为什么我动态创建的事件处理程序时,我得到一个参数异常? [英] Why am I getting an Argument exception when creating event handler dynamically?
问题描述
好日子所有
我写了下面的方法:
private void RegisterEvent(object targetObject, string eventName, string methodName)
{
EventInfo eventInfo = targetObject.GetType().GetEvent(eventName);
MethodInfo method = eventInfo.EventHandlerType.GetMethod("Invoke");
IEnumerable<Type> types = method.GetParameters().Select(param => param.ParameterType);
DynamicMethod dynamicMethod = new DynamicMethod(eventInfo.EventHandlerType.Name, typeof (void), types.ToArray(), typeof (QueryWindow));
MethodInfo methodInfo = typeof (QueryWindow).GetMethod(methodName, new[] { typeof (object) });
ILGenerator ilGenerator = dynamicMethod.GetILGenerator(256);
ilGenerator.Emit(OpCodes.Ldarg_1);
ilGenerator.EmitCall(OpCodes.Call, methodInfo, null);
dynamicMethod.DefineParameter(1, ParameterAttributes.In, "sender");
dynamicMethod.DefineParameter(2, ParameterAttributes.In, "e");
// Get an argument exception here
Delegate methodDelegate = dynamicMethod.CreateDelegate(eventInfo.EventHandlerType, this);
eventInfo.AddEventHandler(targetObject, methodDelegate);
}
我得到的ArgumentException的消息
I get ArgumentException with the message
错误绑定到目标方法。
在该行
Delegate methodDelegate = dynamicMethod.CreateDelegate(eventInfo.EventHandlerType, this);
任何人都可以指出我的错误呢?
Could anyone point out on my mistake?
先谢谢了。
推荐答案
假设方法名
是一个静态 QueryWindow
的方法,这应该工作:
Assuming that methodName
is a static method of QueryWindow
, this should work:
private static void RegisterEvent(object targetObject, string eventName, string methodName)
{
var eventInfo = targetObject.GetType().GetEvent(eventName);
var method = eventInfo.EventHandlerType.GetMethod("Invoke");
var types = method.GetParameters().Select(param => param.ParameterType);
var methodInfo = typeof(QueryWindow).GetMethod(methodName, new[] { typeof(object) });
// replaced typeof(void) by null
var dynamicMethod = new DynamicMethod(eventInfo.EventHandlerType.Name, null, types.ToArray(), typeof(QueryWindow));
ILGenerator ilGenerator = dynamicMethod.GetILGenerator(256);
// Using Ldarg_0 to pass the sender to methodName ; Ldarg_1 to pass the event args
ilGenerator.Emit(OpCodes.Ldarg_0);
ilGenerator.EmitCall(OpCodes.Call, methodInfo, null);
// Added return
ilGenerator.Emit(OpCodes.Ret);
// Removed parameter definition (implicit from DynamicMethod constructor)
// Removed the target argument
var methodDelegate = dynamicMethod.CreateDelegate(eventInfo.EventHandlerType);
eventInfo.AddEventHandler(targetObject, methodDelegate);
}
编辑:
Edit :
因为你可以使用.NET 3.5,您应该创建一个表达式树。这里是另一种解决方案:
Since you can use .NET 3.5, you should create an expression tree. Here is another solution:
public class QueryWindow
{
public void RegisterEvent(object targetObject, string eventName, string methodName)
{
var eventInfo = targetObject.GetType().GetEvent(eventName);
var sender = Expression.Parameter(typeof (object), "sender");
var e = Expression.Parameter(typeof (EventArgs), "e");
var body = Expression.Call(Expression.Constant(this), methodName, null, e);
var lambda = Expression.Lambda(eventInfo.EventHandlerType, body, sender, e);
eventInfo.AddEventHandler(targetObject, lambda.Compile() );
}
public void OnEvent(object o)
{
Console.WriteLine(o);
}
}
注意的OnEvent
方法不再是静态的。我也假设你正在尝试订阅事件都遵循.NET约定(发件人+事件参数)的事件。通过这种方式,我们可以利用逆变始终传递型的lambda:
Notice that the OnEvent
method is no longer static. I also assume that events you are trying to subscribe to are events that follow .NET conventions (sender + event args). This way, we can leverage contravariance and always pass a lambda of type :
(object sender, EventArgs e) => { /* */ }
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