使用委托调用构造 [英] Using a Delegate to call a constructor

问题描述

我发现这但试图利用它和失败。

I found this but tried to use it and failed.

我如何创建使用反射的对象，并把它在一个委托使它快？

How can i create an object using reflections and make it fast by putting it in a delegate?

        DynamicMethod dm = new DynamicMethod("MyCtor", t, new Type[] { });            
        var ctor = t.GetConstructor(new Type[] { });
        ILGenerator ilgen = dm.GetILGenerator();
        ilgen.Emit(OpCodes.Ldarg_0);
        ilgen.Emit(OpCodes.Newobj, ctor);
        ilgen.Emit(OpCodes.Ret);
        var d = (Func<T>)dm.CreateDelegate(t);
        dm.Invoke(null, new object[] { });

把它在一个deleage之前，我想至少调用它，当我在上面做我得到的误差

Before putting it in a deleage i tried to at least invoke it and when i did above i get the error

An unhandled exception of type 'System.Reflection.TargetInvocationException' occurred in mscorlib.dll

更多信息：异常已被调用的目标引发异常

Additional information: Exception has been thrown by the target of an invocation.

如果我叫D（），而不是我得到的异常

If i call d() instead i get the exception

An unhandled exception of type 'System.ArgumentException' occurred in mscorlib.dll

Additional information: Type must derive from Delegate.

我如何把一个无参数的构造成一个委托，并调用它？

How do i put a no param constructor into a delegate and call it?

推荐答案

如果你有机会到.NET 3.5（这你的 Func键<的使用; T> 提示），你可能会发现表达式比的ILGenerator 更容易：

If you have access to .NET 3.5 (which your use of Func<T> suggests), you may find Expression easier than ILGenerator:

class Foo { }
static void Main() {
    Func<Foo> func = GetCtor<Foo>(); // cache this somewhere!
    Foo foo = func();
}
static Func<T> GetCtor<T>() {
    Type type = typeof(T);
    Expression body = Expression.New(type);
    return Expression.Lambda<Func<T>>(body).Compile();        
}

很容易扩展，要使用特定的构造函数，传递参数，或增加构造后属性的绑定;管型，转换等（请参见此相关答案）。如果你有一个特定的情况下，我会高兴地添加一个例子

Pretty easy to extend that to use a specific constructor, passing arguments, or adding post-constructor property bindings; casts, conversions, etc (see this related answer). If you have a specific scenario, I'll happily add an example.

还请注意，您应该缓存并重新使用任何此类构造 - 否则你失去的利益（即不重新每个呼叫的代表）。

Note also that you should cache and re-use any such constructors - otherwise you lose the benefit (i.e. don't recreate the delegate per-call).

这篇关于使用委托调用构造的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！