Question

I’d like to make things more clear to me about using instances of a class in multithreading application:
Can I use instances of one and the same class in different threads? In other words, can I create in different threads instances of the same class?

For example:
I have a class DbConnectionHelper which gets a connection string in its default constructor and make the connection string visible using a public property:

public class DbConnectionHelper
{
    string connstring;

    public DbConnectionHelper()
    {
        string userconnstring = Settings.Default.ConnectionString;
        connstring = GetConnectionString(userconnstring);
        ...
    }

    public string ConnString
    {
        get
        {
            return connstring;
        }
        set
        {
            connstring = value;
        }
    }
  ...

Then I have a number of repository classes which get data from a database using Entity Framework. Some of those repository classes have instances in UI thread, some of them – in other threads (not UI).

Can all of those repository classes get the connection string by creating instance of one class DbConnectionHelper and then reading its ConnString property?

DBConnectionHelper connhelper = new DBConnectionHelper();
string conn = connhelper.ConnString;

Answer 1

Separate instances of the same class are independent and share no common data, unless they all have a dependency to to a common object (such as a static variable in the class or a reference to another object that is the same for all or at least some instances).

In your case this is not a problem at all – you create an isolated instance of the DBConnectionHelper class each time you need it and use it just for building a connection string. You only have to worry about thread safety if multiple threads try and access methods of a shared object.