Add an Actions node under the Activity node, such as:

<Actions>

<Actiontype="Event"

fire="Before" expression="Slickflow.Module.ExternalService.OrderSubmitService"/>

</Actions>

       Action node attribute description:

       type : divided into Event, WebApi, Script and other execution code snippet types;

       fire : trigger location type, divided into two types: before node execution (before) and after node execution (after);

       expression : The code fragment of the program or component to be executed.