c# - 通过在任何类之外声明的反射访问委托(delegate)？

Question

我正在尝试一个用于反射(reflection)的演示。我想在这节课中反射(reflect)的程序集是这样的

namespace DelegatesSampleApplication
{
    delegate  bool IsPromotable (Employee employee); // Declaration Syntax is similar to that of a method's 
    class Program
    {
        public static void Main(string[] args)
        {
             //code goes here
        }
    }

    class Employee
    {
        public int EmployeeId { get; set; }
        public string EmployeeName { get; set; }
        public int Salary { get; set; }
        public int Experience { get; set; }

        public void PromoteEmployees(List<Employee> employeeList, IsPromotable isPromotableObj)
        {

            /*foreach (Employee employee in employeeList)
            {
                if (employee.Experience >= 5 && employee.Salary >= 10000) //That's a hard-coded logic that you have developed as a Framework Developer which makes the class itself not reusable
                {
                    Console.WriteLine(" {0} will be promoted in the next R.P. Cycle ", employee.EmployeeName);
                }
            }
            Console.ReadKey();*/

            foreach (Employee employee in employeeList)
            {
                if (isPromotableObj(employee)) 
                {
                    Console.WriteLine(" {0} will be promoted in the next R.P. Cycle ", employee.EmployeeName);
                }
            }
            Console.ReadKey();
        }
    }
}

现在我面临的问题是，我试图在我的程序中读取这个程序集并尝试调用将类实例作为参数的委托(delegate)。我正在做的是在完全不同的类(class)中做的事情

  namespace ReflectionSample
{
    delegate bool empIsPromotable (Object obj);
    class Program
    {
        static void Main(string[] args)
        {

            Console.WriteLine("***************Loading External assembly*************");
            Assembly assembly = Assembly.LoadFrom(@"C:\Users\Chiranjib\Documents\visual studio 2012\Projects\DelegatesSampleApplication\DelegatesSampleApplication\bin\Debug\DelegatesSampleApplication.exe");
            Type employeeType = assembly.GetType("DelegatesSampleApplication.Employee"); //Gets the System.Type object for the Employee Class from the just loaded assembly with all it's dependencies

            Console.WriteLine("***************Loading External assembly properties*************");

           //Setting properties here

            Console.WriteLine("***************Creating an array list that will hold these employee instances***************");
            List<Object> employeeInstanceList = new List<object>();
            employeeInstanceList.Add(employeeInstance);
            employeeInstanceList.Add(employeeInstance2);

            Console.WriteLine("***************Invoking External assembly methods*************");
                        var args = new Object[] {
new List<employeeType>(),
(((employeeInstance) => { return true; }))

};

            Console.ReadKey();

        }
    }
}

这会引发错误。说 employeeType 缺少程序集引用。我也无法将 lambda 表达式转换为对象。我不能直接输入 cast to (IsPromotable) 对吗？我正在使用反射。所以我应该没有直接访问权限。

我怎样才能通过反射访问委托(delegate)？请帮我解决。提前致谢。

Answer 1

IsPromotable不可调用，它只是一个委托(delegate)定义。把它想象成一个界面。它只是告诉您该方法获取和返回的内容，但实际上不 做任何事情。

您可以调用PromoteEmployees像这样:

PromoteEmployees(new List<Employee>, (employee) => { return employee.Name == "Rob"; });

任何匹配 IsPromotable 签名的方法是该方法的有效参数(即任何接受 Employee 并返回 bool 的方法)。你能详细说明一下你想做什么吗？

如果你只想要一个代表列表，你可以这样做:

GetType().Assembly.GetTypes().Where(t => t.IsSubClassOf(typeof(BaseDelegate))); 

注意；这只会返回您当前集会中的代表。您可能希望将其更改为:

typeof(Employee).GetTypes().Assembly.Where(t => t.IsSubClassOf(typeof(BaseDelegate))); 

获取程序集中所有可转换为 IsPromotable 的方法，你可以这样做:

var delegateMethod = typeof(IsPromotable).GetMethod("Invoke");

var @params = delegateMethod.GetParameters();
var returnType = delegateMethod.ReturnType;

var matchingMethods = typeof(IsPromotable)
    .Assembly
    .GetTypes()
    .SelectMany(t => t.GetMethods())
    .Where(m => {
        if (m.ReturnType != returnType)
            return false;
        var currParams = m.GetParameters();
        if (currParams.Length != @params.Length)
            return false;
        for(var i = 0; i < currParams.Length;i++)
            if (currParams[i] != @params[i])
                return false;

        return true;
    });

要使用反射调用方法，您可以这样做:

var args = new Object[] {
    new List<Employee>(),
    ((IsPromotable)((emp) => { return true; }))
};

var value = employeeType.InvokeMember("PromoteEmployees", BindingFlags.InvokeMethod | BindingFlags.Instance | BindingFlags.Public, null, employeeInstance, args);

或者，您可以将其传递给常规方法:

var args = new Object[] {
    new List<Employee>(),
    ((IsPromotable)Test)
};

var value = employeeType.InvokeMember("PromoteEmployees", BindingFlags.InvokeMethod | BindingFlags.Instance | BindingFlags.Public, null, employeeInstance, args);

使用方法:

private bool Test(Employee emp)
{
    return false;
}