使用Reflection实例化一个类

Question

假设我的sln中有三个项目.

(1) xyz.a{Class Lib}{no reference added}
(2) yzx.b{Class Lib}{added the reference of xyz.a}
(3) zxy.c{Console App}{added the reference of xyz.a}

现在,我需要使用反射从xyz.a中创建驻留在yzx.b中的类的实例.

而且这应该独立于文件夹/目录名.

即使如果我更改yzx.b目录的名称,它应该工作.

有谁有想法吗？

Answer 1

首先,Activator.CreateInstance()是一种正确的方法.

但是,有一种更有趣的方式:

• 快了10倍
• 不要在TargetInvocationException中包装异常

只需创建调用构造函数的表达式:

public static Func<object[], object> CreateConstructorDelegate(ConstructorInfo method)
{
        var args = Expression.Parameter(typeof(object[]), "args");

        var parameters = new List<Expression>();

        var methodParameters = method.GetParameters().ToList();
        for (var i = 0; i < methodParameters.Count; i++)
        {
            parameters.Add(Expression.Convert(
                               Expression.ArrayIndex(args, Expression.Constant(i)),
                               methodParameters[i].ParameterType));
        }

        var call = Expression.Convert(Expression.New(method, parameters), typeof(object));

        Expression body = call;

        var callExpression = Expression.Lambda<Func<object[], object>>(body, args);
        var result = callExpression.Compile();

        return result;
}

性能测试:

    public void activator()
    {
        var stopwatch = new Stopwatch();
        const int times = 10000000;

        stopwatch.Start();
        for (int i = 0; i < times; i++)
        {
            var v = Activator.CreateInstance(typeof (C));
        }
        stopwatch.Stop();

        Console.WriteLine(stopwatch.ElapsedMilliseconds + "ms with activator");

        var del = CreateConstructorDelegate(typeof(C).GetConstructor(new Type[0]));

        stopwatch = new Stopwatch();
        stopwatch.Start();

        var args = new object[0];

        for (int i = 0; i < times; i++)
        {
            var v = del(args);
        }

        stopwatch.Stop();

        Console.WriteLine(stopwatch.ElapsedMilliseconds + "ms with expression");
    }

输出:

1569ms with activator
134ms with expression

但:

• 仅限C#3.0
• Complile()是长时间运行的操作

只是为了好奇.

Answer 2

您可能想要查看Activator.CreateInstance()方法.只需将组件的名称和类型传递给它即可.

如果没有对程序集的编译时引用,则仍可以在运行时使用Assembly.Load()引用它.