dynamically create class object by using assemblyname and type of class

Question

I have a console application in which I declared a class which is defined under a namespace. I want to create an instance of that class at runtime using assemblyname and class name. I tried the below code

var objAssembly = Assembly.Load(assemblyName);
var objType = objAssembly.GetType(className);
var obj = Activator.CreateInstance(objType);

But it is not working. Below is the class structure

namespace ReportService.ReportWriters
{
    class ExcelWriter : IReportWriter
    {
    }
}

I passed assembly name = ExcelWriter class name = ReportService.ReportWriters

Could you be more specific about the "it's not working" part? — Sergey Kalinichenko
– Sergey Kalinichenko, Commented Aug 18, 2015 at 12:03
The exception is - Could not load file or assembly 'ExcelWriter' or one of its dependencies. The system cannot find the file specified. — sandeep.mishra
– sandeep.mishra, Commented Aug 18, 2015 at 12:05
The part about "cannot find the file specified" is more or less self-explanatory, right? — Sergey Kalinichenko
– Sergey Kalinichenko, Commented Aug 18, 2015 at 12:06
Is ExcelWriter.dll signed? Is it in the directory from which your program is started? Does it have dependencies? — Sergey Kalinichenko
– Sergey Kalinichenko, Commented Aug 18, 2015 at 12:14

Mitat Koyuncu · Accepted Answer · 2015-08-18 12:36:00Z

2

Maybe tou should get all types and find ExcelWriter class and initialize it:

var objAssembly = Assembly.Load(assemblyName);
var objType = objAssembly.GetTypes().First(x => x.Name == "ExcelWriter");
var obj = Activator.CreateInstance(objType);

Or use Assembly.CreateInstance() method:

var namespaceName = "ReportService.ReportWriters";
var objAssembly = Assembly.Load(assemblyName);
var obj = objAssembly.CreateInstance(objAssembly.GetName().Name.Replace(" ","_") + "." + namespaceName + "." + "ExcelWriter");

NOTE: If assemblyName contains spaces compiler converts spaces to _ character.

NOTE: Add using System.Linq; to usings.

edited Aug 18, 2015 at 12:36

answered Aug 18, 2015 at 12:22

Mitat Koyuncu

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4 Comments

sandeep.mishra Over a year ago

I tried both condition.Is not working.Giving exception "Could not load file or assembly 'ExcelWriter' or one of its dependencies. The system cannot find the file specified."

Mitat Koyuncu Over a year ago

What returns objAssembly.GetTypes() method at your code?

sandeep.mishra Over a year ago

Assembly.Load(assemblyName); is giving exception mentioned above. The dll is not there in bin folder.Is this causing the issue?

Mitat Koyuncu Over a year ago

Try Assembly.FromFile() method and give it your assembly file location.

Kunal Khatri · Accepted Answer · 2015-08-18 12:58:45Z

0

Yes, because your class does not contain any public or internal default constructor.

create public default constructor and then try, It should work normally.

Check this article -

https://msdn.microsoft.com/en-us/library/wccyzw83(v=vs.110).aspx

edited Aug 18, 2015 at 12:58

answered Aug 18, 2015 at 12:49

Kunal Khatri

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