set class name and object name at run time

Well, it sounds like the Assembly.GetType method is not able to find a type with the name 'NameOfSpace'.

I can't tell from the code exactly what this variable represents but the most likely reasons for the error are:

1. That it's not a 'fully qualified' typename i.e. projectName doesn't represent a namespace or FormName doesn't represent a type.

2. There's a difference in capitalization between the actual type and the variable.

"TypeForm" always is NULL!!! why??
I could not use from that code
please help me

no, i want use from this code:

private void btnCustomers_Click(object sender, EventArgs e)
        {
            Button btn = new Button();
            btn = (Button)sender;
            MessageBox.Show(btn.Name);
            StringBuilder EntityName = new StringBuilder();
            EntityName.Append(btn.Name);
            EntityName.Remove(0, 3);
            string projectName = "AAShS_Forms_" + EntityName.ToString();
            StringBuilder FormName = new StringBuilder();
            FormName.Append("F_C_");
            FormName.Append(EntityName.ToString());
            String NameOfSpace = projectName + "." + FormName.ToString();
            object ObjForm = new object();

         **   Type TypeForm=  System.Reflection.Assembly.GetExecutingAssembly().GetType(NameOfSpace );

            if (TypeForm != null)
            {
                ObjForm = Activator.CreateInstance(TypeForm);
                ((Form)ObjForm).ShowDialog();
            }
        }


.........

but I don't know why answer is Null in (**line) (TypeForm)?!

If you're talking here about creating a 'named' class at runtime rather than compile time, then you can do so using 'reflection emit'.

However, this is quite complicated and requires a knowledge of MSIL opcodes so it's not something which is done very often in practice. Check out this article for details:

http://www.c-sharpcorner.com/uploadfile/puranindia/reflection-and-reflection-emit-in-C-Sharp/