SetDate的CreateDelegate而不是Reflection

Question

我試圖實現Jon Skeet針對此博客文章上發布的問題的解決方案，以使用代表的非反射方法替換SetValue方法。

與博客文章中的解決方案的不同之處在於SetValue為void ，並且我得到了The type 'System.Void' may not be used as a type argument. MethodInfo miConstructedHelper = miGenericHelper.MakeGenericMethod(typeof(G), pMethod.GetParameters()[0].ParameterType, pMethod.ReturnType);行上的異常MethodInfo miConstructedHelper = miGenericHelper.MakeGenericMethod(typeof(G), pMethod.GetParameters()[0].ParameterType, pMethod.ReturnType); 。

這是我對MagicMethod的實現：

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

您在代碼中使用Func 。 Func用於具有返回類型的方法。 對於返回void方法，您需要使用Action 。

---

您的代碼需要看起來像這樣：

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;
    }
}

---

當你不想打電話給像喬恩斯基特任意方法，則可以簡化你的代碼了很多 。 無需在代碼中調用MethodInfo.Invoke ，因此不需要委托。 您可以直接在返回的PropertyInfo上直接調用SetValue 。 無需使用委托的彎路，而該委托反過來又會准確地調用該方法。 另外，類型轉換不是必需的，因為SetValue無論如何都需要一個object 。
您的代碼可以像這樣簡單：

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;
    }
}

性能測試表明，此版本僅占用前一個版本的50％。
由於在呼叫鏈中避免了兩個不必要的委托，因此性能略有提高。 但是，速度改進的絕大部分在於我們刪除了類型轉換。