Handling Events with Microsoft .NET Framework Interoperability
With Microsoft .NET Framework interoperability, a DotNet type variable of a Dynamics NAV object can subscribe to events that are published by a .NET Framework class. In .NET Framework, an event enables an object to notify other objects when something occurs. Typical events in a graphical user interface might be the click of a button or the change of a field. The object that raises the event is the publisher and the object that handles the event is called the subscriber.
This topic discusses the following subjects:
Understanding How Events Work in .NET Interoperability
You set up a DotNet variable to subscribe to events by setting the variable’s WithEvents Property to true. The DotNet variable is exposed to all events that are published by the .NET Framework type that the variable references. For each event, Dynamics NAV automatically adds a blank trigger in the C/AL code of the Dynamics NAV object. You add C/AL code to the trigger to handle the event. When an instance of the .NET Framework type raises the event, the corresponding trigger in C/AL code is invoked and its code is run.
For more information, see How to: Subscribe to Events in a .NET Framework Type.
Client-side and Server-side Events
You can configure a DotNet type variable to instantiate the .NET Framework type to target the Microsoft Dynamics NAV Windows client or the Microsoft Dynamics NAV Server. As a result, events that are published by the .NET Framework type will also target either the Microsoft Dynamics NAV Windows client (client-side) or the Microsoft Dynamics NAV Server (server-side).
Client-Side Events
Client-side events are supported on pages only. A page can subscribe to events from the following sources:
DotNet variable that is defined as a global variable.
Events published by a control add-in. For more information about events in control add-ins, see Exposing Events and Calling Respective C/AL Triggers from a Windows Client Control Add-in.
Understanding Synchronous and Asynchronous Events
Events published by .NET Framework objects can be classified as synchronous or asynchronous. Synchronous events are raised immediately when something occurs in the running application code. Asynchronous events are raised after something occurs. An asynchronous event can be a timer event, which is implemented by the System.Timers.Timer class, or an event that is raised by a network listener or other external source, which is handled by an event sink.
Considerations for Asynchronous Events
Timer events and event sinks are only active as long as the Dynamics NAV object that implements the DotNet variable is running. By using an asynchronous event, it is possible that Dynamics NAV object closes before the event trigger is run. To avoid this condition, you can declare the DotNet variable in a single instance codeunit. Single instance codeunits remain instantiated until you close the Microsoft Dynamics NAV Windows client or close the company database. For more information about single instance codeunits, see Using Codeunits.
When asynchronous events are raised, they are added to the event queue of the .NET Framework, and processed when the connection between the Microsoft Dynamics NAV Windows client and the Microsoft Dynamics NAV Server is idle. A connection is idle when no Dynamics NAV objects are communicating over the connection. If there is a long process that is running over the connection, then you might experience a delay when you run event triggers.
Updating Event Triggers
Event triggers in C/AL code do not update automatically when events are changed or added to the .NET Framework assembly that is used by a DotNet variable. If you want to update event triggers in the Dynamics NAV object to changes in the .NET Framework assembly, then you must delete existing triggers and subscribe to the events again.
Limitations on Events and Event Triggers
Event triggers that are published by .NET Framework types have the following limitations:
Events are only supported on global variables.
Events must adhere to the delegation event model of the .NET Framework. For more information about this model, see Events and Delegates.
Reference parameters in client-side events are not supported.
Events cannot have parameters that are enumeration types.
Return values on event triggers are not supported.
See Also
How to: Subscribe to Events in a .NET Framework Type
Calling .NET Framework Members from C/AL