Dynamic event generation in C# using DynamicMethod and ILGenerator
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21-08-2019 - |
Question
I need to generate an event handler based on an EventInfo object in runtime and call a method within that event handler. Something like the following:
public void RegisterAction(ActionData actionData, EventInfo eventInfo,
Control control)
{
MethodInfo methodInfo = eventInfo.EventHandlerType.GetMethod("Invoke");
List<Type> ps = new List<Type>();
foreach (ParameterInfo info in methodInfo.GetParameters())
{
ps.Add(info.ParameterType);
}
DynamicMethod method = new DynamicMethod("Adapter",
typeof (void),
ps.ToArray(),
GetType(),
true);
ILGenerator generator = method.GetILGenerator();
// Here I need to generate a method to do the following:
// ExecuteAction(actionData);
// Then I can use this runtime method as an event handler and
// bind it to the control
Delegate proxy = method.CreateDelegate(eventInfo.EventHandlerType, this);
eventInfo.AddEventHandler(control, proxy);
}
I need help in generating the IL code for the commented part.
Solution
public void RegisterAction(ActionData actionData, EventInfo eventInfo,
Control control)
{
MethodInfo methodInfo = eventInfo.EventHandlerType.GetMethod("Invoke");
List<Type> ps = new List<Type>();
ps.Add (typeof (ActionData)) ;
foreach (ParameterInfo info in methodInfo.GetParameters())
{
ps.Add(info.ParameterType);
}
DynamicMethod method = new DynamicMethod("Adapter",
typeof (void),
ps.ToArray(),
GetType(),
true);
// compatible signatures for ExecuteAction
// (assuming you aren't interested in sender and eventArgs):
// static void ExecuteAction (ActionData) ;
// void ActionData.ExecuteAction () ;
MethodInfo miExecuteAction = <...> ;
ILGenerator generator = method.GetILGenerator();
generator.Emit (OpCodes.Ldarg_0) ;
generator.Emit (OpCodes.Call, miExecuteAction) ;
generator.Emit (OpCodes.Ret) ;
// if you want to pass this to ExecuteAction,
// you'll need to put it into actionData.
Delegate proxy = method.CreateDelegate(eventInfo.EventHandlerType, actionData);
eventInfo.AddEventHandler(control, proxy);
}
Edit: come to think of it, if all your events follow the (sender, args) pattern, you don't even need do mess with SRE:
public static void Execute<T> (ActionData data, object sender, T args)
where T : EventArgs
{
ExecuteAction (data) ;
}
public void RegisterAction (ActionData actionData, EventInfo eventInfo,
Control control)
{
MethodInfo compatibleMethod = typeof (this).GetMethod ("Execute",
BindingFlags.Static | BindingFlags.Public).MakeGenericMethod (
eventInfo.EventHandlerType.GetMethod ("Invoke").GetParameters ()[1].ParameterType)) ;
eventInfo.AddEventHandler (control,
Delegate.CreateDelegate (eventInfo.EventHandlerType, actionData,
compatibleMethod)) ;
}
OTHER TIPS
I'm guessing you want to make a delegate from the MethodInfo of your event...
If so, here is an article describing how to go about this. The IL codes required are explained in that article.
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