C# 如何从EventToCommandBehavior分离？

在使用从这里获得的EventToCommandBehavior类时，我似乎遇到了重复事件：

我遵循的是MVVM模式，因此在我的XAML中有以下内容：

<Switch IsToggled="{Binding FilterOptions.IsActive}"
        HorizontalOptions="Center">
    <Switch.Behaviors>
        <behaviour:EventToCommandBehaviour EventName="Toggled" Command="{Binding OnActiveCommand}" CommandParameter="{Binding FilterOptions.IsActive}" />
    </Switch.Behaviors>
</Switch>

public ICommand OnActiveCommand => new Command<Boolean>(OnActive);
public ICommand OnDiscontinuedCommand => new Command<Boolean>(OnDiscontinued);

private void OnDiscontinued(Boolean value) {
    Debug.WriteLine(System.Reflection.MethodBase.GetCurrentMethod().Name);
    if (!value) {
        FilterOptions.IsActive = false;
    }
}

private void OnActive(Boolean value) {
    Debug.WriteLine(System.Reflection.MethodBase.GetCurrentMethod().Name);
    if (!value) {
        FilterOptions.IsDiscontinued = false;
    }
}

在我的ViewModel中，我有：

<Switch IsToggled="{Binding FilterOptions.IsActive}"
        HorizontalOptions="Center">
    <Switch.Behaviors>
        <behaviour:EventToCommandBehaviour EventName="Toggled" Command="{Binding OnActiveCommand}" CommandParameter="{Binding FilterOptions.IsActive}" />
    </Switch.Behaviors>
</Switch>

public ICommand OnActiveCommand => new Command<Boolean>(OnActive);
public ICommand OnDiscontinuedCommand => new Command<Boolean>(OnDiscontinued);

private void OnDiscontinued(Boolean value) {
    Debug.WriteLine(System.Reflection.MethodBase.GetCurrentMethod().Name);
    if (!value) {
        FilterOptions.IsActive = false;
    }
}

private void OnActive(Boolean value) {
    Debug.WriteLine(System.Reflection.MethodBase.GetCurrentMethod().Name);
    if (!value) {
        FilterOptions.IsDiscontinued = false;
    }
}

public-ICommand-OnActiveCommand=>new命令（OnActive）；
public ICommand OnDiscontinued=>new命令（OnDiscontinued）；
私有void OnDiscontinued（布尔值）{
Debug.WriteLine（System.Reflection.MethodBase.GetCurrentMethod（）.Name）；
如果（！值）{
FilterOptions.IsActive=false；
}
}
私有void OnActive（布尔值）{
Debug.WriteLine（System.Reflection.MethodBase.GetCurrentMethod（）.Name）；
如果（！值）{
FilterOptions.IsDiscontinued=false；
}
}

它完美地连接在一起，当我与开关交互时，命令按预期调用。但是，我注意到，如果我关闭当前页面并返回到它，当我与任何开关交互时，命令会重复吗

---

我在OnDetachingFrom（）上（在BahviourBase.cs中）和DeregisterEvent（）上（在eventToCommandBehavior.cs中）放置了一个断点，假设在关闭页面时可以调用它们？二者均如下所示：

BahviourBase.cs

public class BehaviourBase<T> : Behavior<T> where T : BindableObject {
    public T AssociatedObject { get; private set; }

    protected override void OnAttachedTo(T bindable) {
        base.OnAttachedTo(bindable);
        AssociatedObject = bindable;

        if (bindable.BindingContext != null) {
            BindingContext = bindable.BindingContext;
        }

        bindable.BindingContextChanged += OnBindingContextChanged;
    }

    protected override void OnDetachingFrom(T bindable) {
        base.OnDetachingFrom(bindable);
        bindable.BindingContextChanged -= OnBindingContextChanged;
        AssociatedObject = null;
    }

    void OnBindingContextChanged(object sender, EventArgs e) {
        OnBindingContextChanged();
    }

    protected override void OnBindingContextChanged() {
        base.OnBindingContextChanged();
        BindingContext = AssociatedObject.BindingContext;
    }
}

public class EventToCommandBehaviour : BehaviourBase<View> {
    Delegate eventHandler;

    public static readonly BindableProperty EventNameProperty = BindableProperty.Create("EventName", typeof(string), typeof(EventToCommandBehaviour), null, propertyChanged: OnEventNameChanged);
    public static readonly BindableProperty CommandProperty = BindableProperty.Create("Command", typeof(ICommand), typeof(EventToCommandBehaviour), null);
    public static readonly BindableProperty CommandParameterProperty = BindableProperty.Create("CommandParameter", typeof(object), typeof(EventToCommandBehaviour), null);
    public static readonly BindableProperty InputConverterProperty = BindableProperty.Create("Converter", typeof(IValueConverter), typeof(EventToCommandBehaviour), null);

    public string EventName {
        get { return (string)GetValue(EventNameProperty); }
        set { SetValue(EventNameProperty, value); }
    }

    public ICommand Command {
        get { return (ICommand)GetValue(CommandProperty); }
        set { SetValue(CommandProperty, value); }
    }

    public object CommandParameter {
        get { return GetValue(CommandParameterProperty); }
        set { SetValue(CommandParameterProperty, value); }
    }

    public IValueConverter Converter {
        get { return (IValueConverter)GetValue(InputConverterProperty); }
        set { SetValue(InputConverterProperty, value); }
    }

    protected override void OnAttachedTo(View bindable) {
        base.OnAttachedTo(bindable);
        RegisterEvent(EventName);
    }

    protected override void OnDetachingFrom(View bindable) {
        DeregisterEvent(EventName);
        base.OnDetachingFrom(bindable);
    }

    void RegisterEvent(string name) {
        if (string.IsNullOrWhiteSpace(name)) {
            return;
        }

        EventInfo eventInfo = AssociatedObject.GetType().GetRuntimeEvent(name);
        if (eventInfo == null) {
            throw new ArgumentException(string.Format("EventToCommandBehavior: Can't register the '{0}' event.", EventName));
        }
        MethodInfo methodInfo = typeof(EventToCommandBehaviour).GetTypeInfo().GetDeclaredMethod("OnEvent");
        eventHandler = methodInfo.CreateDelegate(eventInfo.EventHandlerType, this);
        eventInfo.AddEventHandler(AssociatedObject, eventHandler);
    }

    void DeregisterEvent(string name) {
        if (string.IsNullOrWhiteSpace(name)) {
            return;
        }

        if (eventHandler == null) {
            return;
        }
        EventInfo eventInfo = AssociatedObject.GetType().GetRuntimeEvent(name);
        if (eventInfo == null) {
            throw new ArgumentException(string.Format("EventToCommandBehavior: Can't de-register the '{0}' event.", EventName));
        }
        eventInfo.RemoveEventHandler(AssociatedObject, eventHandler);
        eventHandler = null;
    }

    void OnEvent(object sender, object eventArgs) {
        if (Command == null) {
            return;
        }

        object resolvedParameter;
        if (CommandParameter != null) {
            resolvedParameter = CommandParameter;
        } else if (Converter != null) {
            resolvedParameter = Converter.Convert(eventArgs, typeof(object), null, null);
        } else {
            resolvedParameter = eventArgs;
        }

        if (Command.CanExecute(resolvedParameter)) {
            Command.Execute(resolvedParameter);
        }
    }

    static void OnEventNameChanged(BindableObject bindable, object oldValue, object newValue) {
        var behavior = (EventToCommandBehaviour)bindable;
        if (behavior.AssociatedObject == null) {
            return;
        }

        string oldEventName = (string)oldValue;
        string newEventName = (string)newValue;

        behavior.DeregisterEvent(oldEventName);
        behavior.RegisterEvent(newEventName);
    }
}

公共类行为库：行为，其中T:BindableObject{
公共T关联对象{get；私有集；}
受保护的覆盖无效数据到（T可绑定）{
碱。可粘合的DTO（可粘合）；
AssociatedObject=可绑定；
if（bindable.BindingContext！=null）{
BindingContext=bindable.BindingContext；
}
bindable.BindingContextChanged+=OnBindingContextChanged；
}
受保护的覆盖无效OnDetachingFrom（T可绑定）{
基础。从（可装订）开始连接；
bindable.BindingContextChanged-=OnBindingContextChanged；
AssociatedObject=null；
}
void OnBindingContextChanged（对象发送方，事件参数e）{
OnBindingContextChanged（）；
}
受保护的覆盖无效OnBindingContextChanged（）{
base.OnBindingContextChanged（）；
BindingContext=AssociatedObject.BindingContext；
}
}

eventtocommandbehavior.cs

public class BehaviourBase<T> : Behavior<T> where T : BindableObject {
    public T AssociatedObject { get; private set; }

    protected override void OnAttachedTo(T bindable) {
        base.OnAttachedTo(bindable);
        AssociatedObject = bindable;

        if (bindable.BindingContext != null) {
            BindingContext = bindable.BindingContext;
        }

        bindable.BindingContextChanged += OnBindingContextChanged;
    }

    protected override void OnDetachingFrom(T bindable) {
        base.OnDetachingFrom(bindable);
        bindable.BindingContextChanged -= OnBindingContextChanged;
        AssociatedObject = null;
    }

    void OnBindingContextChanged(object sender, EventArgs e) {
        OnBindingContextChanged();
    }

    protected override void OnBindingContextChanged() {
        base.OnBindingContextChanged();
        BindingContext = AssociatedObject.BindingContext;
    }
}

public class EventToCommandBehaviour : BehaviourBase<View> {
    Delegate eventHandler;

    public static readonly BindableProperty EventNameProperty = BindableProperty.Create("EventName", typeof(string), typeof(EventToCommandBehaviour), null, propertyChanged: OnEventNameChanged);
    public static readonly BindableProperty CommandProperty = BindableProperty.Create("Command", typeof(ICommand), typeof(EventToCommandBehaviour), null);
    public static readonly BindableProperty CommandParameterProperty = BindableProperty.Create("CommandParameter", typeof(object), typeof(EventToCommandBehaviour), null);
    public static readonly BindableProperty InputConverterProperty = BindableProperty.Create("Converter", typeof(IValueConverter), typeof(EventToCommandBehaviour), null);

    public string EventName {
        get { return (string)GetValue(EventNameProperty); }
        set { SetValue(EventNameProperty, value); }
    }

    public ICommand Command {
        get { return (ICommand)GetValue(CommandProperty); }
        set { SetValue(CommandProperty, value); }
    }

    public object CommandParameter {
        get { return GetValue(CommandParameterProperty); }
        set { SetValue(CommandParameterProperty, value); }
    }

    public IValueConverter Converter {
        get { return (IValueConverter)GetValue(InputConverterProperty); }
        set { SetValue(InputConverterProperty, value); }
    }

    protected override void OnAttachedTo(View bindable) {
        base.OnAttachedTo(bindable);
        RegisterEvent(EventName);
    }

    protected override void OnDetachingFrom(View bindable) {
        DeregisterEvent(EventName);
        base.OnDetachingFrom(bindable);
    }

    void RegisterEvent(string name) {
        if (string.IsNullOrWhiteSpace(name)) {
            return;
        }

        EventInfo eventInfo = AssociatedObject.GetType().GetRuntimeEvent(name);
        if (eventInfo == null) {
            throw new ArgumentException(string.Format("EventToCommandBehavior: Can't register the '{0}' event.", EventName));
        }
        MethodInfo methodInfo = typeof(EventToCommandBehaviour).GetTypeInfo().GetDeclaredMethod("OnEvent");
        eventHandler = methodInfo.CreateDelegate(eventInfo.EventHandlerType, this);
        eventInfo.AddEventHandler(AssociatedObject, eventHandler);
    }

    void DeregisterEvent(string name) {
        if (string.IsNullOrWhiteSpace(name)) {
            return;
        }

        if (eventHandler == null) {
            return;
        }
        EventInfo eventInfo = AssociatedObject.GetType().GetRuntimeEvent(name);
        if (eventInfo == null) {
            throw new ArgumentException(string.Format("EventToCommandBehavior: Can't de-register the '{0}' event.", EventName));
        }
        eventInfo.RemoveEventHandler(AssociatedObject, eventHandler);
        eventHandler = null;
    }

    void OnEvent(object sender, object eventArgs) {
        if (Command == null) {
            return;
        }

        object resolvedParameter;
        if (CommandParameter != null) {
            resolvedParameter = CommandParameter;
        } else if (Converter != null) {
            resolvedParameter = Converter.Convert(eventArgs, typeof(object), null, null);
        } else {
            resolvedParameter = eventArgs;
        }

        if (Command.CanExecute(resolvedParameter)) {
            Command.Execute(resolvedParameter);
        }
    }

    static void OnEventNameChanged(BindableObject bindable, object oldValue, object newValue) {
        var behavior = (EventToCommandBehaviour)bindable;
        if (behavior.AssociatedObject == null) {
            return;
        }

        string oldEventName = (string)oldValue;
        string newEventName = (string)newValue;

        behavior.DeregisterEvent(oldEventName);
        behavior.RegisterEvent(newEventName);
    }
}

公共类事件到CommandBehavior:行为库{
委托事件处理程序；
public static readonly BindableProperty EventNameProperty=BindableProperty.Create（“EventName”、typeof（string）、typeof（eventToCommandBehavior）、null、propertyChanged:OnEventNameChanged）；
public static readonly BindableProperty CommandProperty=BindableProperty.Create（“命令”、typeof（ICommand）、typeof（eventtocommandbehavior）、null）；
public static readonly BindableProperty CommandParameterProperty=BindableProperty.Create（“CommandParameter”、typeof（object）、typeof（eventToCommandBehavior）、null）；
public static readonly BindableProperty InputConverterProperty=BindableProperty.Create（“转换器”、typeof（IValueConverter）、typeof（eventtocommandbehavior）、null）；
公共字符串事件名{
获取{return（string）GetValue（EventNameProperty）；}
set{SetValue（EventNameProperty，value）；}
}
公共ICommand命令{
获取{return（ICommand）GetValue（CommandProperty）；}
set{SetValue（CommandProperty，value）；}
}
公共对象命令参数{
获取{return GetValue（CommandParameterProperty）；}
set{SetValue（CommandParameterProperty，value）；}
}
公用变频器{
获取{return（IValueConverter）GetValue（InputConverterProperty）；}
set{SetValue（InputConverterProperty，value）；}
}
受保护的替代数据（视图可绑定）{
碱。可粘合的DTO（可粘合）；
RegisterEvent（事件名称）；
}
受保护的覆盖无效OnDetachingFrom（视图可绑定）{
注销事件（事件名称）；
基础。从（可装订）开始连接；
}
无效RegisterEvent（字符串名称）{
if（string.IsNullOrWhiteSpace（name））{
返回；
}
EventInfo EventInfo=AssociatedObject.GetType（）.GetRuntimeEvent（名称）；
if（eventInfo==null）{
抛出新的ArgumentException（string.Format（“EventToCommandBehavior:无法注册“{0}”事件。”，EventName））；
}
MethodInfo MethodInfo=typeof（EventToCommandBehavior）.GetTypeInfo（）.GetDeclaredMethod（“OneEvent”）；
eventHandler=methodInfo.CreateDelegate（eventInfo.EventHandlerType，this）；
AddEventHandler（关联对象，eventHandler）；
}
作废注销事件（字符串名称）{
if（string.IsNullOrWhiteSpace（name））{
返回；
}
if（eventHandler==null）{
返回；
}
EventInfo EventInfo=AssociatedObject.GetType（）.GetRuntimeEvent（名称）；
if（eventInfo==null）{
抛出新的ArgumentException（string.Format（“EventToCommandBehavior:无法取消注册“{0}”事件。”，EventName））；
}
RemoveEventHandler（关联对象，eventHandler）；
eventHandler=null；
}
void OnEvent（对象发送方、对象事件参数）{
如果（命令==null）{
返回；
}
对象解析参数；
if（CommandParameter！=null）{
resolvedParameter=命令参数；
}else if（转换器！=null）{
resolvedParameter=Converter.Convert（eventArgs，typeof（object），null，null）；
}否则{
resolvedParameter=eventArgs；
}
if（Command.CanExecute（resolvedParameter））{
Command.Execute（resolvedParameter）；
}
}
静态void OnEventNameChanged（BindableObject bindable、object oldValue、object newValue）{
变量行为=（EventToCommandBehavior）可绑定；
if（behavior.AssociatedObject==null）{
返回；
}
字符串oldEventName=（字符串）oldValue；
字符串newEventName=（字符串）newValue；