C#, Converting string variable to class variable

Question

I have function as below .

public static object getClassInstance(string key, object constructorParameter)
{
         // body here
}

Key variable will have my class name . I need to return the new instance of the class . If the constructorParm is null then i need to load the class with default constructor else with the constructor parameter passed. How do i do this ?

ADD :

I wrote the code like this

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Reflection;
using Catalyst.BO.StudentProfileBO;
using Catalyst.BO.ReportBO;
using Catalyst.DAL.ReportDAO;
using System.Collections;
using System.Data;

namespace Catalyst.BO.Factory
{
    public class CFactory
    {
        public static object getClassInstance(string key, params  object[] constructorArgs)
        {
            string assemblyPath = null;
            string customClassName = key.Substring(0, 1) + "Custom" + key.Substring(1);

            DataSet objDataset = getAssemblyInfo(key);
            if (objDataset != null && objDataset.Tables.Count > 0 && objDataset.Tables[0].Rows.Count > 0)
            {
                assemblyPath = objDataset.Tables[0].Rows[0]["ACA_ASSEMBLY_PATH"].ToString();
            }

            Assembly assembly;
            Type type;

            if (assemblyPath != null && assemblyPath != string.Empty)
            {
                assembly = Assembly.LoadFile(assemblyPath);
                type = assembly.GetType(customClassName);
            }
            else // if no customisation
            {
                type = Type.GetType(key);
            }

            object classInstance = constructorArgs == null ? Activator.CreateInstance(type) : Activator.CreateInstance(type, constructorArgs);
            if (classInstance == null) throw new Exception("broke");
            return classInstance;
        }
    }
}

key passed to the function is "CReportBO". CReportBO is accessible in the function's scope . but in //if no customization section (i.e type = Type.GetType(key) ) , type returns me null . whats wrong ?

Answer 1

If key is either assembly-qualified, or namespace-qualified within either the core assemblies or the calling assembly, then:

Type type = Type.GetType(key);
return constructorParameter == null ? Activator.CreateInstance(type)
          : Activator.CreateInstance(type, constructorParameter);

I wonder, though, if:

public static object getClassInstance(string key, params object[] args)

is more flexible, allowing:

Type type = Type.GetType(key);
return Activator.CreateInstance(type, args);

with usage such as:

object o = getClassInstance(key); // uses default constructor
object o = getClassInstance(key, null); // passes null to single parameter
object o = getClassInstance(key, 123, "abc"); // etc

Answer 2

You should be able to do something like this:

Activator.CreateInstance(Type.GetType(keyBindings), constructorParameters)

You can change your method signature to be public static object getClassInstance(string key, params object[] constructorParameters) if you want to allow the possibility of multiple constructor arguments.

Answer 3

You will want something similar to this:

    public object CreateMyObject(string name, object constructorParam)
    {
        Type t = Type.GetType(name);
        if (t != null)
        {
            object o = Activator.CreateInstance(t, constructorParam != null ? new[] { constructorParam } : null);
            return o;
        }

        return null;
    }

Of course you will need to add the appropriate error handling.

Damn, beaten to it by Marc, his answer takes precedence over mine :)

Answer 4

You can achieve the similar function using C# Activator.CreateInstance method.

Have a look at this MSDN document http://msdn.microsoft.com/en-us/library/dd384354.aspx

You could do lot more using Activator class.

Cheers, B

Answer 5

First, you should get type from your string:

Type t = testAssembly.GetType(key);

Then create an instance of your type:

Object o = Activator.CreateInstance(t, constructorParameter);

And o is an object of your type