我的类不能用作 .Net 4 中泛型类型或方法“System.EventHandler<TEventArgs>”中的类型参数“TEventArgs”

Question

我试图了解 EventHandler 并且必须使用通知项目。这是项目的链接： https ://codeload.github.com/mike-eason/WPF_ToastNotifications/zip/master

我所做的只是将 .Net-framework 从 4.5 更改为 4

我遇到了这个错误：

我的类不能用作泛型类型或方法“System.EventHandler”中的类型参数“TEventArgs”

ToastNotification类：

 [TemplatePart(Name = "PART_DismissButton", Type = typeof(Button))]
    public class ToastNotification : ContentControl
    {
        public event EventHandler Dismissed;

        public string Title
        {
            get { return (string)GetValue(TitleProperty); }
            set { SetValue(TitleProperty, value); }
        }

        public static readonly DependencyProperty TitleProperty =
            DependencyProperty.Register("Title", typeof(string), typeof(ToastNotification));

        public string Message
        {
            get { return (string)GetValue(MessageProperty); }
            set { SetValue(MessageProperty, value); }
        }

        public static readonly DependencyProperty MessageProperty =
            DependencyProperty.Register("Message", typeof(string), typeof(ToastNotification));

        public ToastTypes ToastType
        {
            get { return (ToastTypes)GetValue(ToastTypeProperty); }
            set { SetValue(ToastTypeProperty, value); }
        }

        public static readonly DependencyProperty ToastTypeProperty =
            DependencyProperty.Register("ToastType", typeof(ToastTypes), typeof(ToastNotification), new PropertyMetadata(new PropertyChangedCallback(OnToastTypeChanged)));

        private static void OnToastTypeChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            ToastNotification toast = (ToastNotification)d;

            toast.RefreshBackgroundColour();
        }

        private void RefreshBackgroundColour()
        {
            switch (ToastType)
            {
                case ToastTypes.Success:
                    Background = ColourSuccess;
                    break;
                case ToastTypes.Error:
                    Background = ColourDanger;
                    break;
                case ToastTypes.Info:
                    Background = ColourInfo;
                    break;
                case ToastTypes.Warning:
                    Background = ColourWarning;
                    break;
            }
        }

        public bool IsPersistent
        {
            get { return (bool)GetValue(IsPersistentProperty); }
            set { SetValue(IsPersistentProperty, value); }
        }

        public static readonly DependencyProperty IsPersistentProperty =
            DependencyProperty.Register("IsPersistent", typeof(bool), typeof(ToastNotification));

        public double FontSizeTitle
        {
            get { return (double)GetValue(FontSizeTitleProperty); }
            set { SetValue(FontSizeTitleProperty, value); }
        }

        public static readonly DependencyProperty FontSizeTitleProperty =
            DependencyProperty.Register("FontSizeTitle", typeof(double), typeof(ToastNotification));

        public Brush ColourSuccess
        {
            get { return (Brush)GetValue(ColourSuccessProperty); }
            set { SetValue(ColourSuccessProperty, value); }
        }

        public static readonly DependencyProperty ColourSuccessProperty =
            DependencyProperty.Register("ColourSuccess", typeof(Brush), typeof(ToastNotification));

        public Brush ColourDanger
        {
            get { return (Brush)GetValue(ColourDangerProperty); }
            set { SetValue(ColourDangerProperty, value); }
        }

        public static readonly DependencyProperty ColourDangerProperty =
            DependencyProperty.Register("ColourDanger", typeof(Brush), typeof(ToastNotification));

        public Brush ColourInfo
        {
            get { return (Brush)GetValue(ColourInfoProperty); }
            set { SetValue(ColourInfoProperty, value); }
        }

        public static readonly DependencyProperty ColourInfoProperty =
            DependencyProperty.Register("ColourInfo", typeof(Brush), typeof(ToastNotification));

        public Brush ColourWarning
        {
            get { return (Brush)GetValue(ColourWarningProperty); }
            set { SetValue(ColourWarningProperty, value); }
        }

        public static readonly DependencyProperty ColourWarningProperty =
            DependencyProperty.Register("ColourWarning", typeof(Brush), typeof(ToastNotification));

        static ToastNotification()
        {
            DefaultStyleKeyProperty.OverrideMetadata(typeof(ToastNotification), new FrameworkPropertyMetadata(typeof(ToastNotification)));
        }

        public ToastNotification()
        {
            this.Loaded += ToastNotification_Loaded;
        }

        private void ToastNotification_Loaded(object sender, RoutedEventArgs e)
        {
            Storyboard sb = this.FindResource("ToastScaleInStoryboard") as Storyboard;
            Storyboard.SetTarget(sb, this);
            sb.Begin();
        }

        public override void OnApplyTemplate()
        {
            ButtonBase PART_DismissButton = this.GetTemplateChild("PART_DismissButton") as ButtonBase;

            if (PART_DismissButton != null)
                PART_DismissButton.Click += OnDismissed;

            base.OnApplyTemplate();

            RefreshBackgroundColour();
        }

        protected void OnDismissed(object sender, RoutedEventArgs e)
        {
            var eh = Dismissed;

            if (eh != null)
                eh(this, EventArgs.Empty);
        }
    }

吐司类：

  internal class Toast
    {
        public event EventHandler<ToastNotification> ToastClosing;

        private DispatcherTimer _Timer;
        private ToastNotification _Notification;

        public Toast(ToastNotification notification)
        {
            _Notification = notification;

            _Notification.Dismissed += Notification_Dismissed;
        }

        private void Notification_Dismissed(object sender, EventArgs e)
        {
            OnToastClosing();
        }

        private void Timer_Tick(object sender, EventArgs e)
        {
            //Stop and close the window.
            _Timer.Stop();

            OnToastClosing();
        }

        public void Show(TimeSpan displayTime)
        {
            //Only start the timer if the notification is not persistent.
            if (!_Notification.IsPersistent)
            {
                //Set up the timer
                _Timer = new DispatcherTimer();
                _Timer.Interval = displayTime;
                _Timer.Tick += Timer_Tick;

                //Start the timer
                _Timer.Start();
            }
        }

        protected void OnToastClosing()
        {
            //Unsubscribe from the on dismiss event first (to avoid memory leaks)
            _Notification.Dismissed -= Notification_Dismissed;

            var eh = ToastClosing;

            if (eh != null)
                eh(this, _Notification);
        }
    }

Answer 1

System.EventHandler<T>委托在 .NET 4.5 中发生了更改。4.5 之前它有以下签名：

public delegate void EventHandler<TEventArgs>(object sender, TEventArgs e)
    where TEventArgs : EventArgs;

从 .NET 4.5 开始，它有另一个定义：

public delegate void EventHandler<TEventArgs>(object sender, TEventArgs e);

请注意，该where ...部分已被删除。因此，在 .NET 4.5 之前，用于事件处理程序参数的类型应继承自EventArgs. 您ToastNotification没有从该类继承，因此无法使用，因此您的编译器错误。当项目面向 .NET 4.5+ 时，您可以使用任何类型，以便编译良好。

您可以将您的更改ToastClosing为

public event Action<object, ToastNotification> ToastClosing;

它会编译得很好。