SystemEvents.xml

<Type Name="SystemEvents" FullName="Microsoft.Win32.SystemEvents">
  <TypeSignature Language="C#" Value="public sealed class SystemEvents" />
  <TypeSignature Language="ILAsm" Value=".class public auto ansi sealed beforefieldinit SystemEvents extends System.Object" />
  <TypeSignature Language="DocId" Value="T:Microsoft.Win32.SystemEvents" />
  <AssemblyInfo>
    <AssemblyName>System</AssemblyName>
    <AssemblyVersion>4.0.0.0</AssemblyVersion>
  </AssemblyInfo>
  <Base>
    <BaseTypeName>System.Object</BaseTypeName>
  </Base>
  <Interfaces />
  <Docs>
    <summary>Provides access to system event notifications. This class cannot be inherited.</summary>
    <remarks>
      <format type="text/markdown"><![CDATA[  
  
## Remarks  
 The <xref:Microsoft.Win32.SystemEvents> class provides the ability to respond to specific types of system events.  
  
 When a system event is raised, any delegates attached to the event are called using the thread that monitors for system events. Therefore, you should make any calls from your event handlers thread-safe. If you need to call a system event that is not exposed as a member of this class, you can use the <xref:Microsoft.Win32.SystemEvents.InvokeOnEventsThread%2A> method.  
  
> [!CAUTION]
>  Do not perform time-consuming processing on the thread that raises a system event handler because it might prevent other applications from functioning.  
  
> [!NOTE]
>  Some system events might not be raised on [!INCLUDE[windowsver](~/includes/windowsver-md.md)]. Be sure to verify that your application works as expected on [!INCLUDE[windowsver](~/includes/windowsver-md.md)].  
  
   
  
## Examples  
 This section contains two examples. The first example shows how to use system events in an ordinary application, and the second example shows how to use system events in a Windows service.  
  
 **Example 1**  
  
 The following code example registers interest in some system events and then waits for any of those events to occur. The output shown occurs if the user changes the display resolution.  
  
 [!code-cpp[SystemEvents#1](~/samples/snippets/cpp/VS_Snippets_Winforms/SystemEvents/cpp/SystemEvents.cpp#1)]
 [!code-csharp[SystemEvents#1](~/samples/snippets/csharp/VS_Snippets_Winforms/SystemEvents/CS/SystemEvents.cs#1)]
 [!code-vb[SystemEvents#1](~/samples/snippets/visualbasic/VS_Snippets_Winforms/SystemEvents/VB/SystemEvents.vb#1)]  
  
 **Example 2**  
  
 The following code example demonstrates a very simple Windows service that handles the <xref:Microsoft.Win32.SystemEvents.TimeChanged> and <xref:Microsoft.Win32.SystemEvents.UserPreferenceChanged> events. The example includes a service named `SimpleService`, a form named `HiddenForm`, and an installer. The form provides the message loop that is required by system events.  
  
> [!NOTE]
>  Services do not have message loops, unless they are allowed to interact with the desktop. If the message loop is not provided by a hidden form, as in this example, the service must be run under the local system account, and manual intervention is required to enable interaction with the desktop. That is, the administrator must manually check the **Allow service to interact with desktop** check box on the **Log On** tab of the service properties dialog box. In that case, a message loop is automatically provided. This option is available only when the service is run under the local system account. Interaction with the desktop cannot be enabled programmatically.  
  
 The service in this example starts a thread that runs an instance of `HiddenForm`. The events are hooked up and handled in the form. The events must be hooked up in the load event of the form, to make sure that the form is completely loaded first; otherwise the events will not be raised.  
  
> [!NOTE]
>  The example provides all the necessary code, including the form initialization code typically generated by [!INCLUDE[vsprvs](~/includes/vsprvs-md.md)] designers. If you are developing your service in [!INCLUDE[vsprvs](~/includes/vsprvs-md.md)], you can omit the second partial class and use the **Properties** window to set the height and width of the hidden form to zero, the border style to <xref:System.Windows.Forms.FormBorderStyle?displayProperty=fullName>, and the window state to <xref:System.Windows.Forms.FormWindowState?displayProperty=fullName>.  
  
 To run the example:  
  
1.  Compile the code from the command line. The name that you use for the source file is not important.  
  
2.  Install the service from the command line using the [Installutil.exe (Installer Tool)](~/docs/framework/tools/installutil-exe-installer-tool.md) utility. For example, `InstallUtil example.exe` if the source file name is `example.cs` or `example.vb`. You must be an administrator to install the service.  
  
3.  Use the Services console to start the service.  
  
4.  Change the system time, or change user preferences, such as mouse properties.  
  
5.  View the messages in the **Application** category of Event Viewer.  
  
6.  Use the Services console to stop the service.  
  
7.  Uninstall the service from the command line by using the `/u` option. For example, `InstallUtil /u example.exe`.  
  
 [!code-csharp[ManagedWindowsService#1](~/samples/snippets/csharp/VS_Snippets_CLR/ManagedWindowsService/cs/source.cs#1)]
 [!code-vb[ManagedWindowsService#1](~/samples/snippets/visualbasic/VS_Snippets_CLR/ManagedWindowsService/VB/source.vb#1)]  
  
 ]]></format>
    </remarks>
    <permission cref="T:System.Security.NamedPermissionSet">for full access to system resources. Demand values: <see cref="F:System.Security.Permissions.SecurityAction.LinkDemand" />. Associated state:</permission>
  </Docs>
  <Members>
    <Member MemberName="CreateTimer">
      <MemberSignature Language="C#" Value="public static IntPtr CreateTimer (int interval);" />
      <MemberSignature Language="ILAsm" Value=".method public static hidebysig native int CreateTimer(int32 interval) cil managed" />
      <MemberSignature Language="DocId" Value="M:Microsoft.Win32.SystemEvents.CreateTimer(System.Int32)" />
      <MemberType>Method</MemberType>
      <AssemblyInfo>
        <AssemblyName>System</AssemblyName>
        <AssemblyVersion>4.0.0.0</AssemblyVersion>
      </AssemblyInfo>
      <ReturnValue>
        <ReturnType>System.IntPtr</ReturnType>
      </ReturnValue>
      <Parameters>
        <Parameter Name="interval" Type="System.Int32" />
      </Parameters>
      <Docs>
        <param name="interval">Specifies the interval between timer notifications, in milliseconds.</param>
        <summary>Creates a new window timer associated with the system events window.</summary>
        <returns>The ID of the new timer.</returns>
        <remarks>To be added.</remarks>
        <exception cref="T:System.ArgumentException">The interval is less than or equal to zero.</exception>
        <exception cref="T:System.InvalidOperationException">System event notifications are not supported under the current context. Server processes, for example, might not support global system event notifications.</exception>
        <exception cref="T:System.Runtime.InteropServices.ExternalException">The attempt to create a system events window thread did not succeed, or the attempt to create the timer did not succeed.</exception>
      </Docs>
    </Member>
    <Member MemberName="DisplaySettingsChanged">
      <MemberSignature Language="C#" Value="public static event EventHandler DisplaySettingsChanged;" />
      <MemberSignature Language="ILAsm" Value=".event class System.EventHandler DisplaySettingsChanged" />
      <MemberSignature Language="DocId" Value="E:Microsoft.Win32.SystemEvents.DisplaySettingsChanged" />
      <MemberType>Event</MemberType>
      <AssemblyInfo>
        <AssemblyName>System</AssemblyName>
        <AssemblyVersion>4.0.0.0</AssemblyVersion>
      </AssemblyInfo>
      <Attributes>
        <Attribute>
          <AttributeName>System.MonoTODO</AttributeName>
        </Attribute>
      </Attributes>
      <ReturnValue>
        <ReturnType>System.EventHandler</ReturnType>
      </ReturnValue>
      <Docs>
        <summary>Occurs when the user changes the display settings.</summary>
        <remarks>
          <format type="text/markdown"><![CDATA[  
  
## Remarks  
  
> [!CAUTION]
>  Because this is a static event, you must detach your event handlers when your application is disposed, or memory leaks will result.  
  
   
  
## Examples  
 The following code example demonstrates how to monitor the <xref:Microsoft.Win32.SystemEvents.DisplaySettingsChanged> event. This code example is part of a larger example provided for the <xref:Microsoft.Win32.SystemEvents> class.  
  
 [!code-cpp[SystemEvents#2](~/samples/snippets/cpp/VS_Snippets_Winforms/SystemEvents/cpp/SystemEvents.cpp#2)]
 [!code-csharp[SystemEvents#2](~/samples/snippets/csharp/VS_Snippets_Winforms/SystemEvents/CS/SystemEvents.cs#2)]
 [!code-vb[SystemEvents#2](~/samples/snippets/visualbasic/VS_Snippets_Winforms/SystemEvents/VB/SystemEvents.vb#2)]  
  
 ]]></format>
        </remarks>
        <exception cref="T:System.InvalidOperationException">System event notifications are not supported under the current context. Server processes, for example, might not support global system event notifications.</exception>
        <exception cref="T:System.Runtime.InteropServices.ExternalException">The attempt to create a system events window thread did not succeed.</exception>
      </Docs>
    </Member>
    <Member MemberName="DisplaySettingsChanging">
      <MemberSignature Language="C#" Value="public static event EventHandler DisplaySettingsChanging;" />
      <MemberSignature Language="ILAsm" Value=".event class System.EventHandler DisplaySettingsChanging" />
      <MemberSignature Language="DocId" Value="E:Microsoft.Win32.SystemEvents.DisplaySettingsChanging" />
      <MemberType>Event</MemberType>
      <AssemblyInfo>
        <AssemblyName>System</AssemblyName>
        <AssemblyVersion>4.0.0.0</AssemblyVersion>
      </AssemblyInfo>
      <Attributes>
        <Attribute>
          <AttributeName>System.MonoTODO("Currently does nothing on Mono")</AttributeName>
        </Attribute>
      </Attributes>
      <ReturnValue>
        <ReturnType>System.EventHandler</ReturnType>
      </ReturnValue>
      <Docs>
        <summary>Occurs when the display settings are changing.</summary>
        <remarks>
          <format type="text/markdown"><![CDATA[  
  
## Remarks  
  
> [!CAUTION]
>  Because this is a static event, you must detach your event handlers when your application is disposed, or memory leaks will result.  
  
 ]]></format>
        </remarks>
        <exception cref="T:System.InvalidOperationException">System event notifications are not supported under the current context. Server processes, for example, might not support global system event notifications.</exception>
        <exception cref="T:System.Runtime.InteropServices.ExternalException">The attempt to create a system events window thread did not succeed.</exception>
      </Docs>
    </Member>
    <Member MemberName="EventsThreadShutdown">
      <MemberSignature Language="C#" Value="public static event EventHandler EventsThreadShutdown;" />
      <MemberSignature Language="ILAsm" Value=".event class System.EventHandler EventsThreadShutdown" />
      <MemberSignature Language="DocId" Value="E:Microsoft.Win32.SystemEvents.EventsThreadShutdown" />
      <MemberType>Event</MemberType>
      <AssemblyInfo>
        <AssemblyName>System</AssemblyName>
        <AssemblyVersion>4.0.0.0</AssemblyVersion>
      </AssemblyInfo>
      <Attributes>
        <Attribute>
          <AttributeName>System.MonoTODO("Currently does nothing on Mono")</AttributeName>
        </Attribute>
      </Attributes>
      <ReturnValue>
        <ReturnType>System.EventHandler</ReturnType>
      </ReturnValue>
      <Docs>
        <summary>Occurs before the thread that listens for system events is terminated.</summary>
        <remarks>
          <format type="text/markdown"><![CDATA[  
  
## Remarks  
 This event is raised as the thread that listens for system events is about to be terminated. System event delegates are invoked using the thread that listens for system events.  
  
> [!CAUTION]
>  Because this is a static event, you must detach your event handlers when your application is disposed, or memory leaks will result.  
  
 ]]></format>
        </remarks>
        <exception cref="T:System.InvalidOperationException">System event notifications are not supported under the current context. Server processes, for example, might not support global system event notifications.</exception>
        <exception cref="T:System.Runtime.InteropServices.ExternalException">The attempt to create a system events window thread did not succeed.</exception>
      </Docs>
    </Member>
    <Member MemberName="InstalledFontsChanged">
      <MemberSignature Language="C#" Value="public static event EventHandler InstalledFontsChanged;" />
      <MemberSignature Language="ILAsm" Value=".event class System.EventHandler InstalledFontsChanged" />
      <MemberSignature Language="DocId" Value="E:Microsoft.Win32.SystemEvents.InstalledFontsChanged" />
      <MemberType>Event</MemberType>
      <AssemblyInfo>
        <AssemblyName>System</AssemblyName>
        <AssemblyVersion>4.0.0.0</AssemblyVersion>
      </AssemblyInfo>
      <Attributes>
        <Attribute>
          <AttributeName>System.MonoTODO("Currently does nothing on Mono")</AttributeName>
        </Attribute>
      </Attributes>
      <ReturnValue>
        <ReturnType>System.EventHandler</ReturnType>
      </ReturnValue>
      <Docs>
        <summary>Occurs when the user adds fonts to or removes fonts from the system.</summary>
        <remarks>
          <format type="text/markdown"><![CDATA[  
  
## Remarks  
  
> [!CAUTION]
>  Because this is a static event, you must detach your event handlers when your application is disposed, or memory leaks will result.  
  
 ]]></format>
        </remarks>
        <exception cref="T:System.InvalidOperationException">System event notifications are not supported under the current context. Server processes, for example, might not support global system event notifications.</exception>
        <exception cref="T:System.Runtime.InteropServices.ExternalException">The attempt to create a system events window thread did not succeed.</exception>
      </Docs>
    </Member>
    <Member MemberName="InvokeOnEventsThread">
      <MemberSignature Language="C#" Value="public static void InvokeOnEventsThread (Delegate method);" />
      <MemberSignature Language="ILAsm" Value=".method public static hidebysig void InvokeOnEventsThread(class System.Delegate method) cil managed" />
      <MemberSignature Language="DocId" Value="M:Microsoft.Win32.SystemEvents.InvokeOnEventsThread(System.Delegate)" />
      <MemberType>Method</MemberType>
      <AssemblyInfo>
        <AssemblyName>System</AssemblyName>
        <AssemblyVersion>4.0.0.0</AssemblyVersion>
      </AssemblyInfo>
      <Attributes>
        <Attribute>
          <AttributeName>System.MonoTODO</AttributeName>
        </Attribute>
      </Attributes>
      <ReturnValue>
        <ReturnType>System.Void</ReturnType>
      </ReturnValue>
      <Parameters>
        <Parameter Name="method" Type="System.Delegate" />
      </Parameters>
      <Docs>
        <param name="method">A delegate to invoke using the thread that listens for system events.</param>
        <summary>Invokes the specified delegate using the thread that listens for system events.</summary>
        <remarks>
          <format type="text/markdown"><![CDATA[  
  
## Remarks  
 You can use this method any time that you need to handle a system event that is not exposed otherwise by the <xref:Microsoft.Win32.SystemEvents> class.  
  
 When you call this method, the specified delegate will be invoked by the thread that your application is using to process system events.  
  
 ]]></format>
        </remarks>
        <exception cref="T:System.InvalidOperationException">System event notifications are not supported under the current context. Server processes, for example, might not support global system event notifications.</exception>
        <exception cref="T:System.Runtime.InteropServices.ExternalException">The attempt to create a system events window thread did not succeed.</exception>
      </Docs>
    </Member>
    <Member MemberName="KillTimer">
      <MemberSignature Language="C#" Value="public static void KillTimer (IntPtr timerId);" />
      <MemberSignature Language="ILAsm" Value=".method public static hidebysig void KillTimer(native int timerId) cil managed" />
      <MemberSignature Language="DocId" Value="M:Microsoft.Win32.SystemEvents.KillTimer(System.IntPtr)" />
      <MemberType>Method</MemberType>
      <AssemblyInfo>
        <AssemblyName>System</AssemblyName>
        <AssemblyVersion>4.0.0.0</AssemblyVersion>
      </AssemblyInfo>
      <ReturnValue>
        <ReturnType>System.Void</ReturnType>
      </ReturnValue>
      <Parameters>
        <Parameter Name="timerId" Type="System.IntPtr" />
      </Parameters>
      <Docs>
        <param name="timerId">The ID of the timer to terminate.</param>
        <summary>Terminates the timer specified by the given id.</summary>
        <remarks>To be added.</remarks>
        <exception cref="T:System.InvalidOperationException">System event notifications are not supported under the current context. Server processes, for example, might not support global system event notifications.</exception>
        <exception cref="T:System.Runtime.InteropServices.ExternalException">The attempt to create a system events window thread did not succeed, or the attempt to terminate the timer did not succeed.</exception>
      </Docs>
    </Member>
    <Member MemberName="LowMemory">
      <MemberSignature Language="C#" Value="public static event EventHandler LowMemory;" />
      <MemberSignature Language="ILAsm" Value=".event class System.EventHandler LowMemory" />
      <MemberSignature Language="DocId" Value="E:Microsoft.Win32.SystemEvents.LowMemory" />
      <MemberType>Event</MemberType>
      <AssemblyInfo>
        <AssemblyName>System</AssemblyName>
        <AssemblyVersion>4.0.0.0</AssemblyVersion>
      </AssemblyInfo>
      <Attributes>
        <Attribute>
          <AttributeName>System.ComponentModel.Browsable(false)</AttributeName>
        </Attribute>
        <Attribute>
          <AttributeName>System.ComponentModel.EditorBrowsable(System.ComponentModel.EditorBrowsableState.Never)</AttributeName>
        </Attribute>
        <Attribute>
          <AttributeName>System.MonoTODO("Currently does nothing on Mono")</AttributeName>
        </Attribute>
        <Attribute>
          <AttributeName>System.Obsolete("")</AttributeName>
        </Attribute>
      </Attributes>
      <ReturnValue>
        <ReturnType>System.EventHandler</ReturnType>
      </ReturnValue>
      <Docs>
        <summary>Occurs when the system is running out of available RAM.</summary>
        <remarks>
          <format type="text/markdown"><![CDATA[  
  
## Remarks  
 This event wraps the WM_COMPACTING message. This message is sent to all top-level windows when the system detects more than 12.5 percent of system time over a 30- to 60-second interval is being spent compacting memory. This indicates that system memory is low.  
  
> [!NOTE]
>  This event is only raised if the message pump is running. In a Windows service, unless a hidden form is used or the message pump has been started manually, this event will not be raised. For a code example that shows how to handle system events by using a hidden form in a Windows service, see the <xref:Microsoft.Win32.SystemEvents> class.  
  
> [!CAUTION]
>  Because this is a static event, you must detach your event handlers when your application is disposed, or memory leaks will result.  
  
 ]]></format>
        </remarks>
        <exception cref="T:System.InvalidOperationException">System event notifications are not supported under the current context. Server processes, for example, might not support global system event notifications.</exception>
        <exception cref="T:System.Runtime.InteropServices.ExternalException">The attempt to create a system events window thread did not succeed.</exception>
        <block subset="none" type="usage">
          <para>This message is provided only for compatibility with 16-bit Windows-based applications.</para>
        </block>
      </Docs>
    </Member>
    <Member MemberName="PaletteChanged">
      <MemberSignature Language="C#" Value="public static event EventHandler PaletteChanged;" />
      <MemberSignature Language="ILAsm" Value=".event class System.EventHandler PaletteChanged" />
      <MemberSignature Language="DocId" Value="E:Microsoft.Win32.SystemEvents.PaletteChanged" />
      <MemberType>Event</MemberType>
      <AssemblyInfo>
        <AssemblyName>System</AssemblyName>
        <AssemblyVersion>4.0.0.0</AssemblyVersion>
      </AssemblyInfo>
      <Attributes>
        <Attribute>
          <AttributeName>System.MonoTODO("Currently does nothing on Mono")</AttributeName>
        </Attribute>
      </Attributes>
      <ReturnValue>
        <ReturnType>System.EventHandler</ReturnType>
      </ReturnValue>
      <Docs>
        <summary>Occurs when the user switches to an application that uses a different palette.</summary>
        <remarks>
          <format type="text/markdown"><![CDATA[  
  
## Remarks  
  
> [!NOTE]
>  This event is only raised if the message pump is running. In a Windows service, unless a hidden form is used or the message pump has been started manually, this event will not be raised. For a code example that shows how to handle system events by using a hidden form in a Windows service, see the <xref:Microsoft.Win32.SystemEvents> class.  
  
> [!CAUTION]
>  Because this is a static event, you must detach your event handlers when your application is disposed, or memory leaks will result.  
  
   
  
## Examples  
 The following code example demonstrates how to monitor the <xref:Microsoft.Win32.SystemEvents.PaletteChanged> event. This code example is part of a larger example provided for the <xref:Microsoft.Win32.SystemEvents> class.  
  
 [!code-cpp[SystemEvents#2](~/samples/snippets/cpp/VS_Snippets_Winforms/SystemEvents/cpp/SystemEvents.cpp#2)]
 [!code-csharp[SystemEvents#2](~/samples/snippets/csharp/VS_Snippets_Winforms/SystemEvents/CS/SystemEvents.cs#2)]
 [!code-vb[SystemEvents#2](~/samples/snippets/visualbasic/VS_Snippets_Winforms/SystemEvents/VB/SystemEvents.vb#2)]  
  
 ]]></format>
        </remarks>
        <exception cref="T:System.InvalidOperationException">System event notifications are not supported under the current context. Server processes, for example, might not support global system event notifications.</exception>
        <exception cref="T:System.Runtime.InteropServices.ExternalException">The attempt to create a system events window thread did not succeed.</exception>
      </Docs>
    </Member>
    <Member MemberName="PowerModeChanged">
      <MemberSignature Language="C#" Value="public static event Microsoft.Win32.PowerModeChangedEventHandler PowerModeChanged;" />
      <MemberSignature Language="ILAsm" Value=".event class Microsoft.Win32.PowerModeChangedEventHandler PowerModeChanged" />
      <MemberSignature Language="DocId" Value="E:Microsoft.Win32.SystemEvents.PowerModeChanged" />
      <MemberType>Event</MemberType>
      <AssemblyInfo>
        <AssemblyName>System</AssemblyName>
        <AssemblyVersion>4.0.0.0</AssemblyVersion>
      </AssemblyInfo>
      <Attributes>
        <Attribute>
          <AttributeName>System.MonoTODO("Currently does nothing on Mono")</AttributeName>
        </Attribute>
      </Attributes>
      <ReturnValue>
        <ReturnType>Microsoft.Win32.PowerModeChangedEventHandler</ReturnType>
      </ReturnValue>
      <Docs>
        <summary>Occurs when the user suspends or resumes the system.</summary>
        <remarks>
          <format type="text/markdown"><![CDATA[  
  
## Remarks  
  
> [!NOTE]
>  This event is only raised if the message pump is running. In a Windows service, unless a hidden form is used or the message pump has been started manually, this event will not be raised. For a code example that shows how to handle system events by using a hidden form in a Windows service, see the <xref:Microsoft.Win32.SystemEvents> class.  
  
> [!CAUTION]
>  Because this is a static event, you must detach your event handlers when your application is disposed, or memory leaks will result.  
  
 ]]></format>
        </remarks>
        <exception cref="T:System.InvalidOperationException">System event notifications are not supported under the current context. Server processes, for example, might not support global system event notifications.</exception>
        <exception cref="T:System.Runtime.InteropServices.ExternalException">The attempt to create a system events window thread did not succeed.</exception>
      </Docs>
    </Member>
    <Member MemberName="SessionEnded">
      <MemberSignature Language="C#" Value="public static event Microsoft.Win32.SessionEndedEventHandler SessionEnded;" />
      <MemberSignature Language="ILAsm" Value=".event class Microsoft.Win32.SessionEndedEventHandler SessionEnded" />
      <MemberSignature Language="DocId" Value="E:Microsoft.Win32.SystemEvents.SessionEnded" />
      <MemberType>Event</MemberType>
      <AssemblyInfo>
        <AssemblyName>System</AssemblyName>
        <AssemblyVersion>4.0.0.0</AssemblyVersion>
      </AssemblyInfo>
      <Attributes>
        <Attribute>
          <AttributeName>System.MonoTODO("Currently does nothing on Mono")</AttributeName>
        </Attribute>
      </Attributes>
      <ReturnValue>
        <ReturnType>Microsoft.Win32.SessionEndedEventHandler</ReturnType>
      </ReturnValue>
      <Docs>
        <summary>Occurs when the user is logging off or shutting down the system.</summary>
        <remarks>
          <format type="text/markdown"><![CDATA[  
  
## Remarks  
  
> [!NOTE]
>  This event is only raised if the message pump is running. In a Windows service, unless a hidden form is used or the message pump has been started manually, this event will not be raised. For a code example that shows how to handle system events by using a hidden form in a Windows service, see the <xref:Microsoft.Win32.SystemEvents> class.  
  
> [!CAUTION]
>  Because this is a static event, you must detach your event handlers when your application is disposed, or memory leaks will result.  
  
 ]]></format>
        </remarks>
        <exception cref="T:System.InvalidOperationException">System event notifications are not supported under the current context. Server processes, for example, might not support global system event notifications.</exception>
        <exception cref="T:System.Runtime.InteropServices.ExternalException">The attempt to create a system events window thread did not succeed.</exception>
      </Docs>
    </Member>
    <Member MemberName="SessionEnding">
      <MemberSignature Language="C#" Value="public static event Microsoft.Win32.SessionEndingEventHandler SessionEnding;" />
      <MemberSignature Language="ILAsm" Value=".event class Microsoft.Win32.SessionEndingEventHandler SessionEnding" />
      <MemberSignature Language="DocId" Value="E:Microsoft.Win32.SystemEvents.SessionEnding" />
      <MemberType>Event</MemberType>
      <AssemblyInfo>
        <AssemblyName>System</AssemblyName>
        <AssemblyVersion>4.0.0.0</AssemblyVersion>
      </AssemblyInfo>
      <Attributes>
        <Attribute>
          <AttributeName>System.MonoTODO("Currently does nothing on Mono")</AttributeName>
        </Attribute>
      </Attributes>
      <ReturnValue>
        <ReturnType>Microsoft.Win32.SessionEndingEventHandler</ReturnType>
      </ReturnValue>
      <Docs>
        <summary>Occurs when the user is trying to log off or shut down the system.</summary>
        <remarks>
          <format type="text/markdown"><![CDATA[  
  
## Remarks  
 This is a cancelable event. Setting the <xref:Microsoft.Win32.SessionEndingEventArgs.Cancel%2A> property to `true` will request that the session continues to run. It provides no guarantee that the session will not end.  
  
 If you are using <xref:Microsoft.Win32.SystemEvents.SessionEnding> in a Windows form to detect a system logoff or reboot, there is no deterministic way to decide whether the <xref:System.Windows.Forms.Form.Closing> event will fire before this event.  
  
 If you want to perform some special tasks before <xref:System.Windows.Forms.Form.Closing> is fired, you need to ensure that <xref:Microsoft.Win32.SystemEvents.SessionEnding> fires before <xref:System.Windows.Forms.Form.Closing>. To do this, you need to trap the `WM_QUERYENDSESSION` in the form by overriding the `WndProc` function.  This example demonstrates how to do this.  
  
```vb  
Private Shared WM_QUERYENDSESSION As Integer = &H11  
 Private Shared systemShutdown As Boolean = False  
 Protected Overrides Sub WndProc(ByRef m As System.Windows.Forms.Message)  
     If m.Msg = WM_QUERYENDSESSION Then  
         MessageBox.Show("queryendsession: this is a logoff, shutdown, or reboot")  
         systemShutdown = True  
     End If  
     ' If this is WM_QUERYENDSESSION, the closing event should be raised in the base WndProc.  
     MyBase.WndProc(m)  
 End Sub 'WndProc   
 Private Sub Form1_Closing(ByVal sender As System.Object, ByVal e As System.ComponentModel.CancelEventArgs) Handles MyBase.Closing  
     If (systemShutdown) Then  
     ' Reset the variable because the user might cancel the shutdown.  
         systemShutdown = False  
         If (System.Windows.Forms.DialogResult.Yes = _  
                 MessageBox.Show("My application", "Do you want to save your work before logging off?", MessageBoxButtons.YesNo)) Then  
                 e.Cancel = True  
         Else  
                 e.Cancel = False  
         End If  
     End If  
 End Sub  
  
```  
  
```csharp  
private static int WM_QUERYENDSESSION = 0x11;  
private static bool systemShutdown = false;  
protected override void WndProc(ref System.Windows.Forms.Message m)  
{  
    if (m.Msg==WM_QUERYENDSESSION)  
    {  
        MessageBox.Show("queryendsession: this is a logoff, shutdown, or reboot");  
        systemShutdown = true;  
    }  
  
    // If this is WM_QUERYENDSESSION, the closing event should be  
    // raised in the base WndProc.  
    base.WndProc(ref m);  
  
} //WndProc   
  
private void Form1_Closing(  
    System.Object sender,   
    System.ComponentModel.CancelEventArgs e)  
{  
    if (systemShutdown)  
        // Reset the variable because the user might cancel the   
        // shutdown.  
    {  
        systemShutdown = false;  
        if (DialogResult.Yes==MessageBox.Show("My application",   
            "Do you want to save your work before logging off?",   
            MessageBoxButtons.YesNo))  
        {  
            e.Cancel = true;  
        }  
        else  
        {  
            e.Cancel = false;  
        }  
    }  
}  
```  
  
> [!IMPORTANT]
>  Console applications do not raise the <xref:Microsoft.Win32.SystemEvents.SessionEnding> event.  
  
> [!NOTE]
>  This event is only raised if the message pump is running. In a Windows service, unless a hidden form is used or the message pump has been started manually, this event will not be raised. For a code example that shows how to handle system events by using a hidden form in a Windows service, see the <xref:Microsoft.Win32.SystemEvents> class.  
  
> [!CAUTION]
>  Because this is a static event, you must detach your event handlers when your application is disposed, or memory leaks will result.  
  
 ]]></format>
        </remarks>
        <exception cref="T:System.InvalidOperationException">System event notifications are not supported under the current context. Server processes, for example, might not support global system event notifications.</exception>
        <exception cref="T:System.Runtime.InteropServices.ExternalException">The attempt to create a system events window thread did not succeed.</exception>
      </Docs>
    </Member>
    <Member MemberName="SessionSwitch">
      <MemberSignature Language="C#" Value="public static event Microsoft.Win32.SessionSwitchEventHandler SessionSwitch;" />
      <MemberSignature Language="ILAsm" Value=".event class Microsoft.Win32.SessionSwitchEventHandler SessionSwitch" />
      <MemberSignature Language="DocId" Value="E:Microsoft.Win32.SystemEvents.SessionSwitch" />
      <MemberType>Event</MemberType>
      <AssemblyInfo>
        <AssemblyName>System</AssemblyName>
        <AssemblyVersion>4.0.0.0</AssemblyVersion>
      </AssemblyInfo>
      <Attributes>
        <Attribute>
          <AttributeName>System.MonoTODO("Currently does nothing on Mono")</AttributeName>
        </Attribute>
      </Attributes>
      <ReturnValue>
        <ReturnType>Microsoft.Win32.SessionSwitchEventHandler</ReturnType>
      </ReturnValue>
      <Docs>
        <summary>Occurs when the currently logged-in user has changed.</summary>
        <remarks>
          <format type="text/markdown"><![CDATA[  
  
## Remarks  
  
> [!NOTE]
>  This event is only raised if the message pump is running. In a Windows service, unless a hidden form is used or the message pump has been started manually, this event will not be raised. For a code example that shows how to handle system events by using a hidden form in a Windows service, see the <xref:Microsoft.Win32.SystemEvents> class.  
  
> [!CAUTION]
>  Because this is a static event, you must detach your event handlers when your application is disposed, or memory leaks will result.  
  
 ]]></format>
        </remarks>
        <exception cref="T:System.InvalidOperationException">System event notifications are not supported under the current context. Server processes, for example, might not support global system event notifications.</exception>
        <exception cref="T:System.Runtime.InteropServices.ExternalException">The attempt to create a system events window thread did not succeed.</exception>
      </Docs>
    </Member>
    <Member MemberName="TimeChanged">
      <MemberSignature Language="C#" Value="public static event EventHandler TimeChanged;" />
      <MemberSignature Language="ILAsm" Value=".event class System.EventHandler TimeChanged" />
      <MemberSignature Language="DocId" Value="E:Microsoft.Win32.SystemEvents.TimeChanged" />
      <MemberType>Event</MemberType>
      <AssemblyInfo>
        <AssemblyName>System</AssemblyName>
        <AssemblyVersion>4.0.0.0</AssemblyVersion>
      </AssemblyInfo>
      <Attributes>
        <Attribute>
          <AttributeName>System.MonoTODO("Currently does nothing on Mono")</AttributeName>
        </Attribute>
      </Attributes>
      <ReturnValue>
        <ReturnType>System.EventHandler</ReturnType>
      </ReturnValue>
      <Docs>
        <summary>Occurs when the user changes the time on the system clock.</summary>
        <remarks>
          <format type="text/markdown"><![CDATA[  
  
## Remarks  
  
> [!NOTE]
>  This event is only raised if the message pump is running. In a Windows service, unless a hidden form is used or the message pump has been started manually, this event will not be raised. For a code example that shows how to handle system events by using a hidden form in a Windows service, see the <xref:Microsoft.Win32.SystemEvents> class.  
  
> [!CAUTION]
>  Because this is a static event, you must detach your event handlers when your application is disposed, or memory leaks will result.  
  
 ]]></format>
        </remarks>
        <exception cref="T:System.InvalidOperationException">System event notifications are not supported under the current context. Server processes, for example, might not support global system event notifications.</exception>
        <exception cref="T:System.Runtime.InteropServices.ExternalException">The attempt to create a system events window thread did not succeed.</exception>
      </Docs>
    </Member>
    <Member MemberName="TimerElapsed">
      <MemberSignature Language="C#" Value="public static event Microsoft.Win32.TimerElapsedEventHandler TimerElapsed;" />
      <MemberSignature Language="ILAsm" Value=".event class Microsoft.Win32.TimerElapsedEventHandler TimerElapsed" />
      <MemberSignature Language="DocId" Value="E:Microsoft.Win32.SystemEvents.TimerElapsed" />
      <MemberType>Event</MemberType>
      <AssemblyInfo>
        <AssemblyName>System</AssemblyName>
        <AssemblyVersion>4.0.0.0</AssemblyVersion>
      </AssemblyInfo>
      <ReturnValue>
        <ReturnType>Microsoft.Win32.TimerElapsedEventHandler</ReturnType>
      </ReturnValue>
      <Docs>
        <summary>Occurs when a windows timer interval has expired.</summary>
        <remarks>
          <format type="text/markdown"><![CDATA[  
  
## Remarks  
  
> [!NOTE]
>  This event is only raised if the message pump is running. In a Windows service, unless a hidden form is used or the message pump has been started manually, this event will not be raised. For a code example that shows how to handle system events by using a hidden form in a Windows service, see the <xref:Microsoft.Win32.SystemEvents> class.  
  
> [!CAUTION]
>  Because this is a static event, you must detach your event handlers when your application is disposed, or memory leaks will result.  
  
 ]]></format>
        </remarks>
        <exception cref="T:System.InvalidOperationException">System event notifications are not supported under the current context. Server processes, for example, might not support global system event notifications.</exception>
        <exception cref="T:System.Runtime.InteropServices.ExternalException">The attempt to create a system events window thread did not succeed.</exception>
      </Docs>
    </Member>
    <Member MemberName="UserPreferenceChanged">
      <MemberSignature Language="C#" Value="public static event Microsoft.Win32.UserPreferenceChangedEventHandler UserPreferenceChanged;" />
      <MemberSignature Language="ILAsm" Value=".event class Microsoft.Win32.UserPreferenceChangedEventHandler UserPreferenceChanged" />
      <MemberSignature Language="DocId" Value="E:Microsoft.Win32.SystemEvents.UserPreferenceChanged" />
      <MemberType>Event</MemberType>
      <AssemblyInfo>
        <AssemblyName>System</AssemblyName>
        <AssemblyVersion>4.0.0.0</AssemblyVersion>
      </AssemblyInfo>
      <Attributes>
        <Attribute>
          <AttributeName>System.MonoTODO("Currently does nothing on Mono")</AttributeName>
        </Attribute>
      </Attributes>
      <ReturnValue>
        <ReturnType>Microsoft.Win32.UserPreferenceChangedEventHandler</ReturnType>
      </ReturnValue>
      <Docs>
        <summary>Occurs when a user preference has changed.</summary>
        <remarks>
          <format type="text/markdown"><![CDATA[  
  
## Remarks  
  
> [!NOTE]
>  This event is only raised if the message pump is running. In a Windows service, unless a hidden form is used or the message pump has been started manually, this event will not be raised. For a code example that shows how to handle system events by using a hidden form in a Windows service, see the <xref:Microsoft.Win32.SystemEvents> class.  
  
> [!CAUTION]
>  Because this is a static event, you must detach your event handlers when your application is disposed, or memory leaks will result.  
  
 ]]></format>
        </remarks>
        <exception cref="T:System.InvalidOperationException">System event notifications are not supported under the current context. Server processes, for example, might not support global system event notifications.</exception>
        <exception cref="T:System.Runtime.InteropServices.ExternalException">The attempt to create a system events window thread did not succeed.</exception>
      </Docs>
    </Member>
    <Member MemberName="UserPreferenceChanging">
      <MemberSignature Language="C#" Value="public static event Microsoft.Win32.UserPreferenceChangingEventHandler UserPreferenceChanging;" />
      <MemberSignature Language="ILAsm" Value=".event class Microsoft.Win32.UserPreferenceChangingEventHandler UserPreferenceChanging" />
      <MemberSignature Language="DocId" Value="E:Microsoft.Win32.SystemEvents.UserPreferenceChanging" />
      <MemberType>Event</MemberType>
      <AssemblyInfo>
        <AssemblyName>System</AssemblyName>
        <AssemblyVersion>4.0.0.0</AssemblyVersion>
      </AssemblyInfo>
      <Attributes>
        <Attribute>
          <AttributeName>System.MonoTODO("Currently does nothing on Mono")</AttributeName>
        </Attribute>
      </Attributes>
      <ReturnValue>
        <ReturnType>Microsoft.Win32.UserPreferenceChangingEventHandler</ReturnType>
      </ReturnValue>
      <Docs>
        <summary>Occurs when a user preference is changing.</summary>
        <remarks>
          <format type="text/markdown"><![CDATA[  
  
## Remarks  
  
> [!NOTE]
>  This event is only raised if the message pump is running. In a Windows service, unless a hidden form is used or the message pump has been started manually, this event will not be raised. For a code example that shows how to handle system events by using a hidden form in a Windows service, see the <xref:Microsoft.Win32.SystemEvents> class.  
  
> [!CAUTION]
>  Because this is a static event, you must detach your event handlers when your application is disposed, or memory leaks will result.  
  
   
  
## Examples  
 The following code example demonstrates how to monitor the <xref:Microsoft.Win32.SystemEvents.UserPreferenceChanging> event. This code example is part of a larger example provided for the <xref:Microsoft.Win32.SystemEvents> class.  
  
 [!code-cpp[SystemEvents#2](~/samples/snippets/cpp/VS_Snippets_Winforms/SystemEvents/cpp/SystemEvents.cpp#2)]
 [!code-csharp[SystemEvents#2](~/samples/snippets/csharp/VS_Snippets_Winforms/SystemEvents/CS/SystemEvents.cs#2)]
 [!code-vb[SystemEvents#2](~/samples/snippets/visualbasic/VS_Snippets_Winforms/SystemEvents/VB/SystemEvents.vb#2)]  
  
 ]]></format>
        </remarks>
        <exception cref="T:System.InvalidOperationException">System event notifications are not supported under the current context. Server processes, for example, might not support global system event notifications.</exception>
        <exception cref="T:System.Runtime.InteropServices.ExternalException">The attempt to create a system events window thread did not succeed.</exception>
      </Docs>
    </Member>
  </Members>
</Type>