I'm getting the "missing a using directive or assembly reference" and no clue what's going wrong

Question

I'm trying to allow a user to enter data into a textbox that will be added to the web.config file. I've added the relevent lines to the web.config file but when I make this class all goes wrong.

I keep getting the are you missing a using directive or assembly refenrence error whenever I try to run my app. I have looked at the other times this question has been asked and can't seem to figure out where I'm going wrong. The thing is that I am extremely new to Visual Studio and am just left blank at what could be the answer.

Below here is the class file that's generating the error. I hope I've included everything you need to assist me. Thank you.

 using System.Collections.Generic;
 using System.Linq;
 using System.Configuration; 


namespace WebConfigDemo
{    
public class CompanyConfigSection : ConfigurationSection   
{       
    [ConfigurationProperty("", IsRequired = true, IsDefaultCollection = true)]   
    public CompanyConfigCollection Companies       
    {
        get           
        {              
        return (CompanyConfigCollection)this[""];           
        }            
        set            
        {            
            this[""] = value;            
        }       
    }   
}     
public class CompanyConfigElement : ConfigurationElement   
{      
                [ConfigurationProperty("id", IsKey = true, IsRequired = true)]        
    public int Id        
                {            
                    get      
                {                
                        return (int)this["id"];            
                    }            
                    set           
                    {               
                        this["id"] = value;          
                }    
                }         
    [ConfigurationProperty("name", IsRequired = true)]        
    public string Name        
    {            
        get           
        {            
                    return this["name"].ToString();            
        }           
        set           
        {               
            this["name"] = value;           
        }    

    }   
} ' 
public class CompanyConfigCollection : ConfigurationElementCollection    
{       
    protected override ConfigurationElement CreateNewElement()     
{          
    return new CompanyConfigElement();       
    }       
    protected override object GetElementKey(ConfigurationElement element)     
    {          
        return ((CompanyConfigElement)element).Id;        
    }   
}    
public class CompaniesConfig   
{    
            private static readonly Dictionary<int, CompanyConfigElement> 
                Elements;         
    static CompaniesConfig()       
    {         
                Elements = new Dictionary<int, CompanyConfigElement>();       
                var section = (CompanyConfigSection)ConfigurationManager.GetSection          ("companies");           
                foreach (CompanyConfigElement system in section.Companies)        
                    Elements.Add(system.Id, system);       
    }        
    public static CompanyConfigElement GetCompany(int companyId)       
    {          
                        return Elements[companyId];   
    }      
            public static List<CompanyConfigElement> Companies        
            {          
                get
                {
                    return Elements.Values.ToList(); 
                }      
            }  
}
}  '

Any help is appreciated

Answer 1

You probably don't have the System.Configuration dll added to the project references. It is not there by default, and you have to add it manually.

Right-click on the References and search for System.Configuration in the .net assemblies.

Check to see if it is in your references...

Right-click and select Add Reference...

Find System.Configuration in the list of .Net Assemblies, select it, and click Ok...

The assembly should now appear in your references...