Question

我的应用程序可以根据设置动态加载dll 来自数据库（文件，类和方法名称）。为了方便，加快和减少反射的使用，我希望有一个缓存....

遵循使用：

的想法

 MethodInfo.Invoke

没有表现力（Reflection Performance - Create Delegate (Properties C#)）我想翻译任何方法的调用。我想到了一些像这样的东西：

public static T Create<T>(Type type, string methodName) // or
public static T Create<T>(MethodInfo info) // to use like this:
var action = Create<Action<object>>(typeof(Foo), "AnySetValue");

一个要求是所有参数都可以是对象。

我正在尝试处理表达式，到目前为止，我有类似的东西：

    private void Sample()
    {
        var assembly = Assembly.GetAssembly(typeof(Foo));

        Type customType = assembly.GetType("Foo");

        var actionMethodInfo = customType.GetMethod("AnyMethod");
        var funcMethodInfo = customType.GetMethod("AnyGetString");
        var otherActionMethod = customType.GetMethod("AnySetValue");
        var otherFuncMethodInfo = customType.GetMethod("OtherGetString");

        var foo = Activator.CreateInstance(customType);
        var actionAccessor = (Action<object>)BuildSimpleAction(actionMethodInfo);
        actionAccessor(foo);

        var otherAction = (Action<object, object>)BuildOtherAction(otherActionMethod);
        otherAction(foo, string.Empty);

        var otherFuncAccessor = (Func<object, object>)BuildFuncAccessor(funcMethodInfo);
        otherFuncAccessor(foo);

        var funcAccessor = (Func<object,object,object>)BuildOtherFuncAccessor(otherFuncMethodInfo);
        funcAccessor(foo, string.Empty);
    }

    static Action<object> BuildSimpleAction(MethodInfo method)
    {
        var obj = Expression.Parameter(typeof(object), "o");

        Expression<Action<object>> expr =
            Expression.Lambda<Action<object>>(
                Expression.Call(
                    Expression.Convert(obj, method.DeclaringType),
                    method), obj);

        return expr.Compile();
    }

    static Func<object, object> BuildFuncAccessor(MethodInfo method)
    {
        var obj = Expression.Parameter(typeof(object), "o");

        Expression<Func<object, object>> expr =
            Expression.Lambda<Func<object, object>>(
                Expression.Convert(
                    Expression.Call(
                        Expression.Convert(obj, method.DeclaringType),
                        method),
                    typeof(object)),
                obj);

        return expr.Compile();

    }

    static Func<object, object, object> BuildOtherFuncAccessor(MethodInfo method)
    {
        var obj = Expression.Parameter(typeof(object), "o");
        var value = Expression.Parameter(typeof(object));

        Expression<Func<object, object, object>> expr =
            Expression.Lambda<Func<object, object, object>>(
                    Expression.Call(
                        Expression.Convert(obj, method.DeclaringType),
                        method,
                        Expression.Convert(value, method.GetParameters()[0].ParameterType)), 
                        obj, value);

        return expr.Compile();

    }

    static Action<object, object> BuildOtherAction(MethodInfo method)
    {
        var obj = Expression.Parameter(typeof(object), "o");
        var value = Expression.Parameter(typeof(object));

        Expression<Action<object, object>> expr =
            Expression.Lambda<Action<object, object>>(
                Expression.Call(
                    Expression.Convert(obj, method.DeclaringType),
                    method,
                    Expression.Convert(value, method.GetParameters()[0].ParameterType)),
                obj,
                value);

        return expr.Compile();
    }

public class Foo
{
    public void AnyMethod() {}

    public void AnySetValue(string value) {}

    public string AnyGetString()
    {            return string.Empty;        }

    public string OtherGetString(string value)
    {            return string.Empty;        }
}

有没有办法简化这段代码？（我相信有可能只使用泛型创建一个方法..）当你有3,4,5个任何参数时，我会这样做吗？

我在想，如果有这样的事情会怎么样：

https://codereview.stackexchange.com/questions/1070/generic-advanced-delegate-createdelegate-using-expression-trees

但是我会有更多的参数（在行动或功能中），这个参数（第一个参数）是一个要执行的对象。这可能吗？

Answer 1

我制作了一个满足您所有要求的示例程序（我想！）

class Program
{
    class MyType
    {
        public MyType(int i) { this.Value = i; }

        public void SetValue(int i) { this.Value = i; }

        public void SetSumValue(int a, int b) { this.Value = a + b; }

        public int Value { get; set; }
    }

    public static void Main()
    {
        Type type = typeof(MyType);

        var mi = type.GetMethod("SetValue");

        var obj1 = new MyType(1);
        var obj2 = new MyType(2);

        var action = DelegateBuilder.BuildDelegate<Action<object, int>>(mi);

        action(obj1, 3);
        action(obj2, 4);

        Console.WriteLine(obj1.Value);
        Console.WriteLine(obj2.Value);

        // Sample passing a default value for the 2nd param of SetSumValue.
        var mi2 = type.GetMethod("SetSumValue");

        var action2 = DelegateBuilder.BuildDelegate<Action<object, int>>(mi2, 10);

        action2(obj1, 3);
        action2(obj2, 4);

        Console.WriteLine(obj1.Value);
        Console.WriteLine(obj2.Value);

        // Sample without passing a default value for the 2nd param of SetSumValue.
        // It will just use the default int value that is 0.
        var action3 = DelegateBuilder.BuildDelegate<Action<object, int>>(mi2);

        action3(obj1, 3);
        action3(obj2, 4);

        Console.WriteLine(obj1.Value);
        Console.WriteLine(obj2.Value);
    }
}

DelegateBuilder类：

public class DelegateBuilder
{
    public static T BuildDelegate<T>(MethodInfo method, params object[] missingParamValues)
    {
        var queueMissingParams = new Queue<object>(missingParamValues);

        var dgtMi = typeof(T).GetMethod("Invoke");
        var dgtRet = dgtMi.ReturnType;
        var dgtParams = dgtMi.GetParameters();

        var paramsOfDelegate = dgtParams
            .Select(tp => Expression.Parameter(tp.ParameterType, tp.Name))
            .ToArray();

        var methodParams = method.GetParameters();

        if (method.IsStatic)
        {
            var paramsToPass = methodParams
                .Select((p, i) => CreateParam(paramsOfDelegate, i, p, queueMissingParams))
                .ToArray();

            var expr = Expression.Lambda<T>(
                Expression.Call(method, paramsToPass),
                paramsOfDelegate);

            return expr.Compile();
        }
        else
        {
            var paramThis = Expression.Convert(paramsOfDelegate[0], method.DeclaringType);

            var paramsToPass = methodParams
                .Select((p, i) => CreateParam(paramsOfDelegate, i + 1, p, queueMissingParams))
                .ToArray();

            var expr = Expression.Lambda<T>(
                Expression.Call(paramThis, method, paramsToPass),
                paramsOfDelegate);

            return expr.Compile();
        }
    }

    private static Expression CreateParam(ParameterExpression[] paramsOfDelegate, int i, ParameterInfo callParamType, Queue<object> queueMissingParams)
    {
        if (i < paramsOfDelegate.Length)
            return Expression.Convert(paramsOfDelegate[i], callParamType.ParameterType);

        if (queueMissingParams.Count > 0)
            return Expression.Constant(queueMissingParams.Dequeue());

        if (callParamType.ParameterType.IsValueType)
            return Expression.Constant(Activator.CreateInstance(callParamType.ParameterType));

        return Expression.Constant(null);
    }
}

如何运作

核心是 BuildDelegate 方法：

static T BuildDelegate<T>(MethodInfo method)

T是您要创建的委托类型。
方法是您希望由生成的委托调用的方法的MethodInfo。

示例电话：var action = BuildDelegate<Action<object, int>>(mi);

参数规则：

如果传递的方法是实例方法，则生成的委托的第一个参数将接受包含方法本身的对象的实例。所有其他参数都将传递给方法。
如果传递的方法是静态方法，则生成的委托的所有参数都将传递给方法。
缺少参数将传递默认值。
将丢弃额外的参数。

Answer 2

Delegate.CreateDelegate比构建表达式树要简单得多。

    var assembly = Assembly.GetAssembly(typeof(Foo));

    Type customType = assembly.GetType("Foo");

    var actionMethodInfo = customType.GetMethod("AnyMethod");

    var foo = Activator.CreateInstance(customType);

    Action action = (Action)Delegate.CreateDelegate(typeof(Action), foo, actionMethodInfo);

Answer 3

我遇到了一个非常类似的场景，我发现以下内容非常适合。

首先，让我们设置我们的测试Foo类：

public class Foo
{
    private string _name;

    public Foo(string name)
    {
        _name = name;
    }

    public void AnyMethod()
    {
        Console.WriteLine("{0} Called: AnyMethod()", _name);
    }

    public void AnySetValue(string value)
    {
        Console.WriteLine("{0} Called: AnySetValue(string) with {1}", _name, value);
    }

    public string AnySetString(string value)
    {
        Console.WriteLine("{0} Called: AnySetString(string) with {1}", _name, value);
        return value;
    }
}

接下来，我们创建一组方法来创建可重用的方法包装器：

public static Action<object> CreateReusableAction<TClass>(string methodName)
{
    var method = typeof(TClass).GetMethod(methodName);
    var del = Delegate.CreateDelegate(typeof(Action<TClass>), method);
    Action<object> caller = (instance) => del.DynamicInvoke(instance);
    return caller;
}

public static Action<object, object> CreateReusableAction<TClass, TParam1>(string methodName)
{
    var method = typeof(TClass).GetMethod(methodName, new Type[] { typeof(TParam1) });
    var del = Delegate.CreateDelegate(typeof(Action<TClass, TParam1>), method);
    Action<object, object> caller = (instance, param) => del.DynamicInvoke(instance, param);
    return caller;
}

public static Func<object, object, object> CreateReusableFunction<TClass, TParam1, TReturn>(string methodName)
{
    var method = typeof(TClass).GetMethod(methodName, new Type[] { typeof(TParam1) });
    var del = Delegate.CreateDelegate(typeof(Func<TClass, TParam1, TReturn>), method);
    Func<object, object, object> caller = (instance, param) => (TReturn)del.DynamicInvoke(instance, param);
    return caller;
}

然后我们可以按如下方式使用它：

var myFoo = new Foo("myFoo");
var otherFoo = new Foo("otherFoo");

var anyMethod = CreateReusableAction<Foo>("AnyMethod");
anyMethod(myFoo);
anyMethod(otherFoo);

var anySetValue = CreateReusableAction<Foo, string>("AnySetValue");
anySetValue(myFoo, "Value 1");
anySetValue(otherFoo, "Value 2");

var anySetString = CreateReusableFunction<Foo, string, string>("AnySetString");
var firstResult = anySetString(myFoo, "MyFooValue1");
var secondResult = anySetString(otherFoo, "OtherFooValue1");

产生输出：

myFoo Called: AnyMethod()
otherFoo Called: AnyMethod()
myFoo Called: AnySetValue(string) with Value 1
otherFoo Called: AnySetValue(string) with Value 2
myFoo Called: AnySetString(string) with MyFooValue1
otherFoo Called: AnySetString(string) with OtherFooValue1

Answer 4

如果您可以在项目中使用库，请尝试使用Impromptu接口（可在此处获取：http://code.google.com/p/impromptu-interface/）或nuget。

它具有许多用于处理类型反射的功能，还实现了内部缓存。我一直在一个严重依赖反射的项目中使用它，性能非常好。

库本身具有很多功能，但它也可以处理像你这样的场景。

Answer 5

我不确定，但为什么你不使用dynamic类型？例如：

dynamic foo = Activator.CreateInstance(customType);
foo.AnyMethod();
foo.AnySetValue("test string");
foo.OtherMethod("method", "with", "many", "parameters");

Answer 6

我有点不确定你真正想做什么，但也许这有帮助吗？

    public static Func<object, object[], object> CreateDelegate(MethodInfo method)
    {
        return new Func<object, object[], object>((object instance, object[] args) => method.Invoke(instance, args));
    }
    // Merely providing syntactic suger, ie able to write 
    // method.MyInvoke(instance, arg1, arg2, arg3, arg4) 
    // instead of having to put the args in an array, ie Invoke(instance, new object[]{arg1, arg2}) etc
    public static object MyInvoke(this Func<object, object[], object> func, object instance, params object[] args)
    {
        return func(instance, args);
    }

    public static void TestCode()
    {
        var method = typeof(string).GetMethod("get_Length");

        var wrappfunc = CreateDelegate(method);
        // Calling get_Length (ie Length property) on the string "klasjf"
        wrappfunc.MyInvoke("klasjf"); 
    }

你会失去强类型，因为所有的参数都是object，我有点不确定你真正要完成的是什么。

为任何方法创建Func或Action（使用c＃中的反射）

6 个答案:

如何运作