SystemEvents Classe

Definição

public ref class SystemEvents sealed

public sealed class SystemEvents

type SystemEvents = class

Public NotInheritable Class SystemEvents

Herança

Object

SystemEvents

Exemplos

Esta secção contém dois exemplos. O primeiro exemplo mostra como usar eventos do sistema numa aplicação comum, e o segundo exemplo mostra como usar eventos do sistema num serviço Windows.

Exemplo 1

O seguinte exemplo de código regista interesse em alguns eventos do sistema e depois espera que algum desses eventos ocorra. A saída mostrada ocorre se o utilizador alterar a resolução do ecrã.

#using <System.dll>

using namespace System;
using namespace Microsoft::Win32;

// This method is called when a user preference changes.
void SystemEvents_UserPreferenceChanging(Object^ sender,
     UserPreferenceChangingEventArgs^ e)
 {
     Console::WriteLine("The user preference is changing. Category={0}",
         e->Category);
 }

// This method is called when the palette changes.
void SystemEvents_PaletteChanged(Object^ sender, EventArgs^ e)
{
    Console::WriteLine("The palette changed.");
}

// This method is called when the display settings change.
void SystemEvents_DisplaySettingsChanged(Object^ sender,
    EventArgs^ e)
{
    Console::WriteLine("The display settings changed.");
}

int main()
{
    // Set the SystemEvents class to receive event notification
    // when a user preference changes, the palette changes, or
    // when display settings change.
    SystemEvents::UserPreferenceChanging += gcnew
        UserPreferenceChangingEventHandler(
        SystemEvents_UserPreferenceChanging);
    SystemEvents::PaletteChanged += gcnew
        EventHandler(SystemEvents_PaletteChanged);
    SystemEvents::DisplaySettingsChanged += gcnew
        EventHandler(SystemEvents_DisplaySettingsChanged);

    // For demonstration purposes, this application sits idle
    // waiting for events.
    Console::WriteLine("This application is waiting for system events.");
    Console::WriteLine("Press <Enter> to terminate this application.");
    Console::ReadLine();
}

// This code produces the following output.
//
//  This app is waiting for system events.
//  Press <Enter> to terminate this application.
//  Display Settings changed.
//  User preference is changing. Category=General

using System;
using Microsoft.Win32;

public sealed class App 
{
    static void Main() 
    {         
        // Set the SystemEvents class to receive event notification when a user 
        // preference changes, the palette changes, or when display settings change.
        SystemEvents.UserPreferenceChanging += new 
            UserPreferenceChangingEventHandler(SystemEvents_UserPreferenceChanging);
        SystemEvents.PaletteChanged += new 
            EventHandler(SystemEvents_PaletteChanged);
        SystemEvents.DisplaySettingsChanged += new 
            EventHandler(SystemEvents_DisplaySettingsChanged);        

        // For demonstration purposes, this application sits idle waiting for events.
        Console.WriteLine("This application is waiting for system events.");
        Console.WriteLine("Press <Enter> to terminate this application.");
        Console.ReadLine();
    }

    // This method is called when a user preference changes.
    static void SystemEvents_UserPreferenceChanging(object sender, UserPreferenceChangingEventArgs e) 
    {
        Console.WriteLine("The user preference is changing. Category={0}", e.Category);
    }

    // This method is called when the palette changes.
    static void SystemEvents_PaletteChanged(object sender, EventArgs e)
    {
        Console.WriteLine("The palette changed.");
    }

    // This method is called when the display settings change.
    static void SystemEvents_DisplaySettingsChanged(object sender, EventArgs e)
    {
        Console.WriteLine("The display settings changed.");
    }
}

// This code produces the following output.
// 
//  This app is waiting for system events.
//  Press <Enter> to terminate this application.
//  Display Settings changed.
//  User preference is changing. Category=General

Imports Microsoft.Win32
Imports System.Windows.Forms

Friend Class Form1
    Inherits System.Windows.Forms.Form


    Public Sub New()
        MyBase.New()

        'This call is required by the Windows Form Designer.
        InitializeComponent()

        'Set the SystemEvents class to receive event notification 
        'when a user preference changes, the palette changes, or 
        'when display settings change.
        AddHandler SystemEvents.UserPreferenceChanging, _
        AddressOf SystemEvents_UserPreferenceChanging

        AddHandler SystemEvents.PaletteChanged, _
        AddressOf SystemEvents_PaletteChanged

        AddHandler SystemEvents.DisplaySettingsChanged, _
        AddressOf SystemEvents_DisplaySettingsChanged

    End Sub

    'Form overrides dispose to clean up the component list.
    Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
        If disposing Then
            If (components IsNot Nothing) Then
                components.Dispose()
            End If
        End If
        MyBase.Dispose(disposing)
    End Sub


    Private components As System.ComponentModel.IContainer

    <System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()

        Me.SuspendLayout()

        '
        'Form1
        '
        Me.ClientSize = New System.Drawing.Size(648, 398)
        Me.Name = "Form1"
        Me.Text = "Form1"
        Me.ResumeLayout(False)

    End Sub


    ' This method is called when a user preference changes.
    Private Sub SystemEvents_UserPreferenceChanging( _
    ByVal sender As Object, _
    ByVal e As UserPreferenceChangingEventArgs)

        MessageBox.Show("UserPreferenceChanging: " & _
        e.Category.ToString())
    End Sub


    ' This method is called when the palette changes.
    Private Sub SystemEvents_PaletteChanged( _
    ByVal sender As Object, _
    ByVal e As EventArgs)

        MessageBox.Show("PaletteChanged")

    End Sub


    ' This method is called when the display settings change.
    Private Sub SystemEvents_DisplaySettingsChanged( _
    ByVal sender As Object, _
    ByVal e As EventArgs)

        MessageBox.Show("The display settings changed.")

    End Sub

End Class

Exemplo 2

O exemplo de código seguinte demonstra um serviço de Windows muito simples que lida com os eventos TimeChanged e UserPreferenceChanged. O exemplo inclui um serviço chamado SimpleService, um formulário chamado HiddenForm, e um instalador. O formulário fornece o ciclo de mensagens exigido pelos eventos do sistema.

O serviço neste exemplo inicia um thread que executa uma instância de HiddenForm. Os acontecimentos são ligados e tratados na forma. Os eventos devem ser ligados no evento de carregamento do formulário, para garantir que o formulário está completamente carregado primeiro; caso contrário, os acontecimentos não serão levantados.

Para apresentar o exemplo:

1. Compila o código a partir da linha de comandos. O nome que usas para o ficheiro fonte não é importante.

2. Instale o serviço a partir da linha de comandos usando a utilidade Installutil.exe (Ferramenta de Instalação ). Por exemplo, InstallUtil example.exe se o nome do ficheiro fonte for example.cs ou example.vb. Tens de ser administrador para instalar o serviço.

3. Usa a consola de Serviços para iniciar o serviço.

4. Alterar a hora do sistema, ou alterar as preferências do utilizador, como as propriedades do rato.

5. Veja as mensagens na categoria Application de Visualizador de Eventos.

6. Use a consola de Serviços para parar o serviço.

7. Desinstale o serviço da linha de comandos usando a /u opção. Por exemplo, InstallUtil /u example.exe.

using System;
using System.ServiceProcess;
using System.Threading;
using System.Windows.Forms;
using System.Diagnostics;
using Microsoft.Win32;
using System.ComponentModel;
using System.Configuration.Install;

namespace SimpleServiceCs
{
    public class SimpleService : ServiceBase
    {
        static void Main(string[] args)
        {
            ServiceBase.Run(new SimpleService());
        }

        protected override void OnStart(string[] args)
        {
            EventLog.WriteEntry("SimpleService", "Starting SimpleService");
            new Thread(RunMessagePump).Start();
        }

        void RunMessagePump()
        {
            EventLog.WriteEntry("SimpleService.MessagePump", "Starting SimpleService Message Pump");
            Application.Run(new HiddenForm());
        }

        protected override void OnStop()
        {
            Application.Exit();
        }
    }

    public partial class HiddenForm : Form
    {
        public HiddenForm()
        {
            InitializeComponent();
        }

        private void HiddenForm_Load(object sender, EventArgs e)
        {
            SystemEvents.TimeChanged += new EventHandler(SystemEvents_TimeChanged);
            SystemEvents.UserPreferenceChanged += new UserPreferenceChangedEventHandler(SystemEvents_UPCChanged);
        }

        private void HiddenForm_FormClosing(object sender, FormClosingEventArgs e)
        {
            SystemEvents.TimeChanged -= new EventHandler(SystemEvents_TimeChanged);
            SystemEvents.UserPreferenceChanged -= new UserPreferenceChangedEventHandler(SystemEvents_UPCChanged);
        }

        private void SystemEvents_TimeChanged(object sender, EventArgs e)
        {
            EventLog.WriteEntry("SimpleService.TimeChanged", "Time changed; it is now " +
                DateTime.Now.ToLongTimeString());
        }

        private void SystemEvents_UPCChanged(object sender, UserPreferenceChangedEventArgs e)
        {
            EventLog.WriteEntry("SimpleService.UserPreferenceChanged", e.Category.ToString());
        }
    }

    partial class HiddenForm
    {
        private System.ComponentModel.IContainer components = null;

        protected override void Dispose(bool disposing)
        {
            if (disposing && (components != null))
            {
                components.Dispose();
            }
            base.Dispose(disposing);
        }

        private void InitializeComponent()
        {
            this.SuspendLayout();
            this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.ClientSize = new System.Drawing.Size(0, 0);
            this.FormBorderStyle = System.Windows.Forms.FormBorderStyle.None;
            this.Name = "HiddenForm";
            this.Text = "HiddenForm";
            this.WindowState = System.Windows.Forms.FormWindowState.Minimized;
            this.Load += new System.EventHandler(this.HiddenForm_Load);
            this.FormClosing += new System.Windows.Forms.FormClosingEventHandler(this.HiddenForm_FormClosing);
            this.ResumeLayout(false);
        }
    }

    [RunInstaller(true)]
    public class SimpleInstaller : Installer
    {
        private ServiceInstaller serviceInstaller;
        private ServiceProcessInstaller processInstaller;

        public SimpleInstaller()
        {
            processInstaller = new ServiceProcessInstaller();
            serviceInstaller = new ServiceInstaller();

            // Service will run under system account
            processInstaller.Account = ServiceAccount.LocalSystem;

            // Service will have Start Type of Manual
            serviceInstaller.StartType = ServiceStartMode.Automatic;

            serviceInstaller.ServiceName = "Simple Service";

            Installers.Add(serviceInstaller);
            Installers.Add(processInstaller);
        }
    }
}

Imports System.ServiceProcess
Imports System.Threading
Imports System.Windows.Forms
Imports System.Diagnostics
Imports Microsoft.Win32
Imports System.ComponentModel
Imports System.Configuration.Install

Namespace SimpleServiceVb
    Public Class SimpleService
        Inherits ServiceBase
    
        Shared Sub Main(ByVal args() As String) 
            ServiceBase.Run(New SimpleService())
        End Sub
    
        Protected Overrides Sub OnStart(ByVal args() As String) 
            EventLog.WriteEntry("SimpleService", "Starting SimpleService")
            Dim t As New Thread(AddressOf RunMessagePump)
            t.Start()    
        End Sub
    
        Sub RunMessagePump() 
            EventLog.WriteEntry("SimpleService.MessagePump", _
                "Starting SimpleService Message Pump")
            Application.Run(New HiddenForm())
        End Sub
    
        Protected Overrides Sub OnStop() 
            Application.Exit()
        End Sub
    End Class 

    Partial Class HiddenForm
        Inherits Form

        Public Sub New() 
            InitializeComponent()
        End Sub
    
        Private Sub HiddenForm_Load(ByVal sender As Object, ByVal e As EventArgs) 
            AddHandler SystemEvents.TimeChanged, AddressOf SystemEvents_TimeChanged
            AddHandler SystemEvents.UserPreferenceChanged, AddressOf SystemEvents_UPCChanged
        End Sub 
    
        Private Sub HiddenForm_FormClosing(ByVal sender As Object, ByVal e As FormClosingEventArgs) 
            RemoveHandler SystemEvents.TimeChanged, New EventHandler(AddressOf SystemEvents_TimeChanged)
            RemoveHandler SystemEvents.UserPreferenceChanged, _
                New UserPreferenceChangedEventHandler(AddressOf SystemEvents_UPCChanged)
        End Sub 
    
        Private Sub SystemEvents_TimeChanged(ByVal sender As Object, ByVal e As EventArgs) 
            EventLog.WriteEntry("SimpleService.TimeChanged", _
                "Time changed; it is now " & DateTime.Now.ToLongTimeString())
        End Sub 
    
        Private Sub SystemEvents_UPCChanged(ByVal sender As Object, ByVal e As UserPreferenceChangedEventArgs) 
            EventLog.WriteEntry("SimpleService.UserPreferenceChanged", e.Category.ToString())
        End Sub 
    End Class

    Partial Class HiddenForm

        Private components As System.ComponentModel.IContainer = Nothing
    
        Protected Overrides Sub Dispose(ByVal disposing As Boolean) 
            If disposing AndAlso Not (components Is Nothing) Then
                components.Dispose()
            End If
            MyBase.Dispose(disposing)
        End Sub
  
        Private Sub InitializeComponent() 
            Me.SuspendLayout()
            Me.AutoScaleDimensions = New System.Drawing.SizeF(6F, 13F)
            Me.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font
            Me.ClientSize = New System.Drawing.Size(0, 0)
            Me.FormBorderStyle = System.Windows.Forms.FormBorderStyle.None
            Me.Name = "HiddenForm"
            Me.Text = "HiddenForm"
            Me.WindowState = System.Windows.Forms.FormWindowState.Minimized
            AddHandler Me.Load, AddressOf Me.HiddenForm_Load
            AddHandler Me.FormClosing, AddressOf Me.HiddenForm_FormClosing
            Me.ResumeLayout(False)
        End Sub 
    End Class 

    <RunInstaller(True)> _
    Public Class SimpleInstaller
        Inherits Installer

        Private serviceInstaller As ServiceInstaller
        Private processInstaller As ServiceProcessInstaller
    
        Public Sub New() 
            processInstaller = New ServiceProcessInstaller()
            serviceInstaller = New ServiceInstaller()
        
            ' Service will run under system account
            processInstaller.Account = ServiceAccount.LocalSystem
        
            ' Service will have Start Type of Manual
            serviceInstaller.StartType = ServiceStartMode.Automatic
        
            serviceInstaller.ServiceName = "Simple Service"
        
            Installers.Add(serviceInstaller)
            Installers.Add(processInstaller)
        End Sub
    End Class 
End Namespace

Observações

A SystemEvents classe oferece a capacidade de responder a tipos específicos de eventos do sistema.

Quando um evento do sistema é levantado, quaisquer delegados ligados ao evento são chamados usando o thread que monitoriza os eventos do sistema. Por isso, deve fazer todas as chamadas dos seus gestores de eventos em modo thread-safe. Se precisar de chamar um evento do sistema que não é exposto como membro desta classe, pode usar o InvokeOnEventsThread método.

Ver também

• PowerModeChangedEventHandler
• SessionEndedEventHandler
• SessionEndingEventHandler
• SessionSwitchEventHandler
• TimerElapsedEventHandler
• UserPreferenceChangedEventHandler
• UserPreferenceChangingEventHandler