如何在 .NET/C# 中通过反射引发事件？

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）。 我想让一个特定的击键（Alt + Down）模拟单击按钮。 为了避免一遍又一遍地编写此内容，我想创建一个通用的 KeyUp 事件处理程序来引发 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

这是使用泛型的演示（省略错误检查）：

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（因为这基本上就是它们的本质）。 如何实施它们取决于班级。 大多数 WinForms 控件使用 EventHandlerList 作为他们的实现，但是如果你的代码开始获取私有字段和密钥，它将会非常脆弱。

ButtonEdit 控件是否公开了您可以调用的 OnClick 方法？

脚注：实际上，事件可以具有“raise”成员，因此EventInfo.GetRaiseMethod。 然而，C# 从未填充过它，而且我也不认为它存在于一般框架中。

Answer 3

您通常不能引发其他班级事件。 事件实际上存储为私有委托字段，加上两个访问器（add_event 和remove_event）。

要通过反射来完成此操作，您只需找到私有委托字段，获取它，然后调用它。

Answer 4

我编写了一个类扩展，它实现了 INotifyPropertyChanged 以注入 RaisePropertyChange方法，所以我可以像这样使用它：

this.RaisePropertyChanged(() => MyProperty);

无需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。

所以这里是：

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，因此扩展应该按原样工作，而不引用我的库的其他部分。 但它还没有真正经过测试。

PS 部分代码是从别人那里借来的。 真可惜，我忘记了从哪里得到它。 :(

Answer 5

看来 Wiebe Cnossen 的接受的答案中的代码可以简化为：

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

Answer 6

来自提高通过反射的事件，尽管我认为答案在 VB.NET ，也就是说，在此之前的两篇文章将为您提供通用方法（例如，我会在 VB.NET 文章中寻找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 7

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);

但如果我做不到，我就必须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 8

如果您知道该控件是一个按钮，则可以调用其 PerformClick() 方法。 对于其他事件（如 OnEnter、OnExit）我也有类似的问题。 如果我不想为每个控件类型派生新类型，我就无法引发这些事件。

Answer 9

对一些现有答案和评论的进一步细化。

这还考虑到委托字段可以在继承类上定义。

public static void RaiseEvent<TEventArgs>(this object source, string eventName, TEventArgs eventArgs)
    where TEventArgs : EventArgs
{
    // Find the delegate and invoke it.
    var delegateField = FindField(source.GetType(), eventName);
    var eventDelegate = delegateField?.GetValue(source) as Delegate;
    eventDelegate?.DynamicInvoke(source, eventArgs);

    // This local function searches the class hierarchy for the delegate field.
    FieldInfo FindField(Type type, string name)
    {
        while (true)
        {
            var field = type.GetField(name, BindingFlags.Instance | BindingFlags.NonPublic);
            if (field != null)
            {
                return field;
            }

            var baseType = type.BaseType;
            if (baseType == null)
            {
                return null;
            }

            type = baseType;
        }
    }
}