Register-ObjectEvent

Applies To: Windows PowerShell 2.0

Subscribes to the events that are generated by a Microsoft .NET Framework object.

Syntax

Register-ObjectEvent [-InputObject] <psobject> [-EventName] <string> [[-SourceIdentifier] <string>] [[-Action] <scriptblock>] [-Forward] [-MessageData <psobject>] [-SupportEvent] [<CommonParameters>]

Description

The Register-ObjectEvent cmdlet subscribes to events that are generated by .NET Framework objects on the local computer or on a remote computer.

When the subscribed event is raised, it is added to the event queue in your session. To get events in the event queue, use the Get-Event cmdlet.

You can use the parameters of Register-ObjectEvent to specify property values of the events that can help you to identify the event in the queue. You can also use the Action parameter to specify actions to take when a subscribed event is raised and the Forward parameter to send remote events to the event queue in the local session.

When you subscribe to an event, an event subcriber is added to your session. To get the event subscribers in the session, use the Get-EventSubscriber cmdlet. To cancel the subscription, use the Unregister-Event cmdlet, which deletes the event subscriber from the session.

Parameters

-Action <scriptblock>

Specifies commands to handle the events. The commands in the Action run when an event is raised, instead of sending the event to the event queue. Enclose the commands in braces ( { } ) to create a script block.

The value of the Action parameter can include the $Event, $EventSubscriber, $Sender, $SourceEventArgs, and $SourceArgs automatic variables, which provide information about the event to the Action script block. For more information, see about_Automatic_Variables.

When you specify an action, Register-ObjectEvent returns an event job object that represents that action. You can use the Job cmdlets to manage the event job.

Required?	false
Position?	102
Default Value	None.
Accept Pipeline Input?	false
Accept Wildcard Characters?	false

-EventName <string>

Specifies the event to which you are subscribing. Enter the event name. This parameter is required.

The value of this parameter is not a name that you select for the event subscription. It is the name of an event that the .NET Framework object exposes. For example, the ManagementEventWatcher class has events named "EventArrived" and "Stopped." To find the event name of an event, use the Get-Member cmdlet.

Required?	true
Position?	2
Default Value	None
Accept Pipeline Input?	false
Accept Wildcard Characters?	false

-Forward

Sends events for this subscription to a remote session. Use this parameter when you are registering for events on a remote computer or in a remote session.

Required?	false
Position?	named
Default Value	False
Accept Pipeline Input?	false
Accept Wildcard Characters?	false

-InputObject <psobject>

Specifies the .NET Framework object that generates the events. Enter a variable that contains the object, or type a command or expression that gets the object. This parameter is required.

Required?	true
Position?	1
Default Value	None
Accept Pipeline Input?	false
Accept Wildcard Characters?	false

-MessageData <psobject>

Specifies any additional data to be associated with this event subscription. The value of this parameter appears in the MessageData property of all events associated with this subscription.

Required?	false
Position?	named
Default Value	None
Accept Pipeline Input?	false
Accept Wildcard Characters?	false

-SourceIdentifier <string>

Specifies a name that you select for the subscription. The name that you select must be unique in the current session. The default value is the GUID that Windows PowerShell assigns.

The value of this parameter appears in the value of the SourceIdentifier property of the subcriber object and of all event objects associated with this subscription.

Required?	false
Position?	101
Default Value	GUID
Accept Pipeline Input?	false
Accept Wildcard Characters?	false

-SupportEvent

Hides the event subscription. Use this parameter when the current subscription is part of a more complex event registration mechanism and it should not be discovered independently.

To view or cancel a subscription that was created with the SupportEvent parameter, use the Force parameter of the Get-EventSubscriber and Unregister-Event cmdlets.

Required?	false
Position?	named
Default Value	False
Accept Pipeline Input?	false
Accept Wildcard Characters?	false

<CommonParameters>

This command supports the common parameters: Verbose, Debug, ErrorAction, ErrorVariable, OutBuffer, OutVariable, WarningAction, and WarningVariable. For more information, see about_CommonParameters.

Inputs and Outputs

The input type is the type of the objects that you can pipe to the cmdlet. The return type is the type of the objects that the cmdlet returns.

Inputs	None You cannot pipe objects to Register-ObjectEvent.
Outputs	None This cmdlet does not generate any output.

Notes

Events, event subscriptions, and the event queue exist only in the current session. If you close the current session, the event queue is discarded and the event subscription is canceled.

Example 1

C:\PS>$query = New-Object System.Management.WqlEventQuery "__InstanceCreationEvent", (New-Object TimeSpan 0,0,1), "TargetInstance isa 'Win32_Process'" 

C:\PS> $processWatcher = New-Object System.Management.ManagementEventWatcher $query 

C:\PS> register-objectEvent -inputObject $processWatcher -eventName "EventArrived"

Description

-----------

This example subscribes to events generated when a new process starts.

The command uses the ManagementEventWatcher object to get EventArrived events. A query object specifies that the events are instance creation events for the Win32_Process class.

Example 2

C:\PS>$query = New-Object System.Management.WqlEventQuery "__InstanceCreationEvent", (New-Object TimeSpan 0,0,1), "TargetInstance isa 'Win32_Process'" 

C:\PS> $processWatcher = New-Object System.Management.ManagementEventWatcher $query 

C:\PS> $action = { New-Event "PowerShell.ProcessCreated" -Sender $sender -EventArguments $SourceEventArgs.NewEvent.TargetInstance } 

C:\PS> register-objectEvent -inputObject $processWatcher -eventName "EventArrived" -action $action

Id    Name            State      HasMoreData     Location             Command
--    ----            -----      -----------     --------             -------
2     422cfe5a-65e... Running    True                                 New-Event "PowerShe...

Description

-----------

This example shows how to specify an action to respond to an event. When you specify an action, events that are raised are not added to the event queue. Instead, the action responds to the event.

In this example, when an instance creation event is raised indicating that a new process is started, a new ProcessCreated event is raised.

The action uses the $Sender and $SourceEventArgs automatic variables which are populated only for event actions.

The Register-ObjectEvent command returns a job object that represents the action, which runs as a background job. You can use the Job cmdlets, such as Get-Job and Receive-Job, to manage the background job.

For more information, see about_Jobs.

Example 3

C:\PS>$s = new-pssession -computername Server01, Server02

C:\PS> invoke-command -session $s -filepath ProcessCreationEvent.ps1

C:\PS> invoke-command -session $s { get-event }

# ProcessCreationEvent.ps1

function Enable-ProcessCreationEvent 
{ 
   $query = New-Object System.Management.WqlEventQuery "__InstanceCreationEvent", ` 
       (New-Object TimeSpan 0,0,1), ` 
       "TargetInstance isa 'Win32_Process'" 
   $processWatcher = New-Object System.Management.ManagementEventWatcher $query 

   $identifier = "WMI.ProcessCreated" 
   Register-ObjectEvent -input $processWatcher -eventName "EventArrived" `
      -sourceIdentifier $identifier -messageData "Test" -forward 
   } 
} 

EnableProcessCreationEvent

Description

-----------

This example shows how to subscribe to object events on remote computers.

The first command creates PSSessions on two remote computers and saves them in the $s variable.

The second command uses the FilePath parameter of the Invoke-Command cmdlet to run the ProcessCreationEvent.ps1 script in the each of the PSSessions in $s.

The script includes a Register-ObjectEvent command that subscribes to instance creation events on the Win32_Process object through the ManagementEventWatcher object and its EventArrived event.

Example 4

C:\PS>$timer  = New-Object Timers.Timer

C:\PS> $timer.Interval = 500

C:\PS> $job = Register-ObjectEvent -inputObject $timer -eventName Elapsed -sourceIdentifier Timer.Random -Action {$random = Get-Random -Min 0 -Max 100}

C:\PS> $job.gettype().fullname
System.Management.Automation.PSEventJob

C:\PS> $job | format-list -property *

State         : Running
Module        : __DynamicModule_6b5cbe82-d634-41d1-ae5e-ad7fe8d57fe0
StatusMessage :
HasMoreData   : True
Location      :
Command       : $random = Get-Random -Min 0 -Max 100
JobStateInfo  : Running
Finished      : System.Threading.ManualResetEvent
InstanceId    : 88944290-133d-4b44-8752-f901bd8012e2
Id            : 1
Name          : Timer.Random
ChildJobs     : {}
...

C:\PS> $timer.Enabled = $true

C:\PS> & $job.module {$random}
60

C:\PS> & $job.module {$random}
47

Description

-----------

This example shows how to use the dynamic module in the PSEventJob object that is created when you include an Action in a event registration.

The first command uses the New-Object cmdlet to create a timer object. The second command sets the interval of the timer to 500 (milliseconds).

The third command uses the Register-ObjectEvent cmdlet to register the Elapsed event of the timer object. The command includes an action that handles the event. Whenever the timer interval elapses, an event is raised and the commands in the action run. In this case, the Get-Random cmdlet generates a random number between 0 and 100 and saves it in the $random variable.

When you use an Action parameter in a Register-ObjectEvent command, the command returns a PSEventJob object that represents the action. The command saves the job object in the $job variable.

The PSEventJob object that the Register-ObjectEvent cmdlet returns is also available in the Action property of the event subscriber. For more information, see Get-EventSubscriber.

The fourth command shows that the $job variable contains a PSEventJob object. The fifth command uses the Format-List cmdlet to display all of the properties of the PSEventJob object in a list.

The PSEventJob has a Module property that contains a dynamic script module that implements the action.

The sixth command enables the timer.

The remaining commands use the call operator (&) to invoke the command in the module and display the value of the $random variable. You can use the call operator to invoke any command in a module, including commands that are not exported. In this case, the commands show the random number that is being generated when the Elapsed event occurs.

For more information about modules, see about_Modules.

See Also

Concepts

Register-EngineEvent
Register-WmiEvent
Unregister-Event
Get-Event
New-Event
Remove-Event
Wait-Event