ManagementEventWatcher.Query Property
Definition
Important
Some information relates to prerelease product that may be substantially modified before it’s released. Microsoft makes no warranties, express or implied, with respect to the information provided here.
Gets or sets the criteria to apply to events.
public:
property System::Management::EventQuery ^ Query { System::Management::EventQuery ^ get(); void set(System::Management::EventQuery ^ value); };
public System.Management.EventQuery Query { get; set; }
member this.Query : System.Management.EventQuery with get, set
Public Property Query As EventQuery
Property Value
The query to apply to events.
Examples
The following example shows how the client receives notification when an instance of Win32_Process is created because the event class is __InstanceCreationEvent. For more information, see the Windows Management Instrumentation documentation. The client receives events synchronously by calling the WaitForNextEvent method. This example can be tested by starting a process, such as Notepad, while the example code is running.
using System;
using System.Management;
// This example shows synchronous consumption of events.
// The client is blocked while waiting for events.
public class EventWatcherPolling
{
public static int Main(string[] args)
{
// Create event query to be notified within 1 second of
// a change in a service
WqlEventQuery query =
new WqlEventQuery("__InstanceCreationEvent",
new TimeSpan(0,0,1),
"TargetInstance isa \"Win32_Process\"");
// Initialize an event watcher and subscribe to events
// that match this query
ManagementEventWatcher watcher =
new ManagementEventWatcher();
watcher.Query = query;
// times out watcher.WaitForNextEvent in 5 seconds
watcher.Options.Timeout = new TimeSpan(0,0,5);
// Block until the next event occurs
// Note: this can be done in a loop if waiting for
// more than one occurrence
Console.WriteLine(
"Open an application (notepad.exe) to trigger an event.");
ManagementBaseObject e = watcher.WaitForNextEvent();
//Display information from the event
Console.WriteLine(
"Process {0} has been created, path is: {1}",
((ManagementBaseObject)e
["TargetInstance"])["Name"],
((ManagementBaseObject)e
["TargetInstance"])["ExecutablePath"]);
//Cancel the subscription
watcher.Stop();
return 0;
}
}
Imports System.Management
' This example shows synchronous consumption of events.
' The client is blocked while waiting for events.
Public Class EventWatcherPolling
Public Overloads Shared Function _
Main(ByVal args() As String) As Integer
' Create event query to be notified within 1 second of
' a change in a service
Dim query As New WqlEventQuery( _
"__InstanceCreationEvent", _
New TimeSpan(0, 0, 1), _
"TargetInstance isa ""Win32_Process""")
' Initialize an event watcher and subscribe to events
' that match this query
Dim watcher As New ManagementEventWatcher
watcher.Query = query
' times watcher.WaitForNextEvent in 5 seconds
watcher.Options.Timeout = New TimeSpan(0, 0, 5)
' Block until the next event occurs
' Note: this can be done in a loop
' if waiting for more than one occurrence
Console.WriteLine( _
"Open an application (notepad.exe) to trigger an event.")
Dim e As ManagementBaseObject = _
watcher.WaitForNextEvent()
'Display information from the event
Console.WriteLine( _
"Process {0} has created, path is: {1}", _
CType(e("TargetInstance"), _
ManagementBaseObject)("Name"), _
CType(e("TargetInstance"), _
ManagementBaseObject)("ExecutablePath"))
'Cancel the subscription
watcher.Stop()
Return 0
End Function 'Main
End Class
Remarks
Property Value
The criteria to apply to the events, which is equal to the event query.
.NET Framework Security
Full trust for the immediate caller. This member cannot be used by partially trusted code. For more information, see Using Libraries from Partially Trusted Code.