CreateDelegate 而不是 SetValue 的反射

Question

我尝试实现 Jon Skeet 的 this question 解决方案发布在此 blog post 上，以使用委托的非反射方法替换 SetValue 方法。

与blog post 中的解决方案的区别在于SetValue 是void，而我在MethodInfo miConstructedHelper = miGenericHelper.MakeGenericMethod(typeof(G), pMethod.GetParameters()[0].ParameterType, pMethod.ReturnType); 行得到The type 'System.Void' may not be used as a type argument. 异常。

这是我对MagicMethod 的实现：

public class Instantiator<T> where T : new()
{
    private T instance;
    private IDictionary<string, PropertyInfo> properties;

    private Func<PropertyInfo, object, object> _fncSetValue;

    public Instantiator()
    {
        Type type = typeof(T);
        properties = type.GetProperties().GroupBy(p => p.Name).ToDictionary(g => g.Key, g => g.ToList().First());

        MethodInfo miSetValue = typeof(PropertyInfo).GetMethod("SetValue", new Type[] { typeof(object), typeof(object), typeof(object[]) });
        _fncSetValue = SetValueMethod<PropertyInfo>(miSetValue);
    }

    public void CreateNewInstance()
    {
        instance = new T();
    }

    public void SetValue(string pPropertyName, object pValue)
    {
        if (pPropertyName == null) return;
        PropertyInfo property;
        if (!properties.TryGetValue(pPropertyName, out property)) return;
        TypeConverter tc = TypeDescriptor.GetConverter(property.PropertyType);

        //substitute this line
        //property.SetValue(instance, tc.ConvertTo(pValue, property.PropertyType), null);
        //with this line
        _fncSetValue(property, new object[] { instance, tc.ConvertTo(pValue, property.PropertyType), null });
    }

    public T GetInstance()
    {
        return instance;
    }

    private static Func<G, object, object> SetValueMethod<G>(MethodInfo pMethod) where G : class
    {
        MethodInfo miGenericHelper = typeof(Instantiator<T>).GetMethod("SetValueMethodHelper", BindingFlags.Static | BindingFlags.NonPublic);
        MethodInfo miConstructedHelper = miGenericHelper.MakeGenericMethod(typeof(G), pMethod.GetParameters()[0].ParameterType, pMethod.ReturnType);
        object retVal = miConstructedHelper.Invoke(null, new object[] { pMethod });
        return (Func<G, object, object>) retVal;
    }

    private static Func<TTarget, object, object> SetValueMethodHelper<TTarget, TParam, TReturn>(MethodInfo pMethod) where TTarget : class
    {
        Func<TTarget, TParam, TReturn> func = (Func<TTarget, TParam, TReturn>)Delegate.CreateDelegate(typeof(Func<TTarget, TParam, TReturn>), pMethod);
        Func<TTarget, object, object> retVal = (TTarget target, object param) => func(target, (TParam) param);
        return retVal;
    }
}

Answer 1

您在代码中使用了Func。 Func 用于具有返回类型的方法。对于返回void 的方法，您需要使用Action。

---

您的代码需要如下所示：

public class Instantiator<T> where T : new()
{
    private T instance;
    private IDictionary<string, PropertyInfo> properties;

    private Action<PropertyInfo, object, object, object> _fncSetValue;

    public Instantiator()
    {
        Type type = typeof(T);
        properties = type.GetProperties()
                         .GroupBy(p => p.Name)
                         .ToDictionary(g => g.Key, g => g.ToList().First());

        var types = new Type[] { typeof(object), typeof(object),
                                 typeof(object[]) };
        var miSetValue = typeof(PropertyInfo).GetMethod("SetValue", types);
        _fncSetValue = SetValueMethod<PropertyInfo>(miSetValue);
    }

    public void CreateNewInstance()
    {
        instance = new T();
    }

    public void SetValue(string pPropertyName, object pValue)
    {
        if (pPropertyName == null) return;
        PropertyInfo property;
        if (!properties.TryGetValue(pPropertyName, out property)) return;
        TypeConverter tc = TypeDescriptor.GetConverter(property.PropertyType);

        var value = tc.ConvertTo(pValue, property.PropertyType);
        _fncSetValue(property, instance, value, null);
    }

    public T GetInstance()
    {
        return instance;
    }

    private static Action<G, object, object, object> SetValueMethod<G>(MethodInfo pMethod) where G : class
    {
        var miGenericHelper = 
            typeof(Instantiator<T>).GetMethod("SetValueMethodHelper", 
                                              BindingFlags.Static | 
                                              BindingFlags.NonPublic);

        var parameters = pMethod.GetParameters();
        var miConstructedHelper = miGenericHelper.MakeGenericMethod(typeof(G), 
                                      parameters[0].ParameterType,
                                      parameters[1].ParameterType,
                                      parameters[2].ParameterType);

        var retVal = miConstructedHelper.Invoke(null, new object[] { pMethod });
        return (Action<G, object, object, object>) retVal;
    }

    private static Action<TTarget, object, object, object> SetValueMethodHelper<TTarget, TParam1, TParam2, TParam3>(MethodInfo pMethod) where TTarget : class
    {
        var func = (Action<TTarget, TParam1, TParam2, TParam3>)Delegate.CreateDelegate(typeof(Action<TTarget, TParam1, TParam2, TParam3>), pMethod);
        Action<TTarget, object, object, object> retVal =
            (target, param1, param2, param3) => 
                func(target, (TParam1) param1, (TParam2) param2, (TParam3) param3);

        return retVal;
    }
}

---

由于您不想调用 Jon Skeet 之类的任意方法，因此您可以大大简化代码。无需在您的代码中调用MethodInfo.Invoke，因此无需委托。您可以直接在返回的PropertyInfo 上直接调用SetValue。无论如何都不需要使用委托的迂回方法，而委托又会准确地调用该方法。此外，不需要进行类型转换，因为 SetValue 无论如何都需要 object。
你的代码可以这么简单：

public class SimpleInstantiator<T> where T : new()
{
    private T instance;
    private IDictionary<string, PropertyInfo> properties;

    public SimpleInstantiator()
    {
        Type type = typeof(T);
        properties = type.GetProperties()
                         .GroupBy(p => p.Name)
                         .ToDictionary(g => g.Key, g => g.ToList().First());
    }

    public void CreateNewInstance()
    {
        instance = new T();
    }

    public void SetValue(string pPropertyName, object pValue)
    {
        if (pPropertyName == null) return;

        PropertyInfo property;
        if (!properties.TryGetValue(pPropertyName, out property)) return;

        property.SetValue(instance, pValue, null);
    }

    public T GetInstance()
    {
        return instance;
    }
}

性能测试表明，这个版本只占用了前一个版本的 50% 左右。
性能的微小提升是由于我们在调用链中避免了两个不必要的委托。然而，绝大多数速度的提升在于我们移除了类型转换。