Deklarieren mehrerer Ereignisse mithilfe von Ereigniseigenschaften

Wenn eine Klasse viele Ereignisse mithilfe von feldähnlichen Ereignisdeklarationen definiert, generiert der Compiler für jedes ereignisähnliche Feld ein Sicherungsfeld. Jede Instanz dieser Klasse weist Speicher für alle diese Felder zu – auch für Ereignisse, die nie abonniert werden. Bei vielen Ereignissen verschwendet dieser Pro-Instanz-Overhead Arbeitsspeicher.

Um diesen Arbeitsspeicheraufwand zu vermeiden, verwenden Sie Ereigniseigenschaften, die von einer Delegatenauflistung unterstützt werden. Die Auflistung muss Methoden bereitstellen, die Stellvertretungen nach Ereignisschlüssel festlegen, zugreifen und abrufen. EventHandlerList ist für diesen Zweck konzipiert, aber Sie können auch eine Hashtable oder eine Klasse verwenden, die von DictionaryBase abgeleitet ist. Halten Sie die Implementierungsdetails der Sammlung geheim.

Jede Ereigniseigenschaft definiert einen Add-Accessor und einen Remove-Accessor. Der Add-Accessor fügt der Delegatenauflistung den Eingabedelegat hinzu, und der Remove-Accessor entfernt ihn. Beide Accessoren verwenden einen vordefinierten Schlüssel, um Instanzen aus der Auflistung hinzuzufügen und daraus zu entfernen.

Voraussetzungen

Machen Sie sich mit den Konzepten im Artikel "Ereignisse " vertraut.

Definieren mehrerer Ereignisse mithilfe von Ereigniseigenschaften

Mit diesen Schritten wird eine Sensor Klasse erstellt, die 10 Ereigniseigenschaften verfügbar macht, die alle von einer einzelnen EventHandlerListKlasse unterstützt werden.

Definieren Sie eine Ereignisdatenklasse, die von EventArgs.

Fügen Sie Eigenschaften für jeden Datenabschnitt hinzu, den Sie an den Handler übergeben möchten:

public class SensorEventArgs(string sensorId, double value) : EventArgs
{
    public string SensorId { get; } = sensorId;
    public double Value { get; } = value;
}

Public Class SensorEventArgs
    Inherits EventArgs

    Public ReadOnly Property SensorId As String
    Public ReadOnly Property Value As Double

    Public Sub New(sensorId As String, value As Double)
        Me.SensorId = sensorId
        Me.Value = value
    End Sub
End Class

Deklarieren Sie ein EventHandlerList Feld zum Speichern der Stellvertretungen:

protected EventHandlerList listEventDelegates = new();

Protected listEventDelegates As New EventHandlerList()

Deklarieren Sie einen eindeutigen Schlüssel für jedes Ereignis.

EventHandlerList speichert Delegierte anhand eines Schlüssels. Verwenden Sie ein static readonly Objekt (Shared ReadOnly in Visual Basic) für jeden Schlüssel – die Objektidentität stellt sicher, dass jeder Schlüssel wirklich eindeutig ist:

static readonly object temperatureChangedKey = new();
static readonly object humidityChangedKey = new();
static readonly object pressureChangedKey = new();
static readonly object batteryLowKey = new();
static readonly object signalLostKey = new();
static readonly object signalRestoredKey = new();
static readonly object thresholdExceededKey = new();
static readonly object calibrationRequiredKey = new();
static readonly object dataReceivedKey = new();
static readonly object errorDetectedKey = new();

Shared ReadOnly temperatureChangedKey  As New Object()
Shared ReadOnly humidityChangedKey     As New Object()
Shared ReadOnly pressureChangedKey     As New Object()
Shared ReadOnly batteryLowKey          As New Object()
Shared ReadOnly signalLostKey          As New Object()
Shared ReadOnly signalRestoredKey      As New Object()
Shared ReadOnly thresholdExceededKey   As New Object()
Shared ReadOnly calibrationRequiredKey As New Object()
Shared ReadOnly dataReceivedKey        As New Object()
Shared ReadOnly errorDetectedKey       As New Object()

Definieren Sie jedes Ereignis als Ereigniseigenschaft mit benutzerdefinierten Accessoren zum Hinzufügen und Entfernen.

Jeder Accessor ruft AddHandler oder RemoveHandler in der Liste mithilfe des Schlüssels dieses Ereignisses auf. Fügen Sie in C# auch eine protected virtual raise-Methode hinzu, mit der der Delegat aus der Liste anhand des Schlüssels abgerufen und aufgerufen wird. In Visual Basic enthält die Custom Event Deklaration bereits einen RaiseEvent Block, der dies tut:

public event EventHandler<SensorEventArgs> TemperatureChanged
{
    add    { listEventDelegates.AddHandler(temperatureChangedKey, value); }
    remove { listEventDelegates.RemoveHandler(temperatureChangedKey, value); }
}
protected virtual void OnTemperatureChanged(SensorEventArgs e) =>
    ((EventHandler<SensorEventArgs>?)listEventDelegates[temperatureChangedKey])?.Invoke(this, e);

Public Custom Event TemperatureChanged As EventHandler(Of SensorEventArgs)
    AddHandler(Value As EventHandler(Of SensorEventArgs))
        listEventDelegates.AddHandler(temperatureChangedKey, Value)
    End AddHandler
    RemoveHandler(Value As EventHandler(Of SensorEventArgs))
        listEventDelegates.RemoveHandler(temperatureChangedKey, Value)
    End RemoveHandler
    RaiseEvent(sender As Object, e As SensorEventArgs)
        CType(listEventDelegates(temperatureChangedKey), EventHandler(Of SensorEventArgs))?.Invoke(sender, e)
    End RaiseEvent
End Event

Wiederholen Sie dieses Muster für jedes Ereignis unter Verwendung des entsprechenden Schlüssels.

Abonnieren des ereignisses mithilfe des += Operatoren (in Visual Basic, AddHandler):

sensor.TemperatureChanged += Sensor_TemperatureChanged;

AddHandler sensor.TemperatureChanged, AddressOf Sensor_TemperatureChanged

Definieren Sie den Ereignishandler.

Die Signatur muss mit dem EventHandler<TEventArgs> Delegaten übereinstimmen – ein object Sender und Ihre Ereignisdatenklasse als zweiter Parameter:

static void Sensor_TemperatureChanged(object? sender, SensorEventArgs e) =>
    Console.WriteLine($"Sensor {e.SensorId}: temperature changed to {e.Value}.");

Sub Sensor_TemperatureChanged(sender As Object, e As SensorEventArgs)
    Console.WriteLine("Sensor {0}: temperature changed to {1}.", e.SensorId, e.Value)
End Sub

Das folgende Beispiel zeigt die vollständige Sensor Klassenimplementierung:

using System.ComponentModel;

public class SensorEventArgs(string sensorId, double value) : EventArgs
{
    public string SensorId { get; } = sensorId;
    public double Value { get; } = value;
}

// Sensor defines 10 event properties backed by a single EventHandlerList.
// EventHandlerList is memory-efficient for classes with many events: it only
// allocates storage for events that have active subscribers.
class Sensor
{
    protected EventHandlerList listEventDelegates = new();

    static readonly object temperatureChangedKey = new();
    static readonly object humidityChangedKey = new();
    static readonly object pressureChangedKey = new();
    static readonly object batteryLowKey = new();
    static readonly object signalLostKey = new();
    static readonly object signalRestoredKey = new();
    static readonly object thresholdExceededKey = new();
    static readonly object calibrationRequiredKey = new();
    static readonly object dataReceivedKey = new();
    static readonly object errorDetectedKey = new();

    public event EventHandler<SensorEventArgs> TemperatureChanged
    {
        add    { listEventDelegates.AddHandler(temperatureChangedKey, value); }
        remove { listEventDelegates.RemoveHandler(temperatureChangedKey, value); }
    }
    protected virtual void OnTemperatureChanged(SensorEventArgs e) =>
        ((EventHandler<SensorEventArgs>?)listEventDelegates[temperatureChangedKey])?.Invoke(this, e);

    public event EventHandler<SensorEventArgs> HumidityChanged
    {
        add    { listEventDelegates.AddHandler(humidityChangedKey, value); }
        remove { listEventDelegates.RemoveHandler(humidityChangedKey, value); }
    }
    protected virtual void OnHumidityChanged(SensorEventArgs e) =>
        ((EventHandler<SensorEventArgs>?)listEventDelegates[humidityChangedKey])?.Invoke(this, e);

    public event EventHandler<SensorEventArgs> PressureChanged
    {
        add    { listEventDelegates.AddHandler(pressureChangedKey, value); }
        remove { listEventDelegates.RemoveHandler(pressureChangedKey, value); }
    }
    protected virtual void OnPressureChanged(SensorEventArgs e) =>
        ((EventHandler<SensorEventArgs>?)listEventDelegates[pressureChangedKey])?.Invoke(this, e);

    public event EventHandler<SensorEventArgs> BatteryLow
    {
        add    { listEventDelegates.AddHandler(batteryLowKey, value); }
        remove { listEventDelegates.RemoveHandler(batteryLowKey, value); }
    }
    protected virtual void OnBatteryLow(SensorEventArgs e) =>
        ((EventHandler<SensorEventArgs>?)listEventDelegates[batteryLowKey])?.Invoke(this, e);

    public event EventHandler<SensorEventArgs> SignalLost
    {
        add    { listEventDelegates.AddHandler(signalLostKey, value); }
        remove { listEventDelegates.RemoveHandler(signalLostKey, value); }
    }
    protected virtual void OnSignalLost(SensorEventArgs e) =>
        ((EventHandler<SensorEventArgs>?)listEventDelegates[signalLostKey])?.Invoke(this, e);

    public event EventHandler<SensorEventArgs> SignalRestored
    {
        add    { listEventDelegates.AddHandler(signalRestoredKey, value); }
        remove { listEventDelegates.RemoveHandler(signalRestoredKey, value); }
    }
    protected virtual void OnSignalRestored(SensorEventArgs e) =>
        ((EventHandler<SensorEventArgs>?)listEventDelegates[signalRestoredKey])?.Invoke(this, e);

    public event EventHandler<SensorEventArgs> ThresholdExceeded
    {
        add    { listEventDelegates.AddHandler(thresholdExceededKey, value); }
        remove { listEventDelegates.RemoveHandler(thresholdExceededKey, value); }
    }
    protected virtual void OnThresholdExceeded(SensorEventArgs e) =>
        ((EventHandler<SensorEventArgs>?)listEventDelegates[thresholdExceededKey])?.Invoke(this, e);

    public event EventHandler<SensorEventArgs> CalibrationRequired
    {
        add    { listEventDelegates.AddHandler(calibrationRequiredKey, value); }
        remove { listEventDelegates.RemoveHandler(calibrationRequiredKey, value); }
    }
    protected virtual void OnCalibrationRequired(SensorEventArgs e) =>
        ((EventHandler<SensorEventArgs>?)listEventDelegates[calibrationRequiredKey])?.Invoke(this, e);

    public event EventHandler<SensorEventArgs> DataReceived
    {
        add    { listEventDelegates.AddHandler(dataReceivedKey, value); }
        remove { listEventDelegates.RemoveHandler(dataReceivedKey, value); }
    }
    protected virtual void OnDataReceived(SensorEventArgs e) =>
        ((EventHandler<SensorEventArgs>?)listEventDelegates[dataReceivedKey])?.Invoke(this, e);

    public event EventHandler<SensorEventArgs> ErrorDetected
    {
        add    { listEventDelegates.AddHandler(errorDetectedKey, value); }
        remove { listEventDelegates.RemoveHandler(errorDetectedKey, value); }
    }
    protected virtual void OnErrorDetected(SensorEventArgs e) =>
        ((EventHandler<SensorEventArgs>?)listEventDelegates[errorDetectedKey])?.Invoke(this, e);
}

Imports System.ComponentModel

Public Class SensorEventArgs
    Inherits EventArgs

    Public ReadOnly Property SensorId As String
    Public ReadOnly Property Value As Double

    Public Sub New(sensorId As String, value As Double)
        Me.SensorId = sensorId
        Me.Value = value
    End Sub
End Class

' Sensor defines 10 event properties backed by a single EventHandlerList.
' EventHandlerList is memory-efficient for classes with many events: it only
' allocates storage for events that have active subscribers.
Class Sensor

    Protected listEventDelegates As New EventHandlerList()

    Shared ReadOnly temperatureChangedKey  As New Object()
    Shared ReadOnly humidityChangedKey     As New Object()
    Shared ReadOnly pressureChangedKey     As New Object()
    Shared ReadOnly batteryLowKey          As New Object()
    Shared ReadOnly signalLostKey          As New Object()
    Shared ReadOnly signalRestoredKey      As New Object()
    Shared ReadOnly thresholdExceededKey   As New Object()
    Shared ReadOnly calibrationRequiredKey As New Object()
    Shared ReadOnly dataReceivedKey        As New Object()
    Shared ReadOnly errorDetectedKey       As New Object()

    Public Custom Event TemperatureChanged As EventHandler(Of SensorEventArgs)
        AddHandler(Value As EventHandler(Of SensorEventArgs))
            listEventDelegates.AddHandler(temperatureChangedKey, Value)
        End AddHandler
        RemoveHandler(Value As EventHandler(Of SensorEventArgs))
            listEventDelegates.RemoveHandler(temperatureChangedKey, Value)
        End RemoveHandler
        RaiseEvent(sender As Object, e As SensorEventArgs)
            CType(listEventDelegates(temperatureChangedKey), EventHandler(Of SensorEventArgs))?.Invoke(sender, e)
        End RaiseEvent
    End Event

    Public Custom Event HumidityChanged As EventHandler(Of SensorEventArgs)
        AddHandler(Value As EventHandler(Of SensorEventArgs))
            listEventDelegates.AddHandler(humidityChangedKey, Value)
        End AddHandler
        RemoveHandler(Value As EventHandler(Of SensorEventArgs))
            listEventDelegates.RemoveHandler(humidityChangedKey, Value)
        End RemoveHandler
        RaiseEvent(sender As Object, e As SensorEventArgs)
            CType(listEventDelegates(humidityChangedKey), EventHandler(Of SensorEventArgs))?.Invoke(sender, e)
        End RaiseEvent
    End Event

    Public Custom Event PressureChanged As EventHandler(Of SensorEventArgs)
        AddHandler(Value As EventHandler(Of SensorEventArgs))
            listEventDelegates.AddHandler(pressureChangedKey, Value)
        End AddHandler
        RemoveHandler(Value As EventHandler(Of SensorEventArgs))
            listEventDelegates.RemoveHandler(pressureChangedKey, Value)
        End RemoveHandler
        RaiseEvent(sender As Object, e As SensorEventArgs)
            CType(listEventDelegates(pressureChangedKey), EventHandler(Of SensorEventArgs))?.Invoke(sender, e)
        End RaiseEvent
    End Event

    Public Custom Event BatteryLow As EventHandler(Of SensorEventArgs)
        AddHandler(Value As EventHandler(Of SensorEventArgs))
            listEventDelegates.AddHandler(batteryLowKey, Value)
        End AddHandler
        RemoveHandler(Value As EventHandler(Of SensorEventArgs))
            listEventDelegates.RemoveHandler(batteryLowKey, Value)
        End RemoveHandler
        RaiseEvent(sender As Object, e As SensorEventArgs)
            CType(listEventDelegates(batteryLowKey), EventHandler(Of SensorEventArgs))?.Invoke(sender, e)
        End RaiseEvent
    End Event

    Public Custom Event SignalLost As EventHandler(Of SensorEventArgs)
        AddHandler(Value As EventHandler(Of SensorEventArgs))
            listEventDelegates.AddHandler(signalLostKey, Value)
        End AddHandler
        RemoveHandler(Value As EventHandler(Of SensorEventArgs))
            listEventDelegates.RemoveHandler(signalLostKey, Value)
        End RemoveHandler
        RaiseEvent(sender As Object, e As SensorEventArgs)
            CType(listEventDelegates(signalLostKey), EventHandler(Of SensorEventArgs))?.Invoke(sender, e)
        End RaiseEvent
    End Event

    Public Custom Event SignalRestored As EventHandler(Of SensorEventArgs)
        AddHandler(Value As EventHandler(Of SensorEventArgs))
            listEventDelegates.AddHandler(signalRestoredKey, Value)
        End AddHandler
        RemoveHandler(Value As EventHandler(Of SensorEventArgs))
            listEventDelegates.RemoveHandler(signalRestoredKey, Value)
        End RemoveHandler
        RaiseEvent(sender As Object, e As SensorEventArgs)
            CType(listEventDelegates(signalRestoredKey), EventHandler(Of SensorEventArgs))?.Invoke(sender, e)
        End RaiseEvent
    End Event

    Public Custom Event ThresholdExceeded As EventHandler(Of SensorEventArgs)
        AddHandler(Value As EventHandler(Of SensorEventArgs))
            listEventDelegates.AddHandler(thresholdExceededKey, Value)
        End AddHandler
        RemoveHandler(Value As EventHandler(Of SensorEventArgs))
            listEventDelegates.RemoveHandler(thresholdExceededKey, Value)
        End RemoveHandler
        RaiseEvent(sender As Object, e As SensorEventArgs)
            CType(listEventDelegates(thresholdExceededKey), EventHandler(Of SensorEventArgs))?.Invoke(sender, e)
        End RaiseEvent
    End Event

    Public Custom Event CalibrationRequired As EventHandler(Of SensorEventArgs)
        AddHandler(Value As EventHandler(Of SensorEventArgs))
            listEventDelegates.AddHandler(calibrationRequiredKey, Value)
        End AddHandler
        RemoveHandler(Value As EventHandler(Of SensorEventArgs))
            listEventDelegates.RemoveHandler(calibrationRequiredKey, Value)
        End RemoveHandler
        RaiseEvent(sender As Object, e As SensorEventArgs)
            CType(listEventDelegates(calibrationRequiredKey), EventHandler(Of SensorEventArgs))?.Invoke(sender, e)
        End RaiseEvent
    End Event

    Public Custom Event DataReceived As EventHandler(Of SensorEventArgs)
        AddHandler(Value As EventHandler(Of SensorEventArgs))
            listEventDelegates.AddHandler(dataReceivedKey, Value)
        End AddHandler
        RemoveHandler(Value As EventHandler(Of SensorEventArgs))
            listEventDelegates.RemoveHandler(dataReceivedKey, Value)
        End RemoveHandler
        RaiseEvent(sender As Object, e As SensorEventArgs)
            CType(listEventDelegates(dataReceivedKey), EventHandler(Of SensorEventArgs))?.Invoke(sender, e)
        End RaiseEvent
    End Event

    Public Custom Event ErrorDetected As EventHandler(Of SensorEventArgs)
        AddHandler(Value As EventHandler(Of SensorEventArgs))
            listEventDelegates.AddHandler(errorDetectedKey, Value)
        End AddHandler
        RemoveHandler(Value As EventHandler(Of SensorEventArgs))
            listEventDelegates.RemoveHandler(errorDetectedKey, Value)
        End RemoveHandler
        RaiseEvent(sender As Object, e As SensorEventArgs)
            CType(listEventDelegates(errorDetectedKey), EventHandler(Of SensorEventArgs))?.Invoke(sender, e)
        End RaiseEvent
    End Event

End Class

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Last updated on 2026-03-31

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