How to redirect ILoggerFacade to ViewModel? - mvvm

Question

I want write my logs to the ViewModel, so I can expose logs to the users.
First I bind View to ViewModel
<TextBox Grid.Row="1" TextWrapping="Wrap" Text="{Binding Logger}" AcceptsReturn="True" IsReadOnly="True"
ScrollViewer.HorizontalScrollBarVisibility="Disabled" ScrollViewer.VerticalScrollBarVisibility="Auto"/>
This is the ViewModel
private string logger;
public string Logger
{
get { return logger; }
set
{
logger = value;
this.RaisePropertyChanged("Logger");
}
}
Then, I create the customer logger class which implements ILoggerFacade,and override the CreateLogger method in Bootstrapper.
In Bootstrapper
protected override ILoggerFacade CreateLogger()
{
return new MainLogger();
}
In Customer Logger class
public class MainLogger : ILoggerFacade
{
public void Log(string message, Category category, Priority priority)
{
string messageToLog = String.Format(System.Globalization.CultureInfo.InvariantCulture, "{1}: {2}. Priority: {3}. Timestamp:{0:u}.", DateTime.Now, category.ToString().ToUpper(System.Globalization.CultureInfo.InvariantCulture), message, priority.ToString());
//////??????//////
}
}
And what should fill in ???????. I tried Import IEventAggregator to publish data to ViewModel, and directly import ViewModel here. Neither works, because CreatorLogger Method is called before container is registered. So how can I write logs to the ViewModel?

Answer 1

The logger should simply save the log message(s) and expose it in a property:
public interface IMainLogger : ILoggerFacade
{
List Messages { get; }
}
public class MainLogger : IMainLogger
{
public MainLogger()
{
Messages = new ObservableCollection<string>();
}
public ObservableCollection<string> Messages { get; private set; }
public void Log(string message, Category category, Priority priority)
{
string messageToLog = ...;
Messages.Add(messageToLog);
}
}
That's basically what a logger is supposed to do: Log messages. Now you want to display it inside some TextBox which is contained in a View that you inject into a region, right? To do that, you need to pass that logger to the Module of this region's view via constructor dependency injection. I am working with MEF, so I'm not too sure about how to do it with Unity, but it probably looks something like this, when you configure the container in code:
container.RegisterType<IMainLogger, MainLogger>(new ContainerControlledLifetimeManager());
container.RegisterType<ContainingTextBoxModule>(new InjectionConstructor(container.Resolve<IMainLogger>()));
where the module takes and exposes the logger:
public class ContainingTextBoxModule : IModule
{
public IMainLogger Logger { get; private set; }
public ContainingTextBoxModule(IMainLogger logger)
{
Logger = logger;
}
}
Then your ViewModel for the module can relay the message(s) and you can bind to it/them from your view.
Does this answer your question?