Log manager class accessible to all classes

Question

I've been struggling with this for a while... I have a programm written using the MVP pattern, I want to have a LogHandler class that must retrieve a string that corresponds to an ID provided in one of these methods, but it also needs to update the GUI, adding items to a listbox. So to simplyfy, imagine this:

if (name != "Peter")
{
Log.RegisterError(31, 4) //errorType, errorID
}

So in the Log class it would then get the string that matches the type and IDs provided and MessageBox it, but what if I want to add that string to a control on the form? I'm using views implemented by the forms to accomplish GUI updating, but since this is a static class I can't...

Also where should errors be checked and raised? Presenter? View? Model?

Thanks in advance

Answer 1

You could add callbacks in you Log class that other object could subscribe to.

Example:

In this example the Presenter can listen for an error code to be logged then receive the error string from the Log from the Model class

public class Logger
{
   private static Dictionary<int, List<Action<string>>> _callbacks = new Dictionary<int,List<Action<string>>>();

    public static void RegisterLoggerCallback(int errorType, Action<string> callback)
    {
        // Just using errortype in this exaple, but the key can be anything you want.
        if (!_callbacks.ContainsKey(errorType))
        {
            _callbacks.Add(errorType, new List<Action<string>>());
        }
        _callbacks[errorType].Add(callback);
    }

    public static void RegisterLog(int errorType, int errorID)
    {
        // find error sring with codes
        string error = "MyError";

        // show messagebox
        MessageBox.Show(error);

        // tell listeners
        if (_callbacks.ContainsKey(errorType))
        {
            _callbacks[errorType].ForEach(a => a(error));
        }
    }
}

public class Model
{
    public Model()
    {
    }

    public void DoSomething()
    {
      Logger.RegisterLog(1, 2);
    }
}

public class Presenter 
{
    public Presenter()
    {
        Logger.RegisterLoggerCallback(1, AddToListbox);
    }

    private void AddToListbox(string error)
    {
        // add to listbox when errortype 1 is called somewhere
    }
}

This is a very simple example but should give you an idea of a way to achive this.