difference between a command and an event in Composite Application Block

Question

I'm using the Composite Application Block in my app. There are 2 concepts, EventHandlers and CommandHandlers which seem very similar to me... both allow you to invoke functionality in one part of the UI from another. What is the difference between them?

Answer 1

I believe it is a matter of convenience. We use commands for buttons on a ribbon:

Public Sub AddElementToRibbonGroup(WorkItem As WorkItem, elementDescription As String, menuGroupKey As String, commandName As String, commandKey As String)
    WorkItemController.ShellExtensionService.AddButtonToolExtension( _
         WorkItem, _
         commandKey, _
         New ButtonToolAppearance(elementDescription), _
         menuGroupKey, _
         WorkItem.Commands(commandName))
End Sub

But we raise events from a form to handle logic in a controller:

sample_View.vb:

    <EventBroker.EventPublication(Constants.Events.CreateNewNavTab, PublicationScope.Global)> _
    Public Event CreateNewNavTab As EventHandler

    ' Node in Navigation Tree is double clicked
    Private Sub NavTree_DoubleClick(sender As System.Object, e As System.EventArgs) Handles NavTree.DoubleClick
...
        RaiseEvent CreateNewNavTab(Me, Nothing)

    End Sub

sample_controller.vb:

' A new tab is created from the Nav Tree.
<EventSubscription(Constants.Events.CreateNewNavTab, ThreadOption.UserInterface)> _
Public Sub CreateNewNavTab(ByVal pNavView As Object, ByVal e As EventArgs)

... 

End Sub

Hope this helps!