如何通过 .NET/C# 中的反射引发事件？

Question

我有一个第三方编辑器，它基本上包含一个文本框和一个按钮（DevExpress ButtonEdit 控件）。我想让特定的击键 (Alt + Down) 模拟单击​​按钮。为了避免一遍又一遍地写这个，我想制作一个通用的 KeyUp 事件处理程序，它将引发 ButtonClick 事件。不幸的是，控件中似乎没有引发 ButtonClick 事件的方法，所以...

如何通过反射从外部函数引发事件？

Answer 1

这是一个使用泛型的演示（省略了错误检查）：

using System;
using System.Reflection;
static class Program {
  private class Sub {
    public event EventHandler<EventArgs> SomethingHappening;
  }
  internal static void Raise<TEventArgs>(this object source, string eventName, TEventArgs eventArgs) where TEventArgs : EventArgs
  {
    var eventDelegate = (MulticastDelegate)source.GetType().GetField(eventName, BindingFlags.Instance | BindingFlags.NonPublic).GetValue(source);
    if (eventDelegate != null)
    {
      foreach (var handler in eventDelegate.GetInvocationList())
      {
        handler.Method.Invoke(handler.Target, new object[] { source, eventArgs });
      }
    }
  }
  public static void Main()
  {
    var p = new Sub();
    p.Raise("SomethingHappening", EventArgs.Empty);
    p.SomethingHappening += (o, e) => Console.WriteLine("Foo!");
    p.Raise("SomethingHappening", EventArgs.Empty);
    p.SomethingHappening += (o, e) => Console.WriteLine("Bar!");
    p.Raise("SomethingHappening", EventArgs.Empty);
    Console.ReadLine();
  }
}

Answer 2

一般来说，你不能。将事件视为基本上成对的AddHandler/RemoveHandler 方法（因为它们基本上就是这样）。它们的实现方式取决于班级。大多数 WinForms 控件使用EventHandlerList 作为它们的实现，但是如果它开始获取私有字段和键，您的代码将非常脆弱。

ButtonEdit 控件是否公开了您可以调用的OnClick 方法？

脚注：实际上，事件可以有“raise”成员，因此EventInfo.GetRaiseMethod。但是，C# 从未填充过它，而且我也不相信它在一般框架中。

Answer 3

您通常不能引发其他类事件。事件实际上存储为私有委托字段，外加两个访问器（add_event 和 remove_event）。

要通过反射来实现，您只需找到私有委托字段，获取它，然后调用它。

Answer 4

我写了一个类的扩展，它实现了 INotifyPropertyChanged 来注入 RaisePropertyChange 方法，所以我可以这样使用它：

this.RaisePropertyChanged(() => MyProperty);

没有在任何基类中实现该方法。对于我的使用来说它很慢，但也许源代码可以帮助某人。

原来是这样：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Diagnostics;
using System.Linq.Expressions;
using System.Reflection;
using System.Globalization;

namespace Infrastructure
{
    /// <summary>
    /// Adds a RaisePropertyChanged method to objects implementing INotifyPropertyChanged.
    /// </summary>
    public static class NotifyPropertyChangeExtension
    {
        #region private fields

        private static readonly Dictionary<string, PropertyChangedEventArgs> eventArgCache = new Dictionary<string, PropertyChangedEventArgs>();
        private static readonly object syncLock = new object();

        #endregion

        #region the Extension's

        /// <summary>
        /// Verifies the name of the property for the specified instance.
        /// </summary>
        /// <param name="bindableObject">The bindable object.</param>
        /// <param name="propertyName">Name of the property.</param>
        [Conditional("DEBUG")]
        public static void VerifyPropertyName(this INotifyPropertyChanged bindableObject, string propertyName)
        {
            bool propertyExists = TypeDescriptor.GetProperties(bindableObject).Find(propertyName, false) != null;
            if (!propertyExists)
                throw new InvalidOperationException(string.Format(CultureInfo.CurrentCulture,
                    "{0} is not a public property of {1}", propertyName, bindableObject.GetType().FullName));
        }

        /// <summary>
        /// Gets the property name from expression.
        /// </summary>
        /// <param name="notifyObject">The notify object.</param>
        /// <param name="propertyExpression">The property expression.</param>
        /// <returns>a string containing the name of the property.</returns>
        public static string GetPropertyNameFromExpression<T>(this INotifyPropertyChanged notifyObject, Expression<Func<T>> propertyExpression)
        {
            return GetPropertyNameFromExpression(propertyExpression);
        }

        /// <summary>
        /// Raises a property changed event.
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="bindableObject">The bindable object.</param>
        /// <param name="propertyExpression">The property expression.</param>
        public static void RaisePropertyChanged<T>(this INotifyPropertyChanged bindableObject, Expression<Func<T>> propertyExpression)
        {
            RaisePropertyChanged(bindableObject, GetPropertyNameFromExpression(propertyExpression));
        }

        #endregion

        /// <summary>
        /// Raises the property changed on the specified bindable Object.
        /// </summary>
        /// <param name="bindableObject">The bindable object.</param>
        /// <param name="propertyName">Name of the property.</param>
        private static void RaisePropertyChanged(INotifyPropertyChanged bindableObject, string propertyName)
        {
            bindableObject.VerifyPropertyName(propertyName);
            RaiseInternalPropertyChangedEvent(bindableObject, GetPropertyChangedEventArgs(propertyName));
        }

        /// <summary>
        /// Raises the internal property changed event.
        /// </summary>
        /// <param name="bindableObject">The bindable object.</param>
        /// <param name="eventArgs">The <see cref="System.ComponentModel.PropertyChangedEventArgs"/> instance containing the event data.</param>
        private static void RaiseInternalPropertyChangedEvent(INotifyPropertyChanged bindableObject, PropertyChangedEventArgs eventArgs)
        {
            // get the internal eventDelegate
            var bindableObjectType = bindableObject.GetType();

            // search the base type, which contains the PropertyChanged event field.
            FieldInfo propChangedFieldInfo = null;
            while (bindableObjectType != null)
            {
                propChangedFieldInfo = bindableObjectType.GetField("PropertyChanged", BindingFlags.Instance | BindingFlags.NonPublic);
                if (propChangedFieldInfo != null)
                    break;

                bindableObjectType = bindableObjectType.BaseType;
            }
            if (propChangedFieldInfo == null)
                return;

            // get prop changed event field value
            var fieldValue = propChangedFieldInfo.GetValue(bindableObject);
            if (fieldValue == null)
                return;

            MulticastDelegate eventDelegate = fieldValue as MulticastDelegate;
            if (eventDelegate == null)
                return;

            // get invocation list
            Delegate[] delegates = eventDelegate.GetInvocationList();

            // invoke each delegate
            foreach (Delegate propertyChangedDelegate in delegates)
                propertyChangedDelegate.Method.Invoke(propertyChangedDelegate.Target, new object[] { bindableObject, eventArgs });
        }

        /// <summary>
        /// Gets the property name from an expression.
        /// </summary>
        /// <param name="propertyExpression">The property expression.</param>
        /// <returns>The property name as string.</returns>
        private static string GetPropertyNameFromExpression<T>(Expression<Func<T>> propertyExpression)
        {
            var lambda = (LambdaExpression)propertyExpression;

            MemberExpression memberExpression;

            if (lambda.Body is UnaryExpression)
            {
                var unaryExpression = (UnaryExpression)lambda.Body;
                memberExpression = (MemberExpression)unaryExpression.Operand;
            }
            else memberExpression = (MemberExpression)lambda.Body;

            return memberExpression.Member.Name;
        }

        /// <summary>
        /// Returns an instance of PropertyChangedEventArgs for the specified property name.
        /// </summary>
        /// <param name="propertyName">
        /// The name of the property to create event args for.
        /// </param>
        private static PropertyChangedEventArgs GetPropertyChangedEventArgs(string propertyName)
        {
            PropertyChangedEventArgs args;

            lock (NotifyPropertyChangeExtension.syncLock)
            {
                if (!eventArgCache.TryGetValue(propertyName, out args))
                    eventArgCache.Add(propertyName, args = new PropertyChangedEventArgs(propertyName));
            }

            return args;
        }
    }
}

我删除了原始代码的某些部分，因此扩展程序应该可以按原样运行，而无需引用我的库的其他部分。但它并没有真正经过测试。

附：代码的某些部分是从其他人那里借来的。真可惜，我忘记了我是从哪里得到它的。 :(

Answer 5

来自Raising an event via reflection，虽然我认为VB.NET 中的答案，即在此之前的两个帖子将为您提供通用方法（例如，我希望VB.NET 中引用不在同一类中的类型的灵感）：

 public event EventHandler<EventArgs> MyEventToBeFired;

    public void FireEvent(Guid instanceId, string handler)
    {

        // Note: this is being fired from a method with in the same
        //       class that defined the event (that is, "this").

        EventArgs e = new EventArgs(instanceId);

        MulticastDelegate eventDelagate =
              (MulticastDelegate)this.GetType().GetField(handler,
               System.Reflection.BindingFlags.Instance |
               System.Reflection.BindingFlags.NonPublic).GetValue(this);

        Delegate[] delegates = eventDelagate.GetInvocationList();

        foreach (Delegate dlg in delegates)
        {
            dlg.Method.Invoke(dlg.Target, new object[] { this, e });
        }
    }

    FireEvent(new Guid(),  "MyEventToBeFired");

Answer 6

事实证明，我可以做到这一点，但没有意识到：

buttonEdit1.Properties.Buttons[0].Shortcut = new DevExpress.Utils.KeyShortcut(Keys.Alt | Keys.Down);

但如果我不能，我将不得不深入研究源代码并找到引发事件的方法。

谢谢大家的帮助。

Answer 7

Wiebe Cnossen 的accepted answer 中的代码似乎可以简化为：

private void RaiseEventViaReflection(object source, string eventName)
{
    ((Delegate)source
        .GetType()
        .GetField(eventName, BindingFlags.Instance | BindingFlags.NonPublic)
        .GetValue(source))
        .DynamicInvoke(source, EventArgs.Empty);
}

Answer 8

如果你知道控件是一个按钮，你可以调用它的PerformClick() 方法。对于OnEnter、OnExit 等其他事件，我也有类似的问题。如果我不想为每个控件类型派生一个新类型，我就无法引发这些事件。