Question

I’m trying to get into the habit of coding to an interface rather than an implementation and whilst in most cases I can see the reasoning there are a few where I struggle.

Take this really simple example:

public interface IAuditLog
{
    void AddLog(string log);
}

public class AuditLog : IAuditLog
{
    public void AddLog(string log)
    {
        //implementation
    }
}

To call the audit log class:

public partial class AuditLogPage : System.Web.UI.Page
{
    protected void btnAddLog_Click(object sender, EventArgs e)
    {
        IAuditLog objAuditLog = new AuditLog();
        objAuditLog.AddLog("test log");
    }
}

I still have to use AuditLog when instantiating, so what’s the point? If the AddLog method signature changes i’m still going to have to go through all my pages that use it and amend the code. Am I missing the point?

Thanks for any help in advance,
Wilky.

Answer 1

Let imagine that there there are two AuditLog classes

class AuditLogToDatabase : IAuditLog // writes to database

and another is

class AuditLogToFile : IAuditLog // writes to file

like

protected void btnAddLog_Click(object sender, EventArgs e)
{
    IAuditLog objAuditLog = AuditLogFactory.GetAuditLog();
    objAuditLog.AddLog("test log");
}

now you can inject any class based on some configuration at run time without changing the actual implementation