如何创建Custom控件的事件以支持转换为Command？

Question

我创建的自定义控件具有如下事件。

public class Editor : Control
{
    ...
    public event EventHandler<AlarmCollection> AlarmFired = null;
    ...
}

并且在触发TextChanged事件时，将调用上述事件（如果不为null，则为null。）>

private async void TextArea_TextChanged(object sender, TextChangedEventArgs e)
{
    ...
    this.AlarmFired?.Invoke(this, this.alarmList);
    ...
}
现在我尝试如下将上述事件从外部绑定到ViewModel。

<DataTemplate DataType="{x:Type documentViewModels:EditorTypeViewModel}">
    <editor:Editor FontSize="15" FontFamily="Arial"
                                 KeywordForeground="LightBlue">

        <i:Interaction.Triggers>
            <i:EventTrigger EventName="AlarmFired">
                <mvvm:EventToCommand Command="{Binding AlarmFiredCommand}"
                                     PassEventArgsToCommand="True"
                                     EventArgsConverter="{localConverters:RemoveObjectConverter}"/>
            </i:EventTrigger>
        </i:Interaction.Triggers>

    </editor:Editor>

</DataTemplate>
EditorTypeViewModel的定义如下所示。

public class EditorTypeViewModel : DocumentViewModel
{
    public event EventHandler<AlarmCollection> AlarmFired = null;

    public EditorTypeViewModel(string title) : base(title)
    {
    }

    private RelayCommand<AlarmCollection> alarmFiredCommand = null;
    public RelayCommand<AlarmCollection> AlarmFiredCommand
    {
        get
        {
            if (this.alarmFiredCommand == null)
                this.alarmFiredCommand = new RelayCommand<AlarmCollection>(this.OnAlarmFired);

            return this.alarmFiredCommand;
        }
    }

    private void OnAlarmFired(AlarmCollection alarmInfos)
    {


        this.AlarmFired?.Invoke(this, alarmInfos);
    }
}
执行上述程序时，不调用与RelayCommand连接的OnAlarmFired方法。我试图找到原因，并找到了可疑的地方。

可疑点是在调用编辑器的TextChanged方法时，编辑器的AlarmFired事件的值为null。它显示在下面。

我以为AlarmFired不是null，因为它将与Command连接，但不是。

我试图做的是将CustomControl的事件绑定到ViewModel的Command并使用它。

例如，可以将ListView的MouseDoubleClick事件绑定到MouseDoubleClickCommand，如下所示。当触发MouseDoubleClick事件时，MouseDoubleClickCommand将获得控制权。

<ListView>
    <i:Interaction.Triggers>
        <i:EventTrigger EventName="MouseDoubleClick">
            <mvvm:EventToCommand Command="{Binding MouseDoubleClickCommand}"
                                 PassEventArgsToCommand="True"/>
        </i:EventTrigger>
    </i:Interaction.Triggers>

</ListView>
我想创建一个事件以支持转换为类似ListView的MouseDoubleClick的命令

（我不想在CustomControl中创建Command，因为事件数量很多）

为了实现这个目标我应该怎么做？

感谢您阅读。

我创建的自定义控件具有如下事件。公共类编辑器：控件{...公共事件EventHandler AlarmFired = null; ...}上面的事件是...

Answer 1

如果您要将事件参数传递给ViewModel，则应像这样创建一个新的Behavior：

public class EventToCommandBehavior : Behavior<FrameworkElement>
{
    private Delegate _handler;
    private EventInfo _oldEvent;

    // Event
    public string Event
    {
        get => (string)GetValue(EventProperty);
        set => SetValue(EventProperty, value);
    }
    public static readonly DependencyProperty EventProperty = DependencyProperty.Register("Event", typeof(string), typeof(EventToCommandBehavior), new PropertyMetadata(null, OnEventChanged));

    // Command
    public ICommand Command
    {
        get => (ICommand)GetValue(CommandProperty);
        set => SetValue(CommandProperty, value);
    }
    public static readonly DependencyProperty CommandProperty = DependencyProperty.Register("Command", typeof(ICommand), typeof(EventToCommandBehavior), new PropertyMetadata(null));

    // PassArguments (default: false)
    public bool PassArguments
    {
        get => (bool)GetValue(PassArgumentsProperty);
        set => SetValue(PassArgumentsProperty, value);
    }
    public static readonly DependencyProperty PassArgumentsProperty = DependencyProperty.Register("PassArguments", typeof(bool), typeof(EventToCommandBehavior), new PropertyMetadata(false));


    private static void OnEventChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var beh = (EventToCommandBehavior)d;

        if (beh.AssociatedObject != null) // is not yet attached at initial load
            beh.AttachHandler((string)e.NewValue);
    }

    protected override void OnAttached()
    {
        AttachHandler(Event); // initial set
    }

    /// <summary>
    /// Attaches the handler to the event
    /// </summary>
    private void AttachHandler(string eventName)
    {
        // detach old event
        if (_oldEvent != null)
            _oldEvent.RemoveEventHandler(AssociatedObject, _handler);

        // attach new event
        if (!string.IsNullOrEmpty(eventName))
        {
            var ei = AssociatedObject.GetType().GetEvent(eventName);
            if (ei != null)
            {
                var mi = GetType().GetMethod("ExecuteCommand", BindingFlags.Instance | BindingFlags.NonPublic);
                if (mi != null) _handler = Delegate.CreateDelegate(ei.EventHandlerType, this, mi);
                ei.AddEventHandler(AssociatedObject, _handler);
                _oldEvent = ei; // store to detach in case the Event property changes
            }
            else
                throw new ArgumentException($"The event '{eventName}' was not found on type '{AssociatedObject.GetType().Name}'");
        }
    }

    /// <summary>
    /// Executes the Command
    /// </summary>
    // ReSharper disable once UnusedParameter.Local
    private void ExecuteCommand(object sender, EventArgs e)
    {
        object parameter = PassArguments ? e : null;
        if (Command == null) return;
        if (Command.CanExecute(parameter))
            Command.Execute(parameter);
    }
}