creating a object from string with unknown number of parameters in c#

Question

I am trying to create a class that gets from the user a name of a class and unknown number of parameters, and creates a suitable object. when i run my code, i get a MissingMethod Exception.

this is my code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Project2
{
    class Class1
    {
        public static void Main()
        {
            Console.WriteLine("enter a class name");
            string className = Console.ReadLine();
            Console.WriteLine("enter parameters seperate with a space");
            string parametersLine = Console.ReadLine();
            string []parameters = parametersLine.Split(' ');
            //Console.WriteLine(parameters.Length);
            CreateObject createObject = new CreateObject(className, parameters);
            Console.ReadKey();
        }
    }

    class CreateObject
    {
    private readonly string className;
        public CreateObject(string className, string[] parameters)
        {
            this.className = className;
            try
            {
                if (parameters.Length == 1 && parameters[0] == "") // no parameters
                {
                    Activator.CreateInstance(className.GetType());
                }

                else {
                    Activator.CreateInstance(className.GetType(), parameters); 
                }
            }
            catch (Exception e)
            {
                Console.WriteLine(e.GetType());
            }
        }
    }

    class Person
    {
        public int id{ get; set; }
        public string name{ get; set; }
        public Person()
        {
            Console.WriteLine("Created empety Person object");
        }
        public Person(int id, string name)
        {
            this.id = id;
            this.name = name;
            Console.WriteLine("Created Person object. " +"id:" + id + "   name:" + name);
        }
    }

    class Point
    {
        public int x { get; set; }
        public int y { get; set; }
        public int z { get; set; }

        public Point()
        {
            Console.WriteLine("Created empety Point object");
        }
        public Point(int x, int y, int z)
        {
            this.x = x;
            this.y = y;
            this.z = z;
            Console.WriteLine("Created Point object. " + "x:" + x + "   y:" + y + "   z:" + z);
        }
    }
}

Your code can only find constructors that take string as argument types. Having to convert the entered parameter values to the correct types is going to be non-trivial. Pretty hard to guess why you need to solve this problem. — Hans Passant
– Hans Passant, Commented Nov 8, 2014 at 18:19
only in the beggining. it dosent work aslo with a no-parameters constructor. — Zag Gol
– Zag Gol, Commented Nov 8, 2014 at 18:49

Jose M. · Accepted Answer · 2014-11-09 12:06:03Z

2

You were creating instances of String class and this class did not have the constructor that you were calling. If you can get the types of the parameters this code will work. Remember to use the full name of the class (for example CreateObject("Project2.Point", new object[]{1,1,1}); )

    public CreateObject(string className, object[] parameters)
    {
        this.className = className;
        try
        {
            if (parameters.Length == 1 && parameters[0] == "") // no parameters
            {
                Activator.CreateInstance(Type.GetType(className)); 
            }

            else
            {
                Activator.CreateInstance(Type.GetType(className), parameters);
            }
        }
        catch (Exception e)
        {
            Console.WriteLine(e.GetType());
        }
    }

EDIT:

You can simplify the code like this:

    public CreateObject(string className, object[] parameters)
    {
        this.className = className;
        try
        {
            var insntance = Activator.CreateInstance(Type.GetType(className), parameters);
        }
        catch (Exception e)
        {
            Console.WriteLine(e.GetType());
        }
    }

I tried the following examples and working properly:

 CreateObject createObject1 = new CreateObject("Project2.Point", new object[0]);
 CreateObject createObject2 = new CreateObject("Project2.Point", new object[] { 1, 2, 3 });
 CreateObject createObject3 = new CreateObject("Project2.Person", new object[0]);
 CreateObject createObject4 = new CreateObject("Project2.Person", new object[] { 1, "name"});

enter image description here

edited Nov 9, 2014 at 12:06

answered Nov 8, 2014 at 22:16

Jose M.

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2 Comments

Zag Gol Over a year ago

I fix it like you writed, but when i run it with a empty Con', i get a ArgumentNullException.

Jose M. Over a year ago

I think you are doing something wrong when reading the parameters. I edited my initial answer so you can see some examples.

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