[英]How do I raise an event via reflection in .NET/C#?
我有一个第三方编辑器,基本上由一个文本框和一个按钮(DevExpress ButtonEdit 控件)组成。 我想让一个特定的击键( Alt + Down )模拟点击按钮。 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?
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();
}
}
一般来说,您不能。 将事件基本上看作是成对的AddHandler
/ RemoveHandler
方法(因为它们基本上就是它们)。 如何实现它们取决于班级。 大多数WinForms控件使用EventHandlerList
作为其实现,但是如果代码开始获取私有字段和键,则代码将非常脆弱。
ButtonEdit
控件是否公开了可以调用的OnClick
方法?
脚注:实际上,事件可以具有“ raise”成员,因此为EventInfo.GetRaiseMethod
。 但是,C#永远不会填充它,而且我也不认为它通常在框架中。
您通常无法引发其他课堂活动。 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)。
要通过反射进行操作,您只需要找到私有委托字段,获取它,然后调用它即可。
我编写了一个类扩展,该类实现了INotifyPropertyChanged来注入RaisePropertyChange <T>方法,因此可以这样使用它:
this.RaisePropertyChanged(() => MyProperty);
而不在任何基类中实现该方法。 就我的使用而言,这很慢,但是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,因此该扩展应按原样工作,而无需引用库的其他部分。 但这还没有经过实际测试。
PS:代码的某些部分是从别人那里借来的。 真可惜,我忘了从哪里买的。 :(
从“通过反思引发事件”开始 ,尽管我认为VB.NET中的答案是,在该问题之前的两篇文章将为您提供通用的方法(例如,我希望在VB.NET上获得启发)引用不属于同一类的类型):
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");
事实证明,我可以做到这一点,却没有意识到:
buttonEdit1.Properties.Buttons[0].Shortcut = new DevExpress.Utils.KeyShortcut(Keys.Alt | Keys.Down);
但是,如果我做不到,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。
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,例如OnEnter
, OnExit
,我也有类似的问题。 如果我不想为每种控件类型派生新类型,则无法引发这些事件。
Wiebe Cnossen 接受的答案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);
}
对一些现有答案和评论的进一步细化。
这也考虑到委托字段可以在继承的类上定义。
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;
}
}
}
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