How would one implement many classes that have the same methods that do things different?

Question

I am a developer who works primarily with embedded devices (programmed with C and assembly). My C# and OOP knowledge is very limited (although I can fake my way through it when necessary). I have five devices that interface with a PC via USB. The PC does some calculations and sends a result to the device. The same calculations are performed for each device, but the calculations are done differently. For each device, I have a C# Windows Forms application that does some work and sends data back and forth to the device. Currently, I'm trying to get the five different applications merged into one so we can easily make changes, add new devices easily, and have a standard user interface. My problem is that I don't exactly know the best way to do it since I don't know which device will be used until run time. I'm trying to avoid a bunch of if statements and I would like to be able to put each device in a separate file. Here is some psudo-code of what I'm talking about.

class Device //This is what EVERY device can do
{
...
DoWork1();
DoWork2();
DoWork3();
...
}

class Device1
{
...
DoWork1(); //This is how the work is done for this device
DoWork2();
DoWork3();
...
}

class Device2
{
...
DoWork1();  //This is how the work is done for this device (not the same way as   Device1)
DoWork2();
DoWork3();
}


public partial class frmMain : Form
{
private (some kind of object or something) CurrentDevice;
public frmMain()
{
...
//Determine what device (could be one of five) is currently being used
CurrentDevice = (which device is currently being used)
//Could be CurrentDevice = new Device1();
}
}

private void Button1_Click()
{
CurrentDevice.DoWork1(); //But this could be Device1.DoWork1() or Device2.DoWork1(), depending on what device is currently being used (which was determined in the frmMain constructor)
}

I'm not really sure, but I'm thinking I could use an interface or maybe inherit the Device1 class for the Device class and override the methods...But I don't know how I would have one generic way of saying CurrentDevice.DoWork1() since CurrentDevice could be Device1 or Device2.

Any ideas would be greatly appreciated. I'm using Visual Studio 2008 with .NET 3.5 on Windows XP SP3 and Windows 7.

I hope I described the problem well enough. If not, or if I didn't mention something that I should, please let me know. I'm new to stackoverflow and C#.

Thank you,

Michael

Answer 1

In your case, you're basically defining a inheritance hierarchy that can either consist of an abstract base class and two derived types or an interface with two implementors of it. For example

public abstract class BaseDevice
{
    public abstract void DoWork1();
}

public class Device1 : BaseDevice
{
    public override void DoWork1()
    {
        // provide implementation here
    }
}

// also create Device2 : BaseDevice and implement 

OR you could utilize an interface definition

public interface IDevice
{
    void DoWork1();
}

public class Device1 : IDevice
{
    public void DoWork1() 
    {
        // provide implementation 
    }
}

Which methodology you pick is up to you. You would perhaps favor an abstract base class if, for example, you wanted to define some behavior or properties with implementations that were common throughout the hierarchy. With an abstract class, you can provide implementations. An interface is an empty contract, you cannot provide any common behaviors, only a definition for what behaviors or properties may be present.

Either way you go, you would refer to instances of the more derived type via the abstract or interface base. In this manner, you don't care what the implementing type is, only what it can do (it's methods or properties).

Example:

 BaseDevice device1 = new Device1(); 
 BaseDevice device2 = new Device2();
 // maybe you have a list?
 List<BaseDevice> devices = new List<BaseDevice> { device1, device2 };

 foreach (BaseDevice device in devices)
 {
      device.DoWork1(); // notice you don't care about the actual type, just the behavior
 }