the ID 50001 and the name My Subscribers.

  For more information, see To create a new codeunit.

To create the event subscriber function to subscribe to and handle the event

1. On the View menu, choose C/AL Globals.

2. In the C/AL Globals window, choose the Functions tab.

3. In a blank row, in the Name field, enter CheckAddressLine.

4. To open the properties for the CheckAddressLine function, select the function, and then in the View menu, choose Properties. Set the properties as follows:

   1. Set the Event property to Subscriber to make the function an event subscriber.

   2. Set the EventPublisherObject property to Codeunit My Publishers.

      This is the codeunit that contains the event publisher function (OnAddressLineChanged) that you want to subscribe to.

   3. In the EventFunction property, select the OnAddressLineChanged integration event.

      This field reads all the published events in the event publisher object.

      Note

      When you get a message that asks whether you want to overwrite the edited function's signature, choose Yes to continue.

   4. Close the Properties window to return to the C/AL Globals window.

5. A local parameter that has the name line and the data type Text has been automatically added to the new CheckAddressLine function. To verify this, select the function in C/AL Globals window, choose the Locals button, and then see the Parameters tab.

   Close the C/AL Locals window when done.

6. Close the C/AL Globals window.

   The new function appears in the C/AL Editor with the following signature:

   [EventSubscriber] CheckAddressLine(line : Text[100])

   You can now add code to handle the event.

7. To handle the event, add the following code to the CheckAddressLine function in the C/AL editor:

   IF (STRPOS(line, '+') > 0) THEN BEGIN  
    MESSAGE('Cannot use a plus sign (+) in the address [' + line + ']');  
   END  
   

   This code checks the value of the Address field on page 21 Customer Card when is has been changed and returns a message if the value contains a plus sign.

Viewing the New Event Subscription

After you create an event subscriber, you can view information about it in page 9510 Event Subscriptions. This page provides information about all the current event subscriptions in the application. You can open this page directly from the development environment or from a Dynamics NAV client.

To view the event subscription from the development environment

• On the Tools menu, choose Debugger, and then choose Event Subscriptions.

To view the event subscription from a Dynamics NAV client

1. Start the Dynamics NAV client.

2. In the Search box, enter Sessions, and then choose the related link.

3. On the Home tab, in the Events group, choose Subscriptions.

Testing the Event

To test the event implementation, you can run page 21 Customer Card from the development environment.

To test the event

1. In Object Designer, choose Page.

2. Select page 21 Customer Card, and then choose the Run button.

   A customer card opens in the Microsoft Dynamics NAV Windows client.

3. On the Home tab, in the Manage group, choose Edit.

4. In the Address field, add a plus sign, and then choose the OK button.

   The following message appears:

   Cannot use a plus sign (+) in the address [].

   [] contains the value of the Address field.

See Also

Events in Microsoft Dynamics NAV
Introducing Events
Publishing Events
Raising Events
Subscribing to Events
Debugging Events