Creating your own event handler for the TFS Event Handler Service

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Introduction

Creating an event handler with the Team Foundation Server Event Handlers is very easy. You will need to inherit from the AEventHandler class which is part of the RDdotNet.TeamFoundation.dll located in the install directory (I will make an SDK later).

The code

Imports Microsoft.TeamFoundation.Client

Public MustInherit Class AEventHandler(Of TEvent)

 Public MustOverride Sub Run(ByVal EventHandlerItem As EventHandlerItem(Of TEvent), _ 
                             ByVal ServiceHost As ServiceHostItem, _
                             ByVal TeamServer As TeamServerItem, _
                             ByVal e As NotifyEventArgs(Of TEvent))

 Public MustOverride Function IsValid(ByVal EventHandlerItem As EventHandlerItem(Of TEvent), _
                                      ByVal ServiceHost As ServiceHostItem, _
                                      ByVal TeamServer As TeamServerItem, _
                                      ByVal e As NotifyEventArgs(Of TEvent)) As Boolean

End Class

Both of the methods that the AEventHandler exposes have the same signature. Hear is what it all means...

Let's look at the implementation that comes with the TFS Event Handler: the "AssignedToHandler". The IsValid method denotes whether the handler will actually run at all:

Public Overrides Function IsValid(_
       ByVal EventHandlerItem As EventHandlerItem(Of WorkItemChangedEvent), _
       ByVal ServiceHost As ServiceHostItem, _
       ByVal TeamServer As TeamServerItem, _
       ByVal e As NotifyEventArgs(Of WorkItemChangedEvent)) As Boolean
    If e.Event Is Nothing Then
        Return False
    End If
    Dim assignedName As String = WorkItemEventQuerys.GetAssignedToName(e.Event)
    If String.IsNullOrEmpty(assignedName) Then
        Return False
    Else
        Return Not assignedName = WorkItemEventQuerys.GetChangedByName(e.Event)
    End If
End Function

This method initially checks to see if the event exists, and then queries the assigned name from the event using a work item event query which consists of:

Return eventData.CoreFields.StringFields.Find(New _
       Predicate(Of StringField)(AddressOf FindAssignedTo)).NewValue

All this does is search the string fields associated with the core work item bits to find the "System.AssignedTo" value. You could do this manually, but I have a number of queries there and you can add any number you wish.

The logic: If event exists and the assigned name is not empty, then check that the assigned name is not the changed name.

So in English, with all of the crap split out: Did the user assign the work item to himself? If not, then send them an email!

The rest, as they say, is just logic. The "Run" method calls "IsValid" and then sends an email if it is in fact valid, hardly rocket science.

Hopefully, with this knowledge, you will be able to make many many event handlers!

Update

For the delayed CTP 1 of the TFS Event Handler, I have changed the logic quite a lot, but the same IsValid and Run methods exist. The parameters are, however, slightly different. I have taken into account security, and you will have to make your own connection to the TFS server using your own username and password. I have changed this to protect the security of the application as I want developers to be able to upload event handler assemblies and WF workflow without having to get access to the server. I have also changed it so the service that captures the events is not the same that runs the handlers. This allows me to send the events between these services using MSMQ, thus giving the service some much needed redundancy.